CBSE Class 11 Biology Plant Growth And Development Notes

Download CBSE Class 11 Biology Plant Growth And Development Notes in PDF format. All Revision notes for Class 11 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 11. Our teachers have designed these concept notes for the benefit of Grade 11 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 11 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 11 Biology given our website

Plant Growth And Development Class 11 Biology Revision Notes

Class 11 Biology students should refer to the following concepts and notes for Plant Growth And Development in standard 11. These exam notes for Grade 11 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Plant Growth And Development Notes Class 11 Biology

Points to Remember

Growth :

• An irreversible permanent increase in size of an organ or its parts or even of an individual cell.

• Growth is accompanied by metabolic process that occurs at the expense of energy.

Plant growth is generally is indeterminate :

• Plants retain the capacity of unlimited growth throughout their life.

• This ability is due to the presence of meristems at certain locations in their body.

• The cells of such meristems have capacity to divide and self-perpetuate.

• The product eventually looses the capacity to divide and differentiated.

• Apical meristems responsible for primary growth of the plants and principally contribute to the elongation of the plants along their axis.

• The lateral meristem, vascular cambium and cork cambium appears later and responsible for the increase in the girth.

Phases of growth :

• The period of growth is generally divided into three phases

o Meristematic.

o Elongation.

o Maturation.

• Root apex and shoot apex represent the meristematic phase of growth.

• The cells of this region are rich in protoplasm, possesses large conspicuous nuclei.

• Their cell walls are primary in nature, thin and cellulosic with abundant plasmodesmatal connection.

• The cells proximal to that region are the phase of elongation.

• Increased vacuolation, cell enlargement and new cell wall deposition are the characteristic of the cells in this phase.

• Further away from the zone of elongation is the phase of maturation.

• The cells of this zone attain their maximal size in terms of wall thickening and protoplasmic modifications.

Condition of growth :

• Water, oxygen and nutrients as very essential element for growth.

• Turgidity of cells helps in extension growth.

• Water also provides the medium for enzymatic activities needed for growth.

• Oxygen helps in releasing metabolic energy essential for growth activities.

• Nutrients are required by plants for synthesis of protoplasm and act as source of energy.

Differentiation, dedifferentiation and redifferentiation :

• The cells derived from root apical and shoot apical meristems and cambium differentiate and mature to perform specific functions.

• This act of maturation is termed as differentiation.

• During differentiation major changes takes place in their cell wall and protoplasm.

• Differentiated tracheary element cells loose their protoplasm, develop a very strong, elastic lignocellulosic secondary cell walls.

• The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain condition is dedifferentiation.

• Development of interfascicular cambium and cork cambium from fully differentiated parenchymatous cells is the example of dedifferentiation.

• Cells produced by the dedifferentiated tissues again loose the capacity to divide and mature to perform specific function is called redifferentiation.

Plant Growth Regulators :

Characteristics :

• The plant growth regulators are small, simple molecules of diverse chemical composition.

• They could be:

o Indole compounds (indole-3-acetic acid, IAA);

o adenine derivatives (N6-furfurylamino purine, kinetin)

o derivatives of carotenoids (abscisic acid,ABA)

o terpenes (gibberellic acid, GA2)

o Gases (ethylene, C2H4)

• One group of PGRs are involved in growth promoting activities such as cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed germination. These are called plant growth promoters, e.g. auxin, gibberellins and cytokinin.

• Another group of PGRs play important role in plant responses towards to wounds and stresses of biotic and abiotic origin. They involved in inhibitory responses like dormancy and abscission, e.g. abscisic acid.

Discovery of plant growth regulators :

• Auxin was isolated by F.W. Went from tips of oat seedlings.

• The ‘bakane’ (foolish seedling) a disease of rice seedlings, was caused by a fungal pathogen Gibberalla fujikuroi.

• E. Kurosawa reported the appearance of the symptom of the disease in uninfected rice seedlings when treated with sterile filtrate of the fungus. The active substance was later identified as Gibberellic acid.

• Skoog and Miller identified and crystallized the cytokinesis promoting active substance that they termed as kinetin. 

