Reproductive Strategies

Reproduction is a significant step in the life cycle of all living things. Without it, species would simply disappear as their individual members died off. There are two basic processes for reproduction that all life forms use: sexual and asexual reproduction. Why do some living things practice one type rather than the other?

The purpose of this activity is to help you understand the benefits and drawbacks of these two forms of reproduction.

Next: Why Reproduction Matters

All living things have a limited lifespan. For their species to continue, living things need to create offspring that inherit their characteristics, or traits. They do this through a process called reproduction.

Reproduction takes two basic forms. In asexual reproduction, a single parent creates a genetic copy of itself. Therefore, offspring almost always look and behave the same as the parent. In sexual reproduction, two individuals of the same species each contribute one half-set of their genes. Thus, offspring inherit a random mix of traits from the parents.

Using what you already know about human sexual reproduction, write down in the box below some traits that parents pass on to their offspring. In what ways are these traits important, or not important, for survival? Click "save notes" before moving on to the next page.

Next: Asexual Reproduction: Watch This!

An amoeba reproduces by first duplicating its full set of genes and then dividing in two. It can do this so quickly that populations can grow incredibly fast. However, not all asexual reproducers have just one cell, and not all asexual reproducers divide in two to create their offspring.

Watch this video segment to learn about a unique species of lizard. Like all lizards, this desert salamander lays eggs, inside which its young develop. What's extremely unusual about this species is that it thrives even though its entire population is made up of females.

Note: You will hear the following words in the video segment. Click on each word to see its definition.

• clone
• genes
• reproductive strategies

As you watch, think about this: If some species can successfully reproduce without having sex, why don't all living things reproduce in this way? In the box below, write down your thoughts and click "save notes" before moving to the next page.

Next: Sexual Reproduction: Watch This!

Most animal, insect, and plant species reproduce in pairs. Sexual reproduction creates variety, which can help a species adapt to changing environmental conditions.

Watch this video segment about two different species of fish that inhabit the same environment. One reproduces asexually, the other sexually. The video illustrates how sexual reproduction provides a critical advantage against the spread of disease.

Note: You will hear the following words in the video segment. Click on each word to see its definition.

• pathologies
• parasite

As you watch, think about how having males in a species gives sexual reproducers an important advantage over asexual reproducers. Write down your thoughts in the box below, then click "save notes" before moving to the next page.

Next: Did You Know?

You've learned how even complex life forms can successfully reproduce with or without having sex. Here are some examples of how certain living things improve their reproductive chances, and thus ensure the survival of their species.

• Plants rely on both living and non-living things to help them reproduce. Insects, birds, bats, wind, and water all carry pollen from one plant to another so that fertilization can occur.
• Snails and slugs have both male and female reproductive parts. During sex, each partner receives sperm from the other. In this way, both partners' eggs get fertilized.
• Some female birds base their choice of a mate solely on physical appearance. Others consider how good a parent the potential mate will be when chicks are born.

Next: Try This Activity!

Think of what you've learned so far about the two basic forms of reproduction. In this activity, you will categorize some basic ideas according to the reproductive method they describe.

Click "View" on the left to begin the activity. Be sure to print your notes before you exit the activity. Your notes will not be saved.

If you want, you can also watch the videos again.

Asexual Reproducers

QuickTime Video
Length: 2m 05s

Why Sexual Reproduction?

QuickTime Video
Length: 3m 13s

Next: Read and Write About It!

In evolutionary terms, the survival of a species is determined by the ability of its individual members to successfully reproduce. While most living things are born as a result of sexual reproduction, others result from asexual reproduction.

You will now have a chance to read more about both forms of reproduction and their respective advantages. Then you can demonstrate what you have learned about them.

• Print out your notes. (After you print, your notes will be erased. Make sure you are done before printing.)
  
  
• Print out and read Sexual and Asexual Reproduction (Version A) (PDF) or Sexual and Asexual Reproduction (Version B) (PDF). Check with your teacher if you are not sure which version to use.
• After reading, take a look at your chart and make any changes or add new information.
• Then, select a writing assignment from page 2 of the printout.

Note: The following words will appear in the readings. Click on each word to see its definition.

Version A

• genetic variation
• natural selection
• population

Version B

• diluted
• genetic variation
• natural selection
• population