In mature animals, cell division is mainly restricted to repair and…

The idea

In mature animals, most growth has already occurred, so cell division by mitosis is not used for general growth as it is in young organisms. Instead, division is mainly restricted to repairing damaged tissues and replacing worn-out or dead cells. For example, skin cells divide to replace those lost from the surface, and bone marrow stem cells divide to produce new red blood cells and some white blood cells. This limited division means that mature animals cannot easily regenerate complex body parts, unlike many plants. It also means that some tissues, such as nervous tissue, have very limited replacement capacity. Understanding this helps explain why damage to certain organs can be permanent and why the body relies on specific stem cell populations for renewal.

What earns the marks

• In mature animals, most growth is complete, so cell division is not mainly for increasing body size.
• Cell division in mature animals is mainly for repairing damaged tissues and replacing worn-out or dead cells.
• Examples include division of skin cells to replace those lost from the surface and division of bone marrow stem cells to produce new blood cells.
• Some tissues, such as nervous tissue, have very limited capacity for cell division and replacement.
• The body relies on specific stem cell populations, such as those in bone marrow, for replacement of certain cell types.

Common mistakes and how to put them right

• Thinking that mature animals do not carry out cell division at all.

  Put it right: The error is absolute, and the correction is that division continues mainly for repair and replacement.

• Confusing repair and replacement with growth.

  Put it right: The error is treating them as the same, and the correction is that growth is mostly complete in mature animals whereas repair and replacement continue.

• Assuming all tissues are replaced at the same rate.

  Put it right: The error is overgeneralising, and the correction is that some tissues, such as nervous tissue, have very limited replacement.

Exam tips

• Link cell division in mature animals to specific examples such as skin repair or red blood cell replacement.
• Use the phrase 'repair and replacement' rather than just 'growth' when describing division in mature animals.
• If comparing with plants, state that plants can grow and regenerate more readily because many plant cells retain the ability to differentiate.