All organisms pass along their genetic material to their offspring in different ways—that process is called reproduction.
Humans, like other complex organisms, reproduce sexually. This means that half the offspring’s genetic material comes from its mother and the other half comes from its father. The father’s DNA is carried in specialized cells called sperm, small cells with long tails that help them swim. The mother’s DNA is carried in specialized cells called ova (singular ovum), or eggs.
As you can see in the illustration, egg cells are much larger than sperm cells. When a sperm burrows through the outer membrane of the egg, the DNA from both parents joins, and the egg is fertilized. A fertilized egg must be able to live for a few days without another source of fuel, so eggs contain lots of nutrients. That’s why they are so much larger than sperm.
Question?
How much of an offspring’s DNA comes from its mother?
To learn more about the male and female reproductive system, read through the information below and look carefully at the illustrations.
Male Reproductive System
Female Reproductive System
Testes
The two testes (singular testis), or testicles, hang outside the body in a sac called the scrotum. The testes produce sperm as well as the hormone testosterone. Testosterone promotes the development of male sex characteristics such as beard and body-hair growth and a deeper voice. An adult male produces hundreds of millions of sperm each day.
Question?
Do you know why the testes are located outside the body?
Penis
The penis contains the urethra, the tube through which both urine and sperm pass (but not at the same time).
In the United States and throughout the Middle East, circumcision is a common religious and cultural practice. Circumcision is the removal of the foreskin on a newborn’s penis. This practice is much less common in the rest of the world.
Like the male reproductive system, the basic purpose of the female reproductive system is to unite sperm and egg. But because women carry the developing embryo and fetus during pregnancy, achieving a fertilized egg is just the beginning. Learn more by reading the slides below.
OvariesThe ovaries contain, at birth, all the eggs a woman will ever have. These eggs stay dormant, or inactive, until puberty. The ovaries also produce the hormones estrogen and progesterone. These hormones control the development of secondary sex characteristics such as breasts and pubic hair, and they regulate the menstrual cycle and sustain a pregnancy. At puberty, hormones signal the dormant ova to continue their development. Typically, one ovum per month matures and is released. If the egg is fertilized, a pregnancy may result. If it is not fertilized, it passes out of the body. 
Fallopian TubesThe fallopian tubes are trumpet-shaped tubes that extend from the uterus to near the ovaries. After an egg is released by the ovary, the finger-like ends of the fallopian tube sweep the ovum into the tube. If sperm are present in the fallopian tube, the egg may be fertilized. The fertilized egg continues down the tube toward the uterus. 
UterusThe uterus is a stretchy, muscular, fist-sized organ that houses and protects a developing embryo and fetus. Hormones cause the lining of the uterus to thicken every month in preparation for pregnancy. When a fertilized egg implants into the lining of the uterus, pregnancy begins. If it does not implant or if the egg is unfertilized, the lining of the uterus breaks down and passes out of the body through the vagina. This is the process of menstruation. Then, the uterine lining begins to thicken, and the process starts all over again. 
VaginaThe uterus opens into the vagina through the cervix. The vagina has three functions:
Collectively, the external female genitals are called the vulva. In popular culture, people refer to this area as the "vagina," but that is incorrect. |
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Review the male and female reproductive systems in the activity below. Match the reproductive structure with its function.
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fallopian tube
uterus
ovaries
penis
testes
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produce sperm and the hormone testosterone
contain eggs and produce the hormones estrogen and progesterone
contains the tube that allows both urine and sperm to pass out of the body
carries the egg from the ovary to the uterus
muscular organ that houses a developing fetus
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Try again to match the remaining items.
