Question

Write about movement due to growth in plants with one example.

Answer 1

Tropic Movement:

1. Movements caused by environmental triggers are directional.
2. They can be toward the source of the trigger (positive) or away from the trigger source (negative).
3. Movements that take place in the stimulus' direction are called tropic movements.
4. A tropic movement might be directed either towards or away from the stimulus.
5. Tropic movements are of different types. These types are provided below:

(A) Phototropism (Response to light):

1. In this, the plant grows in the direction of light.
2. The plants have a growth regulator called Auxin. It reacts in response to light and causes the cells of the plants to grow longer.
3. Positive phototropism refers to plant development more towards the source of light, whereas negative phototropism refers to plant growth away from the direction of light.
4. The stem is positive phototropic since it grows in the direction of light.
5. The root, however, grows away from the light source, so it is known as negative geotropism.

(B) Chemotropism (Response to chemicals):

1. In simple terms, this is the movement of a plant part towards a chemical stimulus.
2. In plants, for instance, the stigma releases a chemical that directs pollen tubes towards ovules during fertilization.

(C) Hydrotropism (Response to water):

1. It is the root system growing in the direction of the water gradient.
2. Plant roots, for instance, grow towards higher humidity levels. For example, when we stretch a plant, we find that the roots of the plant are growing in all directions.

(D) Geotropism (Response to gravity):

1. It means that plant parts move in response to gravity.
2. Roots grow towards gravity and are therefore positively called geotropic.
3. On the other hand, the stem is negatively geotropic.