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

NCERT Solutions for Biology Chapter 15 Plant Growth and Development Class 11 will help you to ace the unsolved problems in the Class 11 Science book prescribed by the NCERT for all the schools of CBSE. These NCERT Solutions presents the best alternative and a very interesting way to learn, which helps to enhance your abilities and help to get ready for CBSE Class 11 exams.

Plant Growth and Development Class 11 Notes from Chapter 15 are prepared by our expert faculties to help you to prepare for your exams in a better way and enhance your score. Our NCERT Solutions provide step by step solutions for the questions given in NCERT textbook as per CBSE Board guidelines and are also prepared according to the exam pattern. For solving your doubts we have a team of teachers who provide live doubt solving session only for you.

In NCERT Solutions for Class 11 Biology Chapter 15, you will understand about plant growth, differentiation, dedifferentiation and redifferentiation, development, plant growth regulators, photoperiodism, vernalisation and seed dormancy, phases of growth, growth rates, conditions for growth, the discovery of plant growth regulators and physiological effects of plant growth regulators, plant growth and development.

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Page Number 254
Question 1
Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
Hard
Solution
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Growth is an irreversible and permanent process which can be seen by the increase in the length, size of the plant cells and tissues.
Few of the examples showing the growth in plants can be depicted as the lengthening of the roots and stem. 

The increase in the thickness of the woody plants  during their life span is also an example of growth process in plants. 

  

It is a process in which the cells derived from the apical meristem (root and shoot apex) and the cambium undergo structural changes in the cell wall and the protoplasm. 

These structural changes result in the achievement of the specific function.

One of the major example of differentiation in plants is  the formation of interfascicular and cork cambium which is derived from the fully differentiated Parenchyma cells. 

 

Plant development is referred to as the various continuous changes occurring in the plant body. 

The process involves embryogenesis followed by formation of the primary plant body (embryonic root and embryonic shoot) and continuous production of new plant parts such as roots, leaves, branches, and flowers.

The end stage of plant development is senescence. 

 

It is the process in which permanent plant cells regain the power to divide under certain conditions.

Few of the example of dedifferentiation in plants are as follows: 

Parenchymatous medullary rays get dedifferentiated into interfascicular cambium in dicotyledonous stem. 

Differentiated parenchymatous cells  get dedifferentiated into cork cambium. 

 

It is the process in which de-differentiated cells become mature again and lose their capacity to divide.

The example of the process of re-differentiation in plants is the formation of secondary phloem, secondary xylem, secondary cortex, cork, etc. 

This is redifferentiated from interfascicular cambium and cork cambium.

 

The type of plant growth which gets inhibited or limited at a certain stage. 

Examples of determinate growth is as follows:

The limitation of growth of the stem in an inflorescence or other reproductive structure. 

The branches of the stem stop growing continuously while it is deriving from the main branch. 

 

Meristem is the specialised regions in the plant which is specialized in the divisions of the active cells. 

There are three types of meristems that are apical meristem, lateral meristem, and intercalary meristem.

Apical meristem is the tip of the plat root or stem which is capable of division and growth. 

The type of meristem located in the lateral region of the plants and responsible for increasing the lateral growth of the plants , is defined as the lateral meristem. 

The type of meristem located in the middle position of the plants and is associated with the growth in length in the middle position, is defined as the intercalary meristem.  

 

It can be defined as the increased growth in plants per unit time.

It can be calculated by taking the change in size and dividing it by the amount of time it has been growing.
Question 2
Why is not any one parameter good enough to demonstrate growth through the life of a flowering plant?
Medium
Solution
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A plant has many different parts like leaves, stem, roots, flowers, fruits etc. which grow differently during different stages of life cycle. Different parameters are required to measure the growth of different plant parts. For stem and roots, increase in length and diameter are the parameters for measuring growth whereas for leaves, increase in surface area is a parameter for measuring growth.  Measuring the growth of plants using only one parameter does not provide sufficient information and hence, it is not good enough to demonstrate growth.
Question 3
Describe briefly: Arithmetic growth (b) Geometric growth (c) Sigmoid growth curve (d) Absolute and relative growth rates.
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Solution
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(a) Arithmetic growth
In arithmetic growth, one of the daughter cells continues to divide, while the other differentiates into maturity following mitotic cell divsion. The rate of growth is constant and increase in growth occurs in arithmetic progression, i.e., 2,4,6,8,10,.. 
Example: Elongation of roots at a constant rate
(b) Geometric growth
In geometric growth,growth is slow in the initial stages (lag phase) whereas rapid during the later stages (log or exponential phase). The daughter cells formed as a result of mitosis retain the ability to divide, but slow down due to limited supply of nutrients. The size or number increases in multiplicative fashion, i.e., 2,4,6,8,16,32,..
(c) Sigmoid growth curve
It is an S-shaped graph produced on plotting growth of living organisms in their natural environment against time. This curve is divided into three phases: lag phase, log phase or exponential phase of rapid growth, and stationary phase.
Exponential growth can be expressed as:
W1 = W0 e^rt
where,
W1 = Final size
W0 = Initial size
r = Growth rate
t = Time of growth
e = Base of natural logarithms

