10-1
1. The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane.
2. The information that controls a cell’s function is stored in DNA, just as information needed by the public is stored in the books of a library. A cell’s DNA, then, is a “genetic” library.
3. It’s volume.
4. The surface area is 96 cm2, the volume is 64 cm3, and the ratio of surface area to volume is 96/64 = 3:2
10-2
1. A cell grows, prepares for division, and divides to form two daughter cells.
2. Prophase - The chromosomes become visible. The centrioles take up positions on opposite sides of the nucleus.
Metaphase - The chromosomes line up across the center of the cell.
Anaphase - The chromosomes move until they form two groups near the poles of the spindle.
Telophase - A nuclear envelope reforms around each cluster of chromosomes. The nucleolus becomes visible in each daughter nucleus.
3. During the G1 phase the cells do most of their growth, synthesizing proteins and organelles. During the S phase the cell replicates its chromosomes. During the shorter G2 phase the cell makes more of the organelles and molecules required for cell division.
4. DNA which carries the cell’s coded genetic information, and proteins.
5. A prokaryotic cell first replicates its genetic information before cell division begins. In most prokaryotes, the rest of the process of cell division is a simple matter of separating the contents of the cell into two parts.
6. Cytokinesis is the division of the cytoplasm in both types of cells. The difference is that in plant cells a cell plate forms midway between the divided nuclei.
10-3
1. Cyclins regulate the timing of the cell cycle in eukaryotic cells. Cyclin may cause a mitotic spindle to form and trigger cell division.
2. Such cells, called cancer cells, divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
3. Normal cells respond by not growing.
4. The cell cycle is the series of events that cells go through as they grow and divide, and cancer is a disorder in which some of the body’s cells lose the ability to control growth.
5. A typical hypothesis might suggest that cyclin would have no effect because the cell was already in mitosis.
Reviewing Content
1.d 5.c 9.a
2.c 6.a 10.a
3.b 7.b
4.c 8.b
Understanding Concepts
11. During cell division, a cell divides into two new daughter cells.
12. When a cell is small, the information stored in its DNA is able to meet all of the cell’s needs. But if a cell were to grow without limit, an “information crisis” would occur.
13. Cell volume is the amount of material inside the cell. Surface area is the total area of the cell’s membrane. Ratio of surface area to volume is the surface area divided by the volume.
14. A cell’s ratio of surface area to volume decreases as it grows larger. This means that the area available for diffusion also decreases. Thus, if a cell grows too large, it is unable to take in all needed materials and expel all its wastes. These problems impose limits on the growth of a cell.
15. Well before cell division, each chromosome is replicated. At the beginning of cell division, each chromosome consists of two identical sister chromatids.
16. Together, interphase and cell division make up the cell cycle.
17. During interphase, a cell increases in size, synthesizes new proteins and organelles, replicates its chromosomes, and prepares for cell division by producing needed spindle proteins.
18. The genetic information that is passed on from one generation of cells to the next is carried by chromosomes, which are made up of DNA. Before cell division, chromosomes are replicated, so that each chromosome consists of two identical “sister” chromatids. Sister chromatids are attached at an area called the centromere.
19. Prophase: Chromatin condenses into chromosomes; centrioles separate; spindle begins to form; nuclear membrane breaks down. Metaphase: Chromosomes line up across middle of cell with spindle fibers connected to their centromeres. Anaphase: Sister chromatids separate and move apart. Telophase: Chromosomes gather at opposite ends of cell and lose distinct shape; new nuclear membranes form.
20. The number of chromosomes in each of the two cells equals the number in the original cell.
21. A cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again.
22. Yes, new cells will replace the removed cells because of the process of cell division, which will continue until the new cells come in contact with other cells. When that occurs, cell division will stop.
23. Cyclins regulate the timing of the cell cycle in eukaryotic cells.
24. The consequences of uncontrolled cell growth are severe, as in cancer, for example.
25. Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, they form masses of cells called tumors that can damage the surrounding tissues.
Critical Thinking
26. Students’ models should demonstrate that as the size of a cube increases, its volume increases faster than its surface area. As a result, the ratio of surface area to volume decreases as the size of the cube increases.
27. Surface area = 5 mm X 5 mm X 6 = 150 mm2.
Volume = 5 mm x 5 mm x 5 mm = 125 mm3.
Ratio of surface area to volume = 150/1 25 = 6:5.
28. A typical experiment might suggest comparing the rate of cell division over time in the same kind of plant cell at various temperatures.
29. a. The cell is in metaphase. It most resembles that of an animal because there is no evidence of a cell wall, as there would be in the cell of a plant. Also, this cell has centrioles at opposite ends of the spindle, and plant cells do not have centrioles. b. The two strands carry the same genetic information, which is important because the cell needs this information to function.
30. The presence of many nuclei indicates that mitosis has occurred repeatedly without cytokinesis having occurred, because there is still only one cell.
31. Cell division is similar in animal and plant cells. In prophase, though, plant cells do not have centrioles, as animal cells do. Plant cells organize their mitotic spindles from regions known as centrosomes. Also, during cytokinesis in most animal cells, the cell membrane moves inward until the cytoplasm is pinched into two nearly equal parts. In plant cells, a cell plate forms midway between the divided nuclei and gradually develops into a separating membrane. A cell wall then appears in the cell plate.
32. Because nerve cells seldom undergo mitosis, the body is usually unable to repair damage to parts of the nervous system. Thus, complete recovery may not occur.
33. If the pattern were not constant, each type of organism could not stay the same, and there would be no species continuity.