Question 1

The response of plants to the relative lengths of day and night (which affects flowering) is called:

Accepted Answer

Photoperiodism. Photoperiodism is the dependence of flowering on the duration of light/dark periods.

Question 2

The promotion of flowering by a period of low temperature (cold treatment) is called:

Accepted Answer

Vernalisation. Vernalisation is the low-temperature requirement for flowering in some plants (e.g. winter wheat).

Question 3

Short-day plants flower when the ______ exceeds a critical length:

Accepted Answer

Continuous dark period (night). It is actually the uninterrupted dark period that matters — short-day plants need a long enough continuous night.

Question 4

The site of perception of the photoperiodic (light/dark) stimulus is the ______, though flowering occurs at the ______:

Accepted Answer

Leaves; shoot apex. Leaves perceive the photoperiod and produce a hormonal signal (florigen) that induces flowering at the shoot apex.

Question 5

Interrupting the long dark period of a short-day plant with a flash of light will:

Accepted Answer

Prevent flowering. A light break during the critical dark period stops flowering in short-day plants — confirming the dark period is decisive.

Question 6

Vernalisation prevents precocious flowering and allows plants like winter varieties of wheat to flower in ______ by ______:

Accepted Answer

Spring; exposing seedlings/seeds to a period of low temperature. Cold treatment of germinating seeds/seedlings (vernalisation) enables winter varieties to flower in the next spring/summer.

Question 7

A short-day plant flowers only when the uninterrupted dark period exceeds a certain length. This shows that the truly decisive factor in photoperiodic flowering is:

Accepted Answer

A critical continuous duration of darkness (night length). Photoperiodic flowering actually depends on a critical, uninterrupted dark period; interrupting the night blocks flowering in short-day plants.

Question 8

The organ that PERCEIVES the photoperiodic (light/dark) stimulus, even though flowers are produced at the shoot apex, is the:

Accepted Answer

Leaf. Leaves perceive the photoperiod and produce a floral stimulus (florigen) that moves to the shoot apex, where flowering is expressed.

Question 9

The low-temperature treatment that makes certain plants competent to flower, and which is especially important for biennials, is called:

Accepted Answer

Vernalisation. Vernalisation is the promotion of flowering by exposure to low temperature; it is essential in many biennials and winter varieties.

Question 10

Plants that flower irrespective of day length, requiring no specific photoperiod, are called:

Accepted Answer

Day-neutral plants. Day-neutral plants flower over a wide range of photoperiods and do not depend on a critical day/night length.

Question 11

A short-day plant that normally flowers is given a long night, but the night is interrupted by a brief flash of red light. The expected result is that the plant:

Accepted Answer

Fails to flower, because the dark period no longer exceeds the critical length. A red-light night break shortens the effective continuous dark period below the critical value, so the short-day plant does not flower.

Question 12

The pigment that perceives light/dark signals in photoperiodism, existing in interconvertible red- and far-red-absorbing forms, is:

Accepted Answer

Phytochrome. Phytochrome is the photoreceptor of photoperiodism; its Pr and Pfr forms interconvert on absorbing red and far-red light, signalling day length.

Question 13

A long-day plant with a critical photoperiod of 14 hours is grown under a 10-hour night that is interrupted by a red-light flash in the middle. Compared with a continuous 10-hour night, the interruption tends to:

Accepted Answer

Promote flowering, since a night break mimics the effect of a longer day. A night break makes the dark period effectively shorter, mimicking long-day conditions and thus promoting flowering in long-day plants (the opposite of its effect on short-day plants).

Question 14

Winter (biennial) varieties of wheat are sown in autumn, exposed to winter cold, and flower the next season. If sown in spring without cold treatment they remain vegetative. Vernalisation here ensures that the plant:

Accepted Answer

Does not flower prematurely and flowers only after experiencing low temperature. Vernalisation prevents precocious reproductive development and lets winter wheat flower only after a required period of low temperature, timing flowering to the favourable season.

Question 15

The hypothetical, leaf-produced, transmissible floral hormone that moves to the shoot apex to induce flowering is called:

Accepted Answer

Florigen. Florigen is the postulated flowering hormone made in leaves under inductive photoperiods that migrates to the apex to trigger flowering.

Question 16

A biennial such as sugar beet or a cabbage completes its life in two seasons: vegetative growth in the first and flowering in the second after winter. The requirement that couples flowering to the second year is best explained by:

Accepted Answer

A vernalisation requirement — a period of low temperature needed before flowering. Biennials store food in the first year and require exposure to winter cold (vernalisation) before they can flower in the second year.

Question 17

The site of perception of light/dark duration are the:-

Accepted Answer

mature leaves. In photoperiodism the light/dark duration is perceived by the mature leaves, which then produce a flowering hormone that migrates to the shoot apices.

Question 18

Importance of day length in flowering of plants was first shown in:-

Accepted Answer

Tobacco. Garner and Allard first demonstrated the importance of day length (photoperiodism) using the Maryland Mammoth variety of tobacco.

Question 19

Photoperiodism was first characterised in:

Accepted Answer

Tobacco. Photoperiodism was first characterised in tobacco (Maryland Mammoth variety) by Garner and Allard.

Question 20

Vernalisation stimulates flowering in:

Accepted Answer

Carrot. Vernalisation, a cold treatment, promotes flowering in biennials such as carrot.

Photoperiodism & Vernalisation — NEET Biology MCQs with Solutions

Questions with solutions