• During mid 1960s three different kinds of inhibitors purified, i.e. inhibitor-B abscission II and dormin. Later all the three proved to be chemically identical and named as Abscisic acid (ABA).

• Cousinsdiscovered a gaseous PGR called ethylene from ripened orange.

Physiological effect of plant growth regulators :

Auxin :

• The term auxin is applied to indole-3-acetic acid

• Generally produced by growing apices of the stems and roots.

• IAA and IBA have been isolated from plants.

• NAA and 2, 4-D (2, 4-dichlorophenoxyacetic acid) are synthetic auxin.

• Promote rooting in stem cutting.

• Promote flowering.

• Inhibit fruit and leaf drop at early stages.

• Promote abscission of older mature leaves and fruits.

• The growing apical bud inhibit the growth of lateral bud, the phenomenon is called apical dominance.

• Auxin induces parthenocarpy.

• Used as herbicides.

• Controls xylem differentiation.

• Promote cell division.

Gibberellins :

• Ability to cause an increase in length of axis is used to increase the length of grapes stalks.

• Gibberellins cause fruits like apple to elongate and improve its shape.

• Delay senescence

• GA3 is used to speed up the malting process in brewing industry.

• Gibberellins promote to increase length of stem in sugar cane.

• Promote early seed production.

• Promote bolting (internodes elongation) in beet, cabbages.

Cytokinins :

• Cytokinins have specific effects on cytokinesis.

• Zeatin isolated from corn-kernels and coconut milk.

• Promote cell division.

• Help to produce new leaves, chloroplast in leaves, lateral shoot growth

• Promote formation of adventitious shoot.

• Cytokinins help to overcome apical dominance.

• Promote nutrient mobilization.

• Delay senescence.

Ethylene :

• Ethylene is a simple gaseous PGR.

• Synthesized in the tissue undergoing senescence and ripening fruits.

• Promote horizontal growth of seedling.

• Promote swelling of axis and apical hook formation in dicot seedlings.

• Promote senescence and abscission of plant organs like leaf and flower.

• Increase rate of respiration during ripening of fruits, called respiratory climactic.

• Breaks seed and bud dormancy.

• Initiate germination.

• Promote rapid internodes elongation.

• Promote root growth and root hair formation.

• Used to initiate flowering and for synchronizing fruit-set.

• Induce flowering in mango.

• The source of ethylene is ethephon.

• Promote female flower in cucumbers thereby increasing the yield.

Abscisic acid :

• Regulates abscission and dormancy.

• Acts as general plant growth inhibitor and an inhibitor of plant metabolism.

• Inhibit seed germination.

• Stimulates the closure of stomata and increases the tolerance of plants to various kinds of stresses, hence called asstress hormone.

• Important role in seed development, maturation and dormancy.

• Inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth.

• Acts as antagonist to Gas.

Photoperiodism :

• Some plants require a periodic exposure to light to induce flowering.

• Response of plants in terms of day/night in relation to flowering is called photoperiodism.

• Long day plant: plant requires the exposure to light for a period exceeding critical period.

• Short day plant: plant requires the exposure to light for a period less than critical period.

• Day neutral plant: there is no such correlation between exposure to light duration and induction of flowering response.

• The site of perception of light/dark duration is the leaves.

Vernalisation :

• Vernalisation: There are plants for which flowering is either quantitatively or qualitatively dependent on exposure to low temperature.

• It prevents precocious reproductive development late in the growing season.

• Vernalisation refers to the promotion of flowering by a period of low temperature.

Seed Germination
The first step is the process of plant growth is seed germination. The seeds germinate under favourable conditions of the environment. Some seeds undergo a period of dormancy and can germinate only after dormancy period gets over.
Seed germinates to from seeding which grows into a plant. After the dormancy of the seed is over or is broken, and the necessary conditions for germination are available the dormant embryo becomes metabolically active and starts growing. This process is known as seed germination. The conditions necessary for seed germination are availability of water and oxygen. The imbibitions or the uptake of water is the first step towards the germination of seed. It causes swelling of seed that ruptures the seed coat to enable the radical to emerge from one end of embryonic axis the metabolic activities require oxygen for breaking down the food reserves. The mobilization of food reserves involves the hydrolysis of stored polysaccharides, proteins, and lipids with the help of enzymes.

