Question

what are granules in a cell

Answer 1

Since the cells are leukocytes, the granules most likely comprise of held defensins, and molecules that are lethal to the pathogen the leukocyte is trying to kill. Such molecules include enzymes such as lysozymes, or even nitrogen and oxygen compounds which oxidize various chemicals in the plasma membranes of bacteria and/or fungi/protists

Answer 2

Granules are present only in plant cells.
A group of leukocytes called granulocytes contain granules and play an important role in the immune system. The granules of certain cells, such as natural killer cells, contain components which can lead to the lysis of neighboring cells.
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