AQA GCSE Biology (8461) — Cell Biology
Every time a patient with a spinal cord injury hopes to walk again, scientists look to stem cells for an answer. A stem cell is an undifferentiated cell capable of giving rise to many more cells of the same type, and from which specialised cells arise through differentiation.
In medicine, stem cells can treat conditions where cells are damaged. For example, they can create insulin-producing pancreatic cells for Type 1 diabetes or new nerve cells to treat paralysis. However, these medical benefits must be weighed against severe biological risks.
Because stem cells divide rapidly by mitosis, there is a significant risk they may continue dividing uncontrollably inside the patient, leading to the formation of a tumour or cancer. Another major risk is viral transmission. Stem cells can become contaminated with a virus while being grown in the lab, meaning that even if the original donor is healthy, there is a risk of a transfer of viral infection to the vulnerable patient.
Patients also face the risk of their immune system attacking the transplanted cells, requiring them to take immunosuppressant drugs. This specific risk can be bypassed using therapeutic cloning, a process that produces an embryo with the exact same genes as the patient.
Understanding therapeutic cloning explains how scientists can create perfectly matched replacement cells. Because the cells are genetically identical to the patient, they are not rejected by the patient's immune system.
The debate around stem cell research asks us to choose between treating living patients and protecting embryos. Most embryos used in research are "spare" or unwanted from IVF clinics and would otherwise be destroyed. However, the primary ethical objection is that destroying these embryos destroys a potential human life.
Critics argue that an embryo is a human and it cannot give informed consent to be used in research. Furthermore, many religious groups believe that life begins at conception, making the destruction of an embryo morally wrong and viewing the technology as scientists "playing God."
Unlike humans, plants retain the ability to grow an entirely new organism from a tiny cluster of cells at any point in their lives. Plant stem cells are found in meristem tissue, located at the growing tips of roots and shoots. Meristem cells can differentiate into any plant cell type for the plant's entire lifespan.
This lifelong ability allows scientists and farmers to clone plants through a causal mechanism called tissue culture (micropropagation):
Cloning plants using meristems offers massive economic and conservation benefits. Farmers can produce genetically identical crops with desirable features, such as disease resistance or high yield, quickly and economically. Because it uses lab conditions, crops can be produced independently of the seasons. For conservationists, cloning is a vital tool to save rare species from extinction, particularly plants like orchids that are notoriously difficult to breed naturally.
However, because the clones are genetically identical, they have no genetic variation. This means an entire agricultural population is highly vulnerable to being wiped out by a single new disease.
Students often state that stem cells catch viruses inside the patient. Actually, the risk of 'transfer of viral infection' occurs because the virus contaminates the stem cells while being grown in the lab.
Students forget that therapeutic cloning involves cell division; always mention that an electric shock triggers the cell to divide by mitosis.
In 'Evaluate' questions about stem cells, examiners expect you to give arguments for, arguments against, and crucially, a justified conclusion (e.g., weighing the suffering of a living patient against the potential human life of an embryo).
When describing the advantages of plant cloning, always use the exact AQA phrase 'quickly and economically' rather than just saying 'fast and cheap'.
For ethical objections, always use the exact mark scheme phrase 'potential human life' when explaining why some people oppose the use of embryonic stem cells.
Stem cell
An undifferentiated cell capable of giving rise to more cells of the same type, and from which specialised cells can arise from differentiation.
Differentiation
The process by which an undifferentiated stem cell becomes a specialised cell with a specific function.
Mitosis
A type of cell division that results in two genetically identical daughter cells, used for growth, repair, and cloning.
Tumour
A mass of abnormally growing cells that forms when cells divide uncontrollably by mitosis.
Viral transmission
The process by which a virus is spread from one host or lab culture to another, often referred to by AQA as the 'transfer of viral infection'.
Therapeutic cloning
A process where an embryo is produced with the exact same genes as the patient, so its stem cells are not rejected by the patient's immune system.
Enucleated egg cell
An egg cell that has had its nucleus removed, used in the process of therapeutic cloning.
Blastocyst
An early-stage embryo consisting of a hollow ball of cells, which forms approximately 5 days after fertilisation or cloning and contains pluripotent stem cells.
Pluripotent
Stem cells that have the ability to differentiate into any type of specialized human cell.
Meristem
A region in a plant (at the root and shoot tips) where undifferentiated stem cells are found that can divide by mitosis throughout the plant's life.
Tissue culture
A plant cloning method where small groups of cells are grown in a sterile nutrient medium with hormones to quickly and economically produce identical clones.
Explants
Small groups of cells scraped from a plant to be used in tissue culture.
Put your knowledge into practice — try past paper questions for Biology
Stem cell
An undifferentiated cell capable of giving rise to more cells of the same type, and from which specialised cells can arise from differentiation.
Differentiation
The process by which an undifferentiated stem cell becomes a specialised cell with a specific function.
Mitosis
A type of cell division that results in two genetically identical daughter cells, used for growth, repair, and cloning.
Tumour
A mass of abnormally growing cells that forms when cells divide uncontrollably by mitosis.
Viral transmission
The process by which a virus is spread from one host or lab culture to another, often referred to by AQA as the 'transfer of viral infection'.
Therapeutic cloning
A process where an embryo is produced with the exact same genes as the patient, so its stem cells are not rejected by the patient's immune system.
Enucleated egg cell
An egg cell that has had its nucleus removed, used in the process of therapeutic cloning.
Blastocyst
An early-stage embryo consisting of a hollow ball of cells, which forms approximately 5 days after fertilisation or cloning and contains pluripotent stem cells.
Pluripotent
Stem cells that have the ability to differentiate into any type of specialized human cell.
Meristem
A region in a plant (at the root and shoot tips) where undifferentiated stem cells are found that can divide by mitosis throughout the plant's life.
Tissue culture
A plant cloning method where small groups of cells are grown in a sterile nutrient medium with hormones to quickly and economically produce identical clones.
Explants
Small groups of cells scraped from a plant to be used in tissue culture.
