7.3 Stem cells

Question 1

Explain why some cells are not able to become other cell types.

Answer 1

• They are fully differentiated
• Therefore the genes for other cells are fully switched off

Question 2

What are the three types of stem cells

Answer 2

• Totipotent
• Pluripotent
• Multipotent

Question 3

Describe totipotent cells

Answer 3

• Can give rise to any type of cell

Question 4

Describe pluripotent cell

Answer 4

• Undifferentiated cell (give rise to most cells)
• But not extra embryonic cells

Question 5

Describe multipotent stem cells

Answer 5

Adult stem cells, found in bone marrow
Can produce a limited range of cells such as white and red blood cells

Question 6

How does a multipotent cell differentiate into a common myeloid progenitor
cell or a common lymphoid progenitor cell.

Answer 6

• Epigenetic modification
• Such as DNA methylation
• House keeping genes in both cell types stay switched on

Question 7

How can a fertilised egg be a source of human pluripotent stem cell.

Answer 7

• Fertilised egg is allowed to grow for a few days
• This forms a blastocyst
• Cells in inner mass are pluripotent and can be harvested

Question 8

Describe the differences between totipotent, pluripotent and multipotent
stem cells during the development of an embryo.

Answer 8

• Totipotent cells in zygote can differentiate into any cell
• Blastocyst contains pluripotent cells which can differentiate into any cell type but not embryonic membrane cells
• Cells in developing embryo are only multipotent as they can only become some types of cell

Question 9

What are the benefits of stem cells

Answer 9

• Could allow almost all cell types to be made, therefore organs and tissues can be replaced
• May avoid risk of rejection in transplants
• Could provide cells for drug testing therefore no need for animal testing