Plant Hormones — Set 2
Biology · पादप हार्मोन · Questions 11–20 of 50
The 'Bakanae' or 'foolish seedling' disease in rice led to the discovery of?
Correct Answer: D. Gibberellins
The correct answer is 'Gibberellins'. The disease was caused by a fungus that produced excess growth-stimulating chemicals. Japanese scientists isolated gibberellic acid from this fungus in the early 20th century. These seedlings grew abnormally tall and thin, eventually collapsing.
Which plant hormone promotes the formation of adventitious roots in stem cuttings?
Correct Answer: C. Auxin
Auxins are frequently used in plant nurseries as rooting powders for vegetative propagation. They stimulate the undifferentiated cells at the cut end to develop into roots. Indole-3-butyric acid is a common synthetic auxin used for this purpose.
The fall of leaves, fruits, and flowers from a plant is regulated by which hormone?
Correct Answer: D. Abscisic Acid
Abscisic Acid promotes the formation of an abscission layer at the base of the petiole. This layer weakens the connection until the plant part naturally detaches. It is a necessary process for trees to shed leaves before winter.
Which hormone is involved in the 'triple response' of seedlings to mechanical stress?
Correct Answer: C. Ethylene
The triple response involves slowing of elongation, thickening of the stem, and horizontal growth. Ethylene triggers this behavior to help seedlings navigate around obstacles in the soil. It is a vital survival strategy for germinating seeds.
Which plant hormone is most likely to be high in a seed that is beginning to germinate?
Correct Answer: D. Gibberellin
Gibberellins stimulate the production of enzymes like alpha-amylase to break down stored starch. This provides the energy required for the embryo to grow and emerge. The level of abscisic acid typically drops during this stage.
Which hormone is primarily responsible for the expansion of leaf area in plants?
Correct Answer: A. Cytokinin
Cytokinins stimulate cell division in the leaf blade, resulting in larger leaves. They also promote the development of chloroplasts for better photosynthesis. Larger leaves allow the plant to capture more sunlight for energy.
Which plant hormone travels primarily through the phloem from the roots to the shoots?
Correct Answer: B. Cytokinin
Cytokinins are produced in the roots and move upward through the plant's vascular system. They ensure that the shoot receives signals about the nutrient status of the roots. This communication is essential for balanced plant growth.
Which hormone is responsible for 'Geotropism', the response of roots to gravity?
Correct Answer: A. Auxin
Auxin accumulates on the lower side of the root, where it inhibits growth instead of stimulating it. This causes the root to curve downward into the soil. It ensures that roots grow toward water and nutrients.
Which of the following is a synthetic auxin commonly used as a selective herbicide?
Correct Answer: C. 2,4-D
2,4-Dichlorophenoxyacetic acid is used to kill broad-leaved weeds without affecting cereal crops. It causes uncontrolled, rapid growth in weeds, leading to their death. It has been a standard tool in industrial agriculture for decades.
Which hormone inhibits the aging and falling of leaves by promoting nutrient mobilization?
Correct Answer: B. Cytokinin
Cytokinins prevent the breakdown of essential cellular components in aging leaves. They facilitate the movement of nutrients from older parts to developing regions. This keeps the plant productive for a longer duration.