NCERT Solutions for Class 11 Biology Chapter 13: Plant Growth and Development – Free PDF Download

Chapter 13, Plant Growth and Development, explains how a plant builds its body — from an irreversible increase in cell size and number (growth), through the maturation of cells into specialised tissues (differentiation), to the complete sequence of events from seed germination to senescence (development). It also covers the five major plant growth regulators (auxins, gibberellins, cytokinins, ethylene and abscisic acid) and the light- and temperature-controlled flowering responses known as photoperiodism and vernalisation.

Last Updated: September 23, 2026

Exercises

Q1. Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate — Growth: An irreversible and permanent increase in size, volume, weight or number of…

Growth: An irreversible and permanent increase in size, volume, weight or number of cells of an organ, its parts, or even a single cell. It is usually accompanied by metabolic (anabolic and catabolic) activity and, in plants, continues throughout life due to the presence of meristems.

Differentiation: The process by which cells derived from the root apical meristem, shoot apical meristem and cambium undergo structural and biochemical changes in their cell walls and protoplasm to mature and perform specific functions, for example forming tracheary elements, sieve tubes or fibres.

Development: The sum total of all the changes an organism undergoes during its life cycle, from seed germination to senescence. Development is the combined outcome of growth and differentiation.

Dedifferentiation: The process by which living, differentiated cells that have lost the capacity to divide regain the ability to divide under certain conditions. For example, the formation of interfascicular cambium from mature parenchyma cells, or the formation of cork cambium.

Redifferentiation: The process by which dedifferentiated cells divide and produce cells that once again lose the capacity to divide but mature to perform specific functions, such as secondary xylem and secondary phloem formed by the vascular cambium.

Determinate growth: Growth of a cell, tissue or organ that occurs for a limited, definite period of time and stops after reaching maturity, for example the growth of a leaf or a flower.

Meristem: A group of localised, undifferentiated cells in plants that retain the capacity to divide continuously and give rise to new cells, found for example at root tips, shoot tips and in the vascular cambium.

Growth rate: The increase in growth (size, weight, number, etc.) per unit time. Growth rate can be expressed mathematically and may be arithmetic or geometric.

Q2. Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant? — At the cellular level, growth is essentially an increase in the amount of protoplasm,…

At the cellular level, growth is essentially an increase in the amount of protoplasm, but this cannot be measured directly and conveniently at all stages of a plant’s life. Different parameters become more suitable for different organs and different phases of growth — fresh weight and dry weight of tissue, increase in length (roots, stems), increase in surface area (leaves), increase in volume or diameter (fruits, bulbs, corms), and increase in cell number are all used at different times. Since no single one of these measurements applies equally well to every organ and every stage — a growing root is best measured by length while a ripening fruit is best measured by volume or weight — no one parameter alone is good enough to demonstrate growth throughout the entire life of a flowering plant.

Q3. Describe briefly (a) Arithmetic growth (b) Geometric growth (c) Sigmoid growth curve (d) Absolute and relative growth rates — (a) Arithmetic growth: Following mitotic cell division, only one of the two daughter…

(a) Arithmetic growth: Following mitotic cell division, only one of the two daughter cells continues to divide while the other differentiates and matures. The simplest example is a root elongating at a constant rate. Plotting length against time gives a linear curve, expressed as L_t = L₀ + rt, where L_t is the length at time t, L₀ is the length at time zero, and r is the growth rate (elongation per unit time).

(b) Geometric growth: In most systems, growth is slow to begin with (the lag phase) and then increases rapidly, often exponentially (the log or exponential phase), because both daughter cells produced by mitosis retain the ability to divide. As nutrients become limiting, growth slows down and eventually stops, giving a stationary phase.

(c) Sigmoid growth curve: When geometric growth (lag, log/exponential and stationary phases) is plotted against time, an S-shaped or sigmoid curve is obtained. This curve is considered typical of living organisms growing in a natural, resource-limited environment and is also seen in the growth of plant cells, tissues and organs. Exponential growth is expressed as W₁ = W₀e^rt, where W₁ is the final size, W₀ is the initial size, r is the growth rate, t is time, and e is the base of natural logarithms.

(d) Absolute and relative growth rates: Absolute growth rate is the total increase in growth (length, area, weight, etc.) per unit time. Relative growth rate is the growth of a given system expressed per unit of the initial size (i.e., growth per unit time expressed on a common, comparable basis). For example, if two leaves each grow by 5 cm² in a day but one started at 5 cm² and the other at 50 cm², their absolute growth rates are equal, but the relative growth rate of the smaller leaf is much higher.

Q4. List five main groups of natural plant growth regulators. Write a note on the discovery, physiological functions and agricultural/horticultural applications of any one of them — The five main groups of natural plant growth regulators (phytohormones) are: Auxins,…

The five main groups of natural plant growth regulators (phytohormones) are: Auxins, Gibberellins, Cytokinins, Ethylene, and Abscisic acid (ABA).

