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Cell division: mitosis and the cell cycleIB MYP Biology: Revision notes

Section 1

What is mitosis?

Mitosis is a type of cell division. One cell divides to make two cells that are genetically identical to the parent cell. Each new cell has a full copy of the DNA.

Because the DNA is copied exactly, the new cells have the same genetic information and the same structure as the original.

Key termsmitosisgenetically identical
Common mistake

Mitosis makes two cells, not four. And the two cells are identical to each other and to the parent.

Section 2

The stages of mitosis

Before a cell divides, it grows and gets ready. Then mitosis happens in three stages:

  1. The DNA is copied, so there are two full sets.
  2. The nucleus divides into two, each with a full set of DNA.
  3. The cell divides: the cytoplasm and cell membrane split to make two new cells.

The order matters. The DNA must be copied before the nucleus divides.

Key termsDNA copyingcell cycle

Section 3

Why mitosis is important

Mitosis is used for:

  • Growth: an organism gets bigger by making more cells. An onion root grows longer because cells at the tip divide.
  • Repair: damaged or worn-out cells are replaced. A cut on your skin heals this way.
  • Asexual reproduction: a parent makes offspring without sex cells. The offspring are genetically identical to the parent. Examples include a spider plant making plantlets and bacteria dividing.
Key termsgrowthrepairasexual reproduction
Exam tip

To explain why the new cells are the same, say the DNA is copied and mitosis makes genetically identical cells.

Section 4

Cancer

Normally cell division is controlled: cells divide only when new cells are needed.

Cancer happens when cell division becomes uncontrolled. The cells divide again and again and build up into a lump called a tumour. A tumour can damage nearby tissues, and cancer cells can spread to other parts of the body.

Cancers found early are usually easier to treat, which is why screening can save lives. But screening costs money and can give false alarms, so governments must weigh benefits against costs.

Key termscancertumouruncontrolled division

Must Know

  • Mitosis makes two genetically identical cells
  • Stages: DNA copies, nucleus divides, cell divides
  • Uses: growth, repair, asexual reproduction
  • Cancer is uncontrolled cell division that forms a tumour
  • Percentage dividing = dividing cells ÷ total cells × 100

That's the notes covered.

Carry on to the next subtopic.

Exam questions on Cell division: mitosis and the cell cycle

  1. A child falls over and cuts her knee. Over the next week the cut heals, because the skin cells next to the wound divide to replace the cells that were damaged.
    Explain why mitosis is needed for the cut to heal.2 marks
  2. A spider plant grows small plantlets on long stems. When these are planted in soil, each plantlet grows into a new plant that looks identical to the parent plant.
    State two other uses of mitosis in a living organism, apart from asexual reproduction.2 marks
  3. A student wants to find out whether cells at the tip of an onion root divide more often than cells further up the root. She cuts a thin slice from the tip of the root and another slice from 2 cm higher up. She stains each slice to show the nuclei and views it under a light microscope, counting how many cells are dividing.
    State a testable hypothesis for the investigation, with a scientific reason, and identify the independent variable.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).