The emergence of radical which gives rise to root system is considered the first step towards seed germination. As radical emerges from one end of the embryonic axis, plumule which forms the shoot arises from the other end. The rate of respiration increases rapidly during seed germination. The growth of radical and plumule is due to the cell extension, cell division and initiation of several biochemical processes. The seed also needs a suitable temperature (optimum between 25 to35).
Some plants such as Rhizophora and Sonneratia show special type of germination known as vivipary. These plants grow in marshy lands. Vivipary is the germination of a seed while it is still attached to the parent plant and is nourished by it. As the germinating seed forms a seedling, its weight increases and the seedling separates and falls down into the mud. The lateral roots then develop to help proper anchorage of the seedling.

Seed Dormancy

The development of embryo stops once the seed matures. It sheds most of its water content, the metabolic activities become extremely low, the seed coat becomes impermeable to oxygen and moisture and it usually hardens.

In manyplants, the seed undergoes a period of suspended growth and does not germinate as soon as it is formed. The suspension of growth is referred to as quiescence when it is due to exogenous factors, such as the environmental conditions. The seeds may be in a state of dormancy or rest due to endogenous control during which metabolic activity of the seed is greatly reduced. While quiescence is the condition of a seed when it is unable to germinate because the conditions for germination are not available, dormancy is the condition of seed when it is unable to germinate in spite of the availability of all environments conditions suitable for germination.

Dormancy in seeds may be due to impermeable or mechanically resistant seed coats, rudimentary or physiologically immature embryos and even due to the presence of germination inhibitors such as abscisic acid, phenolic acid, short chain fatty acids and coumarin. Dormancy of the seed can be broken, or its duration can be reduced to initiate germination, by mechanical or chemical scarification of the seed coat, stratification of seeds or changing environmental conditions such as temperature, light and pressure.

Scarification of seed involves scratching of seed coat to help break the dormancy caused by hard and impermeable seed coat. Stratification of seeds is subjecting the moist seeds to oxygen for variable periods of low or high temperatures.

MCQ Questions for NCERT Class 11 Biology Plant Growth and Development

Question. Growth substance that stimulates nodule formation in leguminous plants is

(a) NAA
(b) IAA
(c) IBA
(d) ABA.

Answer : B

Question. Match column I with column II and select the correct option.
  Column I                                Column II
(Discovery)                     (Name of scientists)

A. Foolish seedling                 I. R. Gane
disease of rice
B. Crystallised the                 II. F.W. Went
kinetin
C. Release of ethylene gas    III. Skoog and Miller

D. Bioassay of auxin IV. E. Kurosawa
(a) A — III, B — IV, C – I, D – II
(b) A — IV, B — III, C – II, D – I
(c) A — IV, B — III, C – I, D – II
(d) A — IV, B — I, C – III, D – II

Answer : C

Question. The following diagram shows four coleoptiles set up at the start of an experiment.
Razor blade

Which two coleoptiles will bend towards the light source?
(a) I and II
(b) I and IV
(c) II and III
(d) III and IV

Answer : D

Question. 6- furfuryl amino purine, 2-4 dichlorophenoxy acetic acid and indole acetic acids are respectively examples of
(a) kinetin, natural auxin and synthetic auxin
(b) kinetin, synthetic auxin and natural auxin
(c) kinetin, gibberellin and natural auxin
(d) natural auxin, synthetic auxin and kinetin.

Answer : B

Question. Read the given statements and select the correct option.
Statement 1 : Cytokinins are anti senescent.
Statement 2 : Effect of cytokinins is antagonists to ethylene.
(a) Both statement 1 and statement 2 are true and statement 2 is the correct explanation of statement 1.
(b) Both statement 1 and statement 2 are true butstateme nt 2 is not the correct explanation of statement 1.
(c) Statement 1 is true and statement 2 is false.
(d) Both statement 1 and statement 2 are false.

