Topic 3: Stem cells

Question 1

Describe how the body uses stem cells

4 points

Answer 1

1. They are the foundation for every body organ and tissue.
2. When a stem cell divides, each new stem cell either REMAINS A STEM CELL or can become SPECIALISED into a certain cell type.
3. In many body tissues, stem cells divide regularly eg. in gut and skin, stem cells can give rise to new cells to repair and replace {worn out/damaged} tissues.
4. In other organs eg. pancreas and the heart, stem cells divide more rarely

Question 2

Define stem cell (3 points)

Answer 2

1. An {UNDIFFERENTIATED/unspecialised} cell that can GIVE RISE TO other TYPES OF SPECIALISED CELL,
2. are capable of self-renewal with no limit to division
3. and can be totipotent, pluripotent or multipotent.

Question 3

Define totipotent stem cells (2 points)

Answer 3

1. {undifferentiated/unspecialised} cells which are capable of self-renewal, with no limit to division,
2. that can GIVE RISE TO ALL CELL TYPES including extra embryonic cells

Note: Totipotency is therefore a ‘property’ of the very earliest {embryonic/totipotent} stem cells. They have ‘total potential’.

Question 4

What is a source of totipotent stem cells? (2 sources)

Answer 4

1. Zygote to
2. 8 cell embryo

NOTE: Also anywhere between the zygote and 8 cell embryo

Question 5

Define pluripotent stem cells (2 points)

Answer 5

1. {undifferentiated / unspecialised cells}, which have SOME genes switched off,
2. which can give rise to MOST TYPES of specialised cells, but NOT totipotent embryonic stem cells

Question 6

What is a source of pluripotent stem cells? (2 sources)

Answer 6

1. from INNER CELL MASS OF A BLASTOCYST

2. from UMBILICAL CORD BLOOD

Question 7

Define multipotent stem cells (2 points)

Answer 7

1. {undifferentiated / unspecialised} cells, which have MANY genes switched off,
2. which can give rise to a SMALL number of different, closely related specialised cell types

NOTE: Often called “adult stem cells” - but are found in the body from birth onwards - found among the differentiated cells in many parts of body

Question 8

Where from the body can multipotent stem cells be collected? (1 source)

Answer 8

1. bone marrow

NOTE: can also be obtained from the brain (more difficult to obtain)

Question 9

Key Summary: What are the important properties of stem cells?
(3 properties)

Answer 9

1. Have the potential to give rise to specialised cells
2. Can continue to divide with no limit to division
3. Totipotency or pluripotency or multipotency

Question 10

Key Summary: For 7 sources, give: the source, type of cell, and potency of those stem cells.

NOTE: type of cell is either {embryonic/non-embryonic/adult} stem cells

Answer 10

1. Zygote - embryonic stem cells - totipotent
2. 8 cell embryo - embryonic stem cells - totipotent
3. blastocyst inner cell mass - embryonic stem cells - pluripotent
4. umbilical cord blood - non embryonic stem cells - pluripotent
5. placenta - non embryonic stem cells - pluripotent
6. bone marrow - adult stem cells - multipotent
7. {brain/connective/skin/liver} cells - adult stem cells - multipotent

NOTE: {multipotent/adult stem cells} can be extracted from birth onwards

Question 11

(plant stems and tissue culture)

________ _________ in the {medium/agar} help unspecialised stem cells ____________ into specialised cells.

Answer 11

Growth regulators

differentiate

Question 12

(Plant stem cells and tissue culture)
Describe the method to find out which plant tissues are totipotent (contain totipotent stem cells)
(8 steps)

Answer 12

1. Take 5 {samples / explants} from a plant tissue(s)
2. Use aseptic {technique/conditions} eg. sterile agar, scalpel
3. Place 5 explants into bottles of agar which contains growth regulators, glucose, minerals
4. Place under a light bank for 14 days to control light intensity with heat shield between light and explants to absorb heat and control temperature
5. Grow cells into a callus
6. {{Cells / tissue} differentiate / cells become whole plants}
7. Record results (eg. new leaves) every day for 14 days
8. Other controlled variables - same {volume of agar / concentration of growth regulator}

Question 13

(Plant stem cells and tissue culture)

What is the purpose of aseptic technique? (1 point)

Answer 13

1. Prevents pathogenic {microbes/bacteria/fungi} from {contaminating/entering} bottle

Question 14

(Plant stem cells and tissue culture)

What is the purpose of a heat shield? (3 points)

Answer 14

1. Controls temperature,
2. prevents explants drying out
3. and prevents plant enzymes being denatured

Question 15

(Plant stem cells and tissue culture)

What is the purpose of a light bank? (2 points)

Answer 15

1. Controls light intensity

2. provides light for photosynthesis

Question 16

(Plant stem cells and tissue culture)

What is the purpose of having glucose and minerals in agar? (1 point)

Answer 16

1. For plant growth and development (glucose for respiration to release ATP, magnesium for chlorophyll, nitrates to make proteins for growth)

