6.5 - Stem Cells

Question 1

Define differentiation

Answer 1

Process where cells become differentiated, this involves cells selectively expressing genes of its genome.

Question 2

Define stem cells

Answer 2

Undifferentiated cells capable of differentiating into any variety of specialised cell type within an organism for the growth & repair of tissue

Question 3

What happens to stem cells once they differentiate (in terms of the cell cycle)?

Answer 3

They enter G0. They no longer divide

Question 4

Why must stem cell activity be controlled?

Answer 4

• If they don’t divide fast enough, the tissues may age (called ageing), as the cells are not replaced efficiently
• If the cells divide too fast - this is uncontrolled division, causing a build up of cells (a tumour), which could lead to cancer.

Question 5

Define totipotent.

Define pluripotent.

Define multipotent.

Answer 5

Totipotent: Can differentiate into any type of cell and form a whole organism

Pluripotent: Can differentiate into any cell type - but not a whole organism

Multipotent: Can only differentiate into a range of cell types of a certain tissue

Question 6

Explain blood cell replacement of erythrocytes.

Answer 6

Erythrocytes have a role in transporting oxygen around the body

• Lack of nucleus and organelles maximises their function
• Have a 120 day lifespan - must be constantly replaced
• Body produces 3bn erythrocytes per kg of body mass per day

Question 7

Explain blood cell replacement of neutrophils.

Answer 7

Neutrophils have a role in the immune system - most common phagocyte

• Lifespan of 6 hours
• Stem cells in bone marrow produce 1.6bn neutrophils per kg of body mass per day (more during infection)

Question 8

Explain how embryonic stem cells are a source of stem cells.

Answer 8

Embryonic Stem Cells…

• Totipotent, present during early embryo development
• After 7 days, blastocyst (mass of cells) form pluripotent cells and remain in this state in fetus until birth

Question 9

What are the different sources of stem cells?

Answer 9

• Embryonic stem cells, present in young embryo
• Blood from umbilical cord (has multipotent adult stem cells)
• Adult stem cells in developed tissue such as bone marrow
  
  • ​no invasive surgery is needed to get the stem cells​
  • can be stored, cultured tissues of these stem cells will not be rejected by body
• Tissue cells can be induced to become stem cells
  
  • known as iPS (induced pluripotent cells)

Question 10

How do stem cells repair damaged tissues and treat neurological conditions?

Answer 10

• Bone marrow stem cells used to treat blood diseases - e.g. leukaemia
• Stem cells repair spinal cord of rats
• Stem cells treated type 1 diabetes of a mice
• Retinal stem cells produce new light-sensitive cells
• Treat arthritis, stroke, burns, blindness, deafness, heart disease

Neurological Disease

• Stem cells become nerve tissue to treate Alzheimer’s and Parkinson’s

Question 11

How are stem cells used in developmental biology?

Answer 11

Develpomental biology: Study of how organisms develop, grow and mature

Stem cells are used to …

• Study how differentiation occurs - how cells specialise
• Study what occurs when cell specialisation goes wrong
• Trying to see if they can re-enable differentiation in adult cells to repair tissue, or re-grow organs/limbs

Question 12

How are xylem and phloem vessels produced?

Answer 12

By mitosis in meristematic tissue

Xylem:

• Lignin deposited in cell wall to strengthen and waterproof
• Cells die and contents removed as ed walls break
  
  • Form continuous hollow column
• In some areas, lignification is incomplete, bordered pits form

Phloem:

• Sieve tube elements lose nuclei and organelles, end walls develop sieve pores forming sieve plates between elements
• Companion cells retain organelles and nuclei, they carry out metabolism to obtain and use ATP to actively load sugar