Answer : B

Question. Which one is the test for gibberellin?
(a) Bolting in Cabbage
(b) Morphogenesis in tobacco callus
(c) Rapid division in carrot cells
(d) None of these

Answer : A

Question. Match column I with column II. (There can be more than one match for column I).
    Column I              Column II
A. Antiauxin               (i) Zeatin
B. Synthetic auxin      (ii) NAA
C. Natural Cytokinin   (iii) MCPA
(iv) PCIB
(v) TIBA
(a) A-(iv, v), B-(ii, iii), C-(i)
(b) A-(iii, v), B-(iv), C-(i)
(c) A-(v, iv), B-(ii, i), C-(i, iii)
(d) A-(v, iii), B-(v, iv), C-(i)

Answer : A

Question. Which of the following are not the uses of ABA?
(a) Stoppage of cambial activity
(b) Antitranspirant
(c) Apical dominance
(d) Dormancy

Answer : C

Question. The hormone which promotes rapid internodeor petiole  elongation in deep water rice plants, also
(a) initiates germination in peanut seeds and sprouting of potato tubers
(b) breaks seed and bud dormancy
(c) inhibits seed germination
(d) both (a) and (b).

Answer : D

Question. Which of the following is the correct difference between auxin and gibberellin?
(a) Gibberelin promotes rooting while auxin has no such role.
(b) Auxin has feminising effect whereas gibberellin has masculinising effect in some plants.
(c) Auxin mobilises food reserve during seedgerm ination whereas gibberellin has no such effect.
(d) Natural auxin promotes flowering in long day plants whereas natural gibberellin has no such effect.

Answer : B

Question. During mid-1960s, three independent researchers reported the purification and chemical characterisation of three different kinds of inhibitors; inhibitor—B, abscission II
and dormin. Later all the three were proved to be chemically identical. It was named
(a) indole acetic acid
(b) indole butyric acid
(c) naphthalene acetic acid
(d) abscisic acid.

Answer : D

Question. Pick out the false statements.
I. Naphthalene acetic acid increases the number of dwarf shoots as well as the number of fruits.
II. Gibberellic acid (GA3) was isolated in pure form by Cross et al (1961).
III. Most of gibberellic acids occur in plants and fungi.
IV. Excised radish cotyledon expansion test, developed by Letham, is used for bioassay of ethylene.
(a) II and III
(b) II and IV
(c) I, II and III
(d) II, III and IV

Answer : B

Question. Which of the given statements is not true according to Cholodny-Went model?
(a) Acceleration of growth on shaded side accompanies retardation of growth on the irradiated side.
(b) Illumination from one side causes transport of auxin towards the shaded side.
(c) Auxin differential accounts for the growth differential observed in plants.
(d) Auxin movement is polar, being basipetal in both stem and root.

Answer : D

Ques. Highest auxin concentration occurs
(a) in growing tips
(b) in leaves
(c) at base of plant organs
(d) in xylem and phloem. 

Answer: A

Ques. Phytohormones are
(a) chemical regulating flowering
(b) chemical regulating secondary growth
(c) hormones regulating growth from seed to adulthood
(d) regulators synthesised by plants and influencing physiological processes. 

Answer: D

Ques. Abscisic acid controls
(a) cell division
(b) leaf fall and dormancy
(c) shoot elongation
(d) cell elongation and wall formation. 

Answer: B

Ques. Phototropic and geotropic movements are linked to
(a) gibberellins
(b) enzymes
(c) auxin
(d) cytokinins. 

Answer: C

Ques. Which of the following movement is not related to auxin level?
(a) Bending of shoot towards light
(b) Movement of root towards soil
(c) Nyctinastic leaf movements
(d) Movement of sunflower head tracking the sun

Answer: C

Ques. Leaf fall can be prevented with the help of
(a) abscisic acid
(b) auxins
(c) florigen
(d) cytokinins. 

