2.1.6 - Cell division (set D - Stem cells)

Question 1

Define stem cells?

Answer 1

Undifferentiated cells in plants and animials which have originated from mitosis or meiosis - they have the potential to differentiate to become any one of the specialised cell types in the organism

• can undergo mitosis (cell division) again and again

Question 2

Explain an important factor of stem cells division?

Answer 2

Stem cells are able to undergo cell division again and again, so are the source of new cells neccessary for growth, development and tissue repair

• once stem cells become specialised they lose the ability to divide (entering the G0 phase)

Question 3

Explain a problem with stem cells division?

Answer 3

Activity of stem cells has to be strictly controlled, if they do not divide fast enough the tissues are not efficiently replaced - uncontrolled division forms masses called tumours

Question 4

Explain what potency is in regard to stem cells?

Answer 4

A stem cells ability to differentiate into different cell types - stem cells differ depending on the type of cell they can turn into

The greater number of cell types it can differentiate into the greater the potency

Question 5

What is a totipotent stem cell - where are they found?

Answer 5

These stem cells can differentiate into any type of cell - totipotent stem cells include zygote (fertilised egg cell) ,the 8 or 16 cells from first mitotic divisions (which go on to produce a whole organism)

• they can differentiate into extra-embryonic cells such as those in the placenta
• found in the embryo at a stage called blastocyst

Question 6

What is a pluripotent stem cell - where are they found?

Answer 6

These stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (cells that make up the placenta)

• present in early embryos

Question 7

What is a multipotent stem cell - where are they found?

Answer 7

These stem cells can only form a range of cells within a certain type of tissue

• haematopoetic stem cells in bone marrow are multipotent because this gives rise to the various types of blood cells

Question 8

What is a unipotent stem cell - where are they found?

Answer 8

Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells)

Question 9

What are the four main types of stem cells present at various stages of human development?

Answer 9

• unipotent
• multipotent
• pluripotent
• totipotent

Question 10

Define embryonic stem cells, explain what type of stem cell they are?

Answer 10

found in embryos and can develop into almost every cell type under the right conditions in a lab

• are totipotent before the 7 days and pluripotent after blastocyst forms

Question 11

Explain how long embryonic stem cells remain totipotent?

Answer 11

Embryonic stem cells are totipotent before 7 days and pluripotent after the blastocyst forms

Question 12

Define adult stem cells, explain where they are found and what they can differentiate into?

Answer 12

Found in adult tissues (such as bone marrow, brain, muscle, liver stem cells) - can only differentiate into the same type of cell as the tissue the came from, used to replace damaged cells

• are multipotent stem cells but can be artificially triggered to become pluripotent

Question 13

Explain the role of stem cells found in bone marrow - what 4 cells can they differentiate into?

Answer 13

Stem cells found in bone marrow are multipotent adult stem cells - they can only differentiate into erythrocytes (RBC), monocytes, neutrophils and lymphocytes

Question 14

Give two advantages for embryonic stem cells?

Answer 14

• Can treat a wide variety of diseases
• Can become (almost) any cell type because they are pluripotent

Question 15

Give two advantages for adult stem cells?

Answer 15

• No ethical issues as adult can give consent for the stem cells to be collected
• Safer, as this is a well-tested method

Question 16

Give three disadvantages of adult stem cells?

Answer 16

• Possibility of infection during extraction of stem cells
• Adult stem cells can only become one type of cell (same as the tissue it came from) as they are multipotent.
• Can be very painful

Question 17

Give three disadvantages of embryonic stem cells?

Answer 17

• Possible harm/death of the embryo
• Human rights/ethical issues (the embryo cannot give consent)
• Unreliable as this is not a well-tested method

Question 18

Explain briefly how erythrocytes are formed - why does it require stem cells?

Answer 18

• erythrocytes lack a nucleus - cannot divide
• new erythrocytes constantly formed from bone marrow stem cells
• process is erythropoiesis

Question 19

Outline the adaptions of the original stem cell into an erythrocyte?

Answer 19

• shape changes into a biconcave shape - larger SA (more oxygen to be absorbed through cell surface)
• building up of Haemoglobin in cytoplasm
• ejection of nucleus and other organelles (creates more room for haemoglobin)
• elastic membrane - allows erythrocyte to change shape

Question 20

Outline the process of erythropoiesis?

Answer 20

1) cell is multipotent - divides to form proerythrocytes
2) changes occur - cell can now only form an erythrocyte
3) haemoglobin builds up in cytoplasm
4) nucleus is ejected
5) further changes form mature erythrocyte

Question 21

Briefly explain plant stem cells?

Answer 21

• stem cells found in meristems of plant
• stem cells remain totipotent throughout life
• meristem tissue can differentiate into any type of plant cell

Question 22

Explain what the cambium is - what’s its role?

Answer 22

Lies between xylem and phloem - a layer of meristem cells that divide to produce new xylem and phloem

Question 23

Explain the role of stem cells regarding the treatment of diseases - reference alzhemiers?

Answer 23

Stem cells could be used to replace damaged tissues in a range of diseases - for example neurological disorders like Alzheimer’s

• could be used to regrow healthy nerve cells - reducing memory loss

Question 24

Explain the role of stem cells regarding the treatment of damage tissue - reference Parkinson’s?

Answer 24

Patients with Parkinson’s suffer from tremors - the disease causes loss of particular nerve cells in brain which release dopamine (involved in controlling movement) - stem cells could be used to regenerate dopamine-producing cells

Question 25

Outlien some of the ethical problems with using stem cells?

Answer 25

• some people believe life begins at contraception - destruction of embryo is therefore murder
• an answer is using umbilical cord stem cells but they may not be able to be manipulated to produce all cell types - multipotent not pluripotent

Question 26

Explain 2 ways stem cells have been used in medicine?

Answer 26

• treatment of burns - stem cells grown on biodegradable meshes can produce new skins for burn patients - quicker than taking a skin graft
• drug trails - potential new drugs can be tested on cultures on stem cells before being tested on humans