Asperm cell's acrosome

a) contains the sperm's mitochondria
b) fuses with the plasma membrane of the egg cell
c) contains enzymes that are released when the sperm encounters an egg and dissolves a hole in the jellylike matrix that surrounds the egg
d) contains the sperm's nucleus and is the part of the sperm that enters the egg during fertilization

C

Explanation:

Sperm cells do a great and tasking job in their quest for egg fertilization. First, they have to find an egg to fertilize by swimming a long distance, as not all released sperm finds an egg. The few that finds an egg still have to cross the egg's protective coat and fuse their own membrane with the plasma membrane of the the egg. This process of crossing the egg's barrier is referred to as ACROSOME reaction.

The acrosome is a lysosome-like vesicle located in between the sperm's plasma membrane and nuclear membrane (nucleus) derived from the golgi complex of the spermatid. It is closer to the plasma membrane at the tip of the sperm's head. The vesicle contains soluble proteolytic enzymes such as acrosin and inner membrane proteins such as bindin.

The acrosome reaction is the exocytosis of the acrosome, or the fusion of the acrosomal membrane with the sperm's plasma membrane. The process releases the acrosomal contents (lytic enzymes) to the outside of the sperm.

When the acrosome's proteolytic enzymes are released, they begin to degrade the egg's protein-rich protective coat. The egg's plasma membrane is surrounded by a thick ZONA PELLUCIDA layer made of extracellular matrix and a jelly-like cumulus layer surrounding it. This degradation creates a path for the sperm to swim through on its way to the egg's plasma membrane. This enables the plasma membranes of the egg and sperm to fuse placing both haploid nuclei (one from the sperm, the other from the egg) into the same cell, where they form the diploid genome of the new organism.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom