Selina Concise Solutions for ICSE Class 10 Biology Chapter 4 Transpiration

Exercise (A)

Question 1. Transpiration pull will be maximum under which set of the following conditions?
(a) Open stomach, dry atmosphere and moist soil
(b) Open stomata, high humid atmosphere and well irrigated soil
(c) Open stomata, high humid atmosphere and dry soil
(d) Closed stomata, dry atmosphere and dry soil
Answer: (a) Open stomach, dry atmosphere and moist soil
In simple words: Transpiration works like a straw effect - it's strongest when the stomata (leaf pores) are open, the air is dry (pulls water out fast), and soil is moist (provides water supply).

📝 Teacher's Note: Use the analogy of wet clothes drying faster on a hot, dry day versus a humid day. Students often confuse "stomach" with "stomata" - address this spelling carefully.

🎯 Exam Tip: Remember the three conditions for maximum transpiration: open stomata + dry air + moist soil. This combination creates the strongest water-pulling force.

Question 2. With decrease in atmospheric pressure, the rate of transpiration will
(a) increase
(b) decrease rapidly
(c) decrease slowly
(d) remain the same
Answer: (a) increase
In simple words: Lower air pressure makes it easier for water to evaporate from leaves, just like how water boils faster at high altitudes where pressure is low.

📝 Teacher's Note: Connect this to why mountaineers need more water at high altitudes - the same principle applies to plants. Demonstrate with a vacuum pump if available.

🎯 Exam Tip: Remember: low pressure = easy evaporation = high transpiration. Think of high altitude locations where clothes dry faster.

Question 3. The rate of transpiration is more when
(a) atmosphere is dry
(b) temperature is high
(c) humidity is high
(d) atmosphere is dry and temperature is high
Answer: (b) temperature is high
In simple words: Higher temperature gives water molecules more energy to escape as vapor, like how a hot pan makes water evaporate faster than a cold one.

📝 Teacher's Note: Ask students why option (d) seems tempting but isn't the best answer. Emphasize that temperature is the primary factor among the given options.

🎯 Exam Tip: When multiple factors affect transpiration, temperature usually has the strongest direct effect on the evaporation process itself.

Question 4. One of the internal factors which affect the rate of transpiration is
(a) big size of the leaf
(b) colour of the leaf
(c) sunken stomata
(d) sunny day
Answer: (c) sunken stomata
In simple words: Sunken stomata are like pores hidden in valleys on the leaf surface, which reduces water loss compared to stomata on flat surfaces.

📝 Teacher's Note: Draw a cross-section showing normal vs sunken stomata. Explain how desert plants use this adaptation. Option (d) is clearly external.

🎯 Exam Tip: Internal factors are structural features of the plant itself. External factors are environmental conditions like weather.

Question 5. Guttation takes place through
(a) stomata
(b) lenticels
(c) lower epidermis of leaves
(d) hydathodes
Answer: (d) hydathodes
In simple words: Hydathodes are special water-releasing pores at leaf tips that push out liquid water droplets, like tiny water taps on leaves.

📝 Teacher's Note: Show examples of guttation on grass tips in early morning. Students often confuse guttation (liquid water) with transpiration (water vapor).

🎯 Exam Tip: Guttation = liquid water droplets through hydathodes. Transpiration = water vapor through stomata. Don't mix these up!

Question 6. The loss of water as water vapour from the aerial parts of a plant is known as
(a) evaporation
(b) perspiration
(c) guttation
(d) transpiration
Answer: (d) transpiration
In simple words: Transpiration is the plant's way of "sweating" - losing water vapor through its leaves and stems to cool down and transport nutrients.

📝 Teacher's Note: Emphasize the key phrase "water vapour from aerial parts." Compare with human perspiration to make it relatable.

🎯 Exam Tip: The definition question - remember "water vapour" and "aerial parts" are the key terms that define transpiration.

Question 7. Transpiration will be fastest when the day is
(a) cool, humid and windy
(b) hot, humid and still
(c) hot, humid and windy
(d) hot, dry and windy
Answer: (d) hot, dry and windy
In simple words: Hot air speeds up evaporation, dry air pulls moisture out quickly, and wind blows away the water vapor so more can escape.

