Plant Hormones — Set 3

Correct Answer: C. Ethylene

Ethylene is the only major plant hormone that exists in a gaseous state. This allows it to diffuse through the air and affect neighboring fruits or plants. Its chemical formula is $C_2H_4$.

Correct Answer: C. Gibberellin

Gibberellins promote cell expansion in the fruit, leading to larger and more spaced-out grapes. Commercial grape growers use this hormone to improve fruit quality and yield. It also helps the clusters become less prone to fungal rot.

Correct Answer: C. Abscisic Acid

Abscisic Acid triggers the efflux of potassium ions from guard cells. This loss of solute causes water to leave the cells, making them flaccid and closing the pore. This is a critical mechanism for plant survival during water stress.

Correct Answer: D. Ethylene

Ethylene application can shift the sex expression of some plants toward femaleness. In contrast, gibberellins often promote the formation of male flowers. This hormonal balance is crucial for effective pollination and fruit set.

Correct Answer: C. Abscisic Acid

Abscisic Acid often acts in direct opposition to the growth-promoting effects of gibberellins. While gibberellins promote germination and growth, ABA promotes dormancy and stasis. The ratio between these two hormones determines the physiological state of the plant.

Correct Answer: D. Cytokinins

Zeatin was the first natural cytokinin to be isolated from maize (corn) kernels. It proved that cytokinins were not just synthetic laboratory chemicals. It is a highly potent stimulator of plant cell division.

Correct Answer: D. Auxin

High levels of auxin prevent the formation of the abscission layer at the fruit stalk. Once the seed matures, auxin levels drop, and other hormones take over to cause the fruit to fall. This timing is essential for the natural dispersal of seeds.

Correct Answer: D. Gibberellin

Gibberellins can substitute for the requirement of cold treatment or specific day lengths for flowering. This allows for the manipulation of blooming periods in commercial flower production. It bypasses the plant's natural photoperiodic clock.

Correct Answer: A. Auxin

Indole-3-acetic acid (IAA), the most common natural auxin, is chemically derived from tryptophan. This synthesis primarily occurs in the actively growing regions like the shoot apex. Understanding this pathway helps in creating synthetic analogs.

Correct Answer: A. Plant growth regulators

Phytohormones are organic substances produced naturally in plants that control physiological processes. They are active at very low concentrations and can be transported to different parts. They include growth promoters like auxins and inhibitors like ABA.