(d) (i) Absolute growth rate: It refers to the measurement and comparison of total growth per unit time.
     (ii) Relative growth rate: It refers to the growth of a given system per unit time, expressed on a common basis.


Question 4
List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agriculture/horticultural applications of any one of them.
Hard
Solution
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There are five main groups of natural plant growth regulators. They are:
(1) Auxins
(2) Gibberellins
(3) Cytokinins 
(4) Abscisic acid 
(5) Ethylene

Auxins

A) Discovery of Auxin
In 1881, Charles Darwin and Francis Darwin performed experiments on coleoptiles of canary grass and observed that they bend towards the light, when exposed to light from a unidirectional source. They concluded that the tip of the coleoptile was responsible for sensing light, and proposed that a messenger is transmitted in a downward direction from the tip of the coleoptile, causing it to bend.
In 1913, Peter Boysen-Jensen concluded that the substance secreted  at the tip is soluble in water (gelatin).
In 1928, F.W. Went showed that a chemical messenger diffuses from coleoptile tips and causes it to grow towards light. He later proposed that the messenger substance is a growth-promoting hormone, which he named auxin. 
In 1931, Kogl and Haagen Smith isolated crystalline compounds from human urine and named them as auxin-a, auxin-b and heteroauxin.

B) Physiological functions of Auxins
Apical dominance
Control of abscission
Root formation in stem cuttings
Parthenocarpy
Differentiation of xylem and phloem

C) Agricultural/Horticultural Applications
Application of auxin promotes flowering in case of orchards.Examples: pineapple, litchi, etc.
Auxins also induce parthenocarpy in some plants like tomato, cucumber, pepper, etc.
Auxins like IAA, IBA, NAA induce rooting in stem cuttings of various plants.
Auxin like 2,4-D is widely used as a herbicide to kill dicotyledonous weeds and to prepare weed free lawns by gardeners.
Auxins regulate the maturation of fruits on trees of apples, oranges and grape fruit.


Question 6
Why is Abscisic acid called as stress hormone?
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Solution
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Abscisic acid is also known as the stress hormone. It is because this acid induces various types of responses in plants against some stress conditions. Stress conditions include the closure of stomata during drought conditions, seed dormancy. It also ensures seed germination during favourable conditions and withstands desiccation.
Question 7
Both growth and differentiation in higher plants are open. Comment.
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Solution
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Growth and development in higher plants is referred to as being open. This is because various meristems, having the capacity for continuously dividing and producing new cells, are present at different locations in these plant bodies.
Question 9
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.
Hard
Solution
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(a) Induce rooting in a twig – Auxins
(b) Quickly ripen a fruit – Ethylene
(c) Delay leaf senescence – Cytokinins
(d) Induce growth in axillary buds – Cytokinins
(e) Bolt a rosette plant – Gibberellic acid
(f) Induce immediate stomatal closure in leaves – Abscisic acid
Question 10
Would a defoliated plant respond to photoperiodic cycle? Why?
Hard
Solution
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The photoperiodic stimulus is picked up only by the leaves in plants. For this purpose, leaf is of utmost importance. For the perception of photoperiodic cycle, presence of leaves under inductive photoperiod is essential, so that, the hormone required for flowering can be produced. Therefore, in the absence of leaves, i.e, in a defoliated plant light perception would not occur, i.e., the plant would not respond to light.

