Samacheer Kalvi Class 11 Bio Botany Solutions Chapter 15 Plant Growth and Development

Part - I.

 

Question 1. Select the wrong statement from the following:
(a) Formative phase of the cells retain the capability of cell division.
(b) In elongation phase development of central vacuole takes place.
(c) In maturation phase thickening and differentiation takes place.
(d) In maturation phase, the cells grow further.
Answer: (d) In maturation phase, the cells grow further.
In simple words: The question asks to identify the incorrect statement. In the maturation phase, cells mostly stop growing in size and instead develop special functions, not grow further.

🎯 Exam Tip: Remember the distinct characteristics of each phase of cell growth (formative, elongation, maturation) to easily identify incorrect statements about them.

 

Question 2. If the diameter of the pulley is 6 inches, length of pointer is 10 inches and distance travelled by pointer is 5 inches. Calculate the actual growth in length of plant.
(a) 3 inches
(b) 6 inches
(c) 12 inches
(d) 30 inches
Answer: 1.5 inches
Solution:
Step 1: Calculate the radius of the pulley.
Diameter of the Pulley \( = 6 \) inches
Radius of the pulley \( = \frac{6}{2} = 3 \) inches
Now, calculate the actual growth in length.
Actual growth in length \( = \frac{\text{Distance travelled by pointer } \times \text{ Radius of the pulley}}{\text{Length of the pointer}} \)
\( = \frac{5 \times 3}{10} \)
\( = \frac{15}{10} \)
\( = 1.5 \) inches. The options provided in the question are incorrect based on this calculation.
In simple words: First, find half of the pulley's diameter to get its radius. Then, multiply the distance the pointer moved by the pulley's radius, and divide this by the length of the pointer. This calculation gives the actual growth of the plant.

🎯 Exam Tip: Always double-check if the provided options are consistent with your calculations, especially in physics or biology problems involving measurements. Use the formula for arc auxanometer accurately.

 

Question 3. In unisexual plants, sex can changed by the application of
(a) Ethanol
(b) Cytokinins
(c) ABA
(d) Auxin
Answer: (c) ABA
In simple words: In plants that have separate male and female flowers, applying a hormone called ABA can help change their sex. This hormone plays a role in plant development and stress responses.

🎯 Exam Tip: Remember the specific roles of different plant hormones, especially their effects on sex determination and stress responses in plants.

 

Question 4. Select the correctly matched one
A) Humanurine i) Auxin-B
B) Corn gram oil ii) GA3
C) Fungs iii) Abscisic acid II
D) Herring fish sperm iv) Kinetin
E) Unripcrnaizegrains v) AuxinA
F) Young cotton boils vi) Zeatin
(a) A - iii, B - iv, C - v, D - vi, E - i, F- ii
(b) A - v, B - i, C - ii, D - iv, E - vi, F- iii
(c) A - iii, B - v, C - vi, D - i, E - ii, F - iv
(d) A-ii, B - iii, C - v, D - vi, E - iv, F-i
Answer: (b) A – v, B – i, C – ii, D – iv, E – vi, F – iii
In simple words: This question tests knowledge of plant growth regulators and their common names or sources. Matching them correctly helps identify the right hormone for a specific application.

🎯 Exam Tip: Memorize the key plant hormones, their chemical names, and notable sources or applications to correctly match them in questions.

 

Question 5. Seed dormancy allows the plants to:
(a) overcome unfavorable climatic conditions
(b) develop healthy seeds
(c) reduce viability
(d) prevent deterioration of seeds
Answer: (a) overcome unfavorable climatic conditions
In simple words: Seed dormancy is like a resting period for seeds. It stops them from growing when the weather is bad, so they only start growing when conditions are good for survival.

🎯 Exam Tip: Understand that dormancy is a survival strategy, preventing germination until the environment is suitable for the young plant's survival.

 

Question 6. What are the parameters used to measure growth of plants?
Answer: Growth in plants can be measured by several factors:

• Increase in their length or width, like how roots and stems get longer or thicker.
• Increase in their fresh or dry weight, which shows how much material the plant has gained.
• Increase in the area or volume of parts like fruits and leaves, indicating their size growth.
• Increase in the total number of cells produced, showing how many new building blocks the plant has made. Measuring these helps scientists understand how plants develop.

In simple words: We can measure how much a plant grows by checking if it gets longer, heavier, bigger in size, or makes more cells.

🎯 Exam Tip: When describing plant growth parameters, list measurable physical changes like size, weight, and cell count to show a comprehensive understanding.

 

Question 7. What is plasticity?
Answer: Plasticity is when a plant changes its shape or form in response to its environment. For example, in a buttercup plant, the leaves growing in the air look normal, but the leaves growing underwater are very thin and hairy. This difference in leaf shape helps them absorb carbon dioxide better underwater. Another example is seen in young cotton and coriander plants, where their juvenile leaves look different from their mature leaves. This ability to change based on conditions helps plants adapt and survive. However, simply having different leaf shapes at different life stages, like juvenile versus mature leaves, is not considered plasticity if it is not a direct response to a changing environment.
In simple words: Plasticity means a plant can change its shape depending on where it grows, like how some water plants have different leaves in air and water. It's how plants adjust to their surroundings.

🎯 Exam Tip: When explaining plasticity, always provide specific examples that clearly show environmental influence on plant morphology, distinguishing it from normal developmental changes.

 

Question 8. Write the physiological effects of Cytokinins.
Answer: Cytokinins are plant hormones with several important effects:
1. They help cells divide when auxin, another hormone, is also present.
2. They cause cells to get bigger, working together with auxin and gibberellins.
3. They can end the resting period (dormancy) of certain seeds that need light to sprout, like tobacco seeds, and help them germinate.
4. They encourage the growth of side buds (lateral buds) even when the main top bud (apical bud) is present, which usually stops side buds from growing.
5. Applying cytokinin can slow down the aging process in plants by moving nutrients around. This effect is known as the Richmond Lang effect.
6. Cytokinins also help plants make proteins faster. They lead to the formation of interfascicular cambium, which helps in secondary growth. They help overcome apical dominance, allowing side branches to grow more. They also encourage the making of new leaves, chloroplasts, and side shoots.
7. These hormones help plants actively take in and store many dissolved substances.
In simple words: Cytokinins help plant cells divide and grow bigger. They can make dormant seeds sprout and encourage side branches to grow more. They also slow down plant aging and help plants take in nutrients.

🎯 Exam Tip: When listing physiological effects of hormones, group similar functions (e.g., cell division, growth) and mention any associated terms like "Richmond Lang effect" for completeness.

 

Question 9. Describe the mechanism of photoperiodic induction of flowering.
Answer: The mechanism of how photoperiod (the length of day and night) causes flowering is called photoperiodic induction.

• The way a plant's body responds to the length of light and darkness (photoperiod) to start flowering is known as Photoperiodism.
• The specific amount of light duration needed to make a plant flower is called the critical day length. For example, Maryland Mammoth tobacco needs 12 hours, while Xanthium needs 15.05 hours.

Photoperiodic induction involves:

• An appropriate photoperiod within a 24-hour cycle makes up one "inductive cycle." Plants might need one or more of these cycles to start flowering.
• The process where early leaf structures (leaf primordia) change into flower structures because of suitable light-dark cycles is called photoperiodic induction. For instance, Xanthium (a short-day plant) needs just 1 inductive cycle, while Plantago (a long-day plant) needs 25.

Site of photoconductive perception:

• Leaves are the main parts that sense the photoperiodic signal (PPS). They are also where the special hormones for flowering are made and then sent to the growing tips to encourage flowering.
• Experiments on plants like the Cocklebur (a short-day plant) show this. Scientists believe a hormone is responsible, which Chailakyan (1936) named Florigen. However, it's still hard to get this hormone in isolation.

Here is an example of such experiments:

In simple words: Photoperiodism is how plants use day and night length to decide when to flower. Leaves sense the light, make special hormones like Florigen, and send them to the growing tips to trigger blooming. Experiments show that even one leaf can receive this signal and cause flowering.

🎯 Exam Tip: When describing photoperiodism, define key terms like "photoperiodism" and "critical day length," provide examples, and explain the role of leaves as the site of perception.

 

Question 10. Give a brief account of programmed cell death (PCD).
Answer: Programmed cell death (PCD) is when plants intentionally cause certain cells or parts to die, following their own genetic plan. This often happens as the plant ages, a process called senescence. So, the death of a plant or its parts due to aging is known as Programmed Cell Death. For individual cells, this intentional self-destruction is called PCD. In plants, specific enzymes like phytases are involved in PCD, similar to caspases in animals. The nutrients and other useful substances from these dying cells and tissues are then moved to other parts of the plant that are still alive and growing. For example, during the development of xylem vessels and tracheids (which carry water), their inner parts (protoplasts) die and disappear when they become mature. This makes them hollow and efficient for water transport. In water plants, air-filled tissues called aerenchyma form in roots and stems through PCD, creating large air spaces. Also, in the early stages of unisexual flowers, both male and female flowers might start to form, but only one type completes its development, while the other stops growing and dies through PCD.
In simple words: Programmed cell death (PCD) is when a plant's cells or parts are designed to die on purpose, often as the plant ages. This helps the plant reuse nutrients and form important structures like water-carrying tubes or air spaces.

🎯 Exam Tip: Emphasize that PCD is a controlled, genetic process, not accidental death, and highlight its essential roles in nutrient recycling, tissue development, and plant survival.

 

Part - II.

 

I. Choose The Correct Answer

 

Question 1. The open form of the growth occurs in:
(a) leaves and flowers
(b) stem and root
(c) leaves and stem
(d) stem and flowers
Answer: (b) stem and root
In simple words: Open growth in plants means that the stem and roots can keep growing longer throughout the plant's life, unlike leaves and flowers which stop growing after reaching a certain size.

🎯 Exam Tip: Differentiate between indeterminate growth (open form, found in stems and roots) and determinate growth (closed form, found in leaves and flowers).

 

Question 2. An example of a De-Differentiating cell is ...............
(a) Tracheary element
(b) shoot apex
(c) Cork cambium
(d) root apex
Answer: (c) Cork cambium
In simple words: A de-differentiating cell is one that loses its specialized job and can start dividing again, like cork cambium which forms from cells that were once specialized.

🎯 Exam Tip: Understand that de-differentiation is a process where mature cells regain the ability to divide and form new cell types, a key concept in plant tissue culture and secondary growth.

 

Question 3. Primary growth of the plant is due to the activity of:
(a) phloem parenchyma
(b) phloem meristem
(c) vascular cambium
(d) apical meristem
Answer: (d) apical meristem
In simple words: The main growth that makes a plant taller and its roots longer comes from special growing areas at the tips of stems and roots, called apical meristems.

🎯 Exam Tip: Remember that apical meristems are responsible for primary growth (increase in length), while lateral meristems (like vascular cambium) are responsible for secondary growth (increase in girth).

 

Question 4. Choose the natural Auxin of the following
(a) Anti Auxin
(b) NAA
(c) 2.4.D
(d) IndoleAcetic Acid (IAA)
Answer: (d) Indole Acetic Acid (IAA)
In simple words: Indole Acetic Acid, or IAA, is a type of plant hormone that naturally helps plants grow. Other options like NAA and 2,4-D are man-made versions of auxins.

🎯 Exam Tip: Distinguish between naturally occurring plant hormones (like IAA) and synthetic analogues (like NAA, 2,4-D), as their applications and contexts can differ.

 

Question 5. Thickening and differentiation of cells take place during:
(a) elongation phase
(b) formative phase
(c) maturation phase
(d) flowering phase
Answer: (c) maturation phase
In simple words: During the maturation phase, plant cells stop growing in size and instead develop thicker walls and specialized structures to perform their specific jobs.

