Pollen Grain:
A pollen grain is surrounded by a callose wall. Callose is a type of polysaccharide that is deposited on the surface of the pollen grain during its development. This callose wall serves several important functions in the life cycle of a plant.

Microspore Mother Cell:
The microspore mother cell, also known as the pollen mother cell, is the cell that undergoes meiosis to produce microspores. The microspore mother cell is surrounded by a callose wall, which helps protect the developing microspores during their formation. The callose wall also plays a role in cell signaling and communication between the microspore mother cell and surrounding tissues.

Male Gamete:
The male gamete, also known as the sperm cell, is not surrounded by a callose wall. Once the microspores are released from the callose wall, they undergo further development and differentiation to form the male gametes. These male gametes are then released from the pollen grain during pollination.

Egg:
The egg, also known as the female gamete or ovum, is not surrounded by a callose wall. Instead, the egg is surrounded by several layers of cells that make up the embryo sac. These layers of cells provide protection and nourishment to the developing egg.

Summary:
In summary, the pollen grain and microspore mother cell are surrounded by a callose wall, while the male gamete (sperm cell) and egg (ovum) are not. The callose wall plays important roles in protecting and supporting the development of the pollen grain and microspores.