📝 Teacher's Note: Use the analogy of drying hair with a blow dryer - hot, dry air moving fast dries things fastest. Each factor works together.

🎯 Exam Tip: For maximum transpiration, look for: hot (speeds evaporation) + dry (low humidity pulls water) + windy (removes vapor).

Question 8. Most of the transpiration in tall trees occurs through
(a) stomata
(b) Lenticels
(c) cuticle
(d) Bark
Answer: (b) Lenticels
In simple words: Lenticels are like breathing pores on tree bark that allow water vapor to escape, especially important in tall trees with thick bark.

📝 Teacher's Note: Point out lenticels on tree bark during field trips. Explain why stomatal transpiration is limited in woody stems of tall trees.

🎯 Exam Tip: For tall trees specifically, lenticels on bark are more important than leaf stomata because of the large surface area of the trunk.

Question 9. Transpiration is best defined as
(a) loss of water by the plant
(b) evaporation of water from the surfaces of a plant
(c) loss of water, as water vapour, by a plant
(d) release of water by a plant into the atmosphere
Answer: (b) evaporation of water from the surfaces of a plant
In simple words: Transpiration is specifically the evaporation process from plant surfaces, not just any water loss - it's like the plant's version of sweating.

📝 Teacher's Note: Emphasize "evaporation" and "from surfaces" - these terms make the definition precise and distinguish it from other water loss processes.

🎯 Exam Tip: The most precise definition includes "evaporation" - this distinguishes transpiration from other forms of water loss like guttation.

Very Short Answer Type

Question 1. Name the following:
(a) openings on the stem through which transpiration occurs
(b) The process by which the intact plant loses water in the form of droplets
(c) An instrument used to find the rate of transpiration
(d) A plant in which the stomata are sunken
(e) The apparatus to record the rate of transpiration in a cut shoot
(f) Any two parts of a leaf which allows transpiration
(g) The structure in a leaf that allows guttation
(h) Loss of water as droplets from the margins of certain leaves
Answer:
(a) Lenticels
(b) Guttation
(c) Potometer
(d) Nerium
(e) Ganong's photometer
(f) Stomata and cuticle
(g) Hydathodes
(h) Guttation
In simple words: These are key terms for different structures and processes related to water movement in plants - like vocabulary for plant water systems.

📝 Teacher's Note: Make flashcards for these terms. Show real examples of Nerium leaves and point out lenticels on tree branches during nature walks.

🎯 Exam Tip: Learn these terms exactly as given - they're frequently asked in one-word answers and fill-in-the-blanks.

Question 2. Fill in the blanks:
(a) Transpiration is the loss of water as water ............... from the ........... parts of the plant
(b) Closing of ............... and shedding of leaves reduce .............
(c) Transpiration helps in creating ............. Force and in eliminating excess .............
Answer:
(a) vapour, aerial
(b) stomata, transpiration
(c) suction, water (heat)
In simple words: These sentences explain how transpiration works and what it does for plants - like understanding the basics of plant water management.

📝 Teacher's Note: Explain why "aerial" parts are specified - roots don't transpire. Connect suction force to how plants pull water up from roots to leaves.

🎯 Exam Tip: Remember the key function words: vapour (not liquid), aerial (above ground), suction (pulling force), excess water removal.

Short Answer Type

Question 1. Given below is an example of a certain structure and its special functional activity: Chloroplasts and Photosynthesis. In a similar way, write the functional activity against each of the following:
(a) Hydathodes and ..............................
(b) Leaf spines and .............................
(c) Lenticels and ...............................
(d) Thick cuticle and ..........................
Answer:
(a) guttation
(b) protection and reduced transpiration
(c) transpiration
(d) reduced transpiration
In simple words: Each plant structure has a specific job - hydathodes release water droplets, spines protect and reduce water loss, lenticels allow transpiration, and thick cuticles prevent water loss.

📝 Teacher's Note: Use this structure-function approach throughout biology. Ask students to identify the pattern - some structures increase transpiration, others reduce it.

🎯 Exam Tip: Structure-function questions are common. Remember the purpose: protection, transpiration, or water conservation.