🎯 Exam Tip: Connect "maturation" with "specialization" and "differentiation" – this is when cells gain their final form and function, often involving thickening of cell walls.

 

Question 6. The hormone present in Coconut milk is
(a) Gibberellins
(b) Ethylene
(c) Cytokinin
(d) Auxin
Answer: (c) Cytokinin
In simple words: Coconut milk naturally contains a plant hormone called cytokinin, which is important for cell division and growth.

🎯 Exam Tip: Remember specific natural sources of plant hormones, as these often highlight their importance and natural occurrence.

 

Question 7. The total growth of the plant consists of four phases in the following order.
(a) Log phase, lag phase, decelerating phase and maturation phase
(b) Log phase, lag phase, maturation phase and decelerating phase
(c) Lag phase, log phase, maturation phase and decelerating phase
(d) Lag phase, log phase, decelerating phase and maturation phase
Answer: (d) Lag phase, log phase, decelerating phase and maturation phase
In simple words: Plant growth follows a specific order: first a slow start (lag phase), then fast growth (log phase), then slowing down (decelerating phase), and finally reaching full development (maturation phase).

🎯 Exam Tip: Visualize the S-shaped (sigmoid) growth curve; its distinct parts correspond to the lag, log, decelerating, and maturation phases in that specific order.

 

Question 8. Which of the following Phytohormone does not occur naturally in plants?
(a) 2. 4. D
(b) GibberellicAcid
(c) 6. Furfuryl amino purine
(d) IAA
Answer: (a) 2.4.D
In simple words: 2,4-D is a man-made chemical used to kill weeds, not a hormone that plants naturally produce. Other options like Gibberellic Acid and IAA are natural plant hormones.

🎯 Exam Tip: Be able to identify common synthetic plant growth regulators (like 2,4-D and NAA) and distinguish them from naturally occurring phytohormones.

 

Question 9. Absence of light may lead to the yellowish color in plants and this is called:
(a) venation
(b) etiolation
(c) estivation
(d) vernation
Answer: (b) etiolation
In simple words: When plants grow without enough light, they become pale yellow, long, and stretched out, which is called etiolation. This happens because they can't make chlorophyll, the green pigment.

🎯 Exam Tip: Understand that etiolation is a clear sign of insufficient light, resulting in reduced chlorophyll production and abnormal stem elongation, helping plants reach light sources.

 

Question 10. Apical dominance is caused when Auxin
(a) Concentration is more than Cytokinins
(b) Concentration is less than Cytokinins
(c) and Cytokinin concentration are equal
(d) and Cytokinin concentration are fluctuating
Answer: (a) Concentration is more than Cytokinins
In simple words: Apical dominance, where the main stem grows strongly and side branches are suppressed, happens when there is a lot more auxin than cytokinin at the plant's tip.

🎯 Exam Tip: Remember that apical dominance is regulated by the balance of auxin and cytokinin; high auxin at the apex generally inhibits lateral bud growth.

 

Question 11. Indicate a plant growth regulator from the following:
(a) cytocin
(b) cytokinins
(c) acetic acid
(d) methylene
Answer: (b) cytokinins
In simple words: Cytokinins are a group of natural plant hormones that play a key role in cell division and growth.

🎯 Exam Tip: Recognize the common names of the five major classes of plant growth regulators: auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

 

Question 12. Which prevents premature fall of fruit?
(a) NAA
(b) Ethylene
(c) GA3
(d) Zeatin
Answer: (a) NAA
In simple words: NAA, a man-made auxin, is often used by farmers to stop fruits from falling off trees too early, helping them stay on the plant until they are fully ripe.

🎯 Exam Tip: Understand that synthetic auxins like NAA are widely used in agriculture to control fruit drop, promote rooting, and thin fruits, demonstrating their practical significance.

 

Question 13. The activity of synergistic effect involves the activity of:
(a) auxin and gibberellins
(b) auxin and ethylene
(c) ABA and gibberellins
(d) none of the options
Answer: (a) auxin and gibberellins
In simple words: A synergistic effect means two things work together to create a bigger effect than they would alone. In plants, auxin and gibberellins often work this way to promote growth.

🎯 Exam Tip: Synergistic effects in plant hormones are crucial; remember that auxin and gibberellins commonly act together to enhance cell elongation and overall plant growth.

 

Question 14. The term Auxin was coined by
(a) Went
(b) Darwin
(c) Smith
(d) Garner
Answer: (a) Went
In simple words: The scientist who first gave the name "Auxin" to this important plant growth hormone was Went.

🎯 Exam Tip: Knowing the historical figures associated with hormone discovery (like Went for auxin) helps understand the timeline of plant physiology research.

 

Question 15. The term auxin was first coined by:
(a) Charles Darwin
(b) Kogl
(c) F.W. Went
(d) Smith
Answer: (c) F.W. Went
In simple words: The name "auxin" for the plant growth hormone was first used by F.W. Went, a key figure in early plant hormone research.

🎯 Exam Tip: Accurately recall the names of scientists and their contributions to the discovery and naming of plant hormones.

 

Question 16. The term Gibberellin was coined by
(a) Went
(b) Kurosawa
(c) Skoog
(d) Yabuta
Answer: (d) Yabuta
In simple words: The term "Gibberellin" was given by Yabuta, a Japanese scientist who did early research on this plant growth hormone.

🎯 Exam Tip: Associate the name Yabuta with the term "Gibberellin," as historical context is important for understanding scientific terminology.

 

Question 17. Indicate a synthetic auxin.
(a) Indole Acetic Acid
(b) Phenyl Acetic Acid
(c) Indole Butyric Acid
(d) Naphthalene Acetic Acid
Answer: (d) Naphthalene Acetic Acid
In simple words: Naphthalene Acetic Acid, or NAA, is a man-made hormone that works like natural auxins in plants, often used to help plants root or prevent fruit from dropping.

🎯 Exam Tip: Recognize that "Naphthalene Acetic Acid" (NAA) is a synthetic compound designed to mimic natural auxins and is widely used in agriculture.

 

Question 18. The mineral required for the synthesis of IAA is
(a) Copper
(b) Magnesium
(c) Zinc
(d) Boron
Answer: (c) Zinc
In simple words: For plants to make Indole Acetic Acid (IAA), which is a natural growth hormone, they need the mineral zinc. Zinc is a vital component in many enzyme reactions.

🎯 Exam Tip: Remember that micronutrients like zinc are essential cofactors for enzyme activity, including those involved in hormone synthesis, such as IAA.

 

Question 19. Auxin stimulates:
(a) transpiration
(b) respiration
(c) flowering
(d) none of the options
Answer: (b) respiration
In simple words: Auxin, a plant hormone, helps speed up the process of respiration in plant cells. This process releases energy for the plant to grow.

🎯 Exam Tip: While auxins have many roles, remember their influence on metabolic processes like respiration, which is key for energy production and growth.

 

Question 20. The most widely occurring Cytokinin in plants is
(a) ABA
(b) NAA
(c) TNT
(d) IPA
Answer: (d) IPA
In simple words: IPA, or Isopentenyl adenine, is the most common natural cytokinin found in plants. Cytokinins are important for cell division.

🎯 Exam Tip: Identify IPA as a naturally occurring cytokinin, distinct from other hormones or synthetic compounds. This highlights its prevalence in plant physiology.

 

Question 21. Who established the structure of gibberellic acid?
(a) Brain etal
(b) Kurosawa
(c) Cross et al
(d) Yabuta and Sumiki
Answer: (c) Cross et al
In simple words: The detailed chemical structure of gibberellic acid, a plant growth hormone, was worked out and confirmed by a group of scientists led by Cross.

🎯 Exam Tip: For historical questions, associate the scientific discovery (like establishing hormone structure) with the correct researchers or groups involved.

 

Question 23. Cytokinins inducing cell division was first demonstrated by:
(a) Haberlandt
(b) Charles Darwin
(c) Clarke
(d) Hubert
Answer: (a) Haberlandt
In simple words: The very first time someone showed that cytokinins make plant cells divide was Haberlandt. This discovery was a key step in understanding how plant hormones control growth.

🎯 Exam Tip: Remember to associate key discoveries with the scientists who made them, as this is a common type of question in plant physiology.

 

Question 24. Which of the following is a bioassay for Cytokinins?
(a) Chlorophyll preservation test
(b) Dwarf maize Assay
(c) Seed germination Assay test
(d) Neem cotyledon Assay
Answer: (d) Neem cotyledon Assay
In simple words: To test for cytokinins, scientists can use a 'Neem cotyledon Assay'. This test helps them see how much of the hormone is present. Bioassays are important tools for measuring the activity of plant hormones and understanding their effects.

🎯 Exam Tip: Familiarize yourself with different bioassays and which hormone they are used to detect.

 

Question 25. Indicate correct statements.
(i) Genes are intracellular factors for growth.
(ii) Temperature has no role in the growth of plant.
(iii) Oxygen has a vital role in the growth of plants.
(iv) CIN ratio of soil does not affect the growth of plant.
(a) (i) and (iv)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (ii) and (iii)
Answer: (c) (i) and (iii)
In simple words: The correct statements are that genes control growth inside cells, and oxygen is very important for plants to grow. Both internal genetic factors and external environmental factors like oxygen are crucial for healthy plant development.

🎯 Exam Tip: When evaluating statements, carefully consider the exact wording, especially terms like "no role" or "does not affect," which often indicate an incorrect statement.

 

Question 26. Avena curvature test as a BioAssay for
(a) Auxins
(b) GA3
(c) Cytokinin
(d) Ethylene
Answer: (a) Auxins
In simple words: The Avena curvature test is a special way to check for the presence and amount of auxins in plants. This test relies on the ability of auxins to cause bending in oat coleoptiles, a visible sign of their activity.

🎯 Exam Tip: Know the specific bioassay methods for each major plant hormone, as they often illustrate the hormone's primary effect.

 

Question 27. The stress phytohormones (Abscisic acid) was first isolated by:
(a) Linn et al
(b) Addicott et al
(c) Edward et al
(d) Stone and Black
Answer: (b) Addicott et al
In simple words: The plant hormone called Abscisic acid, which helps plants deal with stress, was first separated and identified by scientists named Addicott and his team. Abscisic acid plays a critical role in plant responses to drought, cold, and other challenging environmental conditions.

🎯 Exam Tip: Link important plant hormones with their discoverers or key researchers for easy recall.

 

Question 28. The Gibberellins have been commercially exploited for
(a) increasing the size of grapefruits
(b) inducing rooting in stem cuttings
(c) breaking the dormancy in seeds
(d) production of disease-resistant varieties
Answer: (c) breaking the dormancy in seeds
In simple words: People use Gibberellins in farming to help seeds wake up and start growing, especially those that are sleeping or 'dormant'. This application is vital for ensuring uniform and timely germination in agriculture.

🎯 Exam Tip: Understand the agricultural and commercial applications of plant hormones, as these are often tested.

 

Question 29. Pick out the correct statement from the following:
(i) Abscisic acid is found abundantly inside the chloroplast of green cells.
(ii) ABA is a powerful growth promotor.
(iii) ABA is formed from the pentose phosphate pathway.
(iv) ABA has anti-auxin and anti-gibberellin properties.
(a) (i) and (iv)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer: (a) (i) and (iv)
In simple words: The true statements are that Abscisic acid (ABA) is found a lot in the green parts of cells called chloroplasts, and it works against other growth hormones like auxin and gibberellin. ABA's role as an antagonist helps plants balance growth and stress responses.

🎯 Exam Tip: Pay close attention to the specific locations of hormone synthesis and their primary functions, including any antagonistic relationships with other hormones.