Question 17

(Plant stem cells and tissue culture)

What is the purpose of growth regulators? (1 point)

Answer 17

1. To allow totipotent stem cells to differentiate into different cell types

Question 18

(Plant stem cells and tissue culture)

What is the purpose of covering the bottles in cling film? (3 points)

Answer 18

1. For safety - prevents pathogenic {microbes/bacteria/fungi} from {contaminating/entering} bottle
2. Allows light in for photosynthesis
3. and reduces water loss

Question 19

(Plant stem cells and tissue culture)
For the experiment of which plant tissues are totipotent, how will you know whether the tissue contains totipotent stem cells? (1 point)

Answer 19

1. If the stem cells in the plant tissue are totipotent, then eventually a whole new plant (roots, stem, leaves – all cell types) will be produced.

NOTE: You will find out that ALL plant cells are totipotent – they are capable of developing into any of the cell types needed to make a new plant, so every explant should form a new plant

Question 20

Describe the steps for plant tissue culture in plant breeding
(5 steps)

Answer 20

1. Explant taken from parent plant
2. Placed on nutrient agar with growth regulators
3. Cells divide to form a callus, then embryo
4. Embryo grows into tiny plant
5. Tiny plant can be planted in compost and grown on

Question 21

What are the applications of plant tissue culture?

5 points

Answer 21

1. Developing improved {plant/food crop} species
2. to INCREASE THE DISEASE RESISTANCE of plants
3. to produce commercial plants that are DIFFICULT TO GROW FROM SEED (eg. orchids)
4. Produce increased quantities of PHYTOCHEMICALS USED IN DRUGS (eg. the anti-cancer drug Taxol from Yew trees)
5. CONSERVATION of endangered plant species

Question 22

Commercial benefits of plant tissue culture

2 benefits

Answer 22

1. Can guarantee the QUALITY of the the identical plant produced
2. Often EASIER AND QUICKER THAN GROWING PLANTS FROM SEED

Question 23

Research benefits of plant tissue culture (1 benefit)

Answer 23

1. CAN EXPOSE CLONED PLANTS TO DIFFERENT EXPERIMENTAL CONDITIONS and differences in behaviour or development can then be reliably put down to an experimental variable, as all plants are genetically identical.

Question 24

Key Summary: Give the uses of stem cells in medicine

2 uses

Answer 24

1. Producing ORGANS FOR TRANSPLANT

2. Producing NEW TISSUES FOR REPAIRING OR REPLACING DAMAGED TISSUES eg. in heart or spinal cord

Question 25

How can the shortage of organs for transplants be overcome? (5 ways) What can happen in an organ transplant (1 point) and what are the solutions? (3 solutions)

Answer 25

How? 1. SPARE IVF EMBRYOS 2. Grow to form blastocyst 3. Extract pluripotent stem cells 4. Stem cells cultured to form more identical cells 5. Stem cells stimulated to differentiate to form a tissue or organ What can happen: Rejection (unless can use a person’s own stem cells) Possible solutions to transplant rejection: 1. TISSUE TYPING of donor and recipient to get a match 2. IMMUNOSUPPRESSANT DRUGS 3. THERAPEUTIC CLONING (transfer of the nucleus from a cell of the patient, to an egg cell whose nucleus has been removed)

Question 26

Describe therapeutic cloning (4 steps)

Answer 26

1. The NUCLEUS IS REMOVED from an egg cell. 2. A diploid somatic (body/skin) cell is removed from the patient and the nucleus from this cell is placed in the egg cell. 3. The new cell is stimulated using electricity to divide by mitosis to form a BLASTOCYST. 4. Pluripotent stem cells are removed and encouraged to develop into {tissues/organs} which are GENETICALLY IDENTICAL to those of the patient, which can be used for transplantation. NOTE: therapeutic cloning is also known as "somatic cell nuclear transfer" (SCNT)

Question 27

State the advantages of therapeutic cloning. | 2 advantages

Answer 27

1. NO RISK OF REJECTION – cloned cells are genetically identical to those of the patient 2. NO NEED TO TAKE IMMUNOSUPPRESSANT DRUGS

Question 28

State the disadvantages of therapeutic cloning. | 2 disadvantages

Answer 28

1. Technique COULD BE ABUSED TO CREATE CLONED HUMANS | 2. ETHICAL ISSUES - an embryo is still being created which would need to be destroyed

Question 29

Key Summary: What are the roles of the {regulatory authorities/HFEA}? (in stem cells) (5 roles) NOTE: HFEA - Human Fertilisation and Embryology Authority

Answer 29

1. To decide on maximum age of embryo allowed for research 2. {To set or consider ethical aspects / judge what is acceptable} 3. To check that source of stem cells is acceptable 4. To stop of cloning (of humans) 5. To stop unnecessary repeating of research

Question 30

Why do scientists and non-scientists come together in the topic of stem cells. (2 points)

Answer 30

1. SCIENTISTS INVOLVED IN EMBRYO RESEARCH {fully understand the science / recognise what is possible} 2. PEOPLE NOT INVOLVED IN EMBRYO RESEARCH give a {balanced / alternative / religious / wider} view

Question 31

Both _______ and _______ stem cells are used in stem cell research, but it is generally accepted that _______ stem cells have more potential.