Question 2. (a) State whether the following statements are True (T) Or False (F)?
(i) Most transpiration occurs at midnight
(ii) Transpiration creates a pull for upward movement of the sap
(iii) Wind velocity has an effect on transpiration
(iv) Voltmeter is an instrument used for measuring the rate of transpiration in green plants
(b) Rewrite the false statements, in (a) above, in the correct form by changing either the first or the last word only
Answer:
(a) (i) False (ii) True (iii) True (iv) False
(b) (i) Most transpiration occurs at mid-day (iv) Potometer is an instrument used for measuring the rate of transpiration in green plants
In simple words: Transpiration happens most during the day when it's hot and sunny, creates suction to pull water up, increases with wind, and is measured with a potometer (not voltmeter).

📝 Teacher's Note: Emphasize the correction technique - change only first OR last word. Students often want to change multiple words in corrections.

🎯 Exam Tip: Read correction instructions carefully - "first or last word only" means exactly that. Don't overcomplicate the correction.

Question 3. Give suitable explanation for the following:
(a) A higher rate of transpiration is recorded on a windy day rather than on a calm day
(b) Excessive transpiration results in the wilting of the leaves
(c) Water transpired is the water absorbed
(d) More transpiration occurs from the lower surface of a dorsiventral leaf
(e) Cork and bark of trees help in preventing loss of water
(f) Perspiration and transpiration help to cool the body temperature of the organism
(g) On a bright sunny day, the leaves of certain plants roll up
Answer:
(a) Transpiration increases with the velocity of wind. If the wind blows faster, the water vapours released during transpiration are removed faster and the area surrounding the transpiring leaf does not get saturated with water vapour.
(b) When the rate of transpiration far exceeds the rate of absorption of water by roots, the cells lose their turgidity. Hence, excessive transpiration results in wilting of the leaves.
(c) Plants absorb water continuously through their roots, which is then conducted upwards to all the aerial parts of the plant, including the leaves. Only a small quantity of this water i.e. about 0.02% is used for the photosynthesis and other activities. The rest of the water is transpired as water vapour. Hence water transpired is the water absorbed.
(d) There are more stomatal openings on the lower surface of a dorsiventral leaf. More the number of stomata, higher is the rate of transpiration. Hence more transpiration occurs from the lower surface.
(e) Cork and Bark of trees are tissues of old woody stems. Bark is thick with outermost layer made of dead cells and the cork is hydrophobic in nature. These properties make them water-proof and hence they prevent transpiration.
(f) In both perspiration and transpiration, water is lost by evaporation from the body of the organism as water vapour. This evaporation reduces the temperature of the body surface and brings about cooling in the body of the organism.
(g) On a bright sunny day, the rate of transpiration is much higher than any other days. The leaves of certain plants roll up on a bright sunny day to reduce the exposed surface and thus reduce the rate of transpiration.
In simple words: These are all adaptations and responses that help plants manage water loss - some increase it for cooling, others reduce it for survival.

📝 Teacher's Note: Connect each explanation to everyday examples - wind drying clothes, plants wilting in heat, cooling effect of sweating. Use visual aids for leaf rolling.

🎯 Exam Tip: Each explanation should mention the mechanism (how) and the result (why). Include scientific terms like "turgidity," "hydrophobic," and "stomatal density."

Question 4. Which of the following statements are true and which ones are false? Give reason in support of your answer.
(a) Potometer is an instrument used for Demonstration of transpiration occurring from the lower surface of a leaf
(b) Forest contribute in bringing rains
(c) Hydathodes are similar to stomata in plant physiology
(d) Atmospheric humidity promotes transpiration from a green plant
(e) Some desert plants have sunked stomata on their leaves
(f) Most transpiration occurs during midday
Answer:
(a) False - Reason: Potometer is used to measure the rate of transpiration in a plant. Demonstration of transpiration occurring from the lower surface of a leaf is done by analyzing the changes in colour of pieces of dry cobalt chloride paper attached (and held in place) to the two surfaces of a leaf.
(b) True - Reason: Forests release large amounts of water vapor through transpiration, which increases atmospheric humidity and contributes to cloud formation and rainfall.
(c) False - Reason: Hydathodes release liquid water through guttation, while stomata release water vapor through transpiration. Their functions are different.
(d) False - Reason: High atmospheric humidity reduces the rate of transpiration because there is less difference in water vapor concentration between inside the leaf and the atmosphere.
(e) True - Reason: Desert plants have sunken stomata as an adaptation to reduce transpiration and conserve water in dry environments.
(f) True - Reason: Maximum transpiration occurs during midday when temperature is highest and humidity is usually lowest.
In simple words: These statements test understanding of transpiration measurement, environmental effects, plant adaptations, and the relationship between forests and rainfall.

