NEET Biology Plant Growth and Development MCQs Set 14

Answer: (b) The production of hydrolysing enzymes

Explanation:
1. GA induces alpha-amylase, lipases and proteases in seeds.
2. These enzymes digest stored food and feed the embryo.

Teacher's Note:
1. GA is made by the embryo and acts on the aleurone layer.
2. ABA does the opposite.

Answer: (d) Cytokinin

Explanation:
1. Coconut milk contains the natural cytokinin zeatin.
2. It promotes cell division in tissue culture.

Teacher's Note:
1. Zeatin was found first in immature corn kernels.
2. Coconut milk is used in culture media.

Answer: (c) Delay of senescence

Explanation:
1. Cytokinins slow the ageing of leaves by keeping them supplied with nutrients and chlorophyll.
2. This is the Richmond-Lang effect.

Teacher's Note:
1. Cytokinins also delay yellowing of leafy vegetables.
2. They need auxin for morphogenesis.

Answer: (c) Ethylene

Explanation:
1. Ethylene (C2H4) is a gas.
2. The others are solids made of larger molecules.

Teacher's Note:
1. It is made from methionine.
2. Ethephon releases it slowly.

Answer: (c) Cytokinin

Explanation:
1. Cytokinins promote growth of lateral buds even when the apical bud is present.
2. This removes the effect of auxin.

Teacher's Note:
1. Decapitation also overcomes dominance.
2. Auxin maintains it.

Answer: (a) Exponential phase

Explanation:
1. In the sigmoid curve the lag phase is slow, the exponential (log) phase is fastest and the stationary phase levels off.
2. The maximum rate is in the exponential phase.

Teacher's Note:
1. Geometric growth is exponential.
2. Cells divide fastest in this phase.

Answer: (c) Low auxin to high cytokinin ratio

Explanation:
1. A high cytokinin to auxin ratio gives shoots.
2. A high auxin to cytokinin ratio gives roots.

Teacher's Note:
1. Skoog and Miller discovered this.
2. An equal ratio gives callus.

Answer: (b) Ethylene

Explanation:
1. Ethylene (as ethephon) and auxins like NAA induce and synchronise flowering in pineapple.
2. Zeatin does not do this.

Teacher's Note:
1. Ethylene also induces flowering in mango.
2. Synchronised fruiting makes harvesting easier.

Answer: (d) Leaf fall and dormancy

Explanation:
1. ABA promotes abscission of leaves and fruits and induces bud and seed dormancy.
2. It does not promote elongation or division.

Teacher's Note:
1. It is called the stress hormone.
2. ABA acts against gibberellins.

Answer: (a) Formation of the abscission layer at the base

Explanation:
1. The abscission layer forms at the base of the petiole and cuts the leaf off.
2. It is promoted by ABA and ethylene as auxin falls.

Teacher's Note:
1. Cells of the layer are weakened by cellulase and pectinase.
2. Chlorophyll loss is only a sign.

Answer: (c) Stomatal closure

Explanation:
1. Under water stress ABA makes guard cells lose turgor and the stomata close.
2. It therefore acts as an anti-transpirant.

Teacher's Note:
1. It is made in wilting leaves.
2. ABA does not promote elongation.

Answer: (c) Both coconut milk and immature maize seeds

Explanation:
1. Both coconut milk and immature maize grains have the natural cytokinin zeatin.
2. So both of the first two options are correct.

Teacher's Note:
1. Zeatin was isolated from maize by Letham.
2. Kinetin is synthetic.

Answer: (b) Abscisic acid

Explanation:
1. ABA inhibits germination and maintains seed dormancy.
2. The other options do not impose dormancy.

Teacher's Note:
1. Gibberellins break it.
2. Hard seed coats and immature embryos also cause dormancy.

Answer: (a) ABA

Explanation:
1. ABA promotes senescence and abscission of leaves and fruits.
2. Cytokinins, auxin and gibberellins delay senescence.

Teacher's Note:
1. ABA raises cellulase and pectinase activity.
2. Ethylene also promotes senescence.

Answer: (b) A light period longer than the critical day length

Explanation:
1. A long day plant needs light longer than its own critical day length.
2. The critical value differs from plant to plant, so 12 hours is not general.

Teacher's Note:
1. The light period is critical in LDP.
2. A brief light flash in the night helps LDP.

Answer: (d) Florigen

Explanation:
1. Florigen is a proposed flowering hormone that has not been isolated.
2. Gibberellin, auxin and cytokinin are all known chemicals.

Teacher's Note:
1. Vernalin is also hypothetical.
2. Photoperiod is detected in leaves.

Answer: (d) LDP

Explanation:
1. Both flower when the photoperiod exceeds the critical day length.
2. They are long day plants.

Teacher's Note:
1. LNP means long night plant, which is the same as SDP.
2. Maize and cotton are day neutral.

Answer: (c) Photoperiod shorter than the critical value and an uninterrupted long night

Explanation:
1. SDP need a day shorter than their critical length, and the dark period must be continuous.
2. The 12-hour figure in option b is not a general rule.

Teacher's Note:
1. A flash of light in the night prevents flowering in SDP.
2. They are long-night plants.

Answer: (b) Phytochrome

Explanation:
1. Phytochrome converts between Pr (absorbs red, 660 nm) and Pfr (absorbs far-red, 730 nm).
2. Chlorophyll absorbs mainly red and blue, but it does not switch with far-red.

Teacher's Note:
1. Pfr is the active form.
2. It controls flowering and seed germination.

Answer: (d) Gibberellins

Explanation:
1. Gibberellins promote internodal elongation in green plants.
2. Auxin elongates cells in coleoptiles and stems, but internode lengthening is the gibberellin effect.

Teacher's Note:
1. Bolting is an example.
2. GA also makes dwarfs tall.