Question

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

(A) 16 hours light/8 hours dark

(B) 14 hours light/10 hours dark

(C) 4 hours light/8 hours dark/4 hours light/8 hours dark

(D) 8 hours light/8 hours dark/light flash/8 hours dark

Short answer

1. The statement “16 hours light/8 hours dark” isfalse.

2. The statement “14 hours light/10 hours dark” istrue.

3. The statement “4 hours light/8 hours dark/4 hours light/8 hours dark” is false.

4. The statement “8 hours light/8 hours dark/light flash/8 hours dark” is false.

Step-by-step solution

Plant

The plants are photosynthetic life forms that are rooted in one place. The different features of plants are autotrophs, release oxygen, epiphytes, seed dispersal, and pollination.

Explanation of option ‘(A)’

When flowering in long-day plants is prevented due to dark period length, it is called critical night length.

Thus, plants with a dark phase below 9 hours would flower first.

Therefore, the given statement is false.

Explanation of option ‘(B)’

The plant that blooms on the longest day, like early summer or spring with a shorter night period, is called a long-day plant.

Thus, the light phase should be smaller, like 14 hours light and dark phase must exceed the critical 9 hours of night length of the long-day plant to prevent flowering.

Therefore, the given statement is true.

Explanation of option ‘(C)’

The different features associated with long-day plants are the need for less darkness, flowering in spring, and the requirement of a short night.

Thus, 8 hours of dark period is not exceeding the critical night to prevent flowering.

Therefore, the given statement is false.

Explanation of option ‘(D)’

The phenomenon in which an organism requires a given number of hours for light exposure to induce its growth is called photoperiodism.

Thus, flowering is prevented when the dark phase exceeds the critical night phase.

Therefore, the given statement is false.