Question 1

The hormone that causes "bolting" (rapid internode/stem elongation before flowering) in rosette plants is:

Accepted Answer

Gibberellin. Gibberellins (e.g. GA₃) cause bolting — internode elongation in rosette plants like cabbage.

Question 2

Cytokinins are hormones that mainly promote:

Accepted Answer

Cell division (cytokinesis). Cytokinins promote cytokinesis (cell division) and were first identified as kinetin from herring sperm DNA.

Question 3

Gibberellins can be used commercially to increase the length and yield of ______ and to delay senescence:

Accepted Answer

Sugarcane stems (and fruit size in grapes). GA increases sugarcane yield (longer internodes), grape stalk length and delays senescence/ripening.

Question 4

Cytokinins help overcome apical dominance and promote:

Accepted Answer

Growth of lateral buds and nutrient mobilisation (delaying leaf senescence). Cytokinins counter apical dominance, promote lateral bud growth, and delay senescence (Richmond–Lang effect).

Question 5

In the brewing/malting industry, gibberellins are used to speed up:

Accepted Answer

The malting process (hydrolysis of starch via α-amylase in barley). GA induces α-amylase synthesis in germinating barley, speeding malting for the brewing industry.

Question 6

The natural cytokinin found in plants, synthesised in regions of rapid division such as root apices and developing seeds, is:

Accepted Answer

Zeatin. Zeatin (from maize kernels) is a natural cytokinin; kinetin is a synthetic/degradation product, not naturally in plants.

Question 7

The most extensively studied and commercially important gibberellin, widely referred to in agriculture, is:

Accepted Answer

GA3 (gibberellic acid). Of the many gibberellins, GA3 (gibberellic acid) is the most intensively investigated and commonly used form.

Question 8

Spraying sugarcane with gibberellin increases yield because gibberellin:

Accepted Answer

Elongates the stem, so more sugar-storing internode tissue is produced. Sugar is stored in the stem; GA-induced stem elongation gives longer canes and thus a substantial increase in sugar yield.

Question 9

Which pair of effects is correctly attributed to CYTOKININS?

Accepted Answer

Promotion of cell division (cytokinesis) and delay of leaf senescence. Cytokinins were discovered for their cytokinesis-promoting activity and are also well known for delaying leaf senescence (Richmond–Lang effect).

Question 10

The natural cytokinin isolated from maize (corn) kernels and synthesised in root apices and developing seeds is:

Accepted Answer

Zeatin. Zeatin is a natural cytokinin first isolated from maize kernels; kinetin is a synthetic cytokinin obtained from degraded herring sperm DNA.

Question 11

A dwarf pea variety and a genetically tall pea variety are both sprayed with gibberellin. Typically:

Accepted Answer

The dwarf plant grows as tall as the tall variety, while the tall plant shows little further increase. Genetic dwarfs are often deficient in gibberellin, so applied GA restores tall growth; already-tall genotypes have sufficient GA and respond little.

Question 12

A detached leaf yellows quickly, but if its petiole is supplied with cytokinin the treated leaf stays green far longer and even draws nutrients towards itself. This demonstrates that cytokinin:

Accepted Answer

Delays senescence and directs nutrient mobilisation towards the treated area. This is the Richmond–Lang effect: cytokinin delays senescence and mobilises nutrients toward the cytokinin-rich region, keeping the leaf green.

Question 13

Rosette plants such as cabbage suddenly elongate their internodes just before flowering. This "bolting" can be induced early by applying gibberellin, whereas the same plants normally bolt in response to:

Accepted Answer

A cold treatment or long days, which raises internal gibberellin activity. Bolting (rapid internode elongation before flowering) is a GA-mediated response; it can be triggered by GA application or naturally by cold/long-day conditions.

Question 14

In tissue culture, the ratio of auxin to cytokinin in the medium determines organ formation from a callus. A HIGH cytokinin-to-auxin ratio generally favours:

Accepted Answer

Shoot bud initiation. A high cytokinin:auxin ratio promotes shoot formation, whereas a high auxin:cytokinin ratio promotes root formation — a key principle of micropropagation.

Question 15

In the brewing industry gibberellin speeds the malting of barley. It does so by:

Accepted Answer

Promoting synthesis of hydrolytic enzymes such as α-amylase that mobilise starch. GA induces α-amylase and other hydrolases in germinating barley, breaking down endosperm starch to sugars — the basis of accelerated malting.

Question 16

Cytokinins counter apical dominance. Applying cytokinin to a dormant axillary bud of a plant with a strong shoot apex will typically:

Accepted Answer

Release that bud and promote its outgrowth into a lateral branch. Cytokinins overcome the auxin-imposed apical dominance, so treating an axillary bud with cytokinin frees it to grow into a lateral shoot.

Question 17

An enzyme that can stimulate germination of barley seeds is

Accepted Answer

α amylase. Gibberellins induce the synthesis of α-amylase in barley aleurone layers, which mobilises stored starch to stimulate germination.

Question 18

Which one of the following pairs is not correctly matched?

Accepted Answer

Gibberellic acid – Leaf fall. Gibberellic acid does not cause leaf fall; leaf fall (abscission) is promoted by abscisic acid and ethylene, so this pair is incorrectly matched.

Question 19

"Foolish seedling" disease of rice led to the discovery of:-

Accepted Answer

GA. The bakanae or foolish seedling disease of rice, caused by Gibberella fujikuroi, led to the discovery of gibberellins (GA).

Question 20

You are given a tissue with its potential for differentiation in an artificial culture. Which of the following pairs of hormones would you add to the medium to secure shoots as well as roots?

Accepted Answer

Auxin and cytokinin. In tissue culture, a balanced combination of auxin and cytokinin induces differentiation of both shoots and roots.

Gibberellins & Cytokinins — NEET Biology MCQs with Solutions

Questions with solutions