Cell division — AQA GCSE Combined Science: Trilogy
Chromosomes, the cell cycle and mitosis, and stem cells in embryos, adult animals and plant meristems.
Revision notes
3 short notes, in the order of the specification. Each one in short:
Chromosomes are structures in the nucleus of a cell, made of DNA molecules. Each chromosome carries a large number of genes, and in body cells the chromosomes are normally found in pairs. Keep the order straight: a nucleus contains chromosomes, each chromosome is a long DNA molecule, and each chromosome carries many genes.
The cell cycle is the series of stages in which a cell divides to form two genetically identical cells. First the cell grows, increases its sub-cellular structures and replicates its DNA. In mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide.
A stem cell is an undifferentiated cell that can give rise to many more cells of the same type, and from which certain other cells can arise by differentiation. Stem cells are found in human embryos, adult bone marrow and plant meristems. They may help treat conditions such as diabetes and paralysis, but there are risks, such as transfer of viral infection.
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Quick check questions
What are chromosomes made of, and where are they found?
Show answer
DNA molecules, in the nucleus.
Name the three overall stages of the cell cycle.
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Growth and DNA replication; mitosis; division of the cytoplasm and cell membranes.
What does mitosis produce?
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Two genetically identical cells.
Why are stem cells from therapeutic cloning not rejected?
Show answer
The embryo has the same genes as the patient.
Where are stem cells found in plants?
Show answer
In meristems, throughout the life of the plant.
Frequently asked questions
What are the stages of mitosis?
For AQA GCSE you need the three overall stages of the cell cycle, not the separate phases of mitosis. First the cell grows, makes more sub-cellular structures and replicates its DNA. Then, in mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide.
Why is mitosis important?
Mitosis is important for the growth and development of multicellular organisms, because it produces new cells that are genetically identical to the parent cell. In mature animals, cell division is mainly restricted to repair and replacement, for example when new skin cells heal a cut. It also happens as root and shoot tips lengthen.
Why are stem cells useful in medicine?
Stem cells are useful because they are undifferentiated and can differentiate into other types of cell. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning, an embryo with the same genes as the patient is produced, so its stem cells are not rejected by the patient's body.
What are the risks of using stem cells?
Stem cell treatments carry potential risks, such as the transfer of viral infection. Some people also have ethical or religious objections to using stem cells from embryos. In an evaluation answer, weigh at least one benefit, such as possible treatment of diabetes or paralysis, against a risk or objection, then reach a conclusion.
How are plant stem cells used?
Stem cells from plant meristems can be used to produce clones of plants quickly and economically. Rare species can be cloned to protect them from extinction, and crop plants with special features, such as disease resistance, can be cloned to give farmers large numbers of identical plants. Meristem tissue can form any type of plant cell.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026