Question 1

Q1: Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.

Accepted Answer

Growth: An irreversible and permanent increase in the size of an organ, its parts, or an individual cell. It is generally accompanied by metabolic processes and an increase in dry weight. Differentiation: The process by which cells derived from meristems mature and undergo structural changes in thei...

Question 2

Q10: What would be expected to happen if: (a) $GA_3$ is applied to rice seedlings (b) dividing cells stop differentiating (c) a rotten fruit gets mixed wit...

Accepted Answer

(a) If $GA_3$ (Gibberellic acid) is applied to rice seedlings, they would exhibit excessive elongation of their stems. This phenomenon is similar to the symptoms of the 'bakanae' or 'foolish seedling' disease in rice, which is caused by the fungus Gibberella fujikuroi, the natural source from which...

Question 3

Q2: Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?

Accepted Answer

Growth in a plant is a complex process involving increases in various aspects, and no single parameter is sufficient to measure it throughout the plant's life. Different parameters are suitable for measuring growth at different stages or in different parts of the plant. For example:    Cell number:...

Question 4

Q3: Describe briefly: (a) Arithmetic growth (b) Geometric growth (c) Sigmoid growth curve (d) Absolute and relative growth rates

Accepted Answer

(a) Arithmetic growth: In this type of growth, following mitotic division, only one of the two daughter cells continues to divide, while the other differentiates and matures. This results in a constant rate of growth. When the length of the organ is plotted against time, a linear curve is obtained....

Question 5

Q4: List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applicatio...

Accepted Answer

The five main groups of natural plant growth regulators (PGRs) are: 1.  Auxins 2.  Gibberellins 3.  Cytokinins 4.  Abscisic acid (ABA) 5.  Ethylene A Note on Auxins: Discovery: The discovery of auxins began with the observations of Charles Darwin and his son Francis Darwin. They observed that the co...

Question 6

Q5: Why is abscisic acid also known as stress hormone?

Accepted Answer

Abscisic acid (ABA) is known as the stress hormone because it plays a crucial role in helping plants cope with various adverse environmental conditions or stresses, such as drought, high salinity, and extreme temperatures. Its primary function during stress is to conserve water. When a plant experie...

Question 7

Q6: 'Both growth and differentiation in higher plants are open'. Comment.

Accepted Answer

The statement 'Both growth and differentiation in higher plants are open' refers to the unique ability of plants to grow and develop new cell types and structures throughout their life. Open Growth: Plant growth is described as 'open' or 'indeterminate' because plants possess meristems (e.g., apical...

Question 8

Q7: 'Both a short day plant and a long day plant can produce can flower simultaneously in a given place'. Explain.

Accepted Answer

Yes, it is possible for a short-day plant (SDP) and a long-day plant (LDP) to flower simultaneously in a given place. Flowering in these plants is not determined by the absolute length of day or night, but rather by whether the photoperiod is longer or shorter than a specific critical duration.    S...

Question 9

Q8: 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 sene...

Accepted Answer

(a) Auxins: They are widely used to initiate rooting in stem cuttings. (b) Ethylene: It is highly effective in promoting fruit ripening. (c) Cytokinins: They promote nutrient mobilization, which helps in delaying leaf senescence. (d) Cytokinins: They help overcome apical dominance and promote the gr...

Question 10

Q9: Would a defoliated plant respond to photoperiodic cycle? Why?

Accepted Answer

No, a defoliated plant (a plant from which all leaves have been removed) would not respond to the photoperiodic cycle. This is because the perception of the light and dark stimulus for flowering occurs in the leaves. The leaves contain the photoreceptor pigment (phytochrome) that detects the duratio...

NCERT Solutions