Stem Cells (AQA GCSE Biology): Revision Note

Specialised cells: Review

• Multicellular organisms are organisms made from more than one cell

  • Humans are multicellular, made up of trillions of cells

• Specialised cells have a particular structure and composition that allow them to perform a specific function, and they form through a process known as differentiation

  • There are about 250 specialised cell types in the human body (e.g. red blood cell, motor neurone cell etc.)

• If a specialised cell is able to divide by mitosis, the daughter cells produced will be the same type of specialised cell

• These cells have lost their ability to differentiate into other types of cell

Stem cells

• If cells are isolated at an early stage of growth (before they have started to become too specialised), they can retain their ability to grow into a range of different types of cells – these are stem cells

• A stem cell is an undifferentiated cell of an organism which is capable of dividing (giving rise) to many more cells of the same type (undifferentiated stem cells)

• From these cells, other cells can arise through the process of differentiation

• The table below summarises the different types of stem cell required for this course:

Stem cells

Stem cells: Animals v plants

• Embryonic stem cells are important as they help to form all of the different tissues and organs needed during development to form a new individual

• The role of adult stem cells is predominantly to replace cells lost through damage or to produce new cells for growth – although the bone marrow has to continually make new blood cells throughout life

• In plants, meristem cells are unspecialised cells which can differentiate into the cells needed by the plant in regions where growth is occurring

• For example, meristem cells in the roots can differentiate into root hair cells as well as other cells required in this part of the plant

• The stem cells found in the meristems of plants retain the ability to differentiate into any type of plant cell throughout the life of the plant

Stem cells in medicine

• It is possible to grow human embryos in the lab and to extract embryonic stem cells from them

• These embryonic stem cells can then be encouraged to differentiate into most types of specialised cell

• Scientists and doctors could use stem cell technology to repair damaged organs by growing new tissue from stem cells produced by embryos created using genetic information from the patient

• Adult stem cells can also be cultured in the lab and made to differentiate into specialised cells, but of fewer types than embryonic stem cells (predominantly cells of the blood)

• Stem cells could be used to cure many diseases in the future, such as diabetes and paralysis:

Stem cell treatment

Therapeutic cloning

• In therapeutic cloning, an embryo is produced with the same genes as the patient

• A 5-day-old embryo is the best source of embryonic stem cells

• Stem cells from embryos created in this way are not rejected by the patient’s body

• So they may be used for medical treatment without the patient having to take drugs to suppress their immune system (which reduce the body’s ability to fight infection)

The process of therapeutic cloning

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Evaluating stem cells in medicine

Benefits of using stem cells:

• Great potential to treat a wide variety of diseases from diabetes and paralysis

• Organs developed from a patient’s own stem cells reduces the risk of organ rejection and the need to wait for an organ donation

• Adult stem cells are already used successfully in a variety of treatments, acting as proof of benefits

Risks/issues of using stem cells:

• Stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient

• There is a risk of cultured stem cells accumulating mutations that can lead to them developing into cancer cells

• Low numbers of stem cell donors

Social issues:

• It is possible for embryonic stem cells to be collected before birth (from amniotic fluid) or after birth (umbilical cord blood) and stored by a clinic – but this can be expensive and isn’t an option for everyone

• A lack of peer-reviewed clinical evidence of the success of stem cell treatments

• Educating the public sufficiently about what stem cells can and cannot be used for

Ethical issues

• Stem cells may be sourced from unused embryos produced in IVF treatment – is it right to use them? Who gives permission?

• Is it right to create embryos through therapeutic cloning and then destroy them? Who owns the embryo?

• Should an embryo be treated as a person with human rights? Or as a commodity?

Stem cells in plants

• Unlike in animals, plant stem cells can be obtained easily, and without ethical objection, from meristems

• They can then be used to produce clones of plants quickly and economically

  • Plant clones can be produced in weeks at a relatively low cost for their potential value

• Rare species at risk of extinction as a result of human activity can be cloned to protect them and maintain biodiversity

  • The plants produced are clones, so although numbers increase, genetic diversity within clones is low

  • Cloning rare plants gives scientists more time to study them to see if they can produce any compounds of interest

• Crop plants with special features such as disease or pest resistance can be cloned to produce large numbers of identical plants for farmers

  • This reduces the need to use chemicals such as pesticides, which has environmental benefits