B2.1 Supplying the Cell - Differentiation & Stem cells

Question 1

What is differentiation?

Answer 1

Process by which stem cells become specialised into different types of cells

Question 2

What is produced once a sperm cell enters an egg?

Answer 2

Zygote

Question 3

By what process does a zygote divide?

Answer 3

Mitosis

Question 4

The zygote is composed of what type of cells?

Answer 4

Stem cells

Question 5

When does a zygote become an embryo?

Answer 5

3-5 days after fertilisation

Question 6

How do the cells of a zygote differ from an organisms somatic cells?

Answer 6

They are unspecialised and can therefore differentiate into any type of specialised cell.

Question 7

Where are stem cells found in animals?

Answer 7

Embryos - Embryonic stem cells Brain, bone marrow, skin, liver - Adult stem cells N.B Multipluripotent stem cells have also now been isolated in the umbilical cord

Question 8

Where are stem cells found in plants?

Answer 8

The meristems - unspecialised cells found in the root tips, shoot tips and in rings around the stem

Question 9

How do the cells in the meristem differ from normal plant cells?

Answer 9

Differentiated plant cells cannot divide as they have thick & rigid cell walls Meristem cells are much smaller, have thin walls, small vacuoles and no chloroplasts

Question 10

State a key difference between specialised plant and animal cells?

Answer 10

Once differentiated animal cells can only divide to produce that specialised cells. Plant cells however, under the right conditions, can become unspecialised and then re-specialise in order to adapt to their environment.

Question 11

Name 5 types of specialised cells that a stem cell could differentiate into.

Answer 11

Animal

• Gamete e.g sperm cell, ovum
• Muscle cell
• Adipocyte cell
• Osteoblast
• Blood cell e.g erythrocyte, neutrophils
• Nerve cell
• Cilliate epithelial cell
• Goblet cell

Plant

• Palisade cells
• Root hair cell
• Guard cell

Question 12

How is a red blood cell specialised for its role?

Answer 12

• Biconcave discs - increases surface area
• Haemoglobin - binds to and releases oxygen
• Enucleated - more room for oxygen transport

Question 13

How is sperm cell is specialised to transfer genetic material?

Answer 13

• Flagellum - movement
• Mitochondria - provide energy for movement
• Acrosome - contains digestive enzymes to allow breakdown the outer membrane of ovum

Question 14

How is an adipocyte specialised for its role?

Answer 14

• Can expand to 1000 times original size
• Small layer of cytoplasm
• Fat reservoir.

Question 15

What is the function of a goblet cell?

Answer 15

Produces mucus to trap dust mucus and bacteria which the cillia then waft back up the throat to be swallowed.

Question 16

How are palisade cells adapted for their function?

Answer 16

• regularly shaped - can be closely packed cells that form a continuous layer at the top of the leaf
• Large surface area - able to absorb more light for photosynthesis
• Packed with chloroplasts - for photosynthesis

Question 17

How are root hair cells adapted for their function?

Answer 17

• Surround the stoma and regulate the rate of transpiration and CO₂ uptake.
• Inner wall thicker causing the ‘bean-like’ shape and gap when turgid
• Open to allow exchange
• Close to prevent exchange

Question 18

What type of cells can adult stem cells differenetiate into?

Answer 18

Only into cells from the type of tissue where they are found.

Question 19

Why are adult stem cells not as useful for medical research?

Answer 19

They only differentiate into a narrow range of cell types

Question 20

What are embryonic stem cells and why are they more useful to stem cell research?

Answer 20

• Cells taken from 3-5 day old zygotes
• Thye can specialise into any type of specialised cells
• Potential to cure and treat disease

Question 21

Why are embryonic stem cells controversial?

Answer 21

Embryos are killed to obtain the cells.

Question 22

What are induced-pluripotent stem cells and how may they be useful?

Answer 22

• Adult somatic cells altered to have properties of embryonic stem cells
• May allow use of reprogrammed cells instead of embryonic stem cells
• Solution to immune system rejection of ‘foreign’ stem cells