1. cell membrane 2. surface area 3. cell division
4. The information contained in the DNA would not be able to meet the needs of the larger cell. 5. Food, oxygen, and water enter the cell, and waste products exit the cell via the cell membrane. 6. The ratio of surface area to volume decreases as the cell’s size increases. 7. Cells divide because of the problems of
DNA“overload” and of increasing size that decreases the ratio of surface area to volume. 8. 6 cm
3
9. 6:1
10. 80 cm
2
1. The four phases of the cell cycle are the M phase
(mitosis), G 1 phase (cell growth), S phase (DNA replication), and G 2 phase. 2. The cell replicates its chromosomes. 3. During cytokinesis, the cytoplasm divides from one cell into two cells. 4. metaphase
5. prophase 6. prophase 7. anaphase 8. telophase
9. prophase 10. metaphase 11. anaphase
12. Mitosis refers only to the division of the nucleus, while cell division also includes cytokinesis, or division of the cytoplasm. 13. There would be 64 cells after 7.5 hours. 14. Possible student answers may include any reference to incorrect movement of chromosomes during mitosis, lack of cytokinesis, or
DNA duplication without cell division. 15. An animal cell has centrioles, while a plant cell has regions known as centromeres. During cytokinesis, in most animal cells the cell membrane moves inward and pinches the cytoplasm into two equal parts. In a plant cell, a cell plate forms midway between the two divided nuclei.
1. Cyclin regulates the timing of the cell cycle in eukaryotic cells. 2. Internal regulators prevent a cell from entering mitosis until all chromosomes have been replicated. 3. External regulators, such as growth factors, direct cells to speed up or slow down the cell cycle. 4. The abnormal growth of cancer cells is caused by the failure to respond to signals that regulate growth. 5. No. Some cells complete the cell cycle more quickly than other cells, or spend more time in one phase than another.
External regulators can also alter the growth rate.
For example, when there is an injury to the skin, the cells will increase their growth rate. Another example is when molecules on the surface of neighboring cells cause a cell to decrease its growth rate. 6. Possible student answer: How much cyclin is in cancer cells? 7. Both internal and external regulators regulate the timing of the cell cycle. The external regulators respond to stimuli from outside the cell, and the internal regulators respond to stimuli within the cell. 8. Possible student answer: A cut or injury is followed by a period of increased cell growth. After healing is complete, the cells return to a normal rate of growth.
1. cell division 2. centromere 3. interphase 4. cell cycle 5. spindle 6. Mitosis 7. prophase, metaphase, anaphase, telophase 8. cytokinesis 9. cyclins
10. cancer 11. a 12. c 13. b 14. a 15. a 16. b
17. d 18. G 2 phase 19. prophase 20. metaphase
21. anaphase 22. telophase 23. cytokinesis
24. G 1 phase 25. S phase