NCERT Solutions for Class 11 Biology Chapter 13 – Plant Growth and Development

NCERT Solutions for class 11 Chapter-13 Plant Growth and Development: The chapter on Plant Growth and Development is important for students approaching the home exams. This article introduces NCERT solutions designed to help students explain the concepts of further learning and how to write to get good grades on exams. The solutions are presented in very simple language for ease of understanding.

Solutions of NCERT CBSE Class 11 Chapter 13 Plant Growth and Development explains the growth and development of plants, how the growth of plants occurs and how they are developed, and which factors are essential for the growth and development of the plants, including phytohormones or plant hormones. Revise the basic concepts of Plant Growth and Development for quick revision and class notes.

Q1: Define Growth, Differentiation, Development, Dedifferentiation, Redifferentiation, Determinate Growth, Meristem, and Growth Rate.

Answer:

• Growth: It is a permanent process and it cannot be reversible. It is observed by physically seeing any plant if the length, and size of plant cells are increasing it means that the growth of the plant occurs.
• Differentiation: It is a process in which the cells are derived from the apical meristem and the cambium is undergoing the structural changes of the cell wall and the protoplasm becoming mature and performing specific functions.
• Development: Development refers to all organism’s changes throughout their whole life. The changes are progressive in terms of size, shape, and functions.
• Dedifferentiation: It is a process in which a plant cell regains the ability to divide due to some circumstances after losing its ability to divide.
• Redifferentiation: In this process, the dedifferentiated cells again became mature and lose the ability to divide again.
• Determinate growth: It is the ability to grow cells, tissues, or organs in a particular time period and get inhibited after that time period.
• Meristem: It is a plant tissue that has undifferentiated actively dividing cells to form specialized structures, e.g. flowers, and buds. Meristematic tissues are found in the bark of the trees and tips of the root and shoot.
• Growth rate: It is the amount of growth per unit of time. It can be arithmetic or geometric. The growth is an irreversible and permanent increase in the size of a body or organs. Three major phases are involved in the growth, i.e. cell division (mitosis), cell enlargement, and cell differentiation.

Q2: Why is Not Any One Parameter Good Enough to Demonstrate Growth Throughout the Life of a Flowering Plant?

Answer:

Plant growth is said to have occurred or not on the basis of the amount of protoplast. During growth, the amount of protoplast increases. Protoplasm growth measurement involves different parameters like the weight of the fresh tissue sample, the weight of the dry tissue sample, the difference in length, volume, area, and number of cells measured during the growth period. These parameters are important to measure the growth so that only one parameter is not enough to demonstrate the growth.

Q3: Describe Briefly: 

• (a) Arithmetic Growth 
• (b) Geometric Growth 
• (c) Sigmoid Growth Curve 
• (d) Absolute and Relative Growth Rates

Answer:

• (a) Arithmetic Growth: When one daughter cell continues to divide and the other differentiates into maturity i.e. arithmetic growth. Here, Growth occurs in arithmetic progression.
• (b) Geometric Growth: When the growth is slow during the initial stage (lag phase) and rapid growth during later stages (log or exponential phase) i.e. called geometric growth. Here number and size increase in a multiplicative manner.
• (c) Sigmoid Growth: During this growth, the S-shaped growth curve occurs when the graph is plotted between the growth of living organisms and time. This growth curve is divided into three phases; (a) lag phase, (b) log phase or exponential phase, and (c) stationary phase.
  • Exponential growth can be expressed as follows:
    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
• (d) Absolute Growth Rate: It is the measurement and comparison of growth per unit time. Relative Growth Rate: It is expressed on a common basis, it is the growth of a system per unit time.

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.

Answer:

Five main groups of natural plant growth regulators are:

1. Auxin
2. Gibberellins
3. Cytokinin
4. Abscisic acid
5. Ethylene

1) Auxin

Discovery:

The effects of auxin were first observed by Charles Darwin and Francis Darwin in 1881, they saw that coleoptiles of canary grass were bending towards the unilateral light source. They perform a series of experiments and concluded that coleoptile tip produce some substance that was responsible in bending, and that substance was auxin.

