Question

What causes a green plant exposed to light on only one side, to bend towards the source of light as it grows?
A. Light stimulates plant cells on the lighted side to grow faster.
B. Auxin accumulates on the shaded side, stimulating greater cell elongation there
C. Green plants need light to perform photosynthesis.
D. Green plants seek light because they are phototropic.

Answer 1

Plant known as producer due to its ability to make food in the presence of sunlight. Plants not only produce food in the presence of sunlight but also show phototropism bending of plants towards light.

Step by step answer: There is an experiment to place a potted plant in a dark room and observe its movement. After someday, you will observe plants will grow towards the window from where the plant is receiving sunlight. This shows that plants respond to the light and grow towards the sunlight. This movement is due to the plant hormone called auxin hormone. Auxin is a Greek word that means to grow. It is also called growth hormone due to its role in plant growth. Auxin is present in the tips of the parts of plants. Auxin present in the tip of a plant moves towards the dark region of the plant in the presence of sunlight and accumulates in the dark region of the plant and stimulates the elongation of cells in the dark which results in bending or growth of plants towards the sunlight.
Hence option D is correct.
Auxin stimulating on the shaded side, stimulating greater cell elongation in the shaded region results in bending towards the source of light as it grows.
Additional Information: Function of Auxin: When the level of auxin hormone reduces then auxin inhibits the abscission. Abscission means the shedding and falling of leaves, fruits, and flowers. It helps in growth towards sunlight. Auxin also promotes the flowering process in the plants.

Note: Auxin was the first hormone plant hormone that was discovered by Charles Darwin and his son Francis Darwin observed the phototropism in the tip of canary grass. Auxin was first isolated from human urine samples.