Stem Cells

Question 1

What are stem cells?

Answer 1

Undifferentiated cells which have not “committed” to a particular cell “fate” and have the potential to differentiate into any cell type.

Once differentiated and specialised, they lose the ability to divide and enter the G0 phase.

Question 2

What are the three levels of stem cell potency?

Answer 2

• Totipotent
• Pluripotent
• Multipotent

Question 3

What can totipotent stem cells do?

Answer 3

Can differentiate into any type of cell.
- Zygotes and it’s first 8-16 cells are totipotent.
- Can also differentiate into extra-embryonic tissues.

Question 4

What can pluripotent stem cells do?

Answer 4

Can form all tissue types but not the whole organisms.
- They are present in early embryos - in the blastocyst’s inner cell mass.

Question 5

What can multipotent stem cells do?

Answer 5

Can only form a range of cells within a certain tissue type.
- e.g. Haematopoietic stem cells

Question 6

What are Haematopoietic stem cells?

Answer 6

Stem cells found in the bone marrow which are multipotent and can form a limited number of cells (blood cell types).

Question 7

How are blood cells replenished?

Answer 7

> erythrocytes - lifespan of around 120 days and need constant replenishing - approx 3 billion erythrocytes produced per kg of body mass daily.

> Neutrophils - 1.6 billion per kg produced each hour - rate increases during infection.

Question 8

What are the two sources of animal stem cells?

Answer 8

• Embryonic - totipotent stem cells present during early embryo development. Blastocyst forms after around 7 days - inner cell mass is pluripotent.
• Tissue - multipotent stem cells found in specific areas that can be artificially triggered into pluripotency. Can be harvested from umbilical cords to avoid invasive surgery.

Question 9

How are stem cells being used?

Answer 9

• Treating burns (stem cells grown on biodegradable meshes)
• Drug trials
• Developmental biology

Question 10

What are the potential uses for stem cells?

Answer 10

• type 1 diabetes - targets insulin producing pancreatic cells
• heart disease - repairs muscle tissue post heart attack
• spinal injuries - differentiate into nerve cells - successful in restoring movement to paralysed rats
• macular degeneration - replaces retinal cells to treat blindness

Question 11

What are the ethical concerns regarding stem cells?

Answer 11

Religious objections to the use of embryos - life begins at conception and destroying embryos is considered murder.

The law in the UK is that embryos can be created in a laboratory specifically for use as stem cells.

Question 12

Where are stem cells found in plants?

Answer 12

In the meristematic tissue - tips and roots of shoots.

They are found in the apical meristems and vascular cambium.