 

Question 30. Biennials can be induced to flower in the first season itself by treatment with
(a) Auxin
(b) Kinetin
(c) GA
(d) ABA
Answer: (c) GA
In simple words: Biennial plants usually flower in their second year, but if you treat them with Gibberellic acid (GA), they can be made to flower in their first year instead. This technique, known as bolting, is useful for accelerating breeding cycles in agriculture.

🎯 Exam Tip: Remember that Gibberellins (GA) are commonly used to overcome dormancy and promote bolting in plants.

 

Question 31. Pea and barley are classified under:
(a) short-day plants
(b) short long day plants
(c) long day plants
(d) long short day plants
Answer: (c) long day plants
In simple words: Peas and barley are known as 'long day plants' because they need many hours of light each day to grow well and flower. Understanding photoperiodism helps farmers choose the right crops for different latitudes and seasons.

🎯 Exam Tip: Classify plants correctly into short-day, long-day, or day-neutral categories based on examples.

 

Question 32. Auxin a was isolated from human urine by
(a) F.W. went
(b) Charles Darwin
(c) Kogl and Haugen Smith
(d) Denny
Answer: (c) Kogl and Haugen Smith
In simple words: The plant hormone called Auxin a was first found and taken out of human urine by scientists named Kogl and Haugen Smith. This early discovery showed that substances with plant growth-regulating activity could be found even in animal excretions.

🎯 Exam Tip: Note the historical context of hormone discoveries, as they provide insight into the development of plant physiology.

 

Question 33. Usually, Xanthiumpensylvanicum will flower under:
(a) long day condition
(b) short long day condition
(c) photo neutral condition
(d) short-day condition
Answer: (d) short-day condition
In simple words: The plant Xanthiumpensylvanicum flowers when the days are short, meaning it needs more hours of darkness than light to start making flowers. This plant is a classic example of a short-day plant, often used in photoperiodism studies.

🎯 Exam Tip: Use specific plant examples to remember the conditions required for flowering in short-day plants.

 

Question 34. The most widely occurring Cytokinin in plants is
(a) Indole Acetic Acid (LAA)
(b) Indole Butyric Acid (IBA)
(c) Pentenyl Adenine (IPA)
(d) Naphthalene Acetic Acid (NAA)
Answer: (c) Pentenyl Adenine (IPA)
In simple words: The type of cytokinin found most often in plants is called Pentenyl Adenine, also known as IPA. Cytokinins are crucial for cell division and delaying senescence, contributing significantly to plant growth.

🎯 Exam Tip: Be precise with the full names and abbreviations of hormones, as similar names can be confusing.

 

Question 35. Who found out the phytochrome in plants?
(a) Butler et al
(b) Michell et al
(c) Boumick et al
(d) Gamers and Allard
Answer: (a) Butler et al
In simple words: Scientists led by Butler were the ones who first discovered phytochrome, a special pigment in plants. Phytochrome plays a crucial role in sensing light and controlling various plant processes like flowering and seed germination.

🎯 Exam Tip: Connect the names of key scientists with their groundbreaking discoveries to aid memory.

 

Question 36. Scientists, those who are connected with Ethylene
(I) Denny
(II) R. Gane
(III) Kurosawa
(IV) Cocken
(a) (I) (II) & (III)
(b) (II) (III) & (IV)
(c) (I) (II) & (IV)
(d) (I) (III) & (IV)
Answer: (c) (I)(II)& (IV)
In simple words: The scientists Denny, R. Gane, and Cocken are known for their work related to ethylene, a plant hormone. Their research helped establish ethylene's role in fruit ripening and other plant processes.

🎯 Exam Tip: Be careful with lists of scientists, as some might be famous for other hormones (e.g., Kurosawa for Gibberellins).

 

Question 37. Pick out the wrong statement from the following:
(a) Vernalization increases the cold resistance of plants
(b) It increases the resistance of plants to fungal disease
(c) Vernalization increase the vegetative period of the plant
(d) It accelerates the plant breeding
Answer: (c) Vernalization increase the vegetative period of the plant
In simple words: The incorrect statement is that vernalization makes the plant grow for a longer time before flowering. Actually, it makes the plant flower earlier by shortening the vegetative period. Vernalization allows plants to quickly transition from vegetative growth to reproductive growth after experiencing cold temperatures.

🎯 Exam Tip: Pay close attention to the precise effects of physiological processes like vernalization. "Increase" vs. "decrease" or "shorten" vs. "lengthen" can change the meaning entirely.

 

Question 38. Day-neutral plants are
(a) Sugarcane & Coleus
(b) Bryophyllum& Night Jasmine
(c) Wheat, rice & Oats.
(d) Potato, Tomato & Cotton
Answer: (d) Potato, Tomato & Cotton
In simple words: Plants like potato, tomato, and cotton are 'day-neutral plants'. This means they can flower no matter how long the day or night is. These plants are highly adaptable to various growing regions because their flowering isn't dependent on specific light durations.

🎯 Exam Tip: Remember common examples for each photoperiodic category to quickly identify them.

 

Question 39. In apple and plum, the method of breaking seed dormancy involves the process of:
(a) impaction
(b) Scarification
(c) exposing to red light
(d) Stratification
Answer: (d) Stratification
In simple words: For apple and plum seeds, breaking their dormancy, or helping them wake up to grow, often involves a process called stratification. Stratification mimics natural winter conditions, providing the necessary cold and moisture to initiate germination.

🎯 Exam Tip: Distinguish between different methods of breaking seed dormancy, understanding the specific conditions each method simulates.

 

Question 40. Xanthium (Cocklebur) requires ............ hours of light to induce flowering,
(a) 12
(b) 9
(c) 15.05
(d) 13.05
Answer: (c) 15.05
In simple words: To make Xanthium, also known as Cocklebur, flower, it needs a specific amount of darkness, meaning it needs a day length of about 15.05 hours of light. Xanthium is a short-day plant, and this specific light duration helps define its critical photoperiod for flowering.

🎯 Exam Tip: For specific plant examples like Xanthium, try to remember their critical day/night lengths if provided in the syllabus.

 

Question 41. The hormone that cannot be isolated
(a) IAA
(b) ABA
(c) NAA
(d) Florigen
Answer: (d) Florigen
In simple words: Florigen is a plant hormone that is believed to cause flowering, but scientists have not yet been able to fully separate and study it on its own. Despite extensive research, the exact chemical nature of florigen remains one of the enduring mysteries in plant physiology.

🎯 Exam Tip: Be aware of substances that are hypothesized or inferred but have not yet been chemically isolated, like florigen.

 

Question 42. The term Photoperiodism was coined by
(a) Went
(b) Butler
(c) Gamer
(d) Skoog
Answer: (c) Garner
In simple words: The scientist Garner was the one who first used the term 'Photoperiodism' to describe how plants react to different lengths of day and night. This term describes a plant's developmental responses to the relative lengths of light and dark periods, particularly in relation to flowering.

🎯 Exam Tip: Remember the historical figures associated with key physiological concepts like photoperiodism.

 

Question 43. ABA acts as antagonistic to
(a) Ethylene
(b) Cytokinin
(c) Gibberellic acid
(d) IAA
Answer: (c) Gibberellic acid
In simple words: Abscisic acid (ABA) works against Gibberellic acid, meaning it has opposite effects on plant growth, often slowing it down. This antagonistic relationship is crucial for maintaining a balance between growth promotion and stress adaptation in plants.

🎯 Exam Tip: Understand the synergistic and antagonistic relationships between different plant hormones, as they regulate complex processes.

 

Question 44. If a short-day plant, flowering is induced by
(a) Long nights
(b) Photo periods less than 12 hrs
(c) Photoperiods shorter than critical value and uninterrupted long night
(d) Short photoperiods and interrupted long nights
Answer: (c) Photoperiods shorter than critical value and uninterrupted long night.
In simple words: A short-day plant will flower if the period of light is shorter than a certain limit, and it also needs a continuous long period of darkness without any breaks. The length and continuity of the dark period are more critical for short-day plants than the length of the light period.

🎯 Exam Tip: For short-day plants, the length of the uninterrupted dark period is the most critical factor for flowering.

 

Question 45. Phytochrome is
(a) Reddish phytohormone
(b) Bluish biliprotein pigment
(c) Photoreceptor of apical bud
(d) Unstable pigment molecule
Answer: (b) Bluish biliprotein pigment
In simple words: Phytochrome is a blue-colored protein that plants use to sense light. It helps them react to changes in light, like when to flower. This pigment is essential for a wide array of plant responses, including germination, stem elongation, and shade avoidance.

🎯 Exam Tip: Know the chemical nature and primary function of phytochrome in light perception.

 

Question 46. The growth & ripening is induced by Ethylene in
(a) Tropical fruits
(b) Temperate fruits
(c) Climacteric fruits
(d) Nonclimacteric fruits
Answer: (c) Climacteric fruits
In simple words: Ethylene helps certain fruits, known as climacteric fruits, to ripen and grow. These fruits can continue to ripen even after being picked. This characteristic makes climacteric fruits like bananas and tomatoes easier to harvest early and transport before they fully ripen.

🎯 Exam Tip: Distinguish between climacteric and non-climacteric fruits and their responses to ethylene for ripening.

 

Question 47. The bioassay of ABA was done with
(a) Rice
(b) Wheat
(c) Maize
(d) Barley
Answer: (a) Rice
In simple words: Scientists used rice plants as a test to study the effects of Abscisic acid (ABA), a plant hormone. Rice is a common model plant in physiological studies due to its rapid growth and genetic tractability.

🎯 Exam Tip: Associate common bioassay organisms with the hormones they are used to test.

 

Question 48. Four types of senescence were recognized by
(a) Leopold
(b) Gamer
(c) Addicott
(d) Cocken et al
Answer: (a) Leopold
In simple words: Leopold was the scientist who first identified and described the four different ways plants go through senescence, which is the process of aging. His classification helps in understanding the varied patterns of aging across different plant species and tissues.

🎯 Exam Tip: Know the scientists responsible for major classifications or categorizations in plant biology.

 

Question 49. The final stage of senescence is
(a) PCD
(b) Scarification
(c) Yellowing
(d) Abscission
Answer: (d) Abscission
In simple words: The very last step of plant aging, or senescence, is often abscission, where parts like leaves or fruits fall off the plant. This process ensures that plants shed old or damaged organs efficiently, recycling nutrients before they are lost.

🎯 Exam Tip: Understand the sequence of events during senescence and the key processes involved.

 

Question 50. Match & Find out the Correct Answer

(a) C A B D
(b) D C A B
(c) A D B C
(d) C D B A
Answer: (b) D C A B
In simple words: This question asks you to match important scientists with their discoveries about plant hormones. Yabuta and Sumiki found gibberellin, Lethan and Miller found zeatin, Cocken identified ethylene, and Kogi and Haugen Smith isolated auxin from human urine. These pioneering efforts were fundamental in identifying the key chemical messengers that regulate plant growth and development.

🎯 Exam Tip: Practice matching type questions by creating flashcards of scientists and their key contributions.

 

Question 51. Match the following and Find the Correct Answer

(a) E D B A C
(b) D E A B C
(c) E A B C D
(d) D C A B E
Answer: (b) D E A B C
In simple words: You need to match each plant hormone with its main effect. Auxin is used as a weed killer (d), ABA closes stomata (e), Gibberellin causes rapid stem growth (bolting) (a), Ethylene speeds up respiration (b), and Cytokinin helps cells divide (c). Each plant hormone has specific roles that, when combined, orchestrate the complex symphony of plant growth and development.

🎯 Exam Tip: Create a summary table of each hormone's major physiological effects to ace matching questions.

