TASK DEFINITION: You are given a sentence and your task is to generate another sentence that supports the given input.
PROBLEM: Features of pollen grains used in identification are size, shape, thickness of the exine (outer wall) and intine (inner wall) of the pollen grain.

SOLUTION: Each pollen grain has two coverings: the exine (thicker, outer layer) and the intine.

PROBLEM: An atom that gains electrons would be a negative ion.

SOLUTION: Atoms that have gained electrons and become negatively charged are called negative ions.

PROBLEM: Accordingly, an increase in pressure will cause an increase in density of the gas and a decrease in its volume .

SOLUTION:
If a gas in a closed area experiences increases in pressure and decreases in temperatures, the volume of the gas will be affected.