Lesson Overview

1. Lesson Overview 10.1 Cell Growth, Division, and Reproduction

2. THINK ABOUT IT • When a living thing grows, what happens to its cells? • What is there about growth that requires cells to divide and reproduce themselves?

3. Limits to Cell Size • What are some of the difficulties a cell faces as it increases in size?

4. Limits to Cell Size • What are some of the difficulties a cell faces as it increases in size? • The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane.

5. Information “Overload” • Living cells store critical information in DNA. • As a cell grows, that information is used to build the molecules needed for cell growth. • As size increases, the demands on that information grow as well. If a cell were to grow without limit, an “information crisis” would occur.

6. Information “Overload” • Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access. • A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

7. Exchanging Materials • Food, oxygen, and water enter a cell through the cell membrane. Waste products leave in the same way. • The rate at which this exchange takes place depends on the surface area of a cell. • The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume. • The ratio of surface area to volume is key to understanding why cells must divide as they grow.

8. Ratio of Surface Area to Volume • Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. • If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.

9. Traffic Problems • To use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out. • Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.

10. Division of the Cell • Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division. • Before cell division, the cell copies all of its DNA. • It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA. • Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.

11. Cell Division and Reproduction • How do asexual and sexual reproduction compare?

12. Cell Division and Reproduction • How do asexual and sexual reproduction compare? • The production of genetically identical offspring from a single parent is known as asexual reproduction.

13. Cell Division and Reproduction • How do asexual and sexual reproduction compare? • The production of genetically identical offspring from a single parent is known as asexual reproduction. • Offspring produced by sexual reproduction inherit some of their genetic information from each parent.

14. Asexual Reproduction • In multicellular organisms, cell division leads to growth. It also enables an organism to repair and maintain its body. • In single-celled organisms, cell division is a form of reproduction.

15. Asexual Reproduction • Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them. • Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring. • Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

16. Examples of Asexual Reproduction • Bacteria reproduce by binary fission. • Kalanchoe plants form plantlets. • Hydras reproduce by budding.

17. Sexual Reproduction • In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow. • The offspring produced inherit some genetic information from both parents. • Most animals and plants, and many single-celled organisms, reproduce sexually.

18. Comparing Sexual and Asexual Reproduction

19. Lesson Overview 10.2 The Process of Cell Division

20. THINK ABOUT IT • What role does cell division play in your life? • Does cell division stop when you are finished growing?

21. Chromosomes • What is the role of chromosomes in cell division?

22. Chromosomes • What is the role of chromosomes in cell division? • Chromosomes make it possible to separate DNA precisely during cell division.

23. Chromosomes • The genetic information that is passed on from one generation of cells to the next is carried by chromosomes. • Every cell must copy its genetic information before cell division begins. • Each daughter cell gets its own copy of that genetic information. • Cells of every organism have a specific number of chromosomes.

24. Prokaryotic Chromosomes • Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm. • Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.

25. Eukaryotic Chromosomes • In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.

26. Chromatin is composed of DNA and histone proteins.

27. DNA coils around histone proteins to form nucleosomes.

28. The nucleosomes interact with one another to form coils and supercoils that make up chromosomes.

29. The Cell Cycle • What are the main events of the cell cycle?

30. The Cell Cycle • What are the main events of the cell cycle? • During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells.

31. The Prokaryotic Cell Cycle • The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division. • Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size. • When DNA replication is complete, the cells divide through a process known as binary fission.

32. The Prokaryotic Cell Cycle • Binary fission is a form of asexual reproduction during which two genetically identical cells are produced. • For example, bacteria reproduce by binary fission.

33. The Eukaryotic Cell Cycle • The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. • Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.

34. G1 Phase: Cell Growth • In the G1 phase, cells increase in size and synthesize new proteins and organelles.

35. S Phase: DNA Replication • In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.

36. G2 Phase: Preparing for Cell Division • In the G2 phase, many of the organelles and molecules required for cell division are produced.

37. M Phase: Cell Division • In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. • Mitosis is the division of the cell nucleus. • Cytokinesis is the division of the cytoplasm.

38. Mitosis • What events occur during each of the four phases of mitosis?

39. Mitosis • What events occur during each of the four phases of mitosis? • During prophase, the genetic material inside the nucleus condenses and the duplicated chromosomes become visible. Outside the nucleus, a spindle starts to form.

40. Mitosis • What events occur during each of the four phases of mitosis? • During metaphase, the centromeres of the duplicated chromosomes line up across the center of the cell. Spindle fibers connect the centromere of each chromosome to the two poles of the spindle.

41. Mitosis • What events occur during each of the four phases of mitosis? • During anaphase, the chromosomes separate and move along spindle fibers to opposite ends of the cell.

42. Mitosis • What events occur during each of the four phases of mitosis? • During telophase, the chromosomes, which were distinct and condensed, begin to spread out into a tangle of chromatin.

43. Important Cell Structures Involved in Mitosis • Chromatid – each strand of a duplicated chromosome • Centromere – the area where each pair of chromatids is joined • Centrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindle • Spindle – a fanlike microtubule structure that helps separate the chromatids

44. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.

45. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle.

46. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle. • The spindle forms and DNA strands attach at a point called their centromere.

47. Prophase • During prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible. • The centrioles move to opposite sides of nucleus and help organize the spindle. • The spindle forms and DNA strands attach at a point called their centromere. • The nucleolus disappears and nuclear envelope breaks down.

48. Metaphase • During metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.

49. Metaphase • During metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell. • The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.

50. Anaphase • During anaphase, the third phase of mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.