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35
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?
Explanation

Discovery of plant hormone gibberellins was made by chance. It happened by chance in rice fields. A few plants of rice were observed, which were unusually taller than the normal ones. Scientific investigation revealed, that these were infected with a fungus, known as Gibberella fufikuroi. This fungus releases a plant hormone gibberellic acid in excess concentrations which made the plant to grow unusually tall. This compound was later known as gibberellin is hormones present in all plants.

The term used for accidental finding is Serendipity which means fortunate happenstance. It was coined by Horace Walpole in 1754. He explained it as making discoveries, by accident and sagacity, of things, which were hot in quest of.

36
To get a carpet-like grass lawns are mowed regularly. Is there any scientific explanation for this?
Explanation
Regular mowing (cutting at apex) of lawn grass removes the apical portion of the plant which causes the lateral branches to grow faster. As the apical buds inhibits growth of lateral buds by releasing auxin, the phenomenon called apical dominance. Because of mowing of the grass, it becomes bushy and growth is faster. So, as to make evenness of the grass (carpet-like) in the lawn this practice is followed regularly to overcome the problem of apical dominance.
37
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?
Explanation

The meristematic cells can be identified of the basis of the following characteristics

(i) Cell have thin cellulose wall and dense cytoplasm with large nucleus.

(ii) Plasmodesmal connections are more numerous among meristematic cells.

(iii) Cell division, i.e., mitosis and its various stages are distinctly visible.

(iv) Chromosomes of cells replicate and divide into two homologous chromatids.

All these features contribute to open ended growth where structure is never complete in meristematic regions.

Whereas, cells incapable of divinding show features such as

(i) attains particular shape, size and thickening.

(ii) Undergoes structural and physiological differentiation.

(iii) Different types of cell are formed such as epidermis, cortex, vascular tissues.

38
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).
Explanation
Elasticity Plasticity
The elasticity is stretchability of the plant cells or products, e.g., rubber/latex etc.
The elastic substances can revert back to its original form in relaxed state. e.g., stretching of rubber.
Different pathways in response to environment or phases of life to form different kinds of structure is called plasticity.
The plastic substances and phenomenon of plasticity are not reversible, i.e., irreversible. e.g., difference in shapes of leaves produced in air and those produced in water in buttercup. This is also known as heterophylly.
39

Label the diagram

A. This is which part of a dicotyledonous plants?

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

Explanation

Representation the labelling of the given diagram is as follows

A. The plant part in the given diagram is growing shoot apex.

B. Removal of shoot apex will help to overcome the apical dominance. Thus, the lateral buds grow faster, giving rise to branches and give the plant a bushy appearance.