Mitosis and the cell cycle: Students should be able to recognise and describe situations in given contexts where mitosis is occurring.

The idea

To recognise where mitosis is occurring, look for situations involving growth, repair or replacement of body cells. Mitosis produces genetically identical diploid cells, so it happens when an organism needs more identical cells, not when gametes are being formed. In a plant, mitosis occurs in the meristems at root tips and shoot tips, where new cells are added for growth. In an animal, it occurs during growth of a young organism, healing of a cut or broken bone, and replacement of worn-out cells such as skin or blood cells. In a diagram or written context, clues include a parent cell dividing into two identical daughter cells, chromosomes being copied and separated, or a tissue increasing in cell number. If the context involves gametes or genetic variation, meiosis is more likely.

What earns the marks

• Recognise growth of a multicellular organism as a situation where mitosis occurs.
• Recognise repair of damaged tissue, such as healing a cut or mending a bone, as a situation where mitosis occurs.
• Recognise replacement of worn-out cells, such as skin or blood cells, as a situation where mitosis occurs.
• Identify meristems in root tips and shoot tips as plant regions where mitosis occurs.
• Describe the outcome of mitosis in the context: two genetically identical diploid daughter cells.
• Distinguish mitosis from meiosis by noting that mitosis does not produce gametes or genetic variation.

Common mistakes and how to put them right

• Choosing gamete formation as an example of mitosis.

  Put it right: Gametes are produced by meiosis, so gamete formation is not a mitosis context.

• Assuming any cell division is mitosis.

  Put it right: Check whether the context involves growth, repair or replacement of body cells rather than gamete production.

• Ignoring the word identical when describing daughter cells.

  Put it right: Mitosis produces genetically identical cells, which is why it is suitable for growth and repair.

• Confusing plant growth with mitosis occurring throughout the plant.

  Put it right: Mitosis for growth occurs mainly in meristems such as root tips and shoot tips.

Exam tips

• Read the context carefully and look for keywords such as growth, repair, replacement, root tip or shoot tip.
• When describing a situation, state what is dividing and why, for example a root tip cell dividing to add new cells for growth.
• Use the phrase genetically identical diploid daughter cells to show understanding of the outcome of mitosis.
• If a context mentions gametes or variation, explain that this indicates meiosis rather than mitosis.