Control and Coordination- Chapter 2, Questions and Answers Part-2
Answer: The environmental stimuli that can change the direction of growth in plants are light, moisture, touch, gravity, chemicals,etc.
Answer: The "touch-me-not" plant is very quick to response to stimulus. If any leaflet is touched, it folds up and within two to three seconds the entire leaf droops. Hence, it is apparent that the movement takes place also at a point different from the point of touch. It means that all the leaflets must be communicated to pass the information of touch.
Q.3. Name one chemical substance of plant which promotes ripening of fruits.
Answer: Ethylene.
Q.4. Define chemotropism.
Answer: The directional movement or orientation of the plant parts in response to chemical stimulus is known as chemotropism.
Q.5. A young green plant receives sunlight from one direction only. What will happen to its shoots and roots?
Answer: A young green plant receives sunlight from one direction only. The young shoots will bend towards the direction of light and the young roots will show curvature away from the source of light.
Q.6.Name the plant hormones which help/promote (i) cell division (ii) growth of the stem.
Answer:
- Cytokinins promotes cell division in plants.
- Gibberellins promote the growth of the stem.
Answer: During the process of fertilization, growth of pollen tube towards the ovule in the ovary is an example of chemotropism.
Q.8. Name the plant hormone that retards growth of the plant.
Answer: Abscisic acid.
Q.9. Name the five plant hormones.
Answer: Five plant hormones are-
- Auxins
- Gibberellins
- Cytokinins
- Ethylene
- Abscisic acid.
- Enlargement of cells
- Growth of stem
- Promotion of cell division
- Breaking of dormancy.
- Auxins
- Gibberellins
- Cytokinins
- Abscisic acid.
Answer: The types of nastic movements in plants are-
- Seismonastic movements, for example, immediate fold up of leaves of Mimosa pudica plant.
- Nyctinastic movements, for example, the diurnal variation in the position of flowers and leaves of many plants in day and night.
Answer: Plant hormones or Phytohormones are naturally occurring chemical substances present in plants and bring about control and coordination of various activities in them.
The two important functions of auxin are-
- Auxins promote cell enlargement and cell differentiation in plants.
- Auxins regulate important growth movement, i.e., tropism.
Answer: The control and coordination take place in plants through chemical substances called plant hormones or phytohormones. Different phytohormones help to coordinate growth, development and responses to the environment. Five major hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene. Out of five auxins, gibberellins and cytokinins are growth promoters while abscisic acid is growth inhibitor. Ethylene is gaseous hormone which has dual function of inhibition and promotion of growth.
Q.14. Write down the functions of gibberellins, cytokinins and abscisic acid (one of each).
Answer: Gibberellins: Gibberellins promote the growth in stems, leaves and flowering.
Cytokinins: Cytokinins promote cell division in plants.
Abscisic acid: Abscisic acid promotes the dormancy in seeds and buds and thus inhibits growth.
Q.15. What is phototropism?
Answer: The directional movement of the plant part in response to light is known as phototropism.
Q.16. What is hydrotropism?
Answer: The directional movement or orientation of the plant parts in response to water stimulus is termed as hydrotropism.
Q.17. What is geotropism? Give example.
Answer: The directional movement or orientation of the plant parts in response to gravity is termed as geotropism.
Example- roots of a plant move downwards in the soil in the direction of gravity.
Q.18. How does phototropism occurs in plants?
Answer: The phototropism in plants is due to the action of auxin hormones. The auxin hormone is synthesised by the meristematic tissue at the tip of the stem. The auxin hormone moved from the tip of stem and concentrated more on the side not receiving light. Due to presence of more auxin hormone, the shady side of stem grew faster than the side of stem receiving light. As a result, the stem bent towards the direction of light (phototropism).
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