Answer 31

embryonic adult embryonic

Question 32

Explain 'stem cell line'. (1 point) What kind of research can these cells be used for? (4 things)

Answer 32

1. It is possible to keep embryonic stem cells alive in a laboratory by tissue culture, to produce a ‘stem cell line’. These cells are being used for research such as: 1. how and which genes trigger specific organ development 2. how do cancer cells develop 3. how do certain birth defects occur 4. providing body cells to test drugs in toxicological studies – reduce animal testing

Question 33

Key Summary: {Benefits/advantages} of using embryonic stem cells (4 advantages)

Answer 33

1. are easy to work with 2. are relatively undifferentiated (if pluripotent) 3. are totipotent or pluripotent, so able to give rise to every or most cell types in the body 4. have a wide range of clinical applications

Question 34

What are the arguments FOR the use of embryonic stem cells? | 6 arguments for

Answer 34

1. Using spare IVF embryo which would alternatively be destroyed anyway 2. An embryo is not a new human until it is viable 3. If we ban it in the UK, it’ll still happen in other countries 4. Offers prospect of treatment to many suffering people 5. Research using alternatives, eg. adult stem cells, progressing more slowly than that with embryonic stem cells 6. Research with embryonic stem cells is needed to develop use of adult stem cells

Question 35

What are the arguments AGAINST use of embryonic stem cells? | 5 arguments against

Answer 35

1. ETHICAL ISSUES especially when using spare IVF embryos 2. Embryonic stem cells are from embryos which are unborn children, as an embryo becomes a new human at the moment of conception, so using stem cells is {murder / lack of respect for embryo as a (potential) human} 3. May encourage IVF clinics to ‘create’ more ‘spare’ embryos 4. A lot of current (embryonic) stem cell treatment is {FRAUDULENT / BADLY REGULATED / exploits suffering / encourages IVF clinics to ‘create’ more ‘spare’ embryos} 5. If we wait a few years longer we shall have the same benefits through adult stem cells - not enough funding for alternatives eg. adult stem cells

Question 36

Explain the absolutism view (2 points) on stem cells.

Answer 36

1. Under no circumstances should embryos be used as a source of stem cells for research. 2. No medical advances are worth the {moral evil/murder} of using embryonic tissue.

Question 37

Explain the utilitarianism view (2 points) on stem cells.

Answer 37

1. There is no right or wrong 2. Need to consider - does the {benefit of treatment/medical implications} of the research outweigh the harm to the embryo?

Question 38

Pluripotent stem cells can be taken from SPARE IVF EMBRYOS that have been grown to form blastocysts. The stem cells can be cultured to form {more identical cells/tissues/an organ}. What are the problems? (2 problems)

Answer 38

Problems: 1. Still ETHICAL ISSUES SURROUNDING SPARE IVF EMBRYOS 2. Still problems of REJECTION of cultured cells, tissues or organs

Question 39

What are the advantages of induced pluripotent stem cells? | 2 advantages

Answer 39

1. NO ETHICAL ISSUES, as they are ‘adult’ stem cells that have been reprogrammed (not from embryos) 2. NO TISSUE REJECTION PROBLEMS if tissues for transplant can be grown from patients own cells they will be genetically identical, so NO NEED TO TAKE IMMUNOSUPPRESSANT DRUGS

Question 40

What are the disadvantages of induced pluripotent stem cells? (2 disadvantages)

Answer 40

1. Difficult to create some induced pluripotent cell types, as it is DIFFICULT TO REPROGRAM CELLS TO GET THEM TO DIFFERENTIATE INTO A PARTICULAR TYPE 2. Difficult to CONTROL differentiation – may lead to cancer

Question 41

What are the advantages of using adult stem cells instead of embryonic? (2 advantages)

Answer 41

1. NO ETHICAL ISSUES, as no destruction of embryos 2. NO TISSUE REJECTION PROBLEMS if tissues can be grown from patients own cells they will be genetically identical, so NO NEED TO TAKE IMMUNOSUPPRESANT DRUGS

Question 42

What are the disadvantages of using adult stem cells instead of embryonic? (3 disadvantages)

Answer 42

1. MULTIPOTENT so limited scope for differentiation into different cell types as SOME GENES HAVE BEEN SWITCHED OFF, SO CAN ONLY GIVE RISE TO A SMALL NUMBER OF RELATED CELL TYPES. 2. Very FEW multipotent stem cells within the body, which are HARD TO LOCATE AND DIFFICULT TO EXTRACT 3. INFECTIONS FROM OPERATIONS

Question 43

List the potential risks of stem cells treatment. | 3 risks

Answer 43

1. risk of infection from donor of cells or contaminated {equipment/needle} 2. risk of cancer 3. immunosuppressant drugs make other infections more likely