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Introduction to the chapter
After fertilization, the human embryo is one tiny, undifferentiated cell. This one cell will divide into billions of specialized cells which carry out the necessary functions of the body. There is one key process responsible for this growth: mitosis. In this lesson, we will study mitosis in detail and begin to see how one cell can divide to produce more cells with identical genetic makeup. This lesson may feel long and a bit tedious as there is a lot of summarizing to do but this is a vitally important section which you need to know and remember well so do not be tempted to skip it.
Mitosis
Read the section “Mitosis” on p.97-101 of your text book.
Notes on the cell cycle
Study Figure 5.6 on p.97. Notice that there are three stages in the cell cycle: interphase, nuclear division and cell division (cytokinesis).
- Interphase:
- Notice that interphase refers to that stage after cell division and until the nucleus starts to divide again.
- Notice too that there are three phases to interphase: G1; S; and G2.
- G1: cell growth takes place
- S: the DNA is duplicated in preparation for nuclear division (there are now two identical strands of DNA in one nucleus so that when the nucleus divides into two there will be one strand of DNA for each nucleus)
- G2: cell growth continues slowly as the cell prepares for nuclear division
- Nuclear division:
- Nuclear division follows interphase and may be referred to as the M phase.
- Mitosis consists of four stages:
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cell division:
- Notice that in animals, cell division involves the constriction of the cytoplasm between the two new nuclei. That process is called cytokinesis.
- Plant cells, however, have a cell wall and so a new cell wall is laid between the two nuclei.
Learning Activity 1
Do the following activity in your exercise book.
- Draw your own diagram of the cell cycle (make it large so that you have enough space for your annotations. Annotate (label and provide an explanation) your diagram:
- indicating the three main phases -- interphases, nuclear division and cell division.
- indicating the G1, S, and G2 parts of interphase (including details such as which proteins are made during G1 and what happens during G2 to prepare the cell for nuclear division). Know this well!
- indicating the four stages of nuclear division and a brief sentence-long explanation of each.
Notes on mitosis
- Remember that the process of mitosis is continuous but for ease of understanding we divide it into four main stages.
- The four stages of mitosis are: prophase, metaphase, anaphase and telophase. You need to understand these four stages very well and be able to identify them in a micrograph or diagram of a cell.
- Notice the following differences between plant and animal cells:
- Plant cells do NOT contain centrosomes
- In plant cells, a cell wall is formed between the two nuclei
Learning Activity 2
Answer the following questions in your exercise book.
- Study Fig. 5.8 (p.99) which shows mitosis in an animal cell. Then study Fig. 5.9 (p.100) which shows mitosis in a plant cell. What differences do you notice? What are the similarities/
- Study Fig. 5.7 (p.98) which summarises the process of mitosis:
- Make a list of all the events that take place during early prophase.
- Make a list of all the events that take place during late prophase.
- Make a list of all the events that take place during metphase. (Note the drawing of the chromosome to the right of the metaphase diagram)
- Make a list of all the events that take place during anaphase.
- Make a list of all the events that take place during telophase. What would be different in plant cells at this stage?
- Now study the photomicographs in Fig. 5.8 (p.99)
- Can you identify the different stages?
- How can you tell which phase it is? (Keep comparing the different photomicrographs to the diagrams in Fig. 5.7.)
- Now study Fig. 5.9 (p.100).
- Can you tell which phase the different cells are in? How can you tell? (Compare the cells to Fig. 5.7.) [Do not skip this activity! You will be required in your practical exam to tell the mitotic stage of cells from a microscope slide. It is important that you are very familiar with the different stages.]
- Sum up the role of centromeres, centrosomes and centrioles in your own words. Draw diagrams to illustrate your summary. (You may wish to refer back to Ch1 to refresh your memory about centrosomes.)
- Answer Questions 5.1 on p.100.
- In a short paragraph, discuss the biological significance of mitosis. (Think about the cell theory in Ch1.)
- Answer Question 5.2 (p.101) and Questions 5.3-5.5 (p.102).
Practical Investigation
Read the Purple box “Box 5.1 Investigating mitosis using a root tip squash” on p.102 of your text book, taking note of the procedure. You will do this or similar experiments in the practical but it is worth taking note of it here.
Definitions and review
Definitions
- Mitosis
- Cell cycle
- Nuclear division
- Cytokinesis (animal cells)/Cell division (plant cells)
- Prophase
- Metaphase
- Anaphase
- Telophase
- Kinetochre
- Microtubules
- Spindle fibres
- Clones
- Asexual reproduction
Mindmap
Add this section to your chapter five mindmap.