Question

Give one example of each type of plant (organ) showing the following movement :

1. Negatively geotropism
2. Positively hydrotropism
3. Negatively phototropism
4. Chemotropism
5. Thigmotropism

Answer 1

i) Negatively geotropism

1. The shoot of plants exhibits negative geotropism.
2. Geotropism is called the phenomenon of directional growth and movement of the plant parts in response to the stimulus of gravitational force.
3. Growth toward the stimulus gravity is called positive geotropism showed by the roots and growth opposite to the stimulus gravity is called negative geotropism, demonstrated by the shooting of plants

ii) Positively hydrotropism

1. Seeds of plants exhibit positive hydrotropism.
2. The phenomenon of directional growth and movement of the plant parts in response to the stimulus of water or moisture is known as hydrotropism.
3. Growth toward the stimulus water is called positive hydrotropism and growth opposite the stimulus water is called negative hydrotropism.
4. For example, the growth of roots towards the water. Hydrotropism involves the turning or curling of plant parts.

iii) Negatively phototropism

1. The roots of the plants exhibit negative phototropism.
2. The phenomenon in which the plant organs grow and move in response to the external stimulus light is known as phototropism.
3. The shoot, flower, and stem of the plants grow and bend towards the light showing positive phototropism while the root of the plants grow away from the sunlight showing negative phototropism

iv) Chemotropism

1. Growth of the pollen tube in response to the presence of sugars in the stigma of the flower exhibit chemotropism.
2. The phenomenon in which the plant organs grow and move in response to the external stimulus of any chemical is called chemotropism.

v) Thigmotropism

1. Tendrils of climbers exhibit thigmotropism.
2. The phenomenon of directional growth and movement of the plant parts in response to the stimulus of contact or touch with a solid surface is known as thigmotropism.
3. The soft-stemmed plants such as bitter gourd, and peas have tendrils that search a surface for support. After finding support it coils itself around the support to grow properly.