Auxin — Discovery: Charles Darwin and Francis Darwin (1880) observed that coleoptiles of canary grass (Phalaris sp.) bent towards a unidirectional light source and that this response was lost if the coleoptile tip was covered or removed, showing that the tip was responsible for perceiving light. F.W. Went (1928) later isolated the substance responsible for this bending from coleoptile tips of oat (Avena) seedlings and named it auxin.

Physiological functions: Auxins promote cell elongation, induce cell division in the vascular cambium and differentiation of xylem and phloem, cause apical dominance (inhibition of axillary bud growth by the apical bud), induce parthenocarpy (seedless fruit development), and delay the abscission of leaves and fruits.

Agricultural/horticultural applications: Auxins such as IAA, IBA and NAA are used to induce rooting in stem cuttings, a widely used method of vegetative propagation. 2,4-D is used commercially as a weedicide to selectively kill dicot weeds without harming monocot crops. Auxins are also used to induce parthenocarpic (seedless) fruit development in crops like tomato, and to promote flowering in plants such as pineapple and litchi.

Q5. What do you understand by photoperiodism and vernalisation? Describe their significance — Photoperiodism is the response of plants to the relative length of day and night (i.e.,…

Photoperiodism is the response of plants to the relative length of day and night (i.e., duration of light exposure) that regulates flowering. Based on their photoperiodic response, plants are classified as short-day plants (SDPs), which flower when the day length is shorter than a critical duration (e.g., chrysanthemum), long-day plants (LDPs), which flower when the day length exceeds a critical duration (e.g., radish, wheat), and day-neutral plants (DNPs), whose flowering is unaffected by day length (e.g., tomato, cotton). It is believed that a flowering hormone produced in the leaves under an appropriate photoperiod migrates to the shoot apex and converts it into a flowering apex. Photoperiodism is significant because it allows farmers and plant breeders to control flowering time, extend vegetative growth for higher yield of leaves/tubers, or induce flowering out of season.

Vernalisation is the induction or promotion of flowering by prior exposure of a plant (or its germinating seed) to a period of low temperature. It is essential in plants such as winter varieties of wheat and rye, and biennials like cabbage and carrot, which are sown in autumn, pass through winter as seedlings, and flower in the following summer. Vernalisation is significant because it prevents premature flowering before winter, allows crops to be grown in regions or seasons where they would not otherwise flower, and enables earlier and more reliable harvests.

Q6. Why is abscisic acid also known as the stress hormone? — Abscisic acid (ABA) is called the stress hormone because its levels rise sharply in…

Abscisic acid (ABA) is called the stress hormone because its levels rise sharply in plants under adverse conditions such as drought, waterlogging, injury or mineral deficiency, and it helps the plant cope with this stress. ABA induces the closure of stomata to reduce water loss during drought (antagonising the action of cytokinins), increases the plant’s general tolerance to various stresses, promotes seed dormancy so that seeds germinate only under favourable conditions, and increases the desiccation tolerance of seeds. It also promotes bud dormancy and the abscission of leaves, flowers and fruits at the end of the growing season, which is why it is sometimes also referred to as the growth-inhibiting hormone.

Q7. "Both growth and differentiation in higher plants are open." Comment — Unlike most animals, higher plants show indeterminate, open growth because meristems —…

Unlike most animals, higher plants show indeterminate, open growth because meristems — located at the root tips, shoot tips and in the vascular cambium — retain the ability to divide and produce new cells throughout the plant’s life. As a result, a plant continues to form new organs (leaves, branches, flowers) as long as it lives. Differentiation is also considered open because the very same population of meristematic cells can, depending on need and location, differentiate into many different cell and tissue types (parenchyma, sclerenchyma, xylem, phloem, etc.) at different points in the plant’s life. Since neither the number of organs formed nor the types of cells produced is fixed in advance, both growth and differentiation in higher plants are described as open-ended.

Q8. "Both a short-day plant and a long-day plant can produce flowers simultaneously in a given place." Explain — Flowering in short-day plants (SDPs) and long-day plants (LDPs) depends not on an…

Flowering in short-day plants (SDPs) and long-day plants (LDPs) depends not on an absolute day length but on whether the day length is shorter or longer than each species’ own critical photoperiod. Since different species have different critical day lengths, a location can experience a day length that is simultaneously “short enough” to induce flowering in an SDP and “long enough” to induce flowering in an LDP. For instance, if an SDP has a critical day length of 15 hours and an LDP has a critical day length of 11 hours, both plants will flower together whenever the actual day length lies between 11 and 15 hours. Hence, both types of plants can flower at the same place and time, provided the prevailing photoperiod satisfies each plant’s own critical requirement.

Q9. Which one of the plant growth regulators would you use if you are asked to — (a) Induce rooting in a twig — Auxin (e.g., IAA, IBA or NAA), which promotes…

(a) Induce rooting in a twig — Auxin (e.g., IAA, IBA or NAA), which promotes adventitious root initiation.

