" Plant - Growth and Development Chapter 15 CBSE Class 11 Biology NCERT Solutions, pdf, Videos, Notes, Question Bank, IIT, JEE

NCERT Solutions for Class 11 Biology Chapter 15 - Plant - Growth and Development

CBSE class 11 Biology, chapter 15 Plant - Growth and Development, Notes, pdf, NCERT Solutions, Question Paper,text books pdf and other study materials also availabl in this site.


Plant - Growth and Development

The National Council of Education Research and Training (NCERT) (officaial wesite www.ncert.nic.in) sets the curriculum for all schools that follow the Central Board of Secondary Education (CBSE)(officaial wesite cbse.nic.in) across the nation. NCERT solutions for class 11 Biology Chapter 15 - Plant - Growth and Development has been written to help students understand all the content under Chapter 15 - Plant - Growth and Development in the textbooks prescribed by NCERT and as per the syllabus. The class 11 Biology NCERT solutions help students solve the exercises given in the textbooks and get good marks in their board exam. The book is structured in a step-by-step and logical manner, which allows the student to understand the concepts easily.
Class 11 Biology NCERT solutions for Chapter 15 - Plant - Growth and Development covers Topics such as Plant Growth, Plant Growth Generally is Indeterminate, Growth is Measurable, Phases of Growth, Growth Rates, Conditions for Growth, DIFFERENTIATION, DEDIFFERENTIATION AND REDIFFERENTIATION, DEVELOPMENT, PLANT GROWTH REGULATORS Characteristics, The Discovery of Plant Growth Regulators, Physiological Effects of Plant Growth Regulators, PHOTOPERIODISM and VERNALISATION.

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Chapter 15 - Plant - Growth and Development


Plant - Growth and Development

15.1 Growth

Chapter 15 - Plant - Growth and Development


location of root apical meristem, shoot apical meristem and vascular cambium

15.1.1 Plant Growth Generally is Indeterminate

Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate.

primary growth of the plants and principally contribute to the elongation of the plants along their axis. You also know that in dicotyledonous plants and gymnosperms.

the lateral meristems, vascular cambium and cork-cambium appear later in life. These are the meristems that cause the increase in the girth of the organs in which they are active. This is known as secondary growth of the plant

15.1.2 Growth is Measurable

Growth (in Cellular level): principally a consequence of increase in the amount of protoplasm.

Growth is, therefore, measured by a variety of parameters some of which are: increase in fresh weight, dry weight, length, area, volume and cell number.

15.1.3 Phases of Growth

The period of growth is divided into three phases:
1. meristematic
2. elongation
3. maturation

15.1.4 Growth Rates

The increased growth per unit time is termed as growth rate. Thus, rate of growth can be expressed mathematically. An organism, or a part of the organism can produce more cells in a variety of ways.

On plotting the length of the organ against time, a linear curve is obtained.

Mathematically, it is expressed as

Lt = L0 + rt

Lt = length at time ‘t’
L0 = length at time ‘zero’
r = growth rate / elongation per unit time.

The exponential growth can be expressed as

W1 = W0 ert

W1 = final size (weight, height, number etc.)
W0 = initial size at the beginning of the period
r = growth rate
t = time of growth
e = base of natural logarithms

Quantitative comparisons between the growth of living system can also be made in two ways : (i) measurement and the comparison of total growth per unit time is called the absolute growth rate. (ii) The growth of the given system per unit time expressed on a common basis, e.g., per unit initial parameter is called the relative growth rate.

15.1.5 Conditions for Growth

water required to the plant to cells growth in size by cell enlargement. Turgidity of cells helps in extension growth. Thus, plant growth and further development is intimately linked to the water status of the plant. Water also provides the medium for enzymatic activities needed for growth.

Oxygen helps in releasing metabolic energy essential for growth activities.

Nutrients (macro and micro essential elements) are required by plants for the synthesis of protoplasm and act as source of energy.

every plant organism has an optimum temperature range best suited for its growth. Any deviation from this range could be detrimental to its survival.

Environmental signals such as light and gravity also affect certain phases/stages of growth.

15.2 Differentiation, Dedifferentiation and Redifferentiation

Differentiation:The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed as differentiation.

During differentiation, cells undergo few to major structural changes both in their cell walls and protoplasm. For example, to form a tracheary element, the cells would lose their protoplasm. They also develop a very strong, elastic, lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension. Try to correlate the various anatomical features you encounter in plants to the functions they perform.

dedifferentiation: The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. For example, formation of meristems – interfascicular cambium and cork cambium from fully differentiated parenchyma cells.

redifferentiated: While doing so, such meristems/tissues are able to divide and produce cells that once again lose the capacity to divide but mature to perform specific functions.

15.3 Development

Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence.

Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity, e.g., heterophylly in cotton, coriander and larkspur.

