NCERT Class 11-Biology: Chapter –15 Plant Growth and Development Part 7

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Question 10:

Many discoveries in science have been accidental. This is true for plant

hormones also. Can you justify this statement by giving an example? Also what term is used for such accidental findings?


Many discoveries in science have been accidental which is true for plant hormones’ discovery too. The five major groups of plant growth regulators have all been discovered accidentally.

When Charles Darwin and his son Francis Darwin observed the coleoptiles of canary grass, they noticed that it responded to unilateral illumination by bending and growing towards the light source. Auxin was isolated by F.W. Went from tips of coleoptiles.

Foolish seedling disease of rice was caused by the fungal pathogen Gibberella fujikuroi. The symptoms of which were first reported by Kurosawa who noticed that uninfected rice developed these symptoms when gibberellins were added.

Only when auxins were added, the callus of stems proliferated. This was observed by F. Skoog and his co-workers.

Skoog and Miller crystallised the cytokinesis promoting substance called kinetin.

Scientists confirmed the release of a gaseous substance from ripened oranges - ethylene.

Question 11:

To get a carpet like grass lawns are mowed regularly. Is there any scientific explanation for this?


To get a carpet like grass, lawns are mowed regularly as mowing (process of cutting the grass) causes decapitation that promotes the growth of lateral buds. The process of Decapitation of plants leads to the inactivation of axillary buds and promotes growth of lateral buds giving a carpet like appearance.

Question 12:

In a slide showing different types of cells can you identify which type of the cell may be meristematic and the one which is incapable of dividing and how?


In a slide showing different types of cells, it can be identified as to which cell is meristematic and which is incapable of dividing.

The meristematic cells which actively divide show the following characteristics which are not shown by cells that are non-dividing:

a) The nucleus of the cell is large.

b) Cell wall is thin and composed of cellulose.

c) It is rich in protoplasm.

d) Less vacuoles

e) Cells are differentiated.

Question 13:

A rubber band stretches and reverts back to its original position. Bubble gum stretches, but it would not return to its original position.

Is there any difference between the two processes? Discuss it with respect to plant growth (Hint: Elasticity (reversible) Plasticity (irreversible))


A rubber band stretched and reverts back to its original position due to the property of elasticity where the form gets reversed. Bubble gum would not return to its original position after getting stretched because of the phenomenon of plasticity. It is irreversible.

Plants follows different types of pathways in response to different environmental conditions which leads to form different kinds of structures.

Example is heterophylly (different leaf forms on the same plant) in plants like buttercup.

Question 14:

Label the diagram

Chapter 15 - Question 14 - Images ofLable the Diagram

Chapter 15 - Question 14 - Images ofLable the Diagram

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a. This is which part of a dicotyledonous plant?

b. If we remove part 1 from the plant, what will happen?


(a) This is the shoot apex meristem of a dicotyledonous plant.

The shoot apical meristem is present at the tip of the plant stem, has two functions:

(a) It is the point of source of new cells needed for growth stem

(b) Small cellular outgrowths occurs here called leaf primordia that later develop into leaves

The different parts labelled 1, 2, 3 are:

1: Leaf primordium

2: Axillary bud: During the formation of leaves and elongation of stem, some cells which are left behind make the axillary bud: forms a branch or a flower.

3: Shoot apical meristem

(b) If part 1 is removed from the plant, then the apical bud is inhibited while there is growth of lateral buds.