(b) Quickly ripen a fruit — Ethylene, which triggers the ripening process and is widely used commercially to ripen fruits.

(c) Delay leaf senescence — Cytokinin, which delays ageing (senescence) of leaves.

(d) Induce growth in axillary buds — Cytokinin, which overcomes apical dominance and promotes lateral/axillary bud growth.

(e) “Bolt” a rosette plant — Gibberellin (GA₃), which causes rapid internode elongation (bolting) in rosette plants such as cabbage and beet.

(f) Induce immediate stomatal closure in leaves — Abscisic acid (ABA), which triggers rapid stomatal closure, especially under water stress.

Q10. Would a defoliated plant respond to the photoperiodic cycle? Why? — No, a severely defoliated (leafless) plant would not respond to the photoperiodic cycle.…

No, a severely defoliated (leafless) plant would not respond to the photoperiodic cycle. This is because it is the leaves, not the shoot apex, that perceive the photoperiodic (light/dark duration) stimulus. Even a single leaf, or part of a leaf, is normally sufficient to perceive this stimulus and trigger the production of the flowering hormone, which then migrates to the shoot apex. Without leaves, the plant has no site to perceive the light/dark duration, so it cannot register the photoperiodic signal and will not initiate the flowering response.

Q11. What would be expected to happen if — (a) GA3 is applied to rice seedlings — The seedlings would show rapid internode…

(a) GA₃ is applied to rice seedlings — The seedlings would show rapid internode elongation, resulting in an overall increase in plant height (this response — bolting/elongation of rice seedlings — was in fact how the “bakanae” or foolish seedling disease and gibberellins were first studied).

(b) Dividing cells stop differentiating — The dividing cells would continue to multiply without maturing into specialised tissues, forming an unorganised, undifferentiated mass of cells known as a callus; organs such as leaves and stems would fail to form.

(c) A rotten fruit gets mixed with unripe fruits — The rotten fruit releases ethylene gas, which diffuses to the surrounding unripe fruits and accelerates their ripening (this is why “one bad fruit spoils/ripens the rest”).

(d) You forget to add cytokinin to the culture medium — Cell division, growth and differentiation (particularly shoot bud initiation) in the tissue culture would slow down considerably, since cytokinin is essential for promoting cell division and, along with auxin, for regulating the balance between root and shoot formation in culture.

Class 11 Biology Chapter 13 – Notes and Extra Questions

The Chapter 13 exercise has 11 questions covering definitions (growth, differentiation, development, dedifferentiation, redifferentiation, meristem), the arithmetic/geometric/sigmoid growth curves, the five plant growth regulators (auxin, gibberellin, cytokinin, ethylene, abscisic acid) with their functions and applications, photoperiodism, vernalisation, and short scenario-based “what would happen if” questions. This exercise set is unchanged from the pre-2023 NCERT edition, where the same chapter appeared as Chapter 15 — only the chapter number was updated to 13 as part of the 2023 rationalisation, not the question content. While CBSE had temporarily marked topics such as photoperiodism, vernalisation, seed dormancy and a few exercise questions as “not to be evaluated” under a one-time reduced syllabus for the 2023–24 session, this deletion was not carried forward, and all 11 questions — including those on photoperiodism and vernalisation — are part of the syllabus and exercise set for the current 2026–27 session. For quick revision, focus on matching each plant growth regulator to its specific physiological role (Q9 is a favourite for 1-mark and MCQ-style questions), memorising the sigmoid growth curve phases, and being able to write short, precise definitions rather than long descriptive answers for Q1.

Frequently Asked Questions

How many questions are there in the NCERT Class 11 Biology Chapter 13 exercise, and has this changed after rationalisation?

There are 11 exercise questions in Chapter 13, “Plant Growth and Development.” The number and wording of these questions are the same as in the pre-2023 edition, where this content appeared as Chapter 15 of the same name — the 2023 rationalisation only renumbered the chapter (from 15 to 13) without removing or adding exercise questions.

What is the difference between growth, differentiation and development in plants?

Growth is simply an irreversible increase in size, weight or cell number. Differentiation is the maturation of newly formed cells into structurally and functionally specialised cells and tissues. Development is the broadest term — it is the entire sequence of events, including growth and differentiation together, that a plant undergoes from seed germination through to senescence.

What are the five major plant growth regulators and their main functions?

Auxin promotes cell elongation, rooting and apical dominance; gibberellin (GA₃) causes stem/internode elongation and bolting; cytokinin promotes cell division and delays senescence; ethylene promotes fruit ripening and senescence; and abscisic acid (ABA), the stress hormone, promotes stomatal closure and seed dormancy.

What is the difference between photoperiodism and vernalisation?

Photoperiodism is the flowering response of a plant to the relative duration of light and darkness (day length) it is exposed to. Vernalisation is the flowering response of a plant to a period of exposure to low temperature. Both are environmental cues that a plant uses to time its flowering to the most favourable season, but one is triggered by light duration and the other by cold exposure.

Written by Satish

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