📝 Teacher's Note: Demonstrate the cobalt chloride paper experiment if possible. Explain the water cycle connection between forests and rainfall patterns.

🎯 Exam Tip: Always provide scientific reasoning for true/false answers. Mention specific mechanisms and adaptations to show deep understanding.

Question. Transpiration carried out by the large number of trees in a forest. This increases the moisture in the atmosphere and brings rain.
Answer: (b) True
Reason: Transpiration carried out by the large number of trees in a forest. This increases the moisture in the atmosphere and brings rain.
In simple words: Trees in forests release lots of water vapor into the air through their leaves, which forms clouds and brings more rain to the area.

📝 Teacher's Note: Use local examples of forests in your region to explain this concept. Students can relate better when they understand why hill stations receive more rainfall than plains.

🎯 Exam Tip: Remember the cycle: trees transpire → moisture increases → cloud formation → rainfall. This connection is frequently tested.

Question. Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets are given out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water vapour. Stomatal opening is regulated by guard cells.
Answer: (c) False
Reason: Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets are given out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water vapour. Stomatal opening is regulated by guard cells.
In simple words: Hydathodes cannot open or close like stomata can, and they release liquid water drops while stomata release water vapor.

📝 Teacher's Note: Show students morning dew on grass leaves to demonstrate guttation vs transpiration. The liquid drops are guttation, not dew.

🎯 Exam Tip: Key difference: hydathodes release liquid water (guttation), stomata release water vapor (transpiration). Stomata can be controlled, hydathodes cannot.

Question. Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.
Answer: (d) False
Reason: Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.
In simple words: When the air is already full of moisture (humid), plants can't release much more water vapor, so transpiration slows down.

📝 Teacher's Note: Compare this to drying clothes on a humid day versus a dry day. Students will understand that water evaporates slower in humid conditions.

🎯 Exam Tip: Remember: high humidity = low transpiration, low humidity = high transpiration. It's an inverse relationship.

Question. Desert plants need to reduce transpiration as much as possible so as to survive in the hot and dry environment. Hence some of them have sunken stomata as an adaptation to curtail transpiration.
Answer: (e) True
Reason: Desert plants need to reduce transpiration as much as possible so as to survive in the hot and dry environment. Hence some of them have sunken stomata as an adaptation to curtail transpiration.
In simple words: Desert plants have stomata hidden in pits to protect them from hot, dry winds and reduce water loss.

📝 Teacher's Note: Use the analogy of hiding in shade during hot weather. Sunken stomata create a microenvironment that's more humid than the outside air.

🎯 Exam Tip: List desert adaptations: sunken stomata, thick cuticle, spines instead of leaves, CAM photosynthesis. These are common exam topics.

Question. During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. During mid-day, the outside temperature is higher, due to which there is more evaporation of water from the leaves. Therefore more transpiration occurs during mid-day.
Answer: True
Reason: During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. During mid-day, the outside temperature is higher, due to which there is more evaporation of water from the leaves. Therefore more transpiration occurs during mid-day.
In simple words: Plants keep their pores open during the day for photosynthesis, and the hot midday sun makes water evaporate faster from leaves.

📝 Teacher's Note: Explain the dilemma plants face: they need CO2 for food making but lose water in the process. It's like opening windows for fresh air but losing heat.

🎯 Exam Tip: Connect transpiration to photosynthesis - both processes require open stomata. Maximum transpiration occurs at midday when both light and temperature are highest.

Question. Differentiate between guttation and bleeding in plants.
Answer:

In simple words: Guttation is normal water release through special pores, while bleeding happens when a plant is cut or damaged.

📝 Teacher's Note: Show students how cutting a stem causes bleeding, while morning droplets on leaves are guttation. Both involve liquid water, not vapor.

🎯 Exam Tip: Remember: guttation = natural process through hydathodes, bleeding = response to injury through cut surfaces.