Physiological Functions:

• Control plant growth
• Causes apical dominance
• Control division in the vascular cambium and xylem differentiation
• Induce parthenocarpy
• Prevent leaves and fruits’ abscission.

Horticultural Applications:

• Promotes flowering in litchi and pineapple.
• Induce parthenocarpy in some plants like tomatoes, pepper, cucumber, etc.
• IAA, IBA, and NAA induce rooting in stem-cutting plants.
• 2,4-D is used as a weedicide to kill the dicotyledonous weeds.

Q5: What Do You Understand by Photoperiodism and Vernalization? Describe Their Significance.

Answer:

• Photoperiodism: Photo means light and periodism means duration. Response of a plant in the presence of light or period of light exposure. On the basis of the period of light exposure, plants are classified as short-day, long-day, and day-neutral plants. It helps in studying the flowering response at different exposures of light in different plants.
• Vernalization is the phenomenon in which the process of flowering depends on the low temperature in some plants. In these plants, low temperature is essential for the induction of flowering.

Q6: Why is Abscisic Acid Also Known as Stress Hormone?

Answer:

Abscisic acid is known as a stress hormone because it induces when a plant is in stressful conditions. It inhibits the stomatal opening during drought conditions, it also induces seed dormancy and during favorable conditions, it ensures seed germination.

Q7: Both Growth and Differentiation in Higher Plants Are Open. Comment.

Answer:

Growth and differentiation in higher plants are open because various meristems present at various locations on the plant body have the capacity to continuously divide and produce new cells.

Q8: Both a Short-Day Plant and a Long-Day Plant Can Produce Flower Simultaneously in a Given Place. Explain.

Answer:

Flowering response in short-day plants and long-day plants depends on the duration of light to which plants are exposed. Both short-day and long-day plants can flower simultaneously and at the same place, if they are provided with an adequate photoperiod.

Q9: Which One of the Plant Growth Regulators Would You Use If You Are Asked To: 

• (a) Induce Rooting in a Twig 
• (b) Quickly Ripen a Fruit 
• (c) Delay Leaf Senescence 
• (d) Induce Growth in Axillary Buds 
• (e) ‘Bolt’ a Rosette Plant 
• (f) Induce Immediate Stomatal Closure in Leaves

Answer:

• (a) induce rooting in a twig: Auxin 
• (b) quickly ripen a fruit: Ethylene
• (c) delay leaf senescence: Cytokinin 
• (d) induce growth in axillary buds: Cytokinin 
• (e) ‘bolt’ a rosette plant: Gibberellins
• (f) induce immediate stomatal closure in leaves: Abscisic acid

Q10: Would a Defoliated Plant Respond to Photoperiodic Cycle? Why?

Answer:

Only leaves can pick up the photoperiodic stimulus. The presence of leaves under inductive photoperiod is necessary for the perception of the photoperiodic cycle so that the hormone can be produced which is required for the flowering. Therefore, in the absence of leaves (defoliated plant), the perception of light would not occur (the plant would not respond to light).

Q11: What Would Be Expected To Happen If: 

• (a) GA3 is Applied to Rice Seedlings 
• (b) Dividing Cells Stop Differentiating 
• (c) A Rotten Fruit Gets Mixed With Unripe Fruits 
• (d) You Forget to Add Cytokinin to the Culture Medium

Answer:

• (a) Rice seedlings show internode elongation and height gain. They also remain sterile when GA3 is applied to rice seedlings.
• (b) When dividing cells stop differentiating then leaves and stem will not form and the mass of undifferentiated cell is called as callus or tumor.
• (c) If a rotten fruit is mixed with unripe fruits then the rotten fruit release ethylene and this ethylene ripe the unripe fruit quickly.
• (d) Cytokinin is essential for cell division, growth, and differentiation, so that if cytokinin is not added to the culture medium then the growth will become slow.