1. Table of Contents What Is an Animal? Animal Symmetry
Sponges and Cnidarians
Worms

2. Structure of Animals - What Is an Animal?
The cells of most animals are organized into higher levels of structure, including tissues,
organs, and systems.

3. Classification of Animals
- What Is an Animal?
Classification of Animals
This branching tree shows how the major animal groups are related.

4. Asking Questions - What Is an Animal?
Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.
Question
Answer
What is a cell?
A cell is the basic unit of structure and function in living things.
What is the structure of animals?
The cells of animals are organized into tissues, organs, and systems.
What are the functions of animals?
Animals must obtain food and oxygen, keep a stable environment within their bodies, reproduce, and move about to meet their needs.
How are animals classified?
Animals are classified according to how they are related to other organisms.

5. Links on the Animal Kingdom
- What Is an Animal?
Links on the Animal Kingdom
Click the SciLinks button for links on the animal kingdom.

6. End of Section: What Is an Animal?

7. Comparing and Contrasting
- Animal Symmetry
Comparing and Contrasting
As you read, compare and contrast the characteristics of animals with bilateral symmetry and radial symmetry in a Venn diagram like the one below. Write the similarities in the space where the circles overlap and the differences on the left and right sides.
Radial Symmetry
Bilateral Symmetry
One line of symmetry, halves that are mirror images, front end with sense organs, quick movement
Many lines of symmetry, no distinct front end, live in water, move slowly
Balanced arrangement of parts, perform all the basic life functions

8. Links on Animal Symmetry
Click the SciLinks button for links on animal symmetry.

9. End of Section: Animal Symmetry

10. Sponges - Sponges and Cnidarians
Structures surrounding the central cavity of a sponge are adapted for different functions.

11. Sponges - Sponges and Cnidarians
The sexual reproduction of sponges involves a larval stage that moves. Adult sponges stay in one place.

12. Calculating a Rate - Sponges and Cnidarians
To calculate the rate of water flow in a sponge, divide the volume of water that the sponge filters by the time it takes the water to pass through the sponge.
Flow rate = Volume of water/Time
For example, a marble-sized sponge filters 15.6 liters of water in a day. How many liters does it filter per hour?
Practice Problem
In four days, a sponge filters 1,200 L. What is its rate of water flow per day?
300 L/day

13. Cnidarians - Sponges and Cnidarians
Cnidarians have two basic body plans, the vase-shaped polyp and the bowl-shaped medusa.

14. Cnidarians - Sponges and Cnidarians
Cnidarians use stinging cells to capture food and defend themselves.

15. Cnidarians - Sponges and Cnidarians
The life cycle of a moon jelly has both a polyp and a medusa stage.

16. Comparing and Contrasting
- Sponges and Cnidarians
Comparing and Contrasting
As you read, compare and contrast sponges and cnidarians by completing a table like the one below.
Feature
Sponges
Cnidarians
Polyp or medusa, central body cavity, tentacles
Body structure
Hollow body with pores
Cell type that traps food
Collar cells
Stinging cells
Method(s) of reproduction
Sexual and asexual
Sexual and asexual

17. End of Section: Sponges and Cnidarians

18. Characteristics of Worms
Biologists classify worms into three major phyla—flatworms, roundworms, and segmented worms.

19. Life Cycle of a Dog Tapeworm
- Worms
Life Cycle of a Dog Tapeworm
This flatworm is a parasite that lives in more that one host during its life cycle.

20. Roundworm Numbers - Worms
Biologists counted all the roundworms living in a plot of soil. Then they calculated the percentage that lives in different depths of soil.

21. Roundworm Numbers - Worms Reading Graphs:
Where in the soil was the largest percentage of roundworms found?
In the first centimeter

22. Roundworm Numbers - Worms Calculating:
What is the total percentage of roundworms found in the first 3-cm depth of soil?
About 87%

23. Roundworm Numbers - Worms Drawing Conclusions:
What is the relationship between the depth of soil and the abundance of roundworms in the soil?
The deeper the soil, the fewer the worms

24. Segmented Worms - Worms
Earthworms and other segmented worms have bodies made up of many linked sections called segments.

25. Using Prior Knowledge - Worms
Before you read, write what you know about worms in a graphic organizer like the one below. As you read, write what you learn.
What You Know
Worms are long and skinny.
Worms live in the ground and digest soil.
Worms are slimy and wriggly.
What You Learned
Worms have bilateral symmetry.
Some worms are flat.
Some worms live in water.
Some worms are parasites.
Worms have a nervous system.

26. Click the PHSchool.com button for an activity about worms.
More on Worms
Click the PHSchool.com button for an activity about worms.

27. End of Section: Worms

28. Graphic Organizer The Life of a Sponge Sponge releases sperm.
Sperm enter another sponge and fertilize egg cell.
Larva settles on a surface and develops into adult sponge.
The Life of a Sponge
Water currents carry away larva.
Larva develops.

29. End of Section: Graphic Organizer