Define critical day-length photoperiodism.

Flowering can be inhibited when the plants exposed to light above the critical photoperiod is

Nicotiana tabacum, a Short-Day Plant, when exposed to more than a critical period of light fails to flower. Explain.

On the basis of photoperiodism, which plant is represented by the given diagram?

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$