Answer: D

Ques. Mowing grass lawn facilitates better maintenance because
(a) wounding stimulates regeneration
(b) removal of apical dominance and stimulation of intercalary meristem
(c) removal of apical dominance
(d) removal of apical dominance and promotion of lateral meristem. 

Answer: B

Ques. Cut or excised leaves remain green for long if induced to root or dipped in
(a) gibberellins
(b) cytokinins
(c) auxins
(d) ethylene. 

Answer: B

Ques. Gibberellins promote
(a) seed germination
(b) seed dormancy
(c) leaf fall
(d) root elongation.

Answer: A

Ques. What is the site of perception of photoperiod necessary for induction of flowering in plants?
(a) Leaves
(b) Lateral buds
(c) Pulvinus
(d) Shoot apex

Answer: A

Ques. Phytochrome is a
(a) flavoprotein
(b) glycoprotein
(c) lipoprotein
(d) chromoprotein.

Answer: D

Ques. Study the four statements (A-D) given below and select the two correct ones out of them.
A. Definition of biological species was given by Ernst Mayr.
B. Photoperiod does not affect reproduction in plants.
C. Binomial nomenclature system was given by R.H. Whittaker.
D. In unicellular organisms, reproduction is synonymous with growth.
The two correct statements are
(a) B and C
(b) C and D
(c) A and D
(d) A and B.

Answer: C

Ques. Photoperiodism was first characterised in
(a) tobacco
(b) potato
(c) tomato
(d) cotton. 

Answer: A

Ques. Importance of day length in flowering of plants was first shown in
(a) cotton
(b) Petunia
(c) Lemna
(d) tobacco. 

Answer: D

Ques. The wavelength of light absorbed by Pr form of phytochrome is
(a) 680 nm
(b) 720 nm
(c) 620 nm
(d) 640 nm. 

Answer: A

Ques. One set of the plant was grown at 12 hours day and 12 hours night period cycles and it flowered while in the other set night phase was interrupted by flash of light and it did not produce flower. Under which one of the following categories will you place this plant?
(a) Long day
(b) Darkness neutral
(c) Day neutral
(d) Short day

Answer: D

Ques. Which pigment absorbs the red and far-red light?
(a) Cytochrome
(b) Phytochrome
(c) Carotenoids
(d) Chlorophyll 

Answer: B

Ques. Which plant is LDP?
(a) Tobacco
(b) Glycine max
(c) Mirabilis jalapa
 (d) Spinach

Answer: D

Read the following passage and answer questions from 46 to 50 given below.
X are acidic growth hormones which causes cell elongation of intact plants in general and increase internodal length of genetically dwarfed plants whereas Y are basic growth hormones
that promotes cell division either alone or in conjunction with other hormone.

Question. What could be the X and Y?
(a) X-Auxin, Y-Abscisic acid
(b) X-Gibberellins, Y-Cytokinins
(c) X-Gibberellins, Y-Auxin
(d) X-Ethylene, Y-Cytokinin

Answer : B

Question. Which hormone causes cell elongation other than X?
(a) Auxin
(b) Cytokinin
(c) Ethylene
(d) Both (a) and (b)

Answer : D

Question. Plant growth hormone that promotes femaleness in flowers is/are
(a) X only
(b) Y only
(c) both X and Y
(d) neither X nor Y.

Answer : B

Question. Select the correct statement regarding Y.
(a) Y help in phloem transport.
(b) Y increase the yield of malt from barely grains.
(c) Y promotes apical dominance.
(d) Y hastens the senescence of leaves and flowers.

Answer : B

Question. The precursor for the synthesis of X is
(a) indole−3−acetic acid
(b) phenyl urea
(c) mevalonic acid
(d) methionine.

Answer : C

Assertion & Reasoning Based MCQs

For question numbers 51-57, two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion. (c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Question. Assertion :Abscisic acid is known as dormin.
Reason : Abscisic acid is employed for breaking of seed and bud dormancy.

Answer : C

Question. Assertion : Genetically male plants of Cannabis can be induced to produce female flowers in the presence of gibberellin.
Reason : Gibberellin has masculinising effect in some plants.

