AQA GCSE Biology (8461) — Cell Biology
When you get a paper cut, your skin heals itself within a few days. This vital repair process relies entirely on a reserve of special, unspecialised cells working behind the scenes.
A stem cell is an undifferentiated cell of an organism which is capable of giving rise to indefinitely more cells of the same type, and from which certain other kinds of cell arise by differentiation.
Stem cells have two core capabilities. First, they divide by mitosis to produce genetically identical copies. Then, they differentiate to become specialised cells with specific functions.
Embryonic stem cells are found in early human embryos, such as those left over from IVF treatments.
Their biological role is to allow the embryo to develop into a complex, multi-cellular organism by producing all required specialised tissues. To achieve this, embryonic stem cells have the incredible ability to differentiate into most types of human cells.
As animals develop, their cells lose most of their ability to differentiate. However, adult stem cells remain in specific locations, such as the skin, umbilical cord, and bone marrow.
Their primary function is to replace dying cells and repair damaged tissues. Their potency is more limited than embryonic cells; they can form many types of cells including blood cells. For example, bone marrow stem cells specifically differentiate into red blood cells to carry oxygen, white blood cells to fight infection, and platelets for blood clotting.
In plants, stem cells are located in meristem tissue at the growing tips of roots and shoots, as well as in buds.
Growth in these areas happens in a step-by-step sequence. First, cells divide by mitosis. Next, they undergo elongation by taking in water. Finally, they differentiate into specialised cells like xylem or phloem.
Crucially, meristem cells retain the ability to differentiate into any type of plant cell throughout the entire life of the plant. This is a major contrast to animal cells, which mostly differentiate at an early stage of development.
Stem cells offer revolutionary treatments for serious conditions. They can replace insulin-producing cells to treat diabetes, or create new nerve cells to restore neural pathways in patients with paralysis.
Therapeutic cloning is a process where an embryo is produced with the exact same genes as the patient. The immense benefit of this is that the stem cells are not rejected by the patient’s immune system because they share identical genetic information.
However, using stem cells carries biological risks, such as the potential transfer of a viral infection or the cells dividing uncontrollably to form tumours. Furthermore, there are ethical objections to using embryonic stem cells, as some people believe that destroying an embryo is destroying a potential human life.
Because plant stem cells can differentiate infinitely, meristem tissue can be used to produce a clone of a parent plant quickly and economically.
This tissue culture process is highly valuable. It is used in conservation to clone rare species and protect them from extinction. It is also vital in agriculture to mass-produce crop plants with desirable features, such as disease resistance, providing farmers with thousands of genetically identical, high-quality plants.
Students often state that embryonic stem cells can differentiate into 'all' types of human cells. The AQA specification strictly requires you to say they can form 'most' types of human cells.
When asked about plant stem cells, you must use the exact mark scheme phrase that they can differentiate into any type of plant cell 'throughout the life of the plant'.
In 6-mark evaluation questions about stem cells, examiners expect you to provide a balanced argument comparing medical benefits (e.g., curing paralysis) against biological risks (e.g., viral infections) and ethical objections.
Always describe the specific role of bone marrow stem cells using the exact phrasing: they form 'many types of cells including blood cells'.
Stem cell
An undifferentiated cell of an organism which is capable of giving rise to indefinitely more cells of the same type, and from which certain other kinds of cell arise by differentiation.
Undifferentiated
A cell that has not yet specialised to perform a specific function.
Differentiation
The process by which a cell changes to become specialised for its job.
Mitosis
A type of cell division that produces two genetically identical daughter cells.
Embryonic stem cells
Stem cells found in early human embryos that can differentiate into most types of human cells.
Adult stem cells
Stem cells found in specific locations in adults, such as bone marrow, that can form many types of cells including blood cells.
Bone marrow
The soft tissue inside bones where adult stem cells differentiate into red blood cells, white blood cells, and platelets.
Meristem tissue
Tissue in plants containing undifferentiated cells found in zones where growth can take place, such as the tips of roots and shoots.
Therapeutic cloning
A medical process where an embryo is produced with the same genetic makeup as the patient so the stem cells are not rejected.
Clone
A genetically identical individual produced from a single parent using asexual reproduction or biotechnology.
Put your knowledge into practice — try past paper questions for Biology
Stem cell
An undifferentiated cell of an organism which is capable of giving rise to indefinitely more cells of the same type, and from which certain other kinds of cell arise by differentiation.
Undifferentiated
A cell that has not yet specialised to perform a specific function.
Differentiation
The process by which a cell changes to become specialised for its job.
Mitosis
A type of cell division that produces two genetically identical daughter cells.
Embryonic stem cells
Stem cells found in early human embryos that can differentiate into most types of human cells.
Adult stem cells
Stem cells found in specific locations in adults, such as bone marrow, that can form many types of cells including blood cells.
Bone marrow
The soft tissue inside bones where adult stem cells differentiate into red blood cells, white blood cells, and platelets.
Meristem tissue
Tissue in plants containing undifferentiated cells found in zones where growth can take place, such as the tips of roots and shoots.
Therapeutic cloning
A medical process where an embryo is produced with the same genetic makeup as the patient so the stem cells are not rejected.
Clone
A genetically identical individual produced from a single parent using asexual reproduction or biotechnology.
