Question 1

The hormone known as the "stress hormone", which promotes stomatal closure during water stress, is:

Accepted Answer

Abscisic acid (ABA). ABA closes stomata under drought stress and is a general growth inhibitor.

Question 2

The gaseous plant hormone that promotes fruit ripening is:

Accepted Answer

Ethylene. Ethylene is the only gaseous hormone; it hastens ripening and senescence.

Question 3

Abscisic acid is antagonistic to gibberellins because ABA:

Accepted Answer

Induces and maintains seed dormancy (GA breaks it). ABA promotes dormancy and inhibits germination; gibberellin does the opposite — they are antagonists.

Question 4

Ethylene is used commercially to:

Accepted Answer

Hasten ripening of fruits and promote female flowers in cucumbers. Ethephon (releases ethylene) ripens fruits, promotes flowering in pineapple and female flowers in cucurbits.

Question 5

ABA is also called the ______ because it promotes abscission and the ______ (dormancy of buds/seeds before winter):

Accepted Answer

Dormin; dormancy. ABA was earlier called "dormin" for its role in inducing bud and seed dormancy and promoting abscission.

Question 6

Ethylene promotes rapid internode/petiole elongation in deep-water rice plants, allowing leaves to stay above water; this is because ethylene:

Accepted Answer

Enhances the elongation of submerged internodes. In deep-water rice, ethylene stimulates internode elongation so the plant grows out of rising water (an exception to its usual growth-inhibiting/thickening effect).

Question 7

Which plant hormone is a gas at physiological temperatures, making it unique among the major plant growth regulators?

Accepted Answer

Ethylene. Ethylene is a simple gaseous hormone; the others are non-volatile compounds transported in solution.

Question 8

Under drought, a plant closes its stomata to conserve water. The hormone directly responsible for this rapid stomatal closure is:

Accepted Answer

Abscisic acid. ABA accumulates under water stress and triggers efflux of solutes from guard cells, causing stomatal closure — hence its label as the "stress hormone".

Question 9

To ripen green tomatoes uniformly and rapidly in storage, growers commonly treat them with:

Accepted Answer

Ethylene (or the ethylene-releasing compound ethephon). Ethylene promotes fruit ripening; ethephon in solution releases ethylene and is widely used to ripen fruits like tomatoes and bananas.

Question 10

Regarding their roles in seed physiology, ABA and gibberellin act as antagonists because:

Accepted Answer

ABA promotes and maintains seed dormancy, while gibberellin promotes germination. ABA imposes and maintains seed/bud dormancy, whereas GA breaks dormancy and stimulates germination; hence they are mutually antagonistic.

Question 11

A pea seedling growing through compacted soil shows a "triple response": shortening and thickening of the stem plus horizontal growth. The hormone mediating this response is:

Accepted Answer

Ethylene. The classic triple response — inhibition of elongation, radial swelling, and horizontal (diageotropic) growth — is the hallmark seedling reaction to ethylene.

Question 12

Downward bending of leaves or leaf parts due to more rapid growth on the upper (adaxial) surface of the petiole, often triggered by ethylene, is called:

Accepted Answer

Epinasty. Epinasty is the downward curving of leaves caused by greater growth on the upper petiole surface, a response commonly induced by ethylene.

Question 13

One placed ripe apple can hasten the ripening of unripe fruits kept with it in a closed box. The best explanation is that:

Accepted Answer

The ripe apple releases ethylene gas that triggers ripening in the other fruits. Ripening fruit emits ethylene, and because ethylene is a diffusible gas it accelerates ripening of neighbouring fruits — the "one bad apple" effect.

Question 14

Which of the following effects is NOT typically attributed to ethylene?

Accepted Answer

Promotion of internode elongation and stem thickening independent of the triple response by inducing rapid vertical growth in most land plants. Ethylene generally inhibits (not promotes) elongation in most land plants; its recognised roles include senescence, abscission, dormancy breaking, and root-hair formation.

Question 15

In deep-water rice, rapid elongation of the internodes keeps the upper leaves above rising floodwater. Which combination of factors underlies this rapid elongation?

Accepted Answer

Ethylene accumulation under submergence enhancing gibberellin-promoted internode elongation. Submergence traps ethylene, which enhances GA responsiveness and reduces ABA, driving the rapid internode elongation that lets deep-water rice outgrow the flood.

Question 16

ABA is sometimes called the "dormin". Considering its overall physiology, ABA is best described as an inhibitor because it:

Accepted Answer

Inhibits plant metabolism and growth and promotes dormancy and abscission. ABA acts as a general growth inhibitor: it inhibits growth/metabolism and promotes dormancy, abscission and stress responses such as stomatal closure.

Question 17

Among the following which is not a function of ethylene?

Accepted Answer

Delay senescence. Ethylene promotes (does not delay) senescence and abscission, so 'delay senescence' is not its function.

Question 18

The gaseous plant growth regulator ethylene could fit in the group of :-

Accepted Answer

Both (1) and (2). Ethylene shows both promoting and inhibitory effects, so it could fit into either group of plant growth regulators.

Question 19

Which one of the following acids is a derivative of carotenoids?

Accepted Answer

Abscisic acid. Abscisic acid is synthesised from carotenoids, making it a carotenoid derivative.

Question 20

Which one of the following generally acts as an antagonist to gibberellins?

Accepted Answer

ABA. Abscisic acid (ABA) is a general growth inhibitor that acts antagonistically to gibberellins.

Abscisic Acid & Ethylene — NEET Biology MCQs with Solutions

Questions with solutions