- Define and explain Cell Division: Mitosis in your own words
- Use key terms such as stem cell accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Cell Division: Mitosis: follow the stages of mitosis and learn why growth and repair need identical cells.
Follow the stages of mitosis and learn why growth and repair need identical cells.
Key ideas
Mitosis and the cell cycle
In mitosis, one cell divides to form two genetically identical daughter cells. Before division, the chromosomes are copied so each new cell receives a full set. Mitosis is needed for growth, for replacing worn-out cells, and for repair. Because the chromosome copies are exact, the daughter cells are clones of the parent cell.
Microscopes and magnification
A light microscope uses light and glass lenses to magnify specimens up to about 1500 times. Electron microscopes reach far higher magnifications and resolution but cannot view living cells. Magnification is calculated with: magnification = image size ÷ real size. Always convert both measurements to the same units before dividing, for example millimetres to micrometres (1 mm = 1000 μm).
Key term — stem cell: An unspecialised cell that can divide to produce more stem cells or differentiate into specialised cell types.
Give two reasons why multicellular organisms need mitosis.
Any two of: growth (increasing cell number); repair of damaged tissue; replacement of worn-out cells.
Answer: Any two of: growth (increasing cell number); repair of damaged tissue; replacement of worn-out cells.
- Saying mitosis produces different cells Mitosis produces two genetically identical cells. It is meiosis, used to make gametes, that produces variation.
- Confusing magnification with resolution Magnification makes things bigger; resolution makes them clearer. A blurry image magnified 1000 times is still blurry.
Practice
Mitochondria release energy by respiration. The sperm needs large amounts of energy to swim towards the egg, so many mitochondria supply it.
Losing the nucleus leaves more space for haemoglobin, so each cell can carry as much oxygen as possible.
40 ÷ 200 = 0.2 mm.
The hair increases the cell's surface area, so it can absorb water and mineral ions from the soil more quickly.
Quick check
Which of these best defines "stem cell"?
Oxygen moves from the air in the lungs into the blood. Explain why, using the term concentration gradient.
- Cell Division: Mitosis: follow the stages of mitosis and learn why growth and repair need identical cells.
- Mitosis and the cell cycle: In mitosis, one cell divides to form two genetically identical daughter cells.
- magnification: How many times larger an image appears compared with the real object, calculated as image size divided by real size.
- Watch out for: saying mitosis produces different cells