Cell Division and Stem Cells - Paper 1

Question 1

Describe the order of the stages of the cell cycle.

Answer 1

For most of its cycle, a cell is in the interphase.
Then it divides by mitosis, in 4 stages: prophase, metaphase, anaphase, telophase.
Then cytokinesis occurs and the daughter cells begin their cycles.

Question 2

What happens during the interphase?

Answer 2

All the cell’s DNA is spread out in long strings. This is duplicated and forms X-shaped chromosomes each with 2 identical ‘arms’ (chromatids).
The cell also grows and increases the amount of subcellular structures such as mitochondria and ribosomes.

Question 3

What happens during the prophase?

Answer 3

The chromosomes condense, getting shorter and fatter. The nuclear membrane breaks down so the chromosomes lie free in the cytoplasm.

Question 4

What happens during the metaphase?

Answer 4

The chromosomes line up in the middle of the cell.

Question 5

What happens during the anaphase?

Answer 5

Spindle fibres pull the chromosomes apart. The two chromatids of each chromosome are pulled to opposite ends of the cell.

Question 6

What happens during the telophase?

Answer 6

Nuclear membranes form around each set of chromosomes. These become the nuclei of the daughter cells.

Question 7

What happens during cytokinesis?

Answer 7

The cytoplasm and cell membrane divide to form 2 separate cells.

Question 8

How is mitosis important for growth and repair?

Answer 8

Cell division by mitosis provides new cells - contributing to growth in the number of cells. These cells can also replace others for repair.

Question 9

How is mitosis important for asexual reproduction?

Answer 9

Asexual reproduction creates clones of the parent. Cell division by mitosis creates genetically identical daughter cells - pretty self-explanatory.

Question 10

What is produced by cell division by mitosis?

Answer 10

It produces 2 diploid daughter cells, each genetically identical to the diploid parent cell (having the same set of chromosomes).

Question 11

What is cancer?

Answer 11

Cancer is when a mass of abnormal cells due to uncontrolled cell division (a tumour) invades and destroys surrounding tissue.

Question 12

Describe growth in animals.

Answer 12

All growth in animals happens in cell division. Animals tend to grow while they’re young, so for adults most cell division is for repair. Hence cell differentiation is also usually lost at an early stage.

Question 13

Describe growth in plants.

Answer 13

Most growth in height for plants is due to cell elongation, where the cells themselves expand. Cell division occurs only in the meristems. Yet plants often grow continuously, for example old trees will keep putting out new branches.

Question 14

What is cell differentiation?

Answer 14

It is 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 15

Which measurements are used to monitor a baby’s growth and plotted on percentile growth charts?

Answer 15

• Length
• Mass
• Head circumference

Question 16

What are stem cells?

Answer 16

They are cells that have not yet been differentiated. They can divide undifferentiated or become specialised.

Question 17

What is the function of stem cells in animals?

Answer 17

Embryonic stem cells (found in early human embryos) have the potential to divide and produce any cell type. Adults also have stem cells - found especially in bone marrow - but they can only produce certain cell types.

Question 18

What is the function of meristems in plants?

Answer 18

Meristem tissue, containing the only cells in plants that divide by mitosis, is found only in the growing parts of plants (eg tips of roots and shoots). As long as the plant lives, meristems produce cells with the potential to produce any cell type.

Question 19

What are the benefits associated with stem cells in medicine?

Answer 19

Bone marrow transplants are already in use to treat various blood diseases.
Embryonic stem cells can already, under certain conditions, be stimulated to differentiate into specialised cells. In future, this could potentially treat paralysis, diabetes etc.

Question 20

What are the issues associated with stem cells in medicine?

Answer 20

A lot of research is yet to be done, with risks of tumour development, disease transmission and rejection.
Ethical issues also exist around taking human embryos; however, many think curing existing patients trumps rights of embryos.