Biology Class 11 NCERT Solutions: Chapter 15 Plant Growth and Development Part 1

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Q: 1. Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.

Answer

(A) Growth

It is an irreversible and permanent process, accomplished by an increase in the size of an organ or organ parts or even of an individual cell.

(B) Differentiation

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, becoming mature to perform specific functions.

(C) Development

It refers to the various changes occurring in an organism during its life cycle – from the germination of seeds to senescence.

(D) De-differentiation

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

(E) Re-differentiation

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

(f) Determinate growth

It refers to limited growth. For example, animals and plant leaves stop growing after having reached maturity.

(g) Meristem

In plants, growth is restricted to specialised regions where active cell divisions take place. Such a region is called meristem. There are three types of meristems - apical meristem, lateral meristem, and intercalary meristem.

(h) Growth rate

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

Q: 2. Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?

Answer

In plants, growth is said to have taken place when the amount of protoplasm increases. Measuring the growth of protoplasm involves many parameters such as the weight of the fresh tissue sample, the weight of the dry tissue sample, the differences in length, area, volume, and cell number measured during the growth period. Measuring the growth of plants using only one parameter does not provide enough information and hence, is insufficient for demonstrating growth.

Image of flowering plants life cycle

Image of Flowering Plants Life Cycle

Image of flowering plants life cycle

Q: 3. Describe briefly:

(A) Arithmetic growth

(B) Geometric growth

(C) Sigmoid growth curve

(D) Absolute and relative growth rates

Answer

(A) Arithmetic growth

In arithmetic growth, one of the daughter cells continues to divide, while the other differentiates into maturity. The elongation of roots at a constant rate is an example of arithmetic growth.

(B) Geometric growth

Geometric growth is characterised by a slow growth in the initial stages and a rapid growth during the later stages. The daughter cells derived from mitosis retain the ability to divide, but slow down because of a limited nutrient supply.

Image shows the types of growth rate

Image Shows the Types of Growth Rate

Image shows the types of growth rate

(C) The growth of living organisms in their natural environment is characterised by an S shaped curve called sigmoid growth curve. 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:

Q 3 Image of Exponential Phase

Q 3 Image of Exponential Phase

Q 3 Image of Exponential Phase

Where,

(D) Absolute and relative growth rates

Absolute growth rate refers to the measurement and comparison of total growth per unit time.

Relative growth rate refers to the growth of a particular system per unit time, expressed on a common basis.