Stem cells (j,k,l,m)

Question 1

What is differentiation?

Answer 1

Differentiation is the process of a cell becoming specialised, involving the selective expression of genes in a cell’s genome.

Question 2

What are stem cells?

Answer 2

Stem cells are undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism.

Question 3

Why are stem cells necessary?

Answer 3

They are a renewing source of undifferentiated cells which are necessary for growth, development and repair

Question 4

Why must the activity of stem cells be strictly controlled?

Answer 4

• if they do not divide fast enough then tissues are not efficiently replaced - leading to ageing
• if there is uncontrolled division, then they form tumours - leading to cancer

Question 5

What is the potency of stem cells?

Answer 5

Potency is a stem cell’s ability to differentiate into different cell types. The greater the number of cell types it can differentiate into, the greater its potency.

Question 6

Define totipotent

Answer 6

Can differentiate into any type of cell, destined to produce a whole organism - e.g. a zygote

Question 7

Define pluripotent

Answer 7

Can form all tissue types but not whole organisms

Question 8

Define multipotent

Answer 8

Can form a range of cells within a certain tissue type

Question 9

Where are blood cells derived from?

Answer 9

Stem cells in the bone marrow

Question 10

Describe the replacement of erythrocytes

Answer 10

• essential to transport oxygen around the body
• short lifespan due to lack of organelles (120 days)
• stem cell colonies in bone marrow produce approx. 3bn per kg of body mass per day

Question 11

Describe the replacement of neutrophils

Answer 11

• essential role in the immune system
• live about 6 hours
• colonies of stem cells in bone marrow produce about 1.6bn per kg per hour
• increases during infection

Question 12

Describe embryonic stem cells

Answer 12

Totipotent at early stage of embryo development. After 7 days, the blastocyst is in pluripotent stage (and up-to and before birth)

Question 13

Describe tissue (adult) stem cells

Answer 13

Present from birth. They are multipotent and are found in specific areas. E.g. can be harvested from umbilical cords of newborn babies, but are not as effective as embryonic stem cells.

Question 14

Where are plant stem cells found?

Answer 14

• meristematic tissue (meristems)
• found at the tips of roots and shoots (apical meristems) - wherever growth is occurring
• also located sandwiched between the phloem and xylem tissue = vascular cambium

Question 15

Describe xylem and phloem’s stem cells

Answer 15

• stem cells of the vascular cambium divide + differentiate to become xylem vessels and phloem sieve tubes
• pluripotent stem cells continue to grow throughout the plant’s life

Question 16

What are the potential uses of stem cells?

Answer 16

• repair of damaged tissues - e.g. heart tissue that is damaged from heart attack
• treatment of neurological diseases such as Alzheimer’s disease (brain cells destroyed as a result of the build up of abnormal proteins) and Parkinson’s disease (death of dopamine-producing cells in brain)
• developmental biology

Question 17

What is developmental biology?

Answer 17

The study of the changes that occur as multicellular organisms grow + develop from a single cell, and why things sometimes go wrong

Question 18

Brief ethics on stem cells

Answer 18

• controversy regarding embryonic stem cells from religious and moral objections
• views that life begins at conception and that there is a lack of consensus as to when the embryo itself has rights
• holds back progress in treating incurable diseases
• other stem cells are only multipotent so not as useful as pluripotent embryonic stem cells