Human Sperm
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: February 23, 2015
CONTRIBUTORS
Doris Kraus, Ph.D.
Niamh Gray-Wilson
Jean Brainard, Ph.D.
Sarah Johnson
Jane Willan
Corliss Karasov
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C HAPTER
Chapter 1. Human Sperm
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Human Sperm
• Define sperm.
• Describe the three main parts of a sperm cell.
• Summarize the steps of sperm production.
How many sperm does it take to fertilize an egg?
It might only take one sperm to fertilize an egg, but that sperm is not alone. Hundreds of millions of sperm can be
released during sexual intercourse.
Sperm and Sperm Production
Sperm ( Figure 1.1), the male reproductive cells, are tiny. In fact, they are the smallest cells in the human body.
What do you think a sperm cell looks like? Some people think that it looks like a tadpole. Do you agree?
Sperm
A sperm has three main parts:
1. The head of the sperm contains the nucleus. The nucleus holds the DNA of the cell. The head also contains
enzymes that help the sperm break through the cell membrane of an egg.
2. The midpiece of the sperm is packed with mitochondria. Mitochondria are organelles in cells that produce
energy. Sperm use the energy in the midpiece to move.
3. The tail of the sperm moves like a propeller, around and around. This tail is a long flagella that pushes the
sperm forward. A sperm can travel about 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.
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FIGURE 1.1
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 swim?
Sperm Production
To make sperm, cells start in the testes and end in the epididymis. It takes up to two months to make sperm. The
steps are explained below:
1. Special cells in the testes go through mitosis (cell division) to make identical copies of themselves.
2. The copies of the original cells divide by meiosis, producing cells called spermatids. The spermatids have
half the number of chromosomes as the original cell. The spermatids are immature and cannot move on their
own.
3. The spermatids are transported from the testes to the epididymis. Involuntary muscular contraction moves the
spermatids along.
4. In the epididymis, spermatids slowly grow older and mature. They grow a tail. They also lose some of the
cytoplasm from the head.
5. When sperm are mature, they can “swim.” The mature sperm are stored in the epididymis until it is time for
them to leave the body.
Sperm leave the epididymis through the vas deferens. As they travel through the vas deferens, they pass by the
prostate and other glands. The sperm mix with liquids from these glands, forming semen. The semen travels
through the urethra and leaves the body through the penis. A teaspoon of semen may contain as many as 500 million
sperm!
Summary
• Sperm are male gametes that form in the testes and mature in the epididymis.
• The head of the sperm contains the nucleus, the midpiece is packed with mitochondria, and the tail moves like
a propeller.
Explore More
Use the resource below to answer the questions that follow.
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Chapter 1. Human Sperm
• Spermatogenesis at http://www.youtube.com/watch?v=POpbN6RHOO0 (0:45)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57560
1.
2.
3.
4.
What produces primary spermatocytes? How many chromosomes do primary spermatocytes have?
What produces secondary spermatocytes? How many chromosomes do secondary spermatocytes have?
What makes spermatids? How many chromosomes do spermatids have?
What happens to the spermatids?
Review
1.
2.
3.
4.
5.
How many cells make up a sperm?
List the three main parts of a sperm.
What mostly make up the midpiece of a sperm? Why is this section important?
What is the function of the tail of a sperm?
Explain why sperm production is not completed when spermatids have been produced.
References
1. Image copyright Mmaxer, 2013. This illustration shows the main parts of a sperm . Used under license from
Shutterstock.com
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