 

II. Assertion (A) & Reason (R)

 

Question 52. a. Both A & R are true and 'R' is the correct explanation of A
b. Both A & R are true but 'R' is not the correct explanation of A
c. A is true but R is False
d. Both A and 'R' are False
Assertion (A): The shoot Apical meristems are the only source of Auxin synthesis
Reason (R): Dormancy of lateral buds over Apical buds is due to Auxin
Answer: (c) A is true but R is False
In simple words: The assertion (A) states that shoot apical meristems are the only source of auxin synthesis, which is considered true. However, the reason (R), that the dormancy of lateral buds over apical buds is due to auxin, is false. Auxins from the apical bud cause apical dominance, which suppresses the growth of lateral buds. Auxins produced at the shoot apex are responsible for apical dominance, a phenomenon that inhibits the growth of lateral buds.

🎯 Exam Tip: In Assertion-Reason questions, carefully evaluate the truthfulness of both statements and then determine if the reason correctly explains the assertion.

 

Question 53. Assertion (A): Hormones are also called Growth regulator
Reason (R): Hormones promote or inhibit plant growth
Answer: (a) Both Assertion (A) and Reason (R) are true and Reason is the correct explanation of Assertion
In simple words: Both statements are true. Hormones are called growth regulators because they either help or stop plant growth. The second statement explains why they are called growth regulators. Plant hormones, also known as phytohormones, control nearly every aspect of plant life, from germination to senescence.

🎯 Exam Tip: A correct explanation directly links the mechanism or characteristic described in the reason to the statement in the assertion.

 

Question 54. Assertion (A): In many land Mammoth flowering occurred at different times at different latitude
Reason (R): Many land Mammoth is a tobacco variety
Answer: (b) Both Assertion (A) and, Reason (R) are true and Reason is not the correct explanation of Assertion.
In simple words: Both statements are true: land Mammoth plants did flower at different times depending on their location, and land Mammoth is indeed a type of tobacco. However, the fact that it's a tobacco variety doesn't explain *why* it flowers at different times in different places. Flowering time is often influenced by environmental factors like photoperiod and temperature, which vary with latitude.

🎯 Exam Tip: Even if both assertion and reason are true, ensure there's a direct cause-and-effect relationship for the reason to be a "correct explanation."

 

III. 2 Mark Questions

 

Question 1. Define closed form of growth in plants.
Answer: Closed growth in plants means that some parts, like leaves, flowers, and fruits, stop growing once they reach a certain size. They don't keep growing bigger forever. This type of growth ensures that organs mature and fulfill their specific functions within a defined lifespan.
In simple words: Closed growth is when plant parts like leaves and flowers stop growing after reaching a certain size.

🎯 Exam Tip: Use clear and concise language when defining biological terms, and provide examples if possible.

 

Question 2. Compare between Absolute and Relative growth rates
Answer:

In simple words: Absolute growth measures the total increase in size over time. Relative growth, however, looks at how much growth happens compared to the original size of the plant part. Relative growth rate is often more useful for comparing the growth efficiency of different plants or organs.

🎯 Exam Tip: When comparing, ensure you highlight both the similarities (if any) and distinct differences for each point.

 

Question 3. Name the phases of growth in 'S' shaped growth curve.
Answer: The 'S' shaped growth curve, which shows how things grow over time, has four main parts: a slow start (Lag phase), fast growth (Log phase), slowing down (Decelerating phase), and finally reaching full size (Maturation phase). This characteristic sigmoid growth pattern is observed in various biological systems, from microbial cultures to entire organisms.
(i) Lag phase
(ii) Log phase
(iii) Decelerating phase
(iv) Maturation phase
In simple words: The 'S' shaped growth curve has four stages: Lag, Log, Decelerating, and Maturation.

🎯 Exam Tip: List the phases in the correct order as they naturally occur in the growth curve.

 

Question 4. Mention the phase of growth in plants
Answer: Plants grow in three main stages: first, new cells are made (Formative phase); then, these cells get longer (Elongation phase); and finally, they become fully grown and ready for their jobs (Maturation phase). These distinct phases ensure that plant tissues develop correctly, enabling specialized functions throughout the plant body.
(i) Formative phase
(ii) Elongation phase
(iii) Maturation phase
In simple words: The three phases of plant growth are Formative, Elongation, and Maturation.

🎯 Exam Tip: Clearly define what happens in each phase of growth for a complete answer.

 

Question 5. Distinguish between absolute growth rate and relative growth, rate.
Answer:
Absolute growth rate: An increase in total growth of two organs measured and compared per unit time is called absolute growth rate.
Relative growth rate: The growth of the given system per unit time expressed per unit initial parameter is called relative growth rate.
In simple words: Absolute growth measures the overall increase in a plant part's size over a specific time. Relative growth, on the other hand, measures how much growth happens compared to the plant part's initial size. While absolute growth gives a raw measurement, relative growth provides insight into the efficiency of growth at different developmental stages.

🎯 Exam Tip: For distinction questions, it's best to present points side-by-side or clearly label each contrasting aspect.

 

Question 6. What is the Grand period of growth
Answer: The total period from initial to the final stage of growth is called the Grand period of growth. When this growth is plotted against time, the curve formed is 'S' shaped, also known as a sigmoid curve, and it consists of 4 distinct phases:
(i) Lag phase
(ii) Log phase
(iii) Decelerating phase
(iv) Maturation phase
In simple words: The 'Grand period of growth' is the entire time from when a plant starts growing until it reaches its full size. This overall pattern helps scientists understand the complete life cycle and developmental trajectory of a plant.

🎯 Exam Tip: Define the term clearly and mention its characteristic "S"-shaped curve, along with the names of its phases.

 

Question 7. What is meant by the dedifferentiation of plant cells?
Answer: Differentiated cells can multiply and then change to perform new functions. This process is called redifferentiation. For example, secondary xylem and phloem cells go through this. This allows plants to form new tissues when needed.
In simple words: Specialized plant cells can go back to an unspecialized state and then become specialized again for new jobs.

🎯 Exam Tip: Clearly define the term and provide specific examples of plant tissues that undergo this process.

 

Question 8. Define Phytohormone.
Answer: Phytohormones are special chemical substances that plants make naturally. They work like hormones in animals. Examples include Auxin and Gibberellins. These hormones control many aspects of plant growth and development. Recently, Brassinosteroids and Polyamines have also been found to act like plant hormones.
In simple words: These are natural chemicals in plants that control how they grow, like hormones.

🎯 Exam Tip: Mention that phytohormones are naturally produced chemicals and provide at least two common examples to score full marks.

 

Question 9. Mention any two synthetic auxins.
Answer: Two synthetic auxins are 2,4-Dichloro Phenoxy Acetic Acid (2,4-D) and 2,4,5-Trichloro Phenoxy Acetic Acid (2,4,5-T). These man-made substances are often used in agriculture.
In simple words: Two artificial auxins are 2,4-D and 2,4,5-T, used for plant control.

🎯 Exam Tip: Remember the full names along with their abbreviations, as both might be expected.

 

Question 10. State 3 characteristic features of phytohormones.
Answer: Here are three key features of phytohormones: 1. They are made in places like root tips, stem tips, and leaves, but without special organs for making them. 2. They move through the plant using its transport system (xylem and phloem). 3. Only very small amounts of them are needed. These tiny amounts can have big effects on the plant's overall size and shape.
In simple words: Phytohormones are made in growing parts, move through the plant, and work in tiny amounts to affect growth.

🎯 Exam Tip: Focus on where they are produced, how they are transported, and the quantity needed for their effects.

 

Question 11. Name the natural auxins present in plants.
Answer: Natural auxins found in plants include Indole Acetic Acid (IAA), Indole Propionic Acid (IPA), Indole Butyric Acid (IBA), and Phenyl Acetic Acid (PAA). These auxins help in various growth processes, like cell enlargement.
In simple words: Natural auxins include IAA, IPA, IBA, and PAA.

🎯 Exam Tip: List at least three of these natural auxins, making sure to include their full names and abbreviations.

 

Question 12. Give the historial significance of Agent Orange
Answer: Agent Orange was a mixture of two weed-killing chemicals: 2,4-D (2,4-Dichloro Phenoxy Acetic Acid) and 2,4,5-T (2,4,5-Trichloro Phenoxy Acetic Acid). It gained historical importance because the USA used it during the Vietnam War. Its purpose was to remove leaves from forests, acting as a chemical weapon.
In simple words: Agent Orange was a chemical mix used in the Vietnam War to strip leaves from plants.

🎯 Exam Tip: When discussing historical significance, mention both the composition and the specific historical context and use.

 

Question 13. Does the trimming of plants in gardens have any scientific explanation?
Answer: Yes, trimming plants in gardens has a scientific reason. When the top part (apical bud) is cut off, it stops "apical dominance." This means the side buds can grow more, making the plant look bushy and beautiful. This technique is also used in tea plantations to encourage more leaf growth for harvesting.
In simple words: Trimming plants removes the top bud, allowing side branches to grow, making the plant bushier and increasing yield.

🎯 Exam Tip: Explain how removing the apical bud affects apical dominance and leads to a desired plant shape or yield.

 

Question 14. Where do you find cytokinin hormone in plants?
Answer: Cytokinin hormone is mostly found in the roots of plants, unlike auxins and gibberellins which are more widespread. From the roots, cytokinins are transported to other parts of the plant through the xylem, which is the plant's water-carrying tissue.
In simple words: Cytokinins are mainly made in plant roots and then move to other parts through the plant's water tubes.

🎯 Exam Tip: Remember that roots are the primary site of cytokinin production and that they are transported via the xylem.

 

Question 15. What is bolting?
Answer: Bolting is the rapid growth and elongation of a plant's stem, which then leads to flowering. This process can be artificially induced in genetically dwarf plants, such as some rose varieties, by treating them with gibberellins.
In simple words: Bolting is when a plant stem quickly grows long and then flowers, often helped by gibberellins.

🎯 Exam Tip: Define bolting as sudden stem elongation leading to flowering and link it to gibberellin application, especially in dwarf plants.

 

Question 16. What is Richmond Lang effect?
Answer: The Richmond-Lang effect describes how applying cytokinin can slow down the aging process in plants. It does this by moving nutrients to the parts where cytokinin is applied, keeping those parts fresh. This effect highlights cytokinin's role in delaying senescence and maintaining plant vitality.
In simple words: Cytokinin can make plants age slower by sending nutrients to keep certain parts fresh.

🎯 Exam Tip: Clearly state that it involves cytokinin, delays aging (senescence), and works through nutrient mobilization.

 

Question 17. Why do you call Abscisic acid (ABA) as stress hormone?
Answer: Abscisic acid (ABA) is called a stress hormone because it helps plants cope with difficult conditions, like a lack of water. It does this by slowing down the growth of shoots while encouraging the growth of roots. By promoting root growth, ABA enables the plant to find more water and survive drought conditions.
In simple words: ABA is a stress hormone because it helps plants survive tough times, especially water shortages, by controlling their growth.

🎯 Exam Tip: Emphasize ABA's role in inhibiting shoot growth and promoting root growth, specifically as a protective mechanism against water stress.

 

Question 18. Define photoperiodism & Critical day length.
Answer: Photoperiodism is how plants change their growth, especially flowering, based on how long they are exposed to light and darkness each day. The critical day length is the specific amount of light needed to make a plant flower. Some plants need a certain minimum day length to flower, while others need a maximum. For example, the Maryland Mammoth tobacco needs 12 hours of light, and Cocklebur needs 15.05 hours.
In simple words: Photoperiodism is how plants react to day length, and critical day length is the specific light time needed for flowering.

🎯 Exam Tip: Provide clear definitions for both terms and include examples to illustrate critical day length for different plants.

 

Question 19. Write down the importance of photoperiodism in plants.
Answer: Photoperiodism is important in plants for several reasons. Firstly, knowing about it helps a lot in plant breeding experiments, especially when trying to create new plant types (hybridization). Secondly, it shows how an outside factor, like light, can trigger big changes inside a plant's body. This understanding helps farmers and plant breeders control plant development for better yields.
In simple words: Photoperiodism is important for creating new plant types and shows how light affects plant changes.

