62 WJEC Biology AS Level - Study And Revision Guide - Neil Roberts (1.6 The Cell Cycle And Cell Division) Flashcards
Is cytokinesis the same in plant and animal cells?
No, the division of the cytoplasm into two distinct cells (cytokinesis) is different in plants and animal cells.
What happens in cytokinesis in animal cells?
In animal cells, the membrane infolds via a cleavage furrow, until the two cells become separated.
What happens in cytokinesis in plant cells?
In plant cells, the presence of the cellulose cell wall prevents the infolding of the membrane via a cleavage furrow.
Hence, instead a cell plate develops from the centre outwards, until the cell is divided into two.
What is the importance of producing new cells?
By producing new cells, an organism can
- grow
- repair tissues
- replace dead cells.
Which cells are constantly being replaced in animals?
In animals, the cells that are constantly being replaced as they wear out are:
- skin cells
- blood cells
Which cells in plants are constantly undergoing mitosis?
In plants, the cells that are constantly undergoing mitosis are:
- cells at the root
- shoot tip meristems
What is the mitotic index?
The mitotic index is defined as the ratio of the number of cells in a population undergoing mitosis to the number of cells not undergoing mitosis
What is the mitotic index a measure of?
It is a measure of growth.
Is mitosis important in asexual reproduction? Explain.
Give two examples.
Yes, mitosis is important in asexual reproduction
In asexual reproduction, during favourable conditions, genetically identical offspring can be produced resulting in a rapid increase in numbers
Yeast cells and bacteria.
Is asexual reproduction using mitosis also seen in plants?
Yes, it is also used by some plants, e.g. strawberries, when runners are produced.
What is mitosis controlled by?
Mitosis is controlled by a number of genes including proto-oncogenes.
Name some causes of mutations in protooncogenes?
- Chemicals - e.g. benzene
- Radiation - e.g. UV light
What happens if there is a mutation in a protooncogene?
A mutation will cause them to turn them into oncogenes.
This results in uncontrollable cell division.
This leads to the formation of tumours and cancers.
Why has vincristine been a successful cancer drug?
Vincristine has been a successful drug in the treatment of cancers because:
It prevents the formation of the spindle.
Therefore it arrests mitosis at metaphase
This results in slowing the rate of cell division.
How do you calculate the percentage of cells undergoing mitosis?