Answer : D

Question. Assertion : TIBA acts as antiauxin by blocking the transport of auxin.
Reason : Bound auxin cannot be extracted easily except with the help of organic solvents.

Answer : B

Question. Assertion : ABA promotes rooting in stem cuttings of Poinsettia.
Reason : ABA promotes growth by cell division.

Answer : C

Important Questions for NCERT Class 11 Biology Plant Growth and Development

Very Short Answer Type Questions

Question. Why are apples usually wrapped in wax before being sold to market?

Answer.  To prevent ripening of fruits due to release of ethylene.

Question. Why an overripe fruit affects rest of the fruits kept in the basket?

Answer.  An overripened fruit releases the gaseous hormone ethylene. This when released into the surrounding environment initiates ripening of other fruits in the basket. Soon, all the them get over-ripened.

Question. Why are cytokinins named so?

Answer.  Cytokinins are named so, because they promote cell division.

Question. A farmer grows cucumber plants in his field. He wants to increase the number of female flowers in them. Which plant growth regulator can be applied to achieve this?

Answer.  Ethylene, is a plant growth regulator that has a feminising effect on sex expression. Ethylene promotes formation of female flowers in monoecious plants like cucumber.

Question. A farmer cultivating Cannabis wants to increase the number of male flowers in his field comprising predominantly female Cannabis plants. Which hormone would you suggest him to use?

Answer.  Gibberellin

Short Answer Type Questions

Question. The rice seedlings infected with fungus Gibberella fujikuroi are called foolish seedlings. What was the reason behind it?

Answer. The rice seedlings infected with fungus Gibberella fujikuroi are called foolish seedlings because infected plants grow excessively taller than rest of the non-infected rice plants in the field, fall over and become unharvestable.

Question. Why is ABA known as ‘stress hormone’? Mention any two functions of this hormone. How are they antagonistic to gibberellins?

Answer. A fairly high concentration of abscisic acid (ABA) is found in leaves of plants growing under stress conditions, such as drought, flooding, injury, mineral deficiency, etc. It is accompanied by loss of turgor and closure of stomata. When such plants are transferred to normal conditions, they regain normal turgor and ABA concentration decreases. Since the synthesis of ABA is accelerated under stress condition and the same is destroyed or inactivated when stress is relieved, it is also known as stress hormone. The two functions of ABA are (i) Induces seed and bud dormancy and (ii) Promotes abscission of flowers and fruits. Abscisic acid and gibberellins are antagonistic in following respects.

Question. Name synthetic auxin hormone used as weedicide. Give two more commercial applications of same.

Answer. 2, 4-D is a synthetic auxin used as weedicide. Its two other commercial uses are:
(i) to induce flowering in litchi and pineapples
(ii) to prevent preharvest fruit drop of orange and apple.

Question. Identify the hormone on the basis of their specific characteristic.
(a) Gaseous in nature
(b) Responsible for phototropism
(c) Induces femaleness in flowers of cucumber
(d) Kills weeds (dicots)
(e) Induces flowering in long day plants.

Answer. (a) Ethylene
(b) Auxin
(c) Ethylene
(d) Auxin
(e) Gibberellin

Question. While experimentation, why do you think it is difficult to assign any affect seen to any single hormone? 

Answer. As all the hormones are synergistic to each other in their functions. Thus, during experimentation, we can not judge whether, a particular effect is produce by a single hormone or many. For example (i) Auxins help to initiate rooting in stem cuttings, (an application widely used for plant propagation.) Cytokinins also show the similar function of root formation. Auxins promote flowering, e.g., in pineapples. They also induce parthenocarpy, e.g., in tomatoes.
(ii) Both gibberellins and ethylene are synergistic to auxin in initiating flowering and for synchronising fruit set in pineapples.
(iii) Cytokinins and gibberellins help overcome the apical dominance and delay the process of leaf senescence.
(iv) On the other hand, ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. This shown that all hormones are synergistic to each other in their mode of action in plants.