🎯 Exam Tip: Focus on its application in hybridization and its role as a physiological pre-conditioner influenced by external factors.

 

Question 20. What is the importance of photoperiodism?
Answer: The study of photoperiodism is crucial because it helps in hybridization experiments, where scientists combine different plant types. It also serves as a prime example of how external environmental signals, such as light duration, can trigger significant internal physiological transformations in plants. This allows for better control over plant development.
In simple words: Photoperiodism helps plant breeders and shows how outside conditions cause big changes in plants.

🎯 Exam Tip: Provide two distinct points on the importance, specifically mentioning hybridization and external factors causing physiological changes.

 

Question 21. What is meant by Epigeal germination?
Answer: Epigeal germination is a type of seed sprouting where the seed leaves (cotyledons) come out of the soil and become visible above ground. This happens because the part of the stem below the cotyledons, called the hypocotyl, grows very long and pushes them up. This method allows the cotyledons to perform photosynthesis early in the plant's life. Examples include castor and bean plants.
In simple words: It's when seed leaves pop out of the soil because the stem below them grows long.

🎯 Exam Tip: Clearly explain that cotyledons emerge above ground due to hypocotyl elongation, and provide relevant examples.

 

Question 22. Define Vernalization.
Answer: Vernalization is a process where certain plants, like annuals and biennials, are made to flower earlier by exposing them to cold temperatures for a certain period. This cold treatment helps activate genes related to flowering, ensuring plants flower at the right time in cooler climates. The term was first used by T.D. Lysenko.
In simple words: Vernalization is making plants flower early by giving them a cold treatment.

🎯 Exam Tip: Define it as cold treatment to induce early flowering in annuals and biennials, mentioning its effect on plant development.

 

Question 23. Define the term phytogerontology.
Answer: Phytogerontology is the scientific field within botany that focuses on the study of aging in plants. It examines processes like abscission (shedding of plant parts) and senescence (the overall aging process of plants). Understanding phytogerontology helps us manage plant lifespan and productivity.
In simple words: Phytogerontology is the study of how plants age, including when they shed parts or die.

🎯 Exam Tip: State that it is a branch of botany and clearly list the processes it studies (aging, abscission, senescence).

 

Question 24. Distinguish between Epigeal and Hypogeal germination.
Answer:

Epigeal germination is when seed leaves (cotyledons) are pushed above the soil by the lengthening of the hypocotyl (stem below cotyledons), like in castor and bean. Hypogeal germination is when cotyledons stay underground because the epicotyl (stem above cotyledons) grows long and fast, as seen in maize. These two types represent different strategies for seedling establishment and protection.
In simple words: Epigeal means cotyledons come above soil, while hypogeal means they stay underground.

🎯 Exam Tip: Present the differences in a clear table, focusing on the position of cotyledons and the elongating part of the seedling, with examples.

 

Question 25. Define seed dormancy and what are its types.
Answer: Seed dormancy is when a seed cannot sprout even if conditions like water, warmth, and light are perfect for growth. There are two main types: innate dormancy, which is due to internal factors of the seed itself, and imposed dormancy, caused by external conditions preventing germination. This natural mechanism ensures seeds only germinate when conditions are truly favorable for seedling survival.
In simple words: Seed dormancy is when seeds don't sprout even in good conditions; it can be innate (from inside) or imposed (from outside).

🎯 Exam Tip: Define dormancy clearly as the inability to germinate despite favorable conditions, and list the two main categories of dormancy.

 

Question 26. What is Scarification?
Answer: Scarification is a method used to break seed dormancy. It involves either physically damaging the hard seed coat, like by cutting or chipping it, or using chemicals (organic solvents) to remove waxy or fatty layers. This treatment helps water and gases penetrate the seed, allowing germination to begin. It makes it easier for the seed to sprout.
In simple words: Scarification is roughing up a seed's hard outer coat, either physically or chemically, to help it sprout.

🎯 Exam Tip: Explain scarification as a physical or chemical treatment of the seed coat to break dormancy, allowing water and gases to enter.

 

Question 27. Distinguish between Re differentiation and Devernalization.
Answer:

Redifferentiation is when specialized plant cells multiply and then lose their original function to take on new specific roles, for example, in secondary xylem and phloem. Devernalization, on the other hand, is the reversal of vernalization, meaning the cold-induced flowering effect is undone, often by exposure to high temperatures after the initial cold treatment. These processes showcase the dynamic plasticity and adaptability of plant development.
In simple words: Redifferentiation is when cells change roles; demernalization is when the cold-induced flowering effect is reversed.

🎯 Exam Tip: Clearly define both terms and highlight the key difference: one is about cell fate, the other about reversing a cold-induced developmental process.

 

Question 28. Define Senescence.
Answer: Senescence is the natural process of aging or getting old in plants. It involves a series of collective, gradual, and damaging changes that eventually lead to the complete loss of a plant's structure and function. A common example is when leaves turn yellow and fall off the plant.
In simple words: Senescence is the aging process in plants, leading to a loss of function and eventual death, like leaves turning yellow.

🎯 Exam Tip: Define senescence as the aging process in plants and describe its progressive, deteriorative nature, giving a clear example.

 

Question 29. What is impaction in seed dormancy.
Answer: Impaction is a method to break seed dormancy, specifically when the tiny opening (micropyle) in a seed is blocked by cork cells, stopping water and oxygen from getting in. To overcome this, the seeds are vigorously shaken to dislodge the corky plug. This shaking process, which removes the blockage, is known as impaction.
In simple words: Impaction is shaking seeds hard to clear a blockage, so water and air can get in and they can sprout.

🎯 Exam Tip: Explain impaction as the physical removal of a blockage (e.g., cork cells) in the micropyle by shaking to allow water and oxygen entry.

 

Question 30. What is called stratification in seed dormancy?
Answer: Stratification is a technique used to break seed dormancy by exposing seeds to cool, moist, and well-aerated conditions for several weeks or months, typically at temperatures between \( 0^\circ C \) and \( 10^\circ C \). This cold, moist treatment mimics natural winter conditions, preparing the seed for spring germination. It is commonly used for seeds of Rosaceae plants, such as apples, plums, and peaches.
In simple words: Stratification is giving seeds a cold, wet treatment for a while to help them sprout later.

🎯 Exam Tip: Define stratification as a cold, moist treatment for a specified duration and temperature range, often applied to break dormancy in temperate plant seeds.

 

Question 31. What are the 4 types of Senescence?
Answer: According to Leopold (1961), there are four main types of senescence, or aging, in plants: 1. **Overall senescence:** When the entire plant ages and dies at once. 2. **Top senescence:** Only the upper parts of the plant age, while the roots remain alive. 3. **Deciduous senescence:** Specific organs, like leaves, age and fall off periodically. 4. **Progressive senescence:** Aging starts in older leaves and then moves to younger leaves, stems, and finally roots. Each type reflects a different pattern of resource allocation and survival strategy for the plant.
In simple words: Leopold identified four ways plants age: the whole plant, only the top, just parts like leaves, or a gradual aging from old to new parts.

🎯 Exam Tip: List and briefly describe each of Leopold's four types of senescence, ensuring clarity in their distinct characteristics.

 

Question 32. What is the Abscission layer or Abscission Zone?
Answer: The abscission layer, or abscission zone, is a special area found at the base of a leaf stalk (petiole) or fruit stem. It consists of a few layers of thin-walled cells arranged across the stem. This zone is designed to weaken over time, eventually causing the leaf or fruit to detach from the plant. This separation process is called abscission.
In simple words: The abscission zone is a special layer of cells at the base of leaves or fruits that causes them to fall off.

🎯 Exam Tip: Describe the abscission zone as a specialized layer of cells at the base of a petiole or fruit stalk, responsible for the natural shedding of plant parts.

 

Question 33. The photoperiodic response will not be possible in a defoliated plant. Give scientific reasons.
Answer: Yes, a plant without leaves (defoliated) cannot respond to changes in day length, which is its photoperiodic response. The scientific reason is that the special hormone that triggers flowering, called florigen, is produced in the leaves. Without leaves, the plant cannot detect the light-dark cycle or produce this crucial flowering hormone.
In simple words: A plant without leaves can't flower based on day length because its leaves make the flowering hormone, florigen.

🎯 Exam Tip: State that leaves are the site of photoperiodic perception and florigen production, which is essential for the flowering response.

IV. 3 Mark Questions

 

Question 34. What is gas chromatography?
Answer: Gas chromatography is a scientific method used to separate and analyze different substances in a sample. In botany, it's used as a bioassay technique to accurately measure the amount of ethylene gas produced by plants. This precise measurement helps scientists understand how ethylene influences plant growth and development. It can detect exact ethylene levels from plant parts like lemons and oranges.
In simple words: Gas chromatography is a lab method to measure chemicals like ethylene in plants, helping us understand plant growth.

🎯 Exam Tip: Define gas chromatography as an analytical technique used for measuring specific compounds, and highlight its application in determining ethylene levels in plants.

 

Question 35. Give the occurrence and precursors of Gibberellins and Cytokinins.
Answer:

Gibberellins are found in plant embryos, roots, young leaves, and immature seeds, while cytokinins are mainly formed in root and shoot tips, as well as buds and young fruits. Both hormones play vital roles in plant growth, though they are synthesized from different base molecules. Gibberellins start from a 5-carbon precursor called Isopentenyl Pyrophosphate (IPP), ultimately derived from acetate. Cytokinins, however, are made from a purine base like adenine.
In simple words: Gibberellins are found in young plant parts and seeds, made from IPP (from acetate); cytokinins are in tips, buds, and fruits, made from purine-adenine.

🎯 Exam Tip: Clearly list the primary locations and the main chemical precursors for both gibberellins and cytokinins.

 

Question 1. Explain Arithmetic growth rate and Geometric growth rate by diagrams.
Answer: Arithmetic growth is when one cell divides, but only one of the two new cells keeps dividing, while the other cell grows and stops dividing. This results in a steady, linear increase in the number of cells over time. Geometric growth, however, happens when all new cells produced by division continue to divide themselves. This leads to a much faster, exponential increase in cell numbers, as seen in the early stages of plant development.
In simple words: Arithmetic growth is slow and steady, where only one new cell keeps dividing. Geometric growth is fast, where all new cells keep dividing.

🎯 Exam Tip: Clearly explain that arithmetic growth involves only one daughter cell continuing to divide, while geometric growth involves both daughter cells dividing.

 

Question 2. Explain stages in growth by drawing the sigmoid curve.
Answer: The "Grand period of growth" refers to the entire time a plant or organism grows from start to finish. If you plot the rate of growth against time, the graph usually looks like an 'S' shape, which is called a sigmoid curve. This curve beautifully illustrates how growth starts slow, speeds up, and then slows down again. This growth curve has four main stages: 1. **Lag phase:** Growth is slow at the beginning. 2. **Log phase (or exponential phase):** Growth becomes very fast. 3. **Decelerating phase:** Growth starts to slow down again. 4. **Maturation phase:** Growth stops, and the plant reaches its full size.
In simple words: The sigmoid curve shows the four stages of growth: slow start (lag), rapid growth (log), slowing down (decelerating), and stopping (maturation).

🎯 Exam Tip: Define the Grand period of growth and clearly list and briefly explain each of the four stages of the sigmoid growth curve.

 

Question 3. Mention the internal factors, that affect the growth of plants.
Answer: Inside a plant, several factors influence its growth. These include: * **Genes:** These are the plant's inherited instructions that control how it grows. * **Phytohormones:** These are plant hormones like auxin, gibberellin, and cytokinin, which act as chemical messengers. * **Carbon to Nitrogen (C/N) ratio:** The balance between carbon and nitrogen compounds inside the plant affects its development. These internal factors work together to regulate a plant's overall size and shape.
In simple words: Plant growth is affected by internal factors like genes, plant hormones, and the balance of carbon and nitrogen.

