31 Years NEET Previous Year Questions: Plant Growth & Development - 2 - NEET MCQ

Ethylene breaks dormancy of different plants. Abscisic acid induces dormancy in seeds, buds and underground storage organs

The correct answer is A: phytochrome.

- Phytochrome is a proteinaceous pigment.
- It plays a crucial role in controlling activities related to light in plants.
- Phytochrome is involved in processes like seed germination, flowering, and more.
- This pigment helps plants sense light quality, quantity, and duration.
- Through phytochrome, plants can regulate their growth and development in response to light signals.

During day time, due to photosynthesis CO₂ concentration is low.

 Long day plants undergo flowering after receiving light above a critical day length. e.g. Spinach, sugarbeet.  Short day plants flower only when they receive light below  a critical  day length. e.g. Glycine max, Tobacco.

NAA or Naphthalene Acetic Acid is synthetic auxin. It is used to check fruit fall specially in tomato.

ABA or Abscisic acid is responsible for leaf fall or senescence.

Ethylene breaks seed and bud dormancy, initiates germination in peanut seeds, sprouting of potato tubers.

 Geocarpic fruits are those which develop underground. Groundnut is the fruit which develops underground, onion and carrot also occur within the soil but onion is modified stem while carrot is modified root.

The medium in tissue culture provides all the essential nutrients required for growth and division of callus. Coconut milk contains cytokinins which is useful in tissue culture.

Scarification is the breaking of the seed coat  barriers which can be done by mechanical or chemical methods. 

Gibberellins are involved in shoot elongation. Auxins are important in root elongation and cell division

Photoperiodism is the effect of duration of light and darkness on the growth, development and behaviour of an organism.

 Cytokinins are used in tissue culture to induce shooting of the cultural callus.

Ethylene acts physiologically as a hormone in plants. It stimulates the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves. Its biosynthesis starts from methionine with 1-aminocyclopropane-1-carboxylic acid (ACC) as a key intermediate.

In northern India, during these  months there is observed maximum variation in light intensity and duration and temperature. Hence only plants that are photo-and thermoinsensitive can flower during these months.

Continuous exposure to red light causes

• Conversion of Pr to Pf which is rapidly destroyed.
• Inhibition of synthesis of Pr.
• Total amount of phytochrome decreases.

The phenomenon of thigmotropism is a response to contact with a solid object. It is exhibited by tendrils of climbing plants that grow around a pole or the stem of another plant.

Ethylene is a gaseous plant hormone which plays an important role in fruit ripening. In the presence of ethylene there is an increase in the rate of respiration.

The pigment phytochrome is involved in flowering and many other light-mediated processes. It absorbs red and far red light in plants for photosynthesis.

Auxin is a plant hormone which is involved in various physiological processes of plant. It is synthesized in meristematic tissue like tip of root and stem. In stems, movement of auxin is basipetal. It moves from apex to the base. However, in roots, movement of auxin is acropetal. It moves from the root to the shoot apex.

Thus, the correct answer is option D.

 Apical buds inhibit lateral branching due to apical dominance. Removal of apical bud promotes lateral branching.

Cytokinin help in retaining chlorophyll, hence delay senescense.

Abscisic Acid (ABA) is called stress hormone which works in adverse environmental condition when there is low water content in atmosphere or in drought conditions. ABA causes the stomatal closure of leaves due to which the water loss by the plant is minimized.

Klinostat = Clinostat is an apparatus used to nullify the effect of geotropism. It has a clock to the main axis of which is attached to a rod. Top of the rod is attached to a flower pot. The klinostat is kept in horizontal position and allowed to rotate (to nullify the geotropism) and plant growth is observed

One of the most important effects of gibberellins is the reversal of dwarfism (even in genetically dwarf plants). Dwarf pea & dwarf corn attain almost normal size when treated with gibberellins. It has been proved that dwarf plants have lower level of GA which causes the dwarfism. Thus the external supply causes rapid elongation of internodes. GA does not have any effect of elongation on normal (non dwarf or tall) plant.