7-3

1. The cell membrane regulates what enters and leaves the cell and also provides protection and support. The cell wall provides support and protection for the cell.

2. Particles tend to move from an area where they are more concentrated to an area where they are less concentrated.

3. Osmosis is the diffusion of water through a selectively permeable membrane.

4. The basic structure is a double-layered sheet called a lipid bilayer, in which proteins are embedded.

5. In phagocytosis, extensions of cytoplasm surround a particle and package it within a food vacuole. In pinocytosis, tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell.

6. Active transport requires the input of energy, but diffusion does not require additional energy.

7-4

1. Multicellular organisms have cell specialization.

2. Individual ceIls, tissues, organs, and organ systems.

3. Both unicellular and multicellular organisms grow, respond to the environment, transform energy, and reproduce.

4. Muscle cells have a large number of mitochondria, because mitochondria release energy from stored food molecules and muscle cells need great amounts of energy to do the tasks they do.

CA 7

Reviewing Content

1.d  5.c   9.d

2.b  6.a   10.a

3.b  7.d

4.b  8.c

Understanding Concepts

11. Robert Hooke observed cork slices and named cells. Matthias Schleiden concluded that all plants are made of cells. Theodor Schwann concluded that all animals are made of cells. Rudolf Virchow concluded that all cells come from preexisting cells.

12. Both prokaryotic and eukaryotic cells have two characteristics in common: they are surrounded by a cell membrane, and they contain DNA. Prokaryotes are generally smaller and simpler, and they lack a nucleus. Eukaryotic cells generally contain dozens of structures and internal membranes, including a nucleus that contains their genetic material.

13. chromatin—granular material within nucleus consists of DNA bound to protein; nucleolus—small dense region where the assembly of ribosomes begins; nuclear envelope—a double membrane layer containing many pores that allow materials to move into and out of the nucleus.

14. Ribosomes produce proteins.

15. Rough ER makes membranes and secretory proteins (synthesizes proteins that leave the cell).

16. The Golgi apparatus contains enzymes that attach carbohydrates and lipids to proteins, sorts modifies and packages proteins and other materials for export.

17. Mitochondria and chloroplasts contain their own DNA. They were once unicellular organisms and then were incorporated into a eukaryote.

18. Students should describe microfilaments and microtubules. Microfilaments are threadlike structures made of the protein actin.They produce a tough framework that supports the cell.Microtubules are hollow structures made of tubulin protein.They maintain cell shape.

19. The core of the cell membrane is made up of a lipid bilayer. Protein molecules run through this layer. The proteins form channels and pumps that enable materials to move across the cell membrane. -

20. The concentration of a solution is the mass of solute in a given volume of solution, or mass/volume. For example, it you dissolved 12 grams of salt in 3 liters of water, the concentration of the solution would be 12 g / 3 L, or 4 grams per liter.

21. In diffusion, particles tend to move from an area where they are more concentrated to an area where they are less concentrated. When diffusion is complete, the system has reached equilibrium.

22. Osmosis is the diffusion of water through a selectively permeable membrane. Only water can move by osmosis.

23. An isotonic solution would have the same concentration of solute on both sides of a membrane. The result of placing cells in an isotonic sugar solution would be that the cells would neither shrink nor swell.

24. Cell walls prevent damage by preventing cells from expanding.

25. One possible answer: Muscle cells make up smooth muscle tissue, which is part of the stomach, an organ. The stomach is part of the digestive system.

Critical Thinking

26. The diffusing salt particles (that is, the sodium ions and chloride ions that make up salt) and water molecules will eventually reach equilibrium without a change in the fluid on either side.

27. Solution A is more concentrated because there are 3 grams of salt per liter compared to the 2 grams per liter in Solution B.

28. The blood cells would swell and probably burst.

29. Because muscle cells are responsible for movement, they require more energy than skin cells. Therefore, skin cells contain fewer mitochondria.

30. Most students will develop an experiment in which the rate of diffusion of food coloring is observed by dropping equal amounts of food coloring into each beaker. Make sure that students identify the control (water at room temperature).

31. Ribosomes are responsible for making proteins. Because enzymes are proteins, the ribosomes would be present in the pancreas.

32. Students should demonstrate an understanding of the functions of different parts of the cell.

33. In diffusion, particles tend to move from an area where they are more concentrated to an area where they are less concentrated. As waste chemicals build up in a cell, they become more concentrated inside the cell than outside. As a result, diffusion occurs from inside to outside, and the level of waste chemicals within the cell drops.

34. Answers may vary. Students should define both diffusion and active transport, and they should emphasize that active transport requires energy, whereas diffusion does not. A typical response might mention the excretion of wastes as an example of diffusion and the phagocytosis of large particles to ingest food as an example of active transport.