Edexcel IGCSE Biology 复习笔记 2.2.3 Stem Cells

• A stem cell is an undifferentiated cell of an organism that is capable of dividing to produce many more cells of the same type (undifferentiated stem cells)
• In addition, stem cells can also give rise to other cell types through the process of differentiation
• The table below summarises different types of stem cells

Stem Cells Table

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

   

• Modern scientific techniques mean that 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
• There is the potential for scientists and doctors to use stem cell technology to repair damaged organs by growing new tissue from stem cells
  • The new tissue is produced by human embryos, 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 Table

Therapeutic cloning as a source of stem cells

• 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)

Diagram showing the process of therapeutic cloning for diabetes

Evaluating the use of stem cells in medicine

• There are many benefits and risks associated with using stem cells in medicine, as well as considerable ethical and social concerns

Evaluating Stem Cells in Medicine Table