1. Introduction to the Animal Kingdom
Section 26–1
This section describes characteristics that all animals share and the essential functions that animals carry out. It also explains the important trends in animal evolution.

2. What Is an Animal? Is the following sentence true or false?
The cells that make up animal bodies are eukaryotic.

3. What Is an Animal? What characteristics do all animals share?
Animals are multicellular, eukaryotic heterotrophs whose cells lack cell walls.

4. What Animals Do to Survive

5. What Animals Do to Survive

6. What Is an Animal?
Complete the table about animals.

7. What Is an Animal?
Complete the table about animals.

8. What Animals Do to Survive
What are seven essential functions that animals carry out?
Circulation
Respiration
Response
Reproduction
Feeding
Excretion
Movement

9. What Animals Do to Survive
Explain the difference between a parasite and a host.
A parasite is a type of symbiont that lives within or on another organism, the host.
The parasite feeds on the host, harming it.

10. What does an animal do when it respires?
It takes in oxygen and gives off carbon dioxide.

11. What does the excretory system of most animals do?
It either eliminates ammonia quickly or converts it to a less toxic substance that is removed from the body.

12. What are receptors, and what is their function?

13. They are nerve cells that respond to sound, light, and other stimuli.

14. A motile animal is one that can move.
What does it mean that an animal is motile?
A motile animal is one that can move.

15. What enables motile animals to move around?

16. Muscle contraction enables animals to move around, usually by working in combination with a skeleton.

17. What is the process that helps a species maintain genetic diversity.
sexual reproduction

18. What does asexual reproduction allow animals to do?
It allows animals to increase their numbers rapidly.

19. Trends in Animal Evolution
What are four characteristics that complex animals tend to have?
High levels of cell specialization and internal body organization
Bilateral body symmetry
Cephalization
A body cavity

20. Trends in Animal Evolution
How have the cells of animals changed as animals have evolved?
Their cells have become specialized to carry out different functions, such as movement and response.

21. Trends in Animal Evolution
Groups of specialized cells form______ , which form organs, which form___________.
tissues
Organ systems

22. Trends in Animal Evolution
What does a zygote forms after it undergoes a series of divisions?
blastula

23. Reproduction Early development
The zygote undergoes mitosis and a series of cell divisions to form new cells.
The cells continue to divide, forming a fluid-filled ball of cells called the blastula.
The blastula continues to undergo cell division, and some cells form a gastrula, a two-cell-layer sac with an opening at one end.
Copyright © McGraw-Hill Education
Animal Characteristics

24. Reproduction Tissue development
The inner layer of the gastrula develops into the endoderm, which forms the digestive organs.
The outer layer of the gastrula develops into the ectoderm, which becomes the nervous system and skin.
The mesoderm forms between the ecto- and endoderm, and forms the muscle, circulatory, excretory, and respiratory system in some animals.
Copyright © McGraw-Hill Education
Animal Characteristics

25. What is a protostome?
It is an animal whose mouth is formed from the blastopore.

26. What is a deuterostome?
It is an animal whose anus is formed from the blastopore.

27. Symmetry
Symmetry is the balance or similarity of body structures of an organism.
Copyright © McGraw-Hill Education
Animal Body Plans

28. Complete the table about body symmetry

29. What is cephalization?
It is the concentration of sense organs and nerve cells at the front end of the body.

30. How do animals with cephalization respond differently to the environment than animals without cephalization?
Animals with cephalization respond to the environment more quickly and in more complex ways than simpler animals can.

31. What is a body cavity?
It is a fluid-filled space that lies between the digestive tract and the body wall.

32. Why is having a body cavity important?
It provides a space in which internal organs can be suspended so that they are not pressed on by muscles or twisted out of shape by body movements.