NEET Biology Plant Growth and Development MCQs Set 19

Answer: (c) Gibberellins

Explanation:
1. Gibberellins can replace the cold requirement of vernalisation in biennials such as cabbage.

Teacher's Note:
1. They cause bolting.
2. Other hormones cannot do it.

Answer: (d) removal of apical dominance and promotion of lateral meristem

Explanation:
1. Mowing a lawn removes the apical dominance and stimulates the intercalary meristem of grasses at the base, so the lawn grows thicker.

Teacher's Note:
1. Grass blades grow from the base.
2. Cutting the tip does not harm them.

Answer: (a) in growing tips

Explanation:
1. Auxin is most concentrated in the growing tips (shoot and root apices).

Teacher's Note:
1. It is made in the apical meristem.
2. It moves basipetally.

Answer: (d) regulators synthesized by plants and influencing physiological processes

Explanation:
1. Phytohormones are chemicals made by plants in small amounts that regulate physiological processes.

Teacher's Note:
1. They are not made in specific glands.
2. They act at a different site or the same.

Answer: (b) leaf fall and dormancy

Explanation:
1. Abscisic acid controls leaf fall (abscission) and seed and bud dormancy.

Teacher's Note:
1. It closes stomata in stress.
2. It is a growth inhibitor.

Answer: (c) cytokinin/zeatin

Explanation:
1. Cytokinins (zeatin) promote cell division.

Teacher's Note:
1. Auxins promote cell elongation.
2. They were discovered by Skoog and Miller (kinetin).

Answer: (a) stomatal closure

Explanation:
1. Abscisic acid causes stomatal closure in water stress.

Teacher's Note:
1. It is the stress hormone.
2. Gibberellins cause stem elongation.

Answer: (a) IAA

Explanation:
1. Auxin (IAA) produced at the apical bud suppresses the lateral buds and causes apical dominance.

Teacher's Note:
1. Cytokinin opposes it.
2. Removal of the tip stimulates branching.

Answer: (c) Ethylene

Explanation:
1. Ethylene is the hormone used for artificial ripening of banana and other fruits.

Teacher's Note:
1. It is a gas.
2. Ethephon releases it.

Answer: (c) help retain chlorophyll

Explanation:
1. Cytokinins delay senescence, so they help retain chlorophyll in leaves.

Teacher's Note:
1. Auxins and ethylene promote abscission.
2. They promote cell division.

Answer: (d) vernalization

Explanation:
1. Vernalisation is the promotion of flowering by exposing plants to a low temperature.

Teacher's Note:
1. It occurs in winter varieties of wheat.
2. Lysenko used the term.

Answer: (b) gibberellic acid

Explanation:
1. Gibberellic acid corrects genetic dwarfness by stimulating stem elongation.

Teacher's Note:
1. Dwarf pea plants grow tall with GA.
2. Antigibberellins cause dwarfing.

Answer: (d) abscisic acid

Explanation:
1. Abscisic acid is called the stress hormone as it is produced in adverse conditions such as drought.

Teacher's Note:
1. Ethylene is also produced in stress.
2. ABA closes stomata.

Answer: (d) formation of lateral branching

Explanation:
1. Removal of the apical bud (decapitation) removes apical dominance, and the lateral buds grow into branches.

Teacher's Note:
1. It is used for hedges.
2. Auxin is lost.

Answer: (c) ripening of fruits

Explanation:
1. Ethylene promotes ripening of fruits.

Teacher's Note:
1. It also causes senescence and abscission.
2. Auxin delays abscission.

Answer: (c) phytochrome

Explanation:
1. Phytochrome absorbs red (660 nm) and far-red (730 nm) light and controls photoperiodic responses.

Teacher's Note:
1. It is a chromoprotein.
2. Xanthophyll and carotene are accessory pigments.

Answer: (b) production of hydrolyzing enzymes in germinating seeds

Explanation:
1. Gibberellins induce the synthesis of hydrolysing enzymes such as alpha-amylase in germinating cereal seeds.

Teacher's Note:
1. The aleurone layer produces them.
2. The enzymes digest the endosperm.

Answer: (b) A weedicide containing dioxin

Explanation:
1. Agent Orange is a herbicide (a mix of 2,4-D and 2,4,5-T) contaminated with dioxin, used in the Vietnam war.

Teacher's Note:
1. Dioxin is a hazardous pollutant.
2. 2,4-D kills dicot weeds.

Answer: (d) 80% C2H4 and 20% CO2

Explanation:
1. Ethylene (C₂H₄) is the gas that promotes ripening. A mixture of 80% ethylene and 20% CO₂ is the suitable one.

Teacher's Note:
1. The gas is a plant hormone.
2. CO₂ delays ripening.

Answer: (b) cytokinins

Explanation:
1. Cytokinins induce morphogenesis (shoot formation) in plant tissue culture along with auxin in a suitable ratio.

Teacher's Note:
1. High cytokinin to auxin ratio forms shoots.
2. High auxin forms roots.

Answer: (d) scarification

Explanation:
1. Scarification (by scratching, acid or friction) makes the seed coat permeable to water so the embryo can swell.

Teacher's Note:
1. Stratification is chilling.
2. Vernalisation is for flowering.

Answer: (b) Cytokinins

Explanation:
1. Coconut milk contains cytokinins (and other growth factors), which promote cell division in tissue culture.

Teacher's Note:
1. It is a liquid endosperm.
2. It supports embryo growth.

Answer: (b) NAA

Explanation:
1. NAA (a synthetic auxin) prevents the fall of fruits.

Teacher's Note:
1. Ethylene promotes abscission.
2. Zeatin is a cytokinin.

Answer: (d) Spinach

Explanation:
1. Spinach is a long-day plant; it flowers when the light period is longer than the critical length.

Teacher's Note:
1. Tobacco (some varieties), soybean and Mirabilis are short-day or day-neutral.
2. Photoperiodism was found by Garner and Allard.