Students should be able to describe the function of stem cells in embryos,…

The idea

Stem cells have different roles depending on where they are found. In embryos, stem cells are pluripotent: they can differentiate into almost any cell type, which allows the embryo to develop all its tissues and organs. In adult animals, stem cells are found in tissues such as bone marrow and can replace worn-out or damaged cells, for example making new blood cells, but they are usually more limited in the cell types they can become. In plants, stem cells are found in meristems at the tips of roots and shoots; they divide to produce new cells for growth throughout the plant's life and can form any plant tissue. You should be able to compare these three locations and link each to its function, such as embryonic development, repair in adults, and unlimited growth in plants.

What earns the marks

• Describes embryonic stem cells as able to differentiate into most cell types for growth and development of the embryo.
• Describes adult stem cells as replacing damaged or worn-out cells in specific tissues, such as blood cells from bone marrow.
• Describes meristem stem cells in plants as providing new cells for growth at root and shoot tips.
• Compares the three sources, noting that embryonic and meristem cells are more versatile than most adult stem cells.
• Links each stem cell function to a named process such as development, repair or plant growth.

Common mistakes and how to put them right

• Saying adult stem cells can become any cell type.

  Put it right by stating that they are usually limited to certain cell types.

• Confusing meristems with all plant cells.

  Put it right by stating that meristems are specific regions of active cell division.

• Describing embryonic stem cells as only repairing damage.

  Put it right by stating that their main role is development of the embryo.

Exam tips

• Structure your answer by location: embryo, adult animal, plant meristem.
• Use comparative language such as more versatile or more limited to show understanding.
• Name a specific adult stem cell location, such as bone marrow, to support your description.