Long Answer Type:

Question. What is wilting? Some plants show wilting of their leaves at noon even when the soil is well watered, Why is it so?
Answer: Wilting refers to the loss of cellular turgidity in plants which results in the drooping of leaves or plant as a whole because of lack of water. During noon the rate of transpiration exceeds the rate of absorption of water by roots. Due to the excessive transpiration, the cells of leaves lose their turgidity and wilt.
In simple words: Wilting is when plant leaves droop because they lose water faster than they can absorb it, especially during hot midday hours.

📝 Teacher's Note: Compare wilting to a deflating balloon - when cells lose water, they lose their firmness. Demonstrate with a wilted vs turgid leaf.

🎯 Exam Tip: Explain both the definition of wilting and the reason for midday wilting. Mention that transpiration rate exceeds absorption rate during peak heat.

Question. Why are the stomata in most plants more numerous on the lower surface of a leaf instead of being on the upper surface?
Answer: The lower surface of leaf is sheltered from direct sunlight. If more stomata are on the upper surface of a leaf, then excessive transpiration would occur, resulting in quick wilting of the plant. Hence most plants have more numerous stomata on the lower surface of a leaf to control the rate of transpiration.
In simple words: Stomata are mainly on the bottom of leaves to avoid too much water loss from the hot sun shining on the top surface.

📝 Teacher's Note: Ask students to examine leaves under a magnifying glass to see stomata distribution. Use the umbrella analogy - lower surface is protected like being under an umbrella.

🎯 Exam Tip: Connect this to plant survival strategy - reducing water loss while maintaining gas exchange for photosynthesis.

Question. Suppose you have a small rose plant growing in a pot. How would you demonstrate transpiration in it?
Answer: Take the small potted rose plant and cover it with a transparent polythene bag. Tie its mouth around the base of the stem. Leave the plant in sunlight for an hour or two. Drops of water will soon appear on the inner side of the bag due to the saturation of water vapour given out by the leaves. A similar empty polythene bag with its mouth tied and kept in sunlight will show no drops of water. This is the control to show that plants transpire water in the form of water. If tested with dry cobalt chloride paper, the drops will be confirmed as water only.
In simple words: Cover a plant with a clear plastic bag - water drops will appear inside showing that the plant is releasing water vapor from its leaves.

📝 Teacher's Note: This is a perfect practical activity for students. Emphasize the importance of the control experiment to prove the water comes from the plant, not the environment.

🎯 Exam Tip: Describe the complete procedure including the control setup. Mention the cobalt chloride test to confirm the presence of water.

Question. What is a photometer?
Answer: Potometer is a device that measures the rate of water intake by a plant. This water intake is almost equal to the water lost through transpiration. Potometers do not measure the water lost due to transpiration but measure the water uptake by the shoot.
In simple words: A potometer is a scientific instrument that measures how much water a plant drinks, which tells us indirectly how much water it's losing through transpiration.

📝 Teacher's Note: Clarify that potometers measure water uptake, not transpiration directly. The assumption is that most water absorbed is lost through transpiration.

🎯 Exam Tip: Remember: potometer measures water uptake (input) not transpiration (output), but they're approximately equal in healthy plants.

Question. What is lenticular transpiration? Mention one major difference between lenticular transpiration and stomatal transpiration.
Answer: Transpiration occurring through lenticels i.e. minute openings on the surface of old stems is called lenticular transpiration. Stomatal transpiration is controlled by the plant by altering the size of the stoma, where as this does not happen in case of lenticular transpiration. This is because the lenticels never close, but remain open all the time. The amount of stomatal transpiration is much more than the amount of lenticular transpiration.
In simple words: Lenticular transpiration is water loss through tiny holes in bark that can't be closed, while stomatal transpiration happens through leaf pores that can open and close.

📝 Teacher's Note: Show students the small dots on tree bark - these are lenticels. Explain that old stems need gas exchange too, but can't control water loss like leaves can.

🎯 Exam Tip: Key difference: lenticels are always open (no control), stomata can be controlled by guard cells. Stomatal transpiration is much greater than lenticular.

Question. List any three major factors that accelerate the rate of transpiration.
Answer: The factors that accelerate the rate of transpiration are:
(i) High intensity of sunlight
(ii) High temperature
(iii) Higher wind velocity
(iv) Decrease in atmospheric pressure
(Any three)
In simple words: Bright sunshine, hot weather, and windy conditions all make plants lose water faster through their leaves.

