The site of perception of light in plants for flowering is

Which of the following is a long-day plant?

If a plant needs $10$ hours of darkness to flower,identify the condition under which it will flower:
$I.$ $14$ hours day period
$II.$ $10$ hours dark period
$III.$ $9 \frac{1}{2}$ hours dark period
$IV.$ $9$ hours dark period
Choose the correct option:

Which of the following exerts a profound effect on the reproductive growth of a flowering plant?

Nicotiana tabacum,a short-day plant,when exposed to more than the critical period of light,fails to flower. Explain.

Which of the following factors of light affects plant growth to a great extent?