Free Plant Growth Regulators MCQs with Answers

41. Vernalization is the conversion of:

• A. Spring variety to the winter variety
• B. Winter variety to the spring variety
• C. Winter variety to the summer variety
• D. Summer variety to the winter variety

Explanation: The term vernalization originated from the Latin word Vernalis, which means "of the spring". Vernalization is the artificial exposure of plants (or seeds) to low temperatures to stimulate flowering or enhance seed production. It is the conversion of the winter variety into the spring variety by low-temperature treatment. By satisfying the cold requirement of many temperate-zone plants, flowering can be induced to occur earlier than normal or in warm climates lacking the requisite seasonal chilling. Knowledge of this process has been used to eliminate the normal two-year growth cycle required of winter wheat. By partially germinating the seed and then chilling it to 0° C (32° F) until spring, it is possible to cause winter wheat to produce a crop in the same year.

42. Phytochrome―"Pr" absorbs red light of wavelength.

• A. 600 nm
• B. 660 nm
• C. 560nm
• D. 730 nm

Explanation: Phytochrome exists in two forms i.e. P 660 and P 730. P 660, a quiescent form, absorbs red light at a wavelength of 660 nm and is converted to active P 730, P 730 absorbs far-red light at 730 nm and is converted to P 660. In nature, the P 660 to P 730 conversion takes place in daylight and the P 730 to P 660 conversion occurs in the dark. Thus during the day, a plant has P 730 phytochromes while during the night it contains more phytochromes in the form of P 660. The presence of either form provides the plants with a means of detecting whether it is in a light or dark environment. The rate at which P 730 is converted to P 660 provides the plant with a "clock" for measuring the duration of darkness.

43. The critical day length of a short-day plant is:

• A. 11:00 hours
• B. 15:00 hours
• C. 11 ½ Hours
• D. 15 ½ hours

Explanation: Critical day length is the length of the light period in a 24-hour cycle required to inhibit the flowering of short-day plants. For short-day plants, this is 15 and a half hours (FACT). Short-day plants initiate flowering when the day length becomes shorter than a certain critical period.

44. A hormone that prevents senescence In leaves is:

• A. Abscisic acid
• B. Cytokinin
• C. Seisomonasty
• D. Demonasty

Explanation: Senescence is the aging of individual cells within an organism. The organism itself is still alive and metabolizing energy, but its cells no longer divide to create new cells, which is necessary for growth and repair. Hence, the individual cells remain alive but in a state of dormancy. Cytokinins are plant hormones that influence growth and the stimulation of cell division. Cytokinins also act in conjunction with auxin (another plant hormone) to retard senescence. During leaf senescence, cytokinins reduce sugar accumulation, increase chlorophyll synthesis, and prolong the leaf photosynthetic period.

45. Auxin travels by diffusion towards:

• A. Shoot
• B. Flowers
• C. Leaves
• D. Base of the plant

Explanation: Auxin is a plant hormone that is primarily produced in the shoot tips and young leaves. It travels downwards through the plant by the process of diffusion and active transport, primarily moving towards the base of the plant. This movement is crucial for processes such as cell elongation and root development. The other options are incorrect because auxin does not specifically travel towards the shoot, flowers, or leaves, but rather it moves downwards to the base for broader distribution and effect.

46. The locomotary movement of free swimming organisms or their organs in response to one sided illumination:

• A. Chlamydemonas
• B. Mimesa pudica
• C. Oxalis
• D. Crocus

Explanation: The locomotary movement of free swimming organisms or their organs in response to one-sided illumination is called phototaxis. Organisms like Chlamydomonas can exhibit positive or negative phototaxis, moving towards or away from the light source.

47. Which one of the following is a gaseous plant homone?

• A. Auxins
• B. Gibberellins
• C. Cytokinis
• D. Ethylene

Explanation: Ethylene is a gaseous plant hormone that helps regulate various processes in plants. It's involved in fruit ripening, leaf senescence, and even the response to stress. When plants produce ethylene, it can affect nearby plants, causing them to undergo similar changes. It's like a chemical signal that plants use to communicate with each other.