📝 Teacher's Note: Relate these factors to everyday experiences - clothes dry faster on sunny, hot, windy days. Plants respond similarly to these environmental conditions.

🎯 Exam Tip: Remember the four main factors: light, temperature, wind, and low atmospheric pressure. Any three are usually sufficient for full marks.

Question. There is a general belief that forests tend to bring more frequent rains. Can you explain it scientifically?
Answer: Forests have large number of plants especially trees. Each plant loses water in the form of water vapour everyday into the atmosphere through transpiration. A large apple tree loses as much as 30 litres of water per day. So huge amount of water is escaped into the atmosphere by forests. This increases the moisture in the atmosphere and brings more frequent rains.
In simple words: Forests act like giant water pumps, sending massive amounts of water vapor into the air which forms clouds and creates more rainfall.

📝 Teacher's Note: Use the impressive statistic of 30 liters per day per tree to help students visualize the scale. Relate to local deforestation and its impact on rainfall patterns.

🎯 Exam Tip: Mention specific quantities (like 30 liters per tree per day) and explain the complete cycle: transpiration → atmospheric moisture → cloud formation → rainfall.

Question. List the four advantages of transpiration to the plants.
Answer: The advantages of transpiration to the plants are:
(i) Transpiration brings about a cooling effect to the plant body since evaporation of water reduces the temperature of leaf surface.
(ii) Transpiration helps in the ascent of sap by producing a suction force acting from the top of the plant.
(iii) Transpiration helps in distributing water and mineral salts throughout the plant body.
(iv) Transpiration helps in eliminating excess water.
In simple words: Transpiration cools plants down, pulls water up from roots, spreads nutrients throughout the plant, and gets rid of extra water.

📝 Teacher's Note: Compare transpiration to human sweating for cooling, and to a straw creating suction for water movement. These analogies help students understand the mechanisms.

🎯 Exam Tip: Remember the four benefits using "CADE": Cooling, Ascent of sap, Distribution of nutrients, Elimination of excess water.

Question. Mention any three methods by which the plants tend to reduce transpiration.
Answer: (i) If the water content of the leaves decreases due any reason, the guard cells turn flaccid, thereby closing the stomatal opening and transpiration stops.
(ii) Some plants have sunken stomata whereas others have reduced number of stomata to reduce transpiration.
(iii) In some plants, leaves may be dropped or may be absent or changed into spines as an adaptation to reduce transpiration.
(iv) The leaves may be covered by thick cuticle such as in Banyan tree, so as to reduce transpiration.
In simple words: Plants can close their pores, hide their pores, reduce leaf size or turn leaves into spines, and cover leaves with waxy coatings to save water.

📝 Teacher's Note: Show examples of each adaptation - cacti for spines, banyan for thick cuticle, pine needles for reduced surface area. Local plant examples work best.

🎯 Exam Tip: Mention specific examples like cacti, banyan tree, or pine needles when describing each adaptation. This shows deeper understanding.

Question. Droplets of water may sometimes be seen along the margins of the leaves of a banana plant, growing in wet soil, in the mornings. Are these dew drops? Comment upon your answer.
Answer: No, they are not dew drops. This is water given out by the plant body through guttation. Since the banana plant is growing in humid environment, transpiration is hampered. But the roots continue to absorb water from the soil. This builds up a huge hydrostatic pressure within the plant and forces out the excess water from the hydathodes, which are pores present at the tips of veins in the leaf. This is observed especially during the mornings.
In simple words: These are not dew drops but water pushed out by the plant itself because it absorbed too much water from wet soil but couldn't transpire it due to humid air.

📝 Teacher's Note: Distinguish between dew (condensation from air) and guttation (active water release by plants). Use the analogy of a pressure cooker releasing steam when pressure builds up.

🎯 Exam Tip: Clearly state "No, not dew drops" and explain the guttation process. Mention the conditions: high soil moisture + high humidity = guttation.

