Topic 2a - Cell Division and Stem Cells

Question 1

What do you call body cells that have two copies of each cell?

Answer 1

Diploid cells

Question 2

What is a chromosome?

Answer 2

Long lengths of a molecule called DNA. The DNA is coiled up to form the arms of the chromosome.

Question 3

What is the cell cycle?

Answer 3

The cell cycle starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical diploid cells.

Question 4

What is the stage of the cell cycle where the cell divides, called?

Answer 4

Mitosis

Question 5

What is mitosis?

Answer 5

Mitosis is when a cell reproduces itself by splitting in two to form two genetically identical offspring.
It usually refers to the division of the nucleus rather than the whole cell.

Question 6

What happens during interphase, during the cell cycle?

Answer 6

1) In a cell that’s not dividing, the DNA is all spread out in long strings
2) Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes
3) It then duplicates its DNA- so there’s one copy of each chromosome for each new cell. The DNA is copied and forms X-shaped chromosomes. Each ‘arm’ of the chromosome is an exact duplicate of the other. Each ‘arm’ is called a chromatid.

Question 7

What happens during mitosis, during the cell cycle?

Answer 7

1) Prophase: the chromosomes condense, getting shorter and fatter. The membrane
around the nucleus breaks down and the chromosomes lie free in the cytoplasm.
2) Metaphase: the chromosomes line up at the centre of the cell.
3) Anaphase: spindle fibres pull the chromosomes apart. The two arms of each chromosome (chromatids) are pulled to opposite ends of the cell.
4) Telophase: membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells — the nucleus has been divided.
Before telophase ends, the cytoplasm and cell membrane divide to form two separate cells — this process is called cytokinesis.

Question 8

What happens after mitosis, in the cell cycle?

Answer 8

At the end of mitosis, the cell has produced two new daughter cells. Each daughter cell contains exactly the same set of chromosomes in its nucleus - the two cells are genetically identical. They’re also genetically identical to the diploid parent cell. This makes the daughter cells diploid too.

Question 9

What are the uses of mitosis?

Answer 9

• By multicellular organisms to grow
• By multicellular organisms to replace cells that have been damaged
• By some organisms to reproduce by asexual reproduction

Question 10

How do you calculate the number of cells there are after multiple division of cell by mitosis?

Answer 10

2^n (n = the number of divisions by mitosis)

Question 11

To what processes do animal cells grow and develop?

Answer 11

• Cell division: happens by mitosis
• Cell differentiation: the process by which a cell changes to become specialised for its job. Having specialised cells allows multicellular organisms to work more efficiently because different cell types can carry out different functions.

Question 12

To what processes do plant cells grow and develop?

Answer 12

• Cell division: happens by mitosis
• Cell differentiation: the process by which a cell changes to become specialised for its job. Having specialised cells allows multicellular organisms to work more efficiently because different cell types can carry out different functions.
• Cell elongation: the plant cell expands, making the cell bigger, so making the plant grow

Question 13

When do animal cells grow?

Answer 13

Animal cells tend to grow at a faster rate when they’re younger, than when they’re older

Question 14

When do plant cells grow?

Answer 14

Cell division usually happens at the tips of roots and shoots (in areas called meristems). Plants grow continuously, at all ages.

Question 15

What is the rate at which the cells divide by mitosis controlled by?

Answer 15

chemical genes in an organism’s DNA

Question 16

What happens if there is a change in one of the genes that controls cell division?

Answer 16

The cells start dividing uncontrollably. This can result in a mass of abnormal cells called tumour. If the tumour invades and destroys surrounding tissues, it is called cancer.

Question 17

What is a percentile chart used for?

Answer 17

To assess a child’s growth over time, so an overall pattern can be developed, and any problems highlighted.

Question 18

What 3 results are plotted on a percentile chart?

Answer 18

• Length of baby
• Mass of baby
• Head circumference of baby

Question 19

What do the percentiles show?

Answer 19

e.g., the 50th percentile shows the measurement (e.g., mass, head circumference or length) 50% of babies would have reached at that age

Question 20

What are stem cells?

Answer 20

Cells that are undifferentiated (they haven’t changed to become specialised for a particular function). They can divide to produce lots more undifferentiated cells. These new cells can then develop into different types of cell, depending on what instructions they’re given.

Question 21

Where are stem cells found?

Answer 21

Stem cells are found in early human embryos. These embryonic stem cells have the potential to divide and produce any kind of cell at all. The embryonic stem cells are really important for the growth and development of organisms, as all the cells in a human being have come from those few cells in the early embryo.

Question 22

What are adult stem cells used to do in medicine?

Answer 22

To cure disease, e.g., people with some blood diseases (e.g. sickle cell anaemia, a disease which affects the red blood cells) can be treated by bone marrow transplants. Bone marrow contains adult stem cells that can turn into new blood cells to replace the faulty old ones.

Question 23

What are embryonic stem cells in medicine used for?

Answer 23

Scientists have experimented with extracting stem cells from very early human embryos and growing them. Under certain conditions, the stem cells can be stimulated to differentiate into specialised cells. In the future, it might be possible to use embryonic stem cells to replace faulty cells in sick people.

Question 24

What are the issues involved in using stem cells?

Answer 24

• Tumour development
• Disease transmission
• Rejection

Question 25

How is tumour development an issue involved in using stem cells?

Answer 25

Stem cells divide very quickly. If scientists are unable to control the rate at which the transplanted cells divide inside a patient, a tumour may develop.

Question 26

How is disease transmission an issue involved in using stem cells?

Answer 26

Viruses live inside cells. If donor stem cells are infected with a virus and this isn’t picked up, the virus could be passed on to the recipient and so make them sicker.

Question 27

How is rejection an issue involved in using stem cells?

Answer 27

If the transplanted cells aren’t grown using the patient’s own stem cells, the patient’s body may recognise the cells as foreign and trigger an immune response to try to get rid of them. The patient can take drugs to suppress this response, but this makes them susceptible to diseases.

Question 28

What are the ethical issues involved in using stem cells?

Answer 28

Some people are against it, because they feel that human embryos shouldn’t be used for experiments since each one is a potential human life, but the embryos used are unwanted ones from fertility clinics, so if they weren’t used for research, they’d probably just be destroyed.

Question 29

What are stem cells in plants like?

Answer 29

Meristems produce unspecialised cells that are able to divide and form any cell type in the plant — they act like embryonic stem cells. But unlike human stem cells, these cells can divide and differentiate to generate any type of cell for as long as the plant lives.
The unspecialised cells go on to form specialised tissues like xylem and phloem.