🎯 Exam Tip: List at least two key internal factors like genes and phytohormones, and briefly explain their role in plant growth.

 

Question 4. Mention the Agricultural role of Auxin.
Answer: Auxins play several important roles in agriculture: * **Weed control:** They are used as weed killers, for example, 2,4-D and 2,4,5-T. * **Seedless fruits:** They help in making fruits without seeds (parthenocarpy), like using synthetic auxins for tomatoes. * **Breaking dormancy:** They can help seeds sprout faster. * **Flower induction:** Auxins, like NAA, can make some plants, such as pineapples, flower. * **More female flowers:** They can increase the number of female flowers in plants like gourds (Cucurbita). These applications demonstrate how auxins can be manipulated for improved crop production.
In simple words: Auxins help farmers kill weeds, grow seedless fruits, break seed dormancy, make plants flower, and increase female flowers for better crops.

🎯 Exam Tip: Provide specific examples for at least three agricultural applications of auxins, such as weed eradication, parthenocarpy, or flowering induction.

 

Question 5. List out the agricultural applications of auxins.
Answer: Auxins have many uses in farming. They are good for: * Killing weeds, such as with 2,4-D and 2,4,5-T. * Making fruits without seeds, called parthenocarpic fruits. * Helping seeds to sprout by breaking their resting period. * Making plants like pineapple flower using chemicals like NAA and 2,4-D. * Increasing the number of female flowers and fruits in plants like gourds. By controlling these processes, auxins contribute significantly to modern agricultural practices.
In simple words: Auxins are used in farming to control weeds, produce seedless fruits, help seeds sprout, make specific plants flower, and get more female flowers.

🎯 Exam Tip: List diverse applications like weed control, seedless fruit production, and flowering control, showing the versatility of auxins in agriculture.

 

Question 6. What are the Precursors of Gibberellins?
Answer: Gibberellins are chemically similar to terpenoids, which include things like natural rubber and carotenoids. They are made from 5-carbon units called Isopentenyl Pyrophosphate (IPP). This complex synthesis pathway starts from a simple organic molecule, acetate. So, acetate is considered one of the primary starting materials for making gibberellins.
In simple words: Gibberellins are made from 5-carbon units called IPP, which originally comes from acetate.

🎯 Exam Tip: Identify Isopentenyl Pyrophosphate (IPP) as the 5-carbon precursor and acetate as a primary starting material for gibberellin synthesis.

 

Question 7. What are the uses of ethylene in agriculture?
Answer: Ethylene has several uses in agriculture: * It generally reduces flowering in most plants, but it actually promotes flowering in pineapples and mangoes. * It can increase the number of female flowers while decreasing male flowers. * Spraying ethylene on crops like cucumbers can lead to more female flowers, which then increases the harvest. These applications allow farmers to better manage crop development and productivity.
In simple words: Ethylene helps ripen fruits, makes some plants flower (like pineapples), and can increase female flowers in crops for a better harvest.

🎯 Exam Tip: Mention its dual effect on flowering (reduction in general, promotion in specific cases) and its role in influencing flower sex expression for better yield.

 

Question 8. Explain the mechanism of Vernalization by Hypothesis of hormonal involvement.
Answer: The hypothesis of hormonal involvement explains vernalization, which is the cold treatment needed for flowering. It suggests that a "Precursor" substance is changed into an unstable "Substance B" during chilling. This unstable substance then turns into a stable "Substance D," also known as Vernalin. Vernalin is then believed to be converted into Florigen, the flowering hormone, which ultimately causes the plant to flower. If the plant experiences high temperatures after vernalization, this process can be reversed, leading to "Devernalization," where Florigen is converted into a different "Substance C," preventing flowering.
In simple words: Cold changes a plant substance into Vernalin, which then becomes Florigen (the flowering hormone). Heat can reverse this, stopping flowering.

🎯 Exam Tip: Describe the transformation of substances from precursor to Florigen via Vernalin, and how high temperatures can reverse this process (devernalization).

 

Question 9. What are the practical applications of Vernalization?
Answer: Vernalization has practical uses that benefit farming: * It makes plants flower earlier by shortening the time they spend just growing leaves and stems. * It helps plants become more resistant to cold weather. * It also boosts their ability to fight off fungal diseases. * This technique can speed up the process of creating new plant varieties through plant breeding. Overall, vernalization helps improve crop quality and accelerate development.
In simple words: Vernalization helps plants flower earlier, become stronger against cold and disease, and speeds up plant breeding.

🎯 Exam Tip: List at least three practical benefits, such as inducing early flowering, increasing cold resistance, or accelerating plant breeding.

 

Question 10. What is meant by the viability of seeds?
Answer: The viability of seeds refers to whether a seed is alive and capable of germinating, or sprouting. The "viable period" is the length of time a seed can remain alive and able to germinate. This period is not the same for all plants; it varies greatly depending on the species. For instance, Oxalis seeds are viable for only a few days, while Lotus seeds can remain viable for over 1000 years, and Judean Date Palm seeds (Methuselah) for more than 2000 years.
In simple words: Seed viability means if a seed is alive and can sprout. This "life span" is different for every plant.

🎯 Exam Tip: Define viability as the ability of a seed to germinate and state that the viable period varies significantly among different plant species, giving examples.

 

Question 11. Differentiate between climacteric and non-climacteric fruits.
Answer:

Climacteric fruits show a sudden increase in their breathing rate when they are about to ripen. They can also be ripened on purpose by being exposed to ethylene gas or normal air conditions. Examples include lemons, apples, bananas, and mangoes. Ethylene is a key hormone that triggers ripening in these fruits. Non-climacteric fruits, however, do not ripen further once picked and cannot be ripened by ethylene exposure. Grapes, watermelon, and oranges are examples of non-climacteric fruits.
In simple words: Climacteric fruits ripen after picking and can be forced to ripen, while non-climacteric fruits do not ripen further once picked.

🎯 Exam Tip: Clearly differentiate based on their respiration pattern during ripening, response to ethylene, and whether they ripen post-harvest, providing examples for each type.

 

Question 12. Differentiate between scarification & Stratification in breaking seed dormacy
Answer:

In simple words: Scarification means physically breaking or softening a seed's tough outer layer, while stratification means chilling and moistening seeds for a long time to make them sprout. Both methods help seeds grow.

🎯 Exam Tip: Remember that scarification is a physical or chemical process affecting the seed coat, while stratification is an environmental treatment (cold and moisture) that affects the embryo's readiness to grow.

 

Question 13. Mention the factors causing dormancy of seeds.
Answer: Seed dormancy, which prevents seeds from germinating even under suitable conditions, can be caused by several factors:

• A hard, tough seed coat prevents water and gases from reaching the embryo, and it can also restrict the embryo from expanding. This is a common physical barrier.
• Many types of seeds have embryos that are not fully grown or developed at the time of dispersal; these are called rudimentary embryos and need time to mature.
• Some seeds need a specific amount of light to germinate. If they do not get this light, they remain dormant.
• Dormancy can also be caused by temperatures that are either too high or too low for germination.
• Certain chemicals, known as inhibitors (like phenolic compounds), can be present in the seed and stop it from germinating.

In simple words: Seeds may not grow because their outer shell is too tough, the baby plant inside is not ready, they need a special amount of light, the temperature is wrong, or they have chemicals that stop them from sprouting.

🎯 Exam Tip: When listing dormancy factors, categorize them into physical (seed coat), embryonic (immature embryo), environmental (light, temperature), and chemical (inhibitors) for a comprehensive answer.

 

Question 14. What are the factors that affect senescence?
Answer: Senescence, or the aging process in plants, is influenced by various internal and external factors:

In simple words: Plant aging is sped up by hormones like ABA and Ethylene, high temperatures, and lack of water. It slows down with enough nitrogen and cool temperatures.

🎯 Exam Tip: When discussing factors affecting senescence, remember to distinguish between hormones that promote aging (like ABA and Ethylene) and those that delay it (like auxins and cytokinins), as well as environmental factors.

 

Question 15. What are the morphological and Anatomical changes due to Abscission?
Answer: Abscission is the process where plants shed parts like leaves, flowers, and fruits. This process involves specific morphological (visible) and anatomical (internal structure) changes:

• An Abscission Zone forms at the base of the petiole (leaf stalk). This is where the leaf will detach.
• This zone often appears as a greenish-grey area and consists of 2 to 15 layers of cells with thick primary walls and a middle lamella (a layer that cements plant cells together).
• Internally, the dissolution (breaking down) of pectinase and cellulase enzymes helps to weaken the cell walls in the abscission zone.
• Tyloses (outgrowths in xylem vessels) form, which block the movement of water and nutrients, preparing the leaf for detachment.
• Chlorophyll degrades, causing leaves to change color (often to yellow or brown) before they fall off. This is why leaves change color in autumn.
• After abscission, the outer layers of cells develop a waxy substance called suberin (Suberization) to form a protective periderm, sealing the wound left by the fallen leaf.

In simple words: When a plant part falls off, a special zone forms at its base. Cells in this zone break down, and tubes inside get blocked. The plant part changes color and then drops, leaving behind a sealed wound.

🎯 Exam Tip: Focus on the sequential changes: the formation of the abscission zone, enzymatic breakdown, blocking of transport, visible color change, and finally, the protective sealing of the wound.

 

Question 16. Write down the significance of Abscission.
Answer: Abscission is an important process for plants, serving several key functions:

1. It helps the plant shed dead or old parts like leaves and ripe fruits, which are no longer useful or could harbor diseases.
2. Abscission helps in spreading fruits, which in turn helps continue the plant's life cycle by dispersing seeds.
3. For deciduous plants (plants that shed leaves seasonally), leaf abscission during summer helps conserve water by reducing transpiration from leaves.
4. It plays a role in vegetative propagation by shedding gemmae or plantlets, as seen in some plants like Bryophyta, allowing new plants to grow.

In simple words: Abscission helps plants get rid of old parts, spread seeds, save water in dry times, and grow new plants from special buds.

🎯 Exam Tip: When describing the significance of abscission, remember to include examples for better understanding, like deciduous trees for water conservation and fruits for seed dispersal.

 

V. 5 Mark Questions

 

Question 1. Describe an experiment to measure the growth of a plant or By lever Auxanometer measure the rate of growth in stem tip.
Answer: An arc auxanometer is a device used to measure the growth rate, particularly the increase in length, of a plant's stem tip. Here is how the experiment works:

Experiment: Arc Auxanometer
The arc auxanometer consists of a small pulley. A long pointer is attached to the axis of this pulley, which can slide over a graduated arc. One end of a thread is tied to the stem tip of the potted plant, and the other end is attached to a weight, which keeps the thread taut as it passes over the pulley. As the stem tip grows longer, the pulley rotates, and the pointer moves along the graduated arc. By reading the movement on the arc, the actual increase in the stem's length can be calculated. This calculation is done by knowing the length of the pointer and the radius of the pulley. For example, if the radius of the pulley is 4 inches and the length of the pointer is 20 inches, the actual growth can be calculated using the formula:
Actual growth in length = (Distance travelled by the pointer × Radius of the pulley) / Length of the pointer
For example, if the pointer moves a distance of 10 inches along the arc, then the actual growth in length = (10 × 4) / 20 = 2 inches.
In simple words: To measure how fast a plant stem grows, we use a tool called an auxanometer. It has a string tied to the plant stem, which goes over a wheel and is pulled by a weight. As the plant grows, the string moves the wheel, and a pointer shows the growth on a scale. We can then calculate the plant's actual growth using a simple math formula.

