Plant Growth and Development Class 11 Notes CBSE Biology Chapter 15 [Free PDF Download]

Section–A (1 Mark Questions)

1. What is growth?

Ans. Growth is an irreversible permanent increase in size of an organism.

2. Name the growth regulator which was first isolated from corn kernel and coconut milk.

Ans. Zeatin (Cytokinin) was first isolated from corn kernel and coconut milk.

3. Name the hormone released from over-ripe apples that affects all other apples in a small wooden box.

Ans. Over-ripe apples produce ethylene which is a ripening hormone that affects all other apples in the small wooden box. As a result, all the apples in the wooden box get ripened.

4. Name the plant hormone which was first isolated from human urine.

Ans. Auxin (from the Greek word ‘auxein’, meaning ‘to grow’) was first isolated from human urine.

5. Flowering in certain plants occurs only when they are exposed to low temperature for a few weeks. Name this phenomenon.

Ans. This phenomenon is known as vernalization. It is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent.

Section–B (2 Mark Questions)

6. What is bolting? Which hormone is responsible for it?

Ans. Bolting is the enormous elongation of internodes resulting in an increase in stem height just prior to flowering. Gibberellins promote bolting in beet, cabbages and many plants with rosette habit.

7. Name any two synthetic auxins. How are they used in agriculture?

Ans. Two synthetic auxins are

(i) Naphthalene Acetic Acid (NAA)

(ii) Indole Butyric Acid (IBA) 

They are used as weedicides.

8. How will you induce lateral branching in a plant which normally does not produce them? Give a reason. 

Ans. When the apical bud is removed, lateral branches are produced. Removal of apical bud effect the auxin is destroyed inducing the lateral buds to grow rapidly.

9. Why is abscisic acid also known as stress hormone?

Ans. Abscisic acid is referred to as a stress hormone as it increases the tolerance of plants to various kinds of stresses. It facilitates the seed dormancy and ensures seed germinates under favorable circumstances. It also causes the closing of stomata when there is a drought. They are also critical in withstanding desiccation. Furthermore, they also assist to induce dormancy in plants towards the end of the growing season, facilitating abscission of fruits, leaves and flowers.

10. List a hormone that:

a) Is in charge of phototropism.

b) Influences femaleness in cucumber flowers.

c) Is utilized to kill weeds(dicots).

d) In long-day plants, it induces flowering.

Ans. a) Auxin

b) Ethylene

c) Auxin

d) Gibberellin

11. ‘Both growth and differentiation in higher plants are open’. Comment.

Ans. Growth and differentiation in plants are open as all the cells as well as the tissues arising from the same meristem may possess different structures at maturity. The maturity is determined by the location of cells or tissues e.g. it may be at shoot apex, root apex, cambium etc.

PDF Summary - Class 11 Biology Plant Growth and Development Notes (Chapter 15)

15. 1 Growth

• The stem, roots, leaves, flowers, fruits, and seeds of the plants arise naturally. The order of the growth is in the following manner:

• The plants begin their reproductive phase, where the flowers and fruits are produced to continue the plants' life cycle after completing their vegetative phase.

• Development is the sum of two processes which is growth and differentiation. Few internal and external factors control development and growth.

• Growth is an irreversible increase in dry weight, size, mass, or volume of cell, organ, or organism which is permanent. It is usually internal in living organisms.

• Growth is achieved by cell division, which increases cell number and cell enlargement in the plants. Hence, growth is a quantitative aspect which can be measured according to time.

• Plant growth is generally indeterminate because of the capacity of unlimited growth in their lifespan. Meristem tissues are there at certain parts of the plant body.

• The Open Form of Growth - The plant growth in which there is an addition of new cells to the plant body due to meristem.

• Root Apical Meristem and Shoot Apical - Meristem leads to elongation and the primary growth of the plant body along with the axis.

15.2. Growth is Measurable

• At the cellular level, growth refers to the increase in the amount of protoplasm. It is often difficult to measure this increase. However, we can measure the increase in the cell, cell number, and cell size.

• The growth measure is checked by the increase in fresh weight, length, dry weight, area, volume, and cell number. Some can be measured for measuring some kinds of growth.

• The phase of cell division or cell formation is called the formative phase. It takes place at the shoot apex, root apex, and other regions having meristematic tissue. The rate of respiration is usually very high in the cells undergoing mitosis division in the formative phase.

• Enlargement Phase - The newly formed cells produced in the formative phase will undergo enlargement. This enlargement leads to the development of vacuoles that further lead to an increase in cells' volume.

• Cell enlargement takes place from all directions with maximum elongation in conducting tissues and fibres.

• The Phase of Maturation - the cells that have undergone enlargement develop into a specific type of cells by structural and physiological differentiation.

• Growth Rate - Growth rate is the increase in growth per unit time. The growth rate may be different in nature. Some are arithmetic or geometric.

