1、1 of 18 Boardworks Ltd 2011Stem Cells2 of 18 Boardworks Ltd 20113 of 18 Boardworks Ltd 2011What are stem cells?Stem cells are unspecialized cells capable of developing into many different types of cell.Stem cells found in embryos are called embryonic stem cells and develop into all the different typ
2、es of cell in the body.Adults also contain stem cells.These are found in small numbers in many organs,including bone marrow,brain,skin and muscle.4 of 18 Boardworks Ltd 2011Embryonic stem cellsAfter the eight cell stage,most of the embryonic cells become specialized and can no longer differentiate.S
3、ome will become nerve cells,others will become blood cells,muscle cells,bone cells,etc.Up until the eight cell stage,all of the cells in a human embryo are identical.At this stage,these stem cells are unspecialized and can therefore differentiate into many different types of cell.nerve cellsred bloo
4、dcellscardiac musclecells5 of 18 Boardworks Ltd 2011Adult stem cellsAdult stem cells are found in small numbers in many organs and tissues,such as bone marrow.Research has shown that some adult stem cells can be manipulated to produce many different cell types(e.g.brain stem cells can make muscle ce
5、lls).This is called plasticity.Adult stem cells normally maintain and repair damaged tissue,and,unlike embryonic stem cells,can usually only make a small number of cell types.For example,adult stem cells in the skin only normally form skin cells.6 of 18 Boardworks Ltd 2011l xylem:these cells transpo
6、rt water and minerals up the stem from the roots to the shoots and leaves Plant stem cellsPlants also have stem cells.Plant cells can differentiate to form specific cells throughout the plants life.Animal cells lose this ability early in their life cycle.Unspecialized plant cells are found in tissue
7、s called meristems.Plant stem cells can become specialized to form tissues such as:l phloem:these cells transport sugars,produced in the leaves,up and down the stem.These new types of tissue can be found in the flowers,leaves,stems and roots of the plant.7 of 18 Boardworks Ltd 2011Stem cells true or
8、 false?8 of 18 Boardworks Ltd 20119 of 18 Boardworks Ltd 2011Super starfish!What do plants and starfish have in common?Chop the stem of a plant and it will grow back.Whats more,the cut stem can grow into a completely new plant.The same is true of the starfish!If it loses an arm to a predator,it will
9、 grow back.Even better,if the predator manages to eat everything but the arm,a new individual can grow out of the remaining arm!10 of 18 Boardworks Ltd 2011Animal regenerationWhy can a starfish regenerate missing limbs?Humans and most other animals cannot do this,but scientists are studying how stem
10、 cells could be used to create new tissue and even new organs to treat disease,injury and conditions such as paralysis.The starfish contains stem cells that can divide,differentiate and produce new tissues to replace those that are lost.What type of stem cells should be used?11 of 18 Boardworks Ltd
11、2011A controversial source?Most stem cell research has used cells obtained from embryos left over from fertility treatment.These are called embryonic stem cells(ESCs)and are the most powerful type because they can turn into any type of cell.Their use in research is strongly criticized by people who
12、believe it is unethical to kill embryos for their cells.Work involving embryonic stem cells is subject to government regulation.12 of 18 Boardworks Ltd 2011If you ran the country13 of 18 Boardworks Ltd 2011Therapeutic cloning14 of 18 Boardworks Ltd 2011How could adult stem cells be used?15 of 18 Boa
13、rdworks Ltd 2011Advantages of using adult stem cellsAdult stem cells are not as powerful as embryonic stem cells,but they do have other advantages.l They come from volunteers so they are more ethically acceptable.l They are less likely to become cancerous.l A patients own stem cells could be used to
14、 treat their own disease,avoiding the problem of immune rejection.There is a great deal of research into using adult stem cells to treat diseases.They could reduce the need for organ transplants,which have long waiting lists.l It might be easier to guide their development into specific cell types.16 of 18 Boardworks Ltd 201117 of 18 Boardworks Ltd 2011Glossary18 of 18 Boardworks Ltd 2011Multiple-choice quiz
