Question

Define phototropism and give one example.

Answer 1

The movements of growth in plants due to external factors are called tropic movements. These are also shown by fungi. Bending or curvature of any organ is due to differential growth of two lateral sides.

Complete answer:
The curvature induced in plant organs in response to the unidirectional light is called phototropism. For example- The unidirectional light causes the stem apex to move towards the source of light and in root away from it. The stem shows positive phototropism and the root shows negative phototropism. Another example is the seedling of the plants that grows straight when kept in the dark environment or sown under the soil, to reach sunlight.

Additional information:
The other types of tropic movement shown by plants are:

Geotropism- It is the growth and orientation of the stem and roots in response to the force of gravity. The stem shows negative geotropism while the root shows positive geotropism. Thus if a plant is kept on a horizontal plane, its stem will bend upwards and roots will bend down wards.

Hydrotropism- It is the movement of plant organs in response to variations in the amount of moisture. Roots are positively hydrotropic as they grow towards water.

Chemotropism- The movement of plant organs due to the unilateral stimulus of chemicals. The growth of the pollen tube from stigmatic surface into the style and the ovary is due to chemical stimulus.

Thigmotropism- It is the growth movement of plant organs in response to unilateral stimulus of touch. Tendrils of many cucurbitaceae plants mutate in the air and when come in contact with any support. they coil around it.

Note: Plants are autotrophic in nature and they prepare their own food using the sunlight and carbon dioxide. They convert solar energy into chemical energy and phototropism helps in the process by maximizing its exposure to sunlight.