Stem Cells and Differentiation (2.1.6)

Question 1

What are stem cells?

Answer 1

Unspecialised cells that are able to develop into different types of cells.

This process of specialisation is called differentiation.

Question 2

Provide an example of differentiation in humans and plants

Answer 2

Humans

In the bone marrow - adult stem cells divide and differentiate to replace erythrocytes and neutrophils

Plants

In the meristems - stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes

Question 3

Provide three examples of stem cells in medicine.

Answer 3

Heart disease - Make replacement heart cells to repair damaged tissue.

Alzheimer’s - Regrow healthy nerve cells in the brain.

Parkinson’s - Transplanted stem cells to regenerate the dopamine-producing cells.

Question 4

List 3 specialised types of cells in multicellular organisms (animals) and how they are specialised for their function.

Answer 4

Erythrocytes

Biconcave disc shape - increased surface area for gas exchange
No nucleus - more room for haemoglobin
Flexible to squeeze through narrow capillaries.

Neutrophils

Flexible shape - able to engulf foreign particles or pathogens
Many lysosomes - break down engulfed particles

Sperm

Flagellum - swim to the egg
Lots of mitochondria - energy to swim
Acrosome - digestive enzymes to penetrate the surface of the egg

Question 5

List 3 specialised types of cells in plants and how they are specialised for their function.

Answer 5

Palisade mesophyll (found in leaves)

Many chloroplasts - absorb a lot of sunlight
Thin walls - CO2 can easily diffuse into the cell

Root hair cells

Large surface area - for absorption
Thin permeable cell wall - entry of water and ions
Extra mitochondria - energy for active transport

Guard cells

In the light, they take up water that makes them turgid.
Thin outer walls and thickened inner walls force them to bed outward. Stomata open for gas exchange.

Question 6

Specialised animal tissues

Answer 6

Epithelial

Joined by interlinking membranes and membranes at their base

Ciliated epithelial cells (airways) - beat to move particles
Microvilli ( small intestine) - folds in the cell membrane to increase surface area
Squamous epithelial (lungs) - very thin to allow efficient diffusion of gasses

Cartilage

Connective tissue is found in the ears, nose and the end of bones.
Contains fibres of the proteins elastin and collagen.

Muscle

Needs to be able to shorten in order to move bones.