Cell Specialisation and Stem CellsAQA GCSE Biology: Revision notes
Section 1
What makes a cell 'specialised'?
A specialised cell has a structure adapted to carry out one particular job efficiently. In animals, examples include sperm cells (streamlined, tail for swimming, many mitochondria for energy), nerve cells (long, with connections to carry electrical impulses) and muscle cells (contain proteins that contract to shorten the cell). In plants, root hair cells (large surface area for water/mineral uptake), xylem cells (hollow, strengthened tubes for water transport) and phloem cells (form tubes for transporting sugars) are specialised.
- Structure always relates directly to function
- Specialised cells work together to form tissues, then organs, then organ systems
A sperm cell's long tail and streamlined head are adaptations for swimming towards an egg.
Section 2
Why do cells differentiate?
Differentiation is the process by which a cell changes to become specialised for its job.
- Most animal cells differentiate at an early stage of development and then lose the ability to change further
- Many plant cells retain the ability to differentiate throughout life
This is why plants can regrow damaged parts and be cloned from small cuttings, while most animal tissue repair relies on limited stem cell populations rather than fully differentiated cells changing type.
Don't say a differentiated cell can 'undifferentiate' back into a stem cell — in animals this does not normally happen.
Section 3
What is a stem cell?
A stem cell is an undifferentiated cell that can divide to produce more cells of the same type and, through differentiation, can become other cell types.
| Source | Where found | What it can become |
|---|---|---|
| Embryonic stem cells | Early embryos | Most types of human cell |
| Adult stem cells | Bone marrow | Blood cells and some other cell types |
| Meristem cells | Growing tips of plant shoots and roots | Any type of plant cell, for the plant's whole life |
Section 4
How are stem cells used in medicine?
Embryonic stem cells can be used in therapeutic cloning to produce an embryo with the same genes as the patient, so stem cells taken from it are not rejected by the patient's immune system.
Potential benefits:
- Treating conditions such as diabetes and paralysis by replacing damaged cells
Risks and objections:
- Possible transfer of viral infection
- Ethical and religious objections to using/destroying embryos
In exam answers on stem cells, always give both a benefit AND a risk/objection — these questions are usually evaluation (AO3) questions.
Section 5
How are stem cells used in plants?
Stem cells from plant meristems can be used to clone whole plants from small numbers of cells, quickly and cheaply.
- Protecting rare species: cloning can help prevent extinction of rare plants
- Crop production: plants with desirable features (e.g. disease resistance) can be cloned in large numbers for farmers, guaranteeing the offspring have the same useful characteristics
Must Know
- A specialised cell has a structure adapted to its function (e.g. sperm, nerve, muscle, root hair, xylem, phloem cells)
- Differentiation is how a cell becomes specialised; most animal cells differentiate early, many plant cells can differentiate throughout life
- A stem cell is undifferentiated and can become other cell types
- Sources: embryonic (most cell types), adult/bone marrow (blood cells), plant meristem (any plant cell, for life)
- Therapeutic cloning avoids rejection but raises ethical/viral-infection concerns
- Plant meristem stem cells are used to clone rare species and disease-resistant crops
That's the notes covered.
Carry on to the next subtopic.