Question. Briefly explain how the rate of transpiration is affected by (a) Intensity of light (b) Humidity of the atmosphere
Answer: (a) Intensity of light - During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. At night they are closed. Hence more transpiration occurs during the day. During cloudy days, the stomata are partially closed and the transpiration is reduced.
In simple words: Bright light increases transpiration because stomata open for photosynthesis, while dim light or darkness reduces transpiration as stomata close.

📝 Teacher's Note: Emphasize the dual role of stomata - gas exchange for photosynthesis and water loss through transpiration. Plants can't avoid this trade-off completely.

🎯 Exam Tip: Connect light intensity to stomatal behavior and photosynthesis. Mention day vs night differences and cloudy day effects.

Structured / Application / Skill Type:

Question. In an experiment, four freshly plucked leaves (A-D) of a plant, such as those of china – rose, were treated as follows: (a) Coated with Vaseline on its upper surface. (b) coated on the lower surface. (c) coated on both surface (d) left uncoated. All the four leaves A, B, C & D were left in a room for about 24 hours. (i) which leaf would become most limp? Why? (ii) which leaf would show least limping? Why?
Answer: (i) The leaf D would become most limp. This is because water would be lost through transpiration from upper as well as the lower surface of leaf D since it is uncoated.
(ii) The least limping would be shown by leaf C since its upper and lower surfaces have been coated with vaseline. So no water is lost from the leaf through transpiration since the stomatal openings get blocked by vaseline.
In simple words: The uncoated leaf loses most water and wilts most, while the fully coated leaf can't lose water so stays freshest.

📝 Teacher's Note: This experiment beautifully demonstrates the relationship between transpiration and wilting. Students can actually perform this with local leaves and vaseline.

🎯 Exam Tip: Clearly identify which leaf (D for most limp, C for least limp) and explain the reasoning based on transpiration rates and vaseline blocking stomata.

Question. Given below is a diagrammatic sketch (surface view) of a stomatal apparatus from a dicot leaf.
(a) Label the parts numbers 1-3
(b) Is this state, open or closed?
(c) Is this stoma, of a dicot leaf or a monocot leaf?
(d) Redraw a sketch of the stomatal apparatus in the state opposite to the one shown here.
Answer: (a) 1- Guard Cell, 2- Inner wall of the Guard Cell, 3- Stoma/Stomatal Aperture
(b) Open state
(c) The structure of stoma remains same in monocots as well as in dicots. Hence, the stoma from the diagram can be of a monocot leaf or of a dicot leaf.
(d) [Diagram shows closed stomata where guard cells are flaccid and the stomatal aperture is closed]
In simple words: Stomata are tiny pores on leaves controlled by guard cells. When guard cells swell up with water, the pore opens. When they lose water, the pore closes to prevent water loss.

📝 Teacher's Note: Use a balloon analogy - when guard cells fill with water like inflated balloons, they curve and create a gap (open stoma). When deflated, they close the gap. Have students observe actual leaf samples under a microscope.

🎯 Exam Tip: Always mention both the structure name AND its function. For stomatal diagrams, clearly state whether it's open/closed and relate it to water movement in guard cells.

Question. Given alongside is the diagram of an experimental set-up to demonstrate a certain phenomenon in plants.
(a) Name the phenomenon being demonstrated.
(b) what is the purpose of putting oil the test tube?
(c) Would it make a difference if the experimental set – up is kept in bright sunshine?
(d) what is the purpose of the spring balance in the set-up?
Answer: (a) Transpiration
(b) Oil is put on the surface of water to prevent loss of water by evaporation.
(c) Yes, the transpiration rate will increase. Transpiration would occur faster. The observable changes will occur in less time.
(d) The spring balance progressively measures the change in weight of the set-up. This because as the plant transpires, it creates the suction force in plant which allows roots to absorb more water from the test tube. Hence, the water in the test will get reduced. Thus, the weight of the entire set will decrease.
In simple words: This experiment shows how plants lose water through leaves (transpiration). The oil layer stops water from evaporating directly, so all water loss is through the plant. The scale shows weight decrease as water is used up.

📝 Teacher's Note: Emphasize that oil creates a controlled environment - without it, we can't distinguish between evaporation and transpiration. Set up the experiment a day before class to show visible water level changes.

🎯 Exam Tip: For transpiration experiments, always explain the purpose of each component (oil layer, spring balance, leafy shoot) and how environmental factors like sunlight affect the rate.