AQA GCSE Stem Cells (Biology)
Stem Cells
A stem cell is an undifferentiated cell which can produce more cells of the same type, and from which certain specialised cells can form due to differentiation.
Stem Cells in Animals.
There are two main types of stem cells in animals
1. Embryonic stem cells
2. Adult stem cells
Embryonic stem cells
Embryonic stem cells are found in the early stages of the embryo.
An embryo is a ball of cells that is formed once the zygote (fertilised egg) divides by mitosis.
Below is a diagram to show the formation of an embryo, starting with the sperm and egg cell.
Embryonic stem cells are known to have the potential to form most cell types. This means that they can differentiate to form most types of specialised cell.
Adult Stem cells.
Adult stem cells are already partially differentiated, so they can only form limited cell types.
Adult stem cells in the bone marrow can differentiate to form specialised cells such as blood cells.
Stem Cells in plants
Stem cells in plants are found in the meristem tissue. Meristem tissue in plants is found in regions where growth is actively happening such as the tips of roots and shoots.
Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.
This is different to animals. Once a stem cell in an animal has differentiated and formed a specialised cell, it will stay as that cell.
Plants can be cloned through cuttings because the meristem cells can differentiate to form specialised cells throughout the life of the plant. This allows meristems to produce clones of plants quickly and economically.
Rare species can be cloned to protect from extinction. Banana trees are produced by cloning.
Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers. This way all of the plants would have the advantageous characteristic
Using Stem Cells in Medicine
Stem cells can be used in medicine to treat conditions such as diabetes and paralysis. Embryonic stem cells are the ideal cell type to try to treat these conditions.
Currently, stem-cell treatments are being explored experimentally for conditions like diabetes and paralysis, though they’re not yet standard practice in mainstream medicine.
The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.
At the moment all of this work is experimental, but in the future, we could see treatments like this!
Diabetes and stem cells.
Diabetes is a condition where the blood sugar level cannot be controlled because the pancreas cells do not produce enough insulin.
Embryonic stem cells would undergo differentiation to form a type of pancreatic cell which produces insulin. These insulin producing cells would then be transplanted into the patient. The patient would then produce normal levels of insulin and would no longer suffer from diabetes.
Paralysis and stem cells.
Paralysis can occur when the nerve cells in the spinal cord are damaged such as during a car accident.
Embryonic stem cells could undergo differentiation to form nerve cells which could then be transplanted into the spinal cord to replace the damaged nerve tissue.
Therapeutic cloning
In therapeutic cloning an embryo is produced with the same genes as the patient, who suffers from a disease. In this example the patient suffers form diabetes and cannot produce insulin.
The woman on the left will supply an unfertilised egg cell, the nucleus is discarded leaving an enucleated egg cell.
The man on the right who needs treatment will supply a body cell, the nucleus is extracted and the body cell discarded.
The extracted nucleus is inserted into the enucleated egg cell. This egg cell now behaves like a fertilised egg cell, so it divides by mitosis to form an embryo.
The cells of the embryo are genetically identical to the body cells from the man, because the man provided the nucleus.
This embryo is grown in a petri dish, hormones are used to make the embryonic stem cells differentiate into specialised cell types e.g. pancreatic insulin producing cells.
These cells are then transplated into the man’s pancreas where they produce insulin.
In theory he will not longer have diabetes.
As the transplanted cells are gentically identical, they will not be rejected by the bodies immune system!
See the diagram below
Benefits, Risks, social and ethical issues, for the use of stem cells in medical research and treatments.
Practical benefits
Treatment of diseases and injuries: Stem cells can potentially replace damaged or diseased cells, offering treatments for conditions such as Parkinson’s disease, type 1 diabetes, spinal cord injuries, and some forms of blindness.
Regenerative medicine: They may enable organs and tissues to be repaired or grown, reducing dependence on transplants and donor shortages.
Drug testing and development: Stem cells can be used to grow human tissues for testing new drugs safely before clinical trials.
Understanding human development: Studying stem cells helps researchers understand how different cell types develop and what goes wrong in disease processes.
Risks
Tumour formation: If stem cells divide uncontrollably, they can form cancers.
Immune rejection: Transplanted stem cells may be rejected by the patient’s immune system, requiring immunosuppressants.
Incomplete differentiation: Cells might not fully specialise into the required tissue, leading to ineffective or harmful outcomes.
Unproven treatments: Some clinics offer unregulated stem cell therapies with little scientific backing, putting patients at risk.
Cost and accessibility: Stem cell treatments are expensive and technically demanding, potentially limiting availability.
Social issues
Access and fairness: High costs may mean only wealthy patients benefit, raising concerns about inequality in healthcare.
Exploitation of patients: Vulnerable patients may be persuaded to pay for untested or unsafe “miracle cures.”
Hype vs reality: Public expectations are sometimes raised too high compared to what is scientifically possible in the near future.
Impact on research priorities: Resources may be diverted to stem cell work at the expense of other valuable research areas.
Ethical issues
Embryonic stem cells: Obtaining these involves destroying early-stage embryos, which some people believe is morally wrong because they view the embryo as potential human life.
Consent: Ethical concerns about whether embryos donated for research were given with fully informed parental consent.
Alternatives: Adult stem cells reduce ethical concerns, since they do not involve embryos, but may not always have the same flexibility. Recent research has indicated that some stem cells collected from the umbilical cord act as embryonic stem cells. Using these would help to avoid some of the ethical issues.
Animal use: Stem cell research often involves testing in animals, raising animal welfare concerns.
Long-term consequences: Editing or altering stem cells raises fears of unintended genetic changes or even future use in human enhancement rather than medicine.
Practice Question
1.Define the term stem cell
2.Name the two main types of animal stem cells.
3. Explain how the two types of stem cell named in question 2 are different.
4. Plants contain stem cells. Name the tissue that contains these stem cells.
5. Therapeutic cloning is used to produce pancreatic tissue for treating diabetes. Explain the advantage of using this method.