• Arithmetic Growth - In this type of nature, the rate of growth is constant, and an increase in growth follows an arithmetic progression- 2,4,6,...

It occurs in shoot and root elongation.

L_t = L₀ + rt

Length at beginning + growth rate x time = Length after time.

• Geometric Growth - In this method, the initial Growth is gradual and then rapidly increases. Each cell divides. The daughter cells divide and grow, and further the granddaughter cells that lead to the exponential growth. It is common in a unicellular organism.

• The sigmoid growth curve includes the stationary phase and fast dividing exponential phase. It is very typical of most living beings in their natural habitat.

Exponential Growth can be represented and can be expressed as follows:

W₀ = initial size, W₁ = final size, W1 =W₀e^rt., r = growth rate, and the t = time of growth, and e is the base of natural logarithms (2.71828).

• Quantitative comparison between the Growth of living system can be made by

1. The absolute rate means the measurement and comparison of total Growth per unit time.

2. The relative growth rate is the growth of a given system per unit of time, which is expressed on a common basis.

15.3 Condition for Growth

• Water, oxygen, and essential elements are the essential conditions for growth. Water is highly required for all the cell enlargement and controls the turgidity. Water also acts as a medium for enzymatic conditions.

• Water is required for the formation of Protoplasm, while the micro and macronutrients act as a source of energy.

• Plants also need optimal temperature and other environmental conditions.

• The act of maturation where the cells formed by apical meristem turn into a specialized one to serve a specific function is called differentiation.

• The differentiated living cells which are living that no longer can undergo division can regain the capacity of it. This phenomenon is known as dedifferentiation, for instance, cork cambium and interfascicular cambium and cork cambium.

• Redifferentiation is a process where the dedifferentiated cells mature and lose cell division capacity again to serve specific functions.

15.4 Development

It is the order of the events in the life span of a cell, organ, or organism, including the growth differentiation, seed germination, growth, flowering, senescence, and seed formation.

The sequence of the development process in plant cell:

• Different structures of plants develop in different stages of growth, also as in response to the environment. Plasticity is the ability to change under the influence of internal or external stimuli - for example, Heterophylly in cotton plants.

Plant Growth Regulators are the simple molecules of diverse chemical composition, including the adenine derivatives, indole compounds, or derivatives of carotenoids.

Auxin - It is commonly known as indole-3-acetic acid (IAA). It is produced at the stem and root apex and often migrates to the site of action.

It serves the following functions:

1. Cell enlargement.

2. Cell division.

3. Apical dominance.

4. Induce Parthenocarpy.

5. Inhibition of abscission.

Gibberellins: Gibberellins are promotery PGR seen in more than 100 forms. They are denoted as GA1, GA2, GA3 and so on. Gibberellic Acid is the most common one.

It serves the following functions:

1. Cell elongation.

2. Early maturity.

3. Seed germination.

4. Breaking of dormancy.

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. The most common forms are zeatin, kinetin, etc. They are mainly made in the roots.

Some of the Functions:

1. Cell division and cell differentiation.

2. Overcome apical dominance.

3. Promote nutrient mobilization.

4. Essential for tissue culture.

Ethylene - It is called a gaseous hormone that stimulates isodiametric or transverse growth; however, it retards the longitudinal one.

It serves the following functions:

1. Inhibition of longitudinal Growth.

2. Senescence.

3. Promote apical dominance.

4. Fruit ripening.

Abscisic Acid - It is also referred to as stress hormone or dormin. It works like a general plant growth inhibitor. Abscisic acid is formed at the terminal buds of the top of the plant or in the roots of the plants.

It can serve the following functions:

1. Bud dormancy.

2. Induce Parthenocarpy.

3. Seed development and maturation.

4. Leaf senescence.

Photoperiodism - Photoperiodism is the effect of photoperiods or day duration of light hours on the plant's growth and development, especially flowering. The flowering plants have been divided into the following categories based on photoperiodic response:

1. Short Day Plants - The flowers which need exposure to light for a period less than this critical duration before the flowering is initiated. For example - Xanthium, Sugarcane, Potato Rice.

2. Long Day Plants - The plant flowers when they need a long photoperiod of light, greater than the critical period. Example - Barley, Radish, Lettuce.

3. Day Neutral Plants - These plants can blossom throughout the year - for example - Wild Kidney, Bean.

Vernalisation - is the process of reducing the juvenile or vegetative phase and fastening the flowering procedure by cold treatment. Meristematic cells help in perceiving the stimulus of vernalization.

• Vernalisation reduces the vegetative period of plants and leads to early flowering.

• It applies to temperate plants like Rice, Wheat, Millets, etc..

Class 11 Biology Notes PDF

The Class 11 Revision Notes Chapter 15 is available in PDF files, which can be accessed on any device at your pace, and it can be accessed offline once it is downloaded. These notes can help the student to understand and retain the information whenever needed. This pdf is an excellent resource for scoring good marks in your exams.