Sperm and Sperm Production
Sperm are tiny cells. In fact, they are the smallest cells in the human body. A sperm cell is
shown inFigure22.2. What do you think a sperm cell looks like? Some people think that
it looks like a tadpole. Do you agree?
Figure 22.2: This drawing of a sperm shows its main parts. What is the role of each part?
How do you think the shape of the sperm might help it to “swim”? ( 15 )
Sperm
A sperm has three main parts. They are the head, midpiece, and tail. Each part plays an
important role in reproduction.
- The head of the sperm contains the nucleus. Within the nucleus are the chromosomes.
Remember, in humans, the nucleus of the sperm cell contains 23 chromosomes. The
head also contains enzymes that help the sperm break through the cell membrane of
an egg. You will read more about this process in Lesson 3. - The midpiece of the sperm is packed with mitochondria. Mitochondria are structures
in cells that produce energy (discussed in the Cells and Their Structureschapter).
Sperm use the energy produced in the midpiece to move. - The tail of the sperm rotates like a propeller. This pushes the sperm forward. A sperm
can travel about 0.8 meters (30 inches) per hour. This may not sound very fast, but
don’t forget how small a sperm is. For its size, a sperm moves about as fast as you do
when you walk briskly. You can see how a sperm’s tail rotates to propel it forward by
watching the animation athttp://www.stanford.edu/group/Urchin/sperm-l.htm.
Sperm Production
The process of producing sperm starts in the testes and ends in the epididymis. The entire
process takes up to two months. It begins when special cells in the testes undergo mitosis.
The special cells make identical copies of themselves that continue to go through the process
of sperm formation, while the original cells remain to produce more sperm in the future.
The copies of the original cells divide by meiosis, producing cells called spermatids. The