🎯 Exam Tip: When describing the auxanometer, ensure you clearly explain the function of each part (pulley, pointer, thread, weight) and how the plant's growth translates into a measurable reading on the graduated arc.

 

Question 2. Explain the physiological effect of Auxin? Add a note on its agricultural applications.
Answer: Auxins are a group of plant hormones that play a crucial role in plant growth and development. They are involved in many physiological processes and have significant agricultural applications.

Physiological Effects:

• Cell Elongation: Auxins promote the lengthening of cells, especially in stems and coleoptiles (the protective sheath covering the young shoot of monocotyledons). This effect is central to primary growth.
• Root Growth: At very low concentrations, auxins encourage root growth. However, at higher concentrations, they can inhibit root elongation while still promoting the formation of more lateral roots.
• Apical Dominance: Auxins produced by the apical (tip) bud suppress the growth of lateral buds. This means the plant grows upwards rather than sideways.
• Prevents Abscission: Auxins delay the shedding of leaves, flowers, and fruits by preventing the formation of the abscission layer.
• Secondary Growth: They stimulate cell division in the cambium, which is responsible for the plant's increase in girth (secondary growth). This property is used in tissue culture to help callus formation.
• Respiration: Auxins can stimulate cellular respiration, providing the energy needed for growth.
• Vascular Differentiation: They induce the formation of vascular tissues (xylem and phloem).

Agricultural Applications:

• Weedicides: Synthetic auxins like 2,4-D and 2,4,5-T are used as weed killers, particularly for broad-leaved weeds, without harming monocot crops.
• Induce Parthenocarpy: Auxins can induce the development of seedless fruits (parthenocarpy), such as in tomatoes, without fertilization. This is beneficial for fruit production.
• Break Dormancy: They are used to break seed and bud dormancy, allowing for earlier and more uniform germination or sprouting.
• Induce Flowering: In some plants, like pineapple, auxins can be used to promote uniform flowering.
• Induce Female Flowers: Auxin sprays can increase the number of female flowers in plants like cucumbers, leading to higher fruit yield.
• Rooting in Cuttings: Auxins are widely used to promote root formation in stem cuttings, which helps in vegetative propagation of many plants.

In simple words: Auxins make plant cells grow longer, help roots form, and make plants grow tall instead of bushy. Farmers use auxins to kill weeds, grow fruits without seeds, make seeds sprout, and help new plants grow from cuttings.

🎯 Exam Tip: When explaining auxin's effects, highlight its dual role in promoting growth (like cell elongation) and inhibiting it (like apical dominance on lateral buds), and clearly separate its natural functions from its human-applied uses.

 

Question 3. Give the Agricultural application of Auxin.
Answer: Auxins have several important applications in agriculture to enhance plant growth and yield:

• Weedicides: Synthetic auxins like 2,4-D and 2,4,5-T are used to eliminate weeds, particularly broad-leaved weeds, in fields without harming cereal crops.
• Induce Parthenocarpy: Auxins can trigger the development of fruits without fertilization, resulting in seedless fruits (e.g., tomatoes). This improves fruit quality and market value.
• Break Seed Dormancy: They are used to help seeds germinate by breaking their dormant state, leading to more uniform sprouting.
• Induce Flowering: In certain plants, such as pineapple, auxins can be applied to encourage flowering at a desired time, allowing for synchronized harvesting.
• Induce Female Flowers: Applying auxin sprays can increase the ratio of female flowers in some plants like cucumbers, which leads to a higher fruit yield.
• Promote Rooting: Auxins are commonly used to stimulate root formation in stem cuttings, a key method for propagating many plants vegetatively.

In simple words: Auxins help farmers by killing weeds, making fruits without seeds, helping seeds sprout, making flowers bloom when needed, increasing female flowers for more fruit, and helping new plant cuttings grow roots.

🎯 Exam Tip: Focus on practical, real-world examples for each application, such as 2,4-D for weed killing or parthenocarpy in tomatoes, to demonstrate a clear understanding.

 

Question 4. Explain physiological effects of Gibberellins
Answer: Gibberellins are a class of plant hormones that regulate various growth and developmental processes. Here are their key physiological effects:

• Induction of Cell Division & Cell Elongation: Gibberellins promote both the division and elongation of cells, leading to significant stem elongation. They are particularly known for causing extraordinary stem lengthening, often called 'bolting.'
• Reversal of Dwarfism & Bolting: In genetically dwarf plants (rosette plants), gibberellin treatment can cause excessive internodal growth, making them grow to a normal height. This sudden stem elongation followed by flowering is known as bolting.
• Breaks Dormancy: Gibberellins are effective in breaking dormancy in many seeds and buds, including potato tubers, allowing them to germinate or sprout earlier.
• Biennials Flower in the 1st Year: Biennial plants typically flower in their second year after a period of cold exposure (vernalization). However, treating biennials with gibberellins can induce them to flower in their first year itself, bypassing the need for cold.
• Fruit Development: Gibberellins can influence fruit growth and development, leading to larger fruit sizes in some cases, such as in grapes.

In simple words: Gibberellins make plant stems grow very long and can turn dwarf plants into tall ones. They help seeds and buds wake up from rest and can make some plants flower in their first year instead of waiting.

🎯 Exam Tip: Remember that gibberellins are most strongly associated with stem elongation and overcoming dormancy, often enabling plants to bypass specific environmental requirements like vernalization.

 

Question 5. Write an essay on the role of ethylene on plant physiology and agriculture.
Answer: Ethylene is a simple gaseous plant hormone that plays a crucial role in various aspects of plant physiology and has significant applications in agriculture. It is produced by almost all plant tissues in very small amounts.

1. Discovery: Ethylene's role was first observed in 1924 by Denny, who found it stimulated lemon ripening. In 1934, R. Gane discovered that ripe bananas produce abundant ethylene. By 1935, Cocken and colleagues identified ethylene as a natural plant hormone. This helped scientists understand how plants communicate internally.

2. Occurrence: Ethylene production increases during the climacteric ripening of fruits and during senescence (aging). It is found in almost all parts of a plant, including roots, leaves, flowers, fruits, and seeds.

3. Transport in plants: Being a gas, ethylene easily diffuses within the plant through intercellular spaces, allowing it to act on various tissues. This widespread movement allows it to impact the entire plant. However, it can also be transported through the xylem and phloem.

4. Precursor: Ethylene is derived from the amino acid methionine, along with linolenic acid and fumaric acid, through specific biochemical pathways.

5. Bioassay (Gas Chromatography): Ethylene's gaseous nature allows it to be measured accurately using gas chromatography. This technique is vital for determining the exact amount of ethylene in different plant tissues, such as lemons and oranges, which helps in controlled ripening processes.

6. Physiological Effects:

• Ethylene stimulates respiration and ripening in fruits, which is why it's often used commercially for ripening.
• It promotes radial growth in stems and roots but inhibits linear (lengthwise) growth, making stems thicker rather than taller.
• It breaks the dormancy of buds, seeds, and storage organs, enabling them to sprout.
• It triggers the formation of an abscission zone in leaves, flowers, and fruits, leading to their premature shedding.
• It inhibits stem elongation, leading to shorter internodes.
• At low concentrations, ethylene helps in root initiation.
• It promotes the growth of lateral roots and root hairs, increasing the plant's absorption surface.
• Ethylene can stimulate fruit growth in some plants, particularly climacteric fruits.
• It causes epinasty, which is the downward bending of leaves or other plant parts.

7. Agricultural Role:

• Ethylene generally reduces flowering in most plants, but it promotes it in specific cases like pineapple and mango.
• It can increase the number of female flowers and decrease the number of male flowers in some crops, which can be desirable for fruit production.
• Ethylene sprays on cucumber crops can increase female flower production and boost the overall yield.
• It is widely used in commercial settings for the artificial ripening of fruits such as bananas, mangoes, and tomatoes.

In simple words: Ethylene is a gas that helps plants ripen fruits, causes parts to fall off, and makes stems grow thicker. Farmers use it to ripen fruits faster, control flowering, and increase crop yields. It is a simple hormone with powerful effects.

🎯 Exam Tip: When writing about ethylene, emphasize its gaseous nature and its primary role in ripening and senescence, providing examples for both physiological effects and agricultural uses.

 

Question 6. Explain the physiological Effects of Cytokinins.
Answer: Cytokinins are plant hormones that play a key role in cell division and differentiation. Here are their main physiological effects:

• Promotes Cell Division: In the presence of auxin (IAA), cytokinins strongly promote cell division, especially in tissue culture. This balanced interaction is vital for growth.
• Induces Cell Enlargement: Along with IAA and gibberellins, cytokinins help in cell enlargement, contributing to overall plant growth.
• Breaks Dormancy: They can break the dormancy of certain light-sensitive seeds (like tobacco) and induce seed germination, allowing new plants to sprout.
• Promotes Lateral Bud Growth: Cytokinins encourage the growth of lateral buds, even when apical dominance (suppression by the main tip) is present. This leads to bushier plants.
• Delays Aging: Cytokinins delay the aging process (senescence) by promoting nutrient mobilization. This is known as the Richmond-Lang effect, keeping leaves green longer.
• Induces Protein Synthesis: They increase the rate of protein synthesis, which is essential for cell growth and repair.
• Induces Interfascicular Cambium Formation: Cytokinins help form the interfascicular cambium, which contributes to secondary growth in stems.
• Overcomes Apical Dominance: By promoting lateral bud growth, cytokinins counteract the inhibitory effect of the apical bud.
• Induces New Leaves, Chloroplast, and Lateral Shoots: They stimulate the development of new leaves, chloroplasts (for photosynthesis), and side shoots.
• Induces Solute Accumulation: Cytokinins actively help plants accumulate solutes, which aids in water uptake and overall cell function.

In simple words: Cytokinins make plant cells divide and grow bigger. They help seeds sprout, make plants grow bushy with many side shoots, and keep leaves from getting old too quickly. They also help plants make important proteins and take in nutrients.

🎯 Exam Tip: Highlight the primary role of cytokinins in cell division and their synergistic relationship with auxins. Also, remember their anti-aging (Richmond-Lang effect) and apical dominance-overcoming properties.

 

Question 7. Write down the physiological effects of Ethylene
Answer: Ethylene is a gaseous plant hormone with several key physiological effects that influence plant growth and development:

• Stimulates Respiration and Ripening of Fruits: Ethylene significantly increases the rate of respiration in fruits, leading to their ripening. This is why it is often used commercially to ripen fruits.
• Stimulates Radial Growth and Inhibits Linear Growth: It promotes the thickening of stems and roots (radial growth) but reduces their growth in length (linear growth). This can lead to a more compact plant.
• Breaks Dormancy: Ethylene can help break the dormancy of buds, seeds, and storage organs like tubers, allowing them to sprout or germinate.
• Stimulates Abscission: Ethylene accelerates the formation of an abscission zone, causing parts like leaves, flowers, and fruits to detach and fall off prematurely.
• Prevents Stem Elongation: It inhibits the lengthening of internodes (the parts of the stem between leaf attachments), which can result in shorter, sturdier plants.
• Root Growth in Low Concentration: At very low concentrations, ethylene promotes the growth of roots.
• Stimulates Growth of Lateral Roots and Root Hairs: It encourages the development of side roots and root hairs, which increases the surface area for water and nutrient absorption.
• Ripening of Fruits: Ethylene enhances the ripening process in climacteric fruits (e.g., mango, banana, apple) by initiating a burst of respiration.
• Epinasty: It causes epinasty, which is the downward curving of leaves, often due to faster growth on the upper side of the petiole.

In simple words: Ethylene makes fruits ripen, helps plants shed old parts, and makes stems grow wider instead of taller. It also helps roots grow and makes leaves bend downwards.

🎯 Exam Tip: Remember to link ethylene's gaseous nature to its effect on ripening and senescence. Its unique effect of stimulating radial growth while inhibiting linear growth is a key distinguishing feature.

 

Question 8. Describe the methods of breaking the dormancy of seeds in plants.
Answer: Seed dormancy prevents seeds from germinating even when conditions are favorable. Various methods can be used to break this dormancy:

1. Scarification: This involves physically or chemically treating the tough seed coat to make it permeable to water and gases. Mechanical treatments include cutting, chipping, or rubbing the seed coat. Chemical treatments use organic solvents to remove waxy or fatty compounds. These methods mimic natural processes like digestion by animals or abrasion in soil.2. Impaction: In some seeds, the micropyle (a small opening) can be blocked by cork cells, preventing water and oxygen from entering. Impaction involves vigorously shaking these seeds to dislodge the plug, allowing the seed to hydrate and respire.3. Stratification: This method requires exposing seeds of certain plants (like Rosaceae family members such as apple, plum, peach, and cherry) to well-aerated, moist, and low-temperature conditions (0°C to 10°C) for weeks to months. This cold, moist period simulates winter, preparing the embryo for germination.4. Alternating Temperatures: For some seeds, germination is strongly promoted by cycles of alternating low and high daily temperatures. This fluctuating temperature improves seed germination by signaling a favorable seasonal change.5. Light: The dormancy of photoelastic seeds (seeds that respond to light) can be broken by exposing them to specific wavelengths of light, particularly red light. This stimulates the phytochrome system, which then triggers germination processes.

In simple words: To make dormant seeds sprout, we can scratch their hard outer shell (scarification), shake them to clear tiny holes (impaction), give them a cold, wet period (stratification), or expose them to changing temperatures or light.

🎯 Exam Tip: Organize your answer by distinct methods, clearly explaining what each method does (e.g., "scarification involves breaking the seed coat") and, if possible, mention why it's effective.

 

Question 9. Define photoperiodism – Classify plants based on photoperiodism
Answer:

a. The physiological change in plants, particularly related to flowering, that occurs in response to the relative lengths of light and darkness (photoperiod) is called Photoperiodism.

• Gamer and Allard coined the term "photoperiodism" in 1920 after studying a variety of soybean called Biloxi (Glycine max) and different varieties of tobacco, which helped establish this concept.

b. Plants are classified into several types based on their photoperiodic responses for flowering:

1. Long-Day Plants (LDP): These plants need a photoperiod (light period) that is longer than a certain critical day length to induce flowering, along with short nights. The critical day length is usually more than 12 hours. For example, Pea, Barley, and Oats are long-day plants. In these plants, long periods of light promote the transition to flowering.

2. Short-Day Plants (SDP): These plants require a photoperiod that is shorter than a critical day length to induce flowering, usually with long, uninterrupted dark periods. For example, Tobacco, Cocklebur, Soya, Rice, and Chrysanthemum are short-day plants. Some short-day plants also need long days during their early growth period for flowering, such as certain varieties of Bryophyllum & Night Jasmine.

3. Intermediate Day Plants: These plants need a specific range of photoperiod, neither too long nor too short, to flower. They require a photoperiod between a long day and a short day. Examples include Sugarcane and Coleus.

4. Day-Neutral Plants (DNP): These plants can flower under all possible photoperiods (short, long, or intermediate days) as their flowering is not controlled by day length. Examples include Potato, Rhododendron, Tomato, and Cotton. Their flowering is mainly driven by internal developmental signals.

In simple words: Photoperiodism is how plants react to how long the day is, especially for flowering. Plants are grouped by this: 'Long-Day' plants need many hours of light to flower, 'Short-Day' plants need fewer hours of light, 'Intermediate Day' plants need a specific range of light hours, and 'Day-Neutral' plants flower no matter how long the day is.

🎯 Exam Tip: Clearly define photoperiodism first, then accurately classify plants based on their light requirements for flowering, providing common examples for each category. Remember the critical role of the uninterrupted dark period, especially for short-day plants.

 

Question 10. Describe the role of phytochrome in inducing Flowering
Answer:

Definition: Phytochrome is a bluish biliprotein, a type of pigment, that is responsible for sensing light in plants during various photophysiological processes. It exists in two interconvertible forms, Pr and Pfr, which are mainly involved in inducing flowering. These forms act as a switch, telling the plant about the length of day and night.

• Butler et al. (1959) were instrumental in naming this crucial pigment.
• Phytochrome exists in two forms that can change into each other depending on the light conditions.

Mechanism:

During the day, Pr (inactive form) quickly changes to Pfr (active form) when it absorbs red light (660 nm). During the night, Pfr slowly changes back to Pr. The amount of Pfr available at the end of the day determines if the plant will flower. For short-day plants, a low level of Pfr after a long night triggers flowering. For long-day plants, a high level of Pfr or a short night that keeps Pfr levels high is needed for flowering. This mechanism acts as the plant's internal clock, sensing day length.

Other functions:Phytochrome also plays a role in seed germination and causes changes in membrane conformation within cells. This helps the plant respond to light cues in various ways, not just flowering.

In simple words: Phytochrome is like a plant's light switch that tells it when to flower. It has two forms: one absorbs red light and changes to the other, which absorbs far-red light. The balance between these forms, based on how long it's light or dark, tells the plant if it's time to bloom.

🎯 Exam Tip: When explaining phytochrome, focus on the interconversion between Pr and Pfr forms and how the ratio of these forms, especially Pfr, acts as the signal for flowering in short-day and long-day plants.

 

Question 11. Write an Essay on Vernalization
Answer:

Definition: Vernalization is a process where many annual and perennial plants are induced to flower by exposing them to low temperatures (typically 0°C to 5°C). This treatment allows plants to achieve reproductive maturity earlier than they would naturally. T.D. Lysenko was the first to widely use this term.

Mechanism of Vernalization: Two main theories explain how vernalization works:

1. Hypothesis of Phasic Development (T.D. Lysenko): This theory suggests that an annual plant's development occurs in two distinct phases:

• Thermostage-Vegetative Stage: This initial stage requires low temperatures and adequate moisture. During this phase, the plant prepares for flowering by completing its vegetative growth.
• Photostage: After the cold treatment, the plant needs high temperatures and suitable light conditions to synthesize florigen, a hypothetical flowering hormone.

2. Hypothesis of Hormonal Involvement (Purvis 1961): This theory proposes that specific hormonal substances are involved in the vernalization process. It suggests a sequence of substance transformations:

Precursor \( \rightarrow \) Substance A (Chilling) \( \rightarrow \) Substance B (unstable)
Substance B (unstable) \( \xrightarrow{\text{proper temperature}} \) Substance D (stable) (Vernalin)
Substance D or Vernalin \( \rightarrow \) Substance F (Florigen)
Florigen \( \xrightarrow{\text{induces}} \) Flowering

In this model, cold treatment converts an unstable precursor into a stable compound called Vernalin, which then leads to the formation of Florigen, the actual flowering hormone.

The Technique of Vernalization:

• Seeds are soaked in water to ensure they are fully hydrated.
• They are then allowed to germinate briefly at a temperature range of 10°C to 12°C.
• After this initial germination, the seeds are transferred to low-temperature conditions (3°C to 5°C) for a period ranging from a few days to 30 days.
• Once the cold treatment is complete, the germinated seeds are allowed to dry and then sown.
• This process ensures quickened flowering compared to untreated control seedlings.

Devernalization: The effect of vernalization can sometimes be reversed if the plant is exposed to high temperatures immediately after the cold treatment before the flowering process is fully established. This reversal is called Devernalization. Florigen \( \xrightarrow{\text{high temperature}} \) Substance C (Devernalization)

Practical Applications:

• Vernalization shortens the vegetative growth period, causing plants to flower earlier, which can lead to multiple harvests in a single growing season.
• It increases the cold resistance of plants, making them more resilient to adverse weather conditions.
• It boosts the resistance of plants to fungal diseases, improving overall plant health.
• Vernalization accelerates plant breeding by reducing the time required for plants to flower, allowing breeders to complete more generations per year.

In simple words: Vernalization is a method where plants are given a cold treatment to make them flower sooner. This helps farmers get crops faster, makes plants stronger against cold, and helps scientists create new plant types more quickly.

🎯 Exam Tip: For an essay on vernalization, include a clear definition, discuss both the phasic development and hormonal involvement theories, describe the practical technique, and list its agricultural benefits.

 

Question 12. Define Senescence and give its types
Answer:

Definition: Senescence refers to the aging or getting old process in plants. It encompasses all the collective, progressive, and deteriorative changes that ultimately lead to the complete loss of organization and function of cells, tissues, organs, or the entire plant. This process results in visible signs like leaves turning yellow and eventually falling off.

Types – 4 types (Leopold -1961): Leopold (1961) explained four main types of senescence:

1. Overall Senescence: This type occurs when the entire plant is affected and eventually dies. It is common in annual plants like wheat and soybeans, where the whole plant completes its life cycle and then senesces. Perennial plants like Agave and Bamboo also show overall senescence after flowering.
2. Top Senescence: In this type, only the aerial (above-ground) parts of the plant undergo senescence, while the underground parts (like bulbs or rhizomes) remain alive. Examples include perennial plants like Banana and Gladiolus, where the shoots die back but the rootstock survives to grow again.
3. Deciduous Senescence: This occurs when only the leaves senesce and fall off, while the rest of the plant (stem, branches, roots) remains alive. This is typical of deciduous trees like Elm and Maple, which shed their leaves seasonally to conserve water or survive cold periods.
4. Progressive Senescence: This type of senescence occurs progressively, starting with older leaves or parts and then moving to younger ones, stems, and finally the root system. It is observed in annual plants where older leaves senesce first, followed by newer leaves, then the stem, and finally the roots.

In simple words: Senescence is simply how plants get old and eventually die. There are different ways plants age: the whole plant can die (overall), only the top parts die (top), only leaves fall off (deciduous), or older parts die first, then newer ones (progressive).

🎯 Exam Tip: Clearly define senescence as a progressive, deteriorative process. When listing types, provide distinct examples for each to illustrate the different patterns of aging in plants.

 

Question 13. Explain the physiology of senescence and Factors affecting senescence
Answer:

Physiology of Senescence: Senescence is a highly organized and genetically controlled process in plants involving a series of physiological changes:

• Change in the structure of cells: Cells undergo structural degradation, leading to a decline in their function.
• Vacuoles act like lysosomes: The vacuoles in plant cells become more acidic and release hydrolytic enzymes (like proteases and nucleases). These enzymes break down cellular components, much like lysosomes in animal cells.
• Reduction in photosynthetic rate: There is a significant decrease in the rate of photosynthesis due to the loss of chlorophyll (leading to yellowing) and an accumulation of anthocyanin pigments, reducing the plant's ability to produce food.
• Decrease in Starch and Protein content: Stored food reserves, such as starch and proteins, are broken down and mobilized from senescing organs to younger, growing parts of the plant.
• Decrease in r RNA level: There is a notable decrease in ribosomal RNA (rRNA) levels, indicating reduced protein synthesis, which is linked to increased activity of the enzyme RNA ase (ribonuclease).
• Degeneration of DNA: DNA also degenerates due to increased activity of DNA ase (deoxyribonuclease), impairing the cell's ability to repair and maintain genetic material.

Factors Affecting Senescence: Both internal and external factors influence the onset and progression of senescence:

In simple words: Senescence is when plants get old, causing cells to break down, leaves to turn yellow, and food to be moved to younger parts. Hormones like ABA and ethylene speed it up, while good nitrogen and cool weather slow it down.

🎯 Exam Tip: When explaining the physiology, focus on the breakdown of key cellular components (chlorophyll, starch, protein, DNA) and the role of vacuoles. For factors, differentiate between internal hormones and external environmental conditions.

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