Question 11
Both a short day plant and a long day plant can produce flower simultaneously in a given place. Explain.
Medium
Solution
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The flowering response in short-day plants and long-day plants is dependent on the durations for which these plants are exposed to light. The short-day plant and long-day plant can flower at the same place, provided they have been given an adequate photoperiod.
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NCERT Solutions for Class 11 Biology Chapter 15 : Plant Growth and Development

NCERT Solutions for Class 11 Biology Chapter 15 Plant Growth and Development – Brief Overview

  • 15.1 – Growth
  • 15.1.1 – Plant Growth Generally is Indeterminate
  • 15.1.2 – Growth is Measurable
  • 15.1.3 – Phases of Growth
  • 15.1.4 – Growth Rates
  • 15.1.5 – Conditions for Growth
  • 15.2 – Differentiation, Dedifferentiation, and Redifferentiation
  • 15.3 – Development
  • 15.4 – Plant Growth Regulators
  • 15.4.1 – Characteristics
  • 15.4.2 – The Discovery of Plant Growth Regulators
  • 15.4.3 – Physiological Effects of Plant Growth Regulators
  • 15.5 – Photoperiodism
  • 15.6 – Vernalisation
15.1 – Growth In this, you will study about the growth of plants which is accomplished by cell division, increase in cell number and cell enlargement. 15.1.1 – Plant Growth Generally is Indeterminate In this, you will study plant growth is generally indeterminate due to the capacity of unlimited growth throughout life. 15.1.2 – Growth is Measurable In this, you will study to measure the growth of plants by parameter used to measure growth is an increase in fresh weight, dry weight, length, area, and volume and cell number. 15.1.3 – Phases of Growth In this, you will study about the different phases of growth which includes formative phase, phase of enlargement, maturation phase. 15.1.4 – Growth Rates In this, you will study about growth rate which is the increase in growth per unit time, it may be arithmetic or geometrical. 15.1.5 – Conditions for Growth In this, you will study the necessary condition for growth includes water, oxygen, and essential elements. 15.2 – Differentiation, Dedifferentiation, and Redifferentiation In this, you will study about differentiation, dedifferentiation, and redifferentiation. 15.3 – Development In this, you will study about development which is the sequence of events that occur in the life history of cell, organ or organism which includes seed germination, growth, differentiation, maturation, flowering, seed formation, and senescence 15.4 – Plant Growth Regulators In this, you will study about plant growth regulators are simple molecules of diverse chemical composition which may be indole compounds, adenine derivatives or derivatives of carotenoids. 15.4.1 – Characteristics In this, you will study about characteristics of the plant growth regulator like auxin, etc. 15.4.2 – The Discovery of Plant Growth Regulators In this, you will study about discovery of plant growth regulators. 15.4.3 – Physiological Effects of Plant Growth Regulators In this, you will study about physiological effects of plant growth regulators. 15.5 – Photoperiodism In this, you will study about photoperiodism is the effect of photoperiods or day duration of light hours on the growth and development of a plant, especially flowering. 15.6 – Vernalisation In this, you will study about vernalisation is the process of shortening of the juvenile or vegetative phase and hastening of flowering by cold treatment.

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Frequently Asked Questions on NCERT Class 11 Biology Chapter 15 : Plant Growth and Development

Q1. What are the key features of NCERT Solutions for Biology Chapter 15 Plant Growth and Development Class 11?

Answer: In NCERT Solutions for Class 11 Biology Chapter 15 you will learn about plant growth generally is indeterminate, growth is measurable, phases of growth, growth rates, conditions for growth, differentiation, dedifferentiation, redifferentiation, development,  plant growth regulators, characteristics, physiological effects of plant growth regulators, photoperiodism, and vernalization.

  1. All the fundamental concepts important for the board exam are explained elaborately.
  2. The answers created are based on the latest CBSE Syllabus and its guidelines.
  3. Students can also refer to these solutions and prepare for competitive exams like JEE, NEET, etc.
  4. The faculty uses simple and understandable language to help students ace the board exam without fear.

Q2. What are the uses of referring to the NCERT Solutions for Class 11 Biology Chapter 15?

Answer:  1. All the textbook questions are answered in a descriptive manner. 2. Students will be able to solve complex questions effortlessly using the solutions PDF. 3. By regular practice, students can jot down their areas of weakness and work on them for a better score. 4. Diagrams are present under each concept to help students learn them easily.