In such plants, the leaves of the juvenile plant are different in shape from those in mature plants. So development is considered as the sum of growth and differentiation.

sequence of the development process in a plant cell

sequence of the development process in a plant cell

Heterophylly in (a) larkspur and (b) buttercup

Heterophylly in (a) larkspur and (b) buttercup

15.4 Plant Growth Regulators


experiment to demonstrate the tip of coleoptile is the source of auxin and arrows indicate the direction of light. a, b, c, d are the different stages of grass:

15.1.4 Growth Rates

The plant growth regulators (PGRs) are small, simple molecules of diverse chemical composition. They could be indole compounds (indole-3-acetic acid, IAA); adenine derivatives (N6-furfurylamino purine, kinetin), derivatives of carotenoids (abscisic acid, ABA); terpenes (gibberellic acid, GA3) or gases (ethylene, C2H4).

Plant growth regulators are variously described as plant growth substances, plant hormones or phytohormones in literature.

The PGRs can be broadly divided into two groups based on their functions in a living plant body. One group of PGRs are involved in growth promoting activities, such as
1. cell division
2. cell enlargement
3. pattern formation
4. tropic growth
5. flowering, fruiting and seed formation.

These are also called plant growth promoters, e.g., auxins, gibberellins and cytokinins.

15.4.2 The Discovery of Plant Growth Regulators

Charlesb Darwin and his son Francis Darwin when they observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism).

After a series of experiments, it was concluded that the tip of coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile

Gibberellic acid:
The ‘bakane’ (foolish seedling) disease of rice seedlings, was caused by a fungal pathogen Gibberella fujikuroi. E. Kurosawa reported the appearance of symptoms of the disease in uninfected rice seedlings when they were treated with sterile filtrates of the fungus. The active substances were later identified as gibberellic acid.

F. Skoog and his co-workers observed that from the internodal segments of tobacco stems the callus (a mass of undifferentiated cells) proliferated only if, in addition to auxins the nutrients medium was supplemented with one of the following: extracts of vascular tissues, yeast extract, coconut milk or DNA. Skoog and Miller, later identified and crystallised the cytokinesis promoting active substance that they termed kinetin.

Cousins confirmed the release of a volatile substance from ripened oranges that hastened the ripening of stored unripened bananas. Later this volatile substance was identified as ethylene, a gaseous PGR.

15.4 Physiological Effects of Plant Growth Regulators Auxins

Auxins (from Greek ‘auxein’ : to grow) was first isolated from human urine. The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth regulating properties. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.

Auxins isolated from plants.

1. IAA
2. indole butyric acid (IBA)

synthetic auxins

1. NAA (naphthalene acetic acid) and 2
2. 4-D (2, 4-dichlorophenoxyacetic)

All these auxins have been used extensively in agricultural and horticultural practices.

They help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits.

In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance. Auxins

Auxins means to grow was first isolated from human urine. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.

They help to initiate rooting in stem cuttings, an application widely used for plant propagation.

In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance. Gibberellins

Gibberellins are another kind of promotery PGR. There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants.

They are denoted as GA1, GA2, GA3 and so on. Cytokinins

Cytokinins have specific effects on cytokinesis, and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA.

Kinetin does not occur naturally in plants. Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn-kernels and coconut milk.

It helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot formation. Cytokinins help overcome the apical dominance. Ethylene

Ethylene is a simple gaseous PGR. It is synthesised in large amounts by tissues undergoing senescence and ripening fruits.

Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings.

Increase plants absorption surface
Ethylene breaks seed and bud dormancy, initiates germination in peanut seeds, sprouting of potato tubers. Ethylene promotes rapid internode/petiole elongation in deep water rice plants. It helps leaves/ upper parts of the shoot to remain above water. Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface. Abscisic acid

abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development.

stress hormon:
ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

15.5 Photoperiodism

It has been observed that some plants require a periodic exposure to light to induce flowering. It is also seen that such plants are able to measure the duration of exposure to light.

For example, some plants require the exposure to light for a period exceeding a well defined critical duration This group of plants are called long day plants while others must be exposed to light for a period less than this critical duration before the flowering is initiated in them. this group of plants are termed as short day plants.

The critical duration is different for different plants. There are many plants, however, where there is no such correlation between exposure to light duration and induction of flowering response; such plants are called day-neutral plants

it can be said that flowering in certain plants depends not only on a combination of light and dark exposures but also their relative durations. This response of plants to periods of day/night is termed photoperiodism.


short day and long day plants.

15.6 Vernalisation

There are plants for which flowering is either quantitatively or qualitatively dependent on exposure to low temperature. This phenomenon is termed vernalisation.

It prevents precocious reproductive development late in the growing season, and enables the plant to have sufficient time to reach maturity.

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