Question

what is the function of a leaf apex?

Answer 1

specifically it is the outer end of a leaf and that is opposite to the petihol

Answer 2

Heya friend!!
Rajdeep here...

According to my knowledge, there are small pores called Hydathodes at the tip of the veins (leaf apex) and present at the margins of leaves.

On humid nights, when the plant is fully turgid as it is continuously absorbing water, without transpiring (as humidity decreases the rate of transpiration), Guttation takes place through the hydathodes at the apex of the leaves.
Guttation is the exudation of water and other minerals in form of liquid. Thus, it helps the plants to lose water.

Hope my answer is satisfactory!
Thanks....