Directed Reading A. Section: The Cell Cycle. you finish reading this sentence? THE LIFE OF A CELL. cell. Skills Worksheet

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1 Skills Worksheet Directed Reading A Section: The Cell Cycle 1. Why is it important for your body to produce millions of new cells by the time you finish reading this sentence? THE LIFE OF A CELL 2. When does the cell cycle begin? a. when the cell is formed b. when the cell divides c. when the cell uses energy d. when the cell takes in oxygen 3. When does the cell cycle end? a. when the cell is formed b. when the cell divides and makes new cells c. when the cell uses energy d. when the cell takes in oxygen 4. What must a cell do before it can divide to make a new cell? 5. What makes sure that each new cell will be an exact copy of its parent cell? 6. A cell without a nucleus is a(n) cell. 7. A cell with a nucleus is a(n) cell. 8. A chromosome is the ring of DNA in a(n) cell. 9. A chromosome is made up of DNA and protein in the nucleus of a(n) cell. Holt Science and Technology 7 The Cell in Action

2 10. Are bacteria prokaryotic cells or eukaryotic cells? 11. Bacteria create new cells through a kind of cell division called. 12. When binary fission is complete, the result is two cells that each contain one copy of. 13. The chromosomes of eukaryotic cells have more than do the chromosomes of prokaryotic cells. 14. Humans have chromosomes, while fruit flies have only chromosomes.. Potatoes have 15. Chromosomes that line up in pairs are called. 16. What do pairs of homologous chromosomes have in common? 17. In the beginning of the eukaryotic cell cycle, the cell grows and duplicates its and. 18. After a chromosome is duplicated, the two copies are called. 19. Where are chromatids held together? 20. Chromatids in eukaryotic cells separate during a process called. Holt Science and Technology 8 The Cell in Action

3 21. Describe what happens during the first stage of the cell cycle in a eukaryotic cell. 22. Describe what happens during the second stage of the cell cycle in a eukaryotic cell. 23. Describe what happens during the third stage of the cell cycle in a eukaryotic cell. MITOSIS AND THE CELL CYCLE 24. Before mitosis begins, what paired cell structures are copied? a. the cell plates b. the chromosomes c. the cell membranes d. the nuclear membrane Holt Science and Technology 9 The Cell in Action

4 Use the diagram below to help answer questions 25-30, which describe the phases of the cell cycle. Write the correct phase in each blank, using Interphase, Mitosis Phase 1, Mitosis Phase 2, Mitosis Phase 3, Mitosis Phase 4, or Cytokinesis. Interphase Mitosis Phase 1 Mitosis Phase 2 Mitosis Phase 3 Mitosis Phase 4 Cytokinesis 25. Chromatids separate and move to opposite sides of the cell. 26. The chromosomes line up along the equator of the cell. Homologous chromosomes pair up. 27. Before mitosis begins, chromosomes are copied. 28. A nuclear membrane forms around the two sets of chromosomes, and the chromosomes unwind. Mitosis is complete. 29. Mitosis begins. The nuclear membrane dissolves. Chromosomes condense into rodlike structures. 30. In cells that lack a cell wall, the cell pinches in two. In cells that have a cell wall, a cell plate forms between the two new cells. Holt Science and Technology 10 The Cell in Action

5 31. Describe how animal cells and eukaryotes without cell walls divide their cytoplasm during cytokinesis. Place the following structures in the order in which they form in eukaryotic cells with cell walls during cytokinesis. Write the appropriate number in the space provided. 32. cell wall 33. cell plate 34. cell membrane Holt Science and Technology 11 The Cell in Action

6 Skills Worksheet Section Review The Cell Cycle USING KEY TERMS 1. In your own words, write a definition for each of the following terms: cell cycle and cytokinesis. UNDERSTANDING KEY IDEAS 2. Eukaryotic cells a. do not divide. b. undergo binary fission. c. undergo mitosis. d. have cell walls. 3. Why is it important for chromosomes to be copied before cell division? 4. Describe mitosis. MATH SKILLS 5. Cell A takes 6 h to complete division. Cell B takes 8 h to complete division. After 24 h, how many more copies of cell A would there be than cell B? Show your work below. Holt Science and Technology 33 The Cell in Action

7 Section Review continued CRITICAL THINKING 6. Predicting Consequences What would happen if cytokinesis occurred without mitosis? 7. Applying Concepts How does mitosis ensure that a new cell is just like its parent cell? 8. Making Comparisons Compare the processes that animal cells and plant cells use to make new cells. How are the processes different? Holt Science and Technology 34 The Cell in Action