Question. Plant growth substances (PGS) have innumerable practical applications. Name the PGS you should use to
(a) Increase yield of sugarcane.
(b) Promote lateral shoot growth.
(c) Cause sprouting of potato tuber.
(d) Inhibit seed germination.

Answer. (a) Gibberellin increase yield of sugarcane.
(b) Cytokinin promote lateral shoot growth.
(c) Ethylene causes sprouting of potato tuber.
(d) Abscisic acid inhibit seed germination.

Long Answer Type Questions

Question. Write a brief account of abscisic acid and explain how it is antagonistic to most of the other plant growth regulators.

Answer. Abscisic acid serves to increase plant tolerance to several stresses, such as drought, waterlogging, etc., hence, it is also known as stress hormone. It is also called as dormin because it induces dormancy in buds, underground stems and seeds. It is synthesized in mesophyll cells, guard cells and vascular tissue mainly from mevalonic acid or xanthophyll. It is highly mobile and rapidly moves out of the leaves to other parts of the plant body, specially sink tissues through diffusion, as well as through xylem and phloem transport. Abscisic acid has been found to have effects mainly on seed germination, dormancy and stomatal closure. It acts antagonistically with gibberellins, auxins and cytokinins (e.g., seed germination, seed or bud dormancy, ripening of fruits, senescence, transpiration) and keeps them in check, thus controlling growth. Functions of abscisic acid :
(i) ABA plays an important role in embryo maturation and seed germination, controlling the growth of embryo at maturation stage, causing accumulation of nutrients in the endosperm and increasing the capacity of tolerance to desiccation.
(ii) It prevents precocious germination or vivipary and promotes dormancy.
(iii) It plays an important role in stomatal closure due to water stress and gets accumulated in water-stressed or wilted leaves.
(iv) It inhibits the development of lateral or secondary roots that are promoted by auxin.
(v) It is found to promote flowering in some short day plants.
(vi) It is found to induce parthenocarpy in some plants, such as rose.
(vii) It promotes leaf senescence by preventing the synthesis of protein and RNA in the leaves. (viii) It promotes the abscission of fruits and flowers. Uses of abscisic acid :
(i) ABA is used as an antitranspirant as it reduces transpiration to a great extent through stomatal closure when applied to leaves.
(ii) It is used in short day plants such as black current, strawberry to induce flowering even during unfavorable photoperiods.
(iii) It is used to prolong dormancy in buds, storage organs and seeds.

Please click the link below to download pdf file for CBSE Class 11 Biology Plant Growth And Development Notes.

Chapter 10 Cell Cycle and Cell Division
CBSE Class 11 Biology Cell Cycle And Cell Division Notes
Chapter 13 Photosynthesis in Higher Plants
CBSE Class 11 Biology Photosynthesis In Higher Plants Notes
Chapter 14 Respiration in Plants
CBSE Class 11 Biology Respiration In Plants Notes
Chapter 15 Plant Growth and Development
CBSE Class 11 Biology Plant Growth And Development Notes
Chapter 16 Digestion and Absorption
CBSE Class 11 Biology Digestion and Absorption Notes
Chapter 17 Breathing and Exchange of Gases
CBSE Class 11 Biology Breathing And Exchange Of Gases Notes
Chapter 18 Body Fluids and Circulation
CBSE Class 11 Biology Body Fluids And Circulation Notes
Chapter 19 Excretory Products and their Elimination
CBSE Class 11 Biology Excretory Products And Their Elimination Notes
Chapter 2 Biological Classification
CBSE Class 11 Biology Biological Classification Notes
Chapter 20 Locomotion and Movement
CBSE Class 11 Biology Locomotion And Movement Notes
Chapter 21 Neural Control and Coordination
CBSE Class 11 Biology Neural Control And Coordination Notes
Chapter 5 Morphology of Flowering Plants
CBSE Class 11 Biology Morphology Of Flowering Plants Notes
Chapter 6 Anatomy of Flowering Plants
CBSE Class 11 Biology Anatomy Of Flowering Plants Notes
Chapter 7 Structural Organisation in Animals
CBSE Class 11 Biology Structural Organisation In Animals Notes

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