Cell Division Explained: Life Sciences Grade 10

1. Life sciences Grade 10 CAPSstructured, clear, practical - Helping teachers unlock the power of NCS KNOWLEDGE AREA: Life at Molecular, Cellular and Tissue Level TOPIC 1.3: Cell Division The Cell Cycle-Mitosis

2. Summary of presentation

3. introduction • Before we start with cell division there are some terms that we need to understand. • The body is made up of two kinds of cells. • These are the body cells and the sex cells. • The body cells are called the somatic cells . • The somatic cells make up every part of your body for example the cells making up the bone. • The sex cells are called the gametes. • There are two types of gametes. • These are the sperm cells and ovum.

4. TERMINOLOGY:

5. TERMINOLOGY:

6. introduction • Cell division occurs in the somatic cells and in the formation of the gametes. • The cell that undergoes cell division is called the mother cell. • The new cells that are formed after cell division are called the daughter cells. • There are two types of cell division. • These are: • Mitosis and • Meiosis

7. introduction • Mitosisis the type of cell division that occurs in somatic cells. • It is simply when one cell divides and form two cells. • Remember the new cells that are formed are called the daughter cells. • The daughter cells are identical to each other and the mother cell is every way. • The chromosomal number stays the same during mitosis.

8. TERMINOLOGY:

9. introduction • During meiosisthe mother cell divides twice to form 4 differentdaughter cells. • Each daughter cell has half the number of chromosomes as the mother cell. • For example if the mother cell had 46 chromosomes then after meiosis each daughter cell would have 23 chromosomes. • Meiosis occurs to form gametes.

10. The cell cycle • The cell cycle is also known as the cell division cycle. • The cell cycle takes place within a cell, it is the series of events that occurs when a cell divides and duplicate. • In eukaryotic cells, cell division occurs in 2 periods. • These are interphaseand mitosis and cytokinesis.

11. The cell cycle • During interphase the cell growsby making proteins and organelles. • Also during interphase the DNA duplicates. • The cell also collects nutrients that are needed for mitosis during interphase. • During the mitosis phase the mother cell divides to from two identical daughter cells. • Mitosis is very important because it can allow a single cell to develop into a multicellular organism.

12. The cell cycle • From the diagram alongside you can see that most of the time of the cell cycle is taken up by interphase. • You can also see that mitosis and cytokinesis only takes up about 10% of the cell cycle. Time Allocation of each phase

13. mitosis • As mentioned earlier mitosis is the process by which one cell divides to form two identical daughter cells. • These identical daughter cells have the same number and type of chromosomes. • Cells that have the same number and kind of chromosomes are said to be genetically alike. • Remember that all the cells in the human body are genetically alike except for the sex cells.

14. Mitosis-geneticallyidentical What exactly does genetically identical mean? • DNA is made up of small parts that controls or carries the genetic code for one or more characteristics or functions. • This portion of DNA is called a gene. • DNA contains the code for the appearance and function of many parts. Like eye colour, or the type of protein to be made.

15. Mitosis-geneticallyidentical • People do not have the same DNA. However parts of their DNA may be similar to their parents or grandparents. • Remember! Identical twins have the same DNA!

16. Mitosis- the process • Mitosis is a type of cell division. • The actual process of mitosis is made up of two parts. • These two are the division of the… • Nucleus • Cytoplasm. • The nucleus divides first and the cytoplasm divides. • Now lets look at the division of the nucleus in an animal cell.

17. Mitosis- the process INTERPHASE: • This is preparation for nuclear division. • The DNA undergoes replication so that the genetic material in the chromatin material is doubled. Interphase

18. Mitosis- the process • The diagram alongside shows a micrograph of Interphase. Micrograph of Interphase

19. Mitosis- the process PROPHASE: • The chromatin network unwinds to form the single chromosomes. • The nuclear membrane and nucleolus start to disappear. • The centrioles move to the opposite poles.

20. Mitosis- the process • Study the micrograph of prophase. Micrograph of Prophase

21. Mitosis- the process METAPHASE: • During metaphase the chromosomes are found at the equator of the cell. • They occur in a single row. • They are attached to spindle fibers. centrioles Spindle fibers

22. Mitosis- the process ANAPHASE: • The spindle fibers shorten and the chromatids are pulled apart. • The chromatids are pulled towards the opposite end of the cell, towards the poles. • Each chromatid is a single stranded chromosome. Can you explain why this is the case?

23. Mitosis- the process • The micrograph alongside is of anaphase Micrograph of Anaphase

24. solution • Each chromatid is considered to be a single chromosome and the DNA underwent replication before the start of the division.

25. Mitosis- the process TELOPHASE: • There are now two groups of chromosomes at each pole of the cell. • The nuclear membrane and nucleolus reappear. • Now the cell has two nuclei with the same number and kind of chromosome as the mother cell.

