Q41. What term describes the growth of plant roots away from light?
a) Positive phototropism
b) Negative phototropism
c) Positive hydrotropism
d) Negative geotropism
Show Answer
Correct Answer: b) Negative phototropism
Explanation: Negative phototropism is the term that describes the growth of plant roots away from light. While stems typically grow towards light (positive phototropism), roots usually grow in the opposite direction, exhibiting negative phototropism. This helps the roots to grow deeper into the soil where they can access water and nutrients.
Q42. What role do auxins play in plant cell elongation?
a) They decrease cell wall rigidity.
b) They promote cell division.
c) They increase photosynthesis in the cell.
d) They stimulate chlorophyll production.
Show Answer
Correct Answer: a) They decrease cell wall rigidity.
Explanation: Auxins play a critical role in plant cell elongation by decreasing the rigidity of cell walls. They promote the elongation of cells within the growing tips of plants by loosening the cell walls, allowing the cells to take up more water and expand. This hormone-driven mechanism is key to plant growth.
Q43. Which hormone in plants stimulates stem elongation, germination, and flowering?
a) Ethylene
b) Cytokinin
c) Gibberellin
d) Abscisic acid
Show Answer
Correct Answer: c) Gibberellin
Explanation: Gibberellin is a plant hormone that stimulates various aspects of growth and development, such as stem elongation, seed germination, and flowering. Gibberellins play a key role in overcoming seed dormancy, stimulating the growth of young seedlings, and are involved in the flowering process and fruit development.
Q44. How do plant tendrils find support to cling to?
a) They grow towards light.
b) They respond to gravitational pull.
c) They detect chemicals in the air.
d) They grow in response to touch.
Show Answer
Correct Answer: d) They grow in response to touch.
Explanation: Plant tendrils find support to cling to by growing in response to touch, a phenomenon known as thigmotropism. When tendrils come into contact with an object, they wrap around it for support, allowing the plant to climb. This response increases the plant’s ability to access light and can help it compete more effectively for space.
Q45. What is the process of plant roots growing towards nutrients called?
a) Phototropism
b) Chemotropism
c) Hydrotropism
d) Geotropism
Show Answer
Correct Answer: b) Chemotropism
Explanation: Chemotropism is the process of plant roots growing towards nutrients. It is a directional growth response where plants grow towards or away from chemical stimuli. In the case of roots, they often exhibit positive chemotropism, growing towards essential nutrients in the soil that are crucial for their development and survival.
Q46. What is the primary function of root cap cells in plants?
a) Absorbing nutrients
b) Protecting root tip
c) Conducting water
d) Storing food
Show Answer
Correct Answer: b) Protecting root tip
Explanation: The primary function of the root cap is to protect the tip of the growing root in plants. It covers the delicate apical meristem (growth tissue) at the root tip and acts as a buffer against the mechanical stress as the root pushes through soil. The root cap also plays a role in sensing gravity, aiding in directing root growth.
Q47. Which of the following is a function of the plant hormone cytokinin?
a) Promoting fruit ripening
b) Stimulating leaf senescence
c) Delaying leaf aging
d) Enhancing root elongation
Show Answer
Correct Answer: c) Delaying leaf aging
Explanation: Cytokinins are a class of plant hormones that have several functions, including delaying leaf aging or senescence. They promote cell division and growth, and their presence can extend the lifespan of leaves by inhibiting the processes associated with aging. Cytokinins also work in concert with auxins to regulate growth and development.
Q48. In plants, what is the growth movement in response to water called?
a) Phototropism
b) Geotropism
c) Hydrotropism
d) Thigmotropism
Show Answer
Correct Answer: c) Hydrotropism
Explanation: Hydrotropism is the growth movement of plants in response to moisture. It is particularly noticeable in plant roots, which grow towards higher moisture concentrations in the soil. This response enables plants to find water more effectively and is crucial for their survival, especially in environments where water distribution is uneven.
Q49. What is the process of losing water vapor through leaves in plants known as?
a) Condensation
b) Transpiration
c) Evaporation
d) Perspiration
Show Answer
Correct Answer: b) Transpiration
Explanation: Transpiration is the process by which plants lose water vapor through their leaves. It occurs primarily through the stomata, small openings on the leaf surface that facilitate gas exchange. Transpiration helps in cooling the plant and creates a pull that draws water and nutrients from the roots to the leaves.
Q50. Which plant hormone plays a crucial role in the response to stress and injury?
a) Ethylene
b) Auxin
c) Abscisic acid
d) Gibberellin
Show Answer
Correct Answer: c) Abscisic acid
Explanation: Abscisic acid (ABA) is a major phytohormone regulating stress responses, and it interacts with the jasmonic acid (JA) and salicylic acid (SA) signaling pathways to channel resources into mitigating the effects of abiotic stresses versus defending against pathogens.