26. Mitosis- the process • Study the micrograph alongside, carefully.

27. Mitosis- the process CYTOKINESIS: In animal cells • Cytokinesis is the division of the cytoplasm. • It occurs once two new nuclei are formed. • In animal cells the cell membrane constricts. • The constriction eventually meet in the middle forming two new cells.

28. Mitosis- the process CYTOKINESIS: In plant cell • A cell plate forms between the two new nuclei. • The cell plate divides the cell into two new identical cells. Cytokinesis Cell plate

29. TERMINOLOGY:

30. Mitosis in plant and animal cells • There are difference in how mitosis occurs in plant and animal cells. • The table in the next slide discusses some of these differences.

31. Mitosis in plant and animal cells • Differences in mitosis between Plant and Animal cells.

32. Importance of mitosis • From the above discussion you now know that mitosis results in the formation of identical cells. • This is extremely important in the growth of an organism, because in order to grow the organism would need a large number of identical cells. • Therefore it is mitosis that makes it possible for the unicellular zygote to grow into a multicellular organism by providing a large number of identical cells.

33. Importance of mitosis • Some unicellular organisms, such as the Amoeba, undergo a type of reproduction called binary fission. • During this process one cell simply divides to form two new cells that are identical to each other and the original cell. • From the above statement it is clear that binary fission is actually mitosis. • In spore producing organisms such as fungi, moss and fern, asexual reproduction occurs by mitosis.

34. Importance of mitosis • When cells naturally wear off they need to be replaced. Mitosis produces the identical cells that are needed to replace these lost cells. • When tissues are accidentally damaged they need to be repaired, once again mitosis provides the identical cells that make the repair possible.

35. Importance of mitosis • The importance of mitosis can be summarized as follows: • Formation of new cells that may be used for growth, replacement and repair. • Allows for asexual and vegetative reproduction.

36. Something for you to do Study the micrograph below and answer the questions that follow: A

37. Something for you to do • Name the phase shown. • Give one visible reason for your answer. • Name the phase that comes before this. • Identify label A. • Draw a diagram of the phase that follows the one shown.

38. Solution: • Anaphase • The chromatids are moving to the opposite poles. • Metaphase. • Chromatin. • Your teacher will provide you with a labelled diagram.

39. cancer-uncontrolledcell division and growth • Usually after mitosis has occurred some of the cells undergo structural and chemical changes so that they can perform specific functions. • These cells are said to be differentiated or specialized. • When these differentiated cells come together to perform a single function a tissueis formed. • These differentiated or specialized cells can no longer divide by mitosis.

40. cancer-uncontrolledcell division and growth • Some cells however do not differentiate, they continue to divide in an uncontrolled manner. • Sometimes even the specialized cells begin to undifferentiate and continue to divide by mitosis. These cells become simplified again. • This continual and uncontrolled division of cells results in the formation of swellings or growths in various parts of the body. • These growths or swellings are called tumors.

41. TERMINOLOGY:

42. cancer-uncontrolledcell division and growth • Two types of tumors maybe formed. • They are: • Benign tumors and • Malignant tumors. Benign tumors • These tumors stop growing. • They occur in small groups. • They do not invade the most important organs of the body. • They are not cancerous.

43. TERMINOLOGY:

44. cancer-uncontrolledcell division and growth Malignant tumors • Malignant tumors continue to grow. • They invade important organs. • Some of the cancer cells may break off and enter the blood or lymphatic system and are then carried to all parts of the body. • Therefore they are spread to even distant parts of the body. • They invade even the most distant parts of the body.

45. TERMINOLOGY:

46. cancer-causes • The exact cause of the cell behavior is unknown. • Cancer causing agents have been identified by scientists. • These agents bring about cancer in certain people under certain conditions. • These cancer causing agents are called carcinogens.

47. cancer-causes • The carcinogens do not always cause cancer. • Some people are exposed to these carcinogen over a life time and never develop cancer while other people are exposed to these carcinogens for only a short period and develop cancer.

48. cancer-causes • Scientist believe that these people that develop cancer are predisposed to it. They have a weakness or susceptibility to the disease. • This weakness might be inherited. • It is important to know that cancer can not be inherited only the predisposition for cancer can be inherited. • But in very rare cases the actual cancer itself can be inherited.

49. Cancer-carcinogens • Here is a list of some of these carcinogens: • Radiation (sun rays, x-rays, from atomic weapons) • Smoking • Hormonal imbalances • Some processed foods • Exposure to certain pollutants (for example industrial wastes, car exhaust fumes) • Pesticides • Viruses • Constant and prolonged irritation (e.g. mouth cancer can be caused by pipe smoking.

50. TERMINOLOGY: