CELL DIVISON

Question 1

what is cell division needed for ?

Answer 1

it is needed for the growth and repair of organisms and to replace worn out tissues.

Question 2

name the 2 types of cell division that takes place in eukaryotic cells ?

Answer 2

mitosis
meiosis

Question 3

what is mitosis ?

Answer 3

it is a form of asexual reproduction and it is the process of growth of tissues , replacement of damaged cells and the repairment of worn out tissues. it produces 2 genetically identical diploid daughter cells.

Question 4

what is meiosis ?

Answer 4

meiosis is a method of cell division which takes place in reproductive organs and produces haploid sex cells (gametes) needed for sexual reproduction. Meiosis produces 4 non identical haploid daughter cells.

Question 4

explain the 3 stages in interphase

Answer 4

cells usually stay in interphase for most of their time and interphase has 3 stages :
. G1 : this is the phase where the cell elongates and produces new organelles and new proteins are made.
. S phase : this is where the DNA is replicated
. G2 phase : the cell continues to elongate and protein needed for the cell division are made.

Question 5

explain the structure of chromosomes

Answer 5

the chromosome is made up of two strands called the (sister) chromatids which are joined together at the centre of the chromosome by the centromere.

Question 5

Name the stages that occur during interphase

Answer 5

. interphase
. prophase
.metaphase
. anaphase
. telophase
+ cytokinesis

Question 6

explain what occurs in interphase

Answer 6

in interphase the DNA is uncondensed so the chromosomes are not visible. the nucleolus is still visible and the nuclear envelope is intact. centrioles have been replicated and are visible.

Question 7

explain what occurs in prophase

Answer 7

in prophase , the chromosomes condense so are now visible and and the centrioles move to each poles of the cell, on the other hand the nuclear envelope has started to break down and the centrioles begin to produce spindle fibres which start to extend towards the chromosomes.

Question 8

explain what occurs in metaphase

Answer 8

in metaphase the nuclear envelope has completely broken down and the spindle fibres have attached to the centromeres of the chromosomes pulling the chromosomes to the equator of the cell.

Question 9

explain what occurs in anaphase

Answer 9

in anaphase the spindle fibres contract and the centromere of the chromosomes spit in half so that one chromatid from each chromosome is at each opposite poles of the cell . this creates a v shape of the chromatids which can be seen.

Question 10

explain what occurs in telophase

Answer 10

in telophase the nuclear envelope begins to reform around the new group of chromosomes and the spindle fibres have disappeared and the chromosomes have uncoiled. the cytoplasm begins to divide to form two new genetically identical diploid daughter cells.

Question 11

explain what occurs in cytokinesis

Answer 11

the cytoplasm divides and separates to form 2 new genetically identical diploid daughter cells.

Question 12

what is the formula for mitotic index ?

Answer 12

number of cells in mitosis / total number of cells x 100

Question 13

explain why toluidine blue stain is used in the mitosis practical

Answer 13

the blue stain binds to the chromatin DNA which stains the chromosomes blue so that they can become visible to the naked eye.

Question 14

explain why the root tips are suspended in a drop of distilled water on a slide

Answer 14

as the water helps it elongate by osmosis and they swell up and this allows the chromosomes to separate so they are easier too see.

Question 15

why is it necessary to use hydrochloric acid in the mitosis practical ?

Answer 15

as it helps break down the cell walls so that the cell walls are more permeable for the stain to reach the chromosomes

Question 16

explain why the coverslip is gently pressed during the mitosis practical ?

Answer 16

this is to gentle squash the cells and to produce a layer that is one cell thick so the light from the microscope can travel through the slide

Question 17

explain why you should only press down gently on the coverslip and not harshly

Answer 17

if you press down harshly on the coverslip this will cause the layer of the cells rolling on top of one another, obscuring the view of the chromosomes and can potentially cause the rupturing of the chromosomes .

Question 18

why could the results of the mitosis practical vary, linked to the root tips ?

Answer 18

it could vary depending on the root tip used as the results seen may be different due to the different types of plants used and depending on the age of the root tip or time of day root tip was cut and also depending on the conditions the plant was grown in.

Question 19

how can u make the results of mitosis practical more variable ?

Answer 19

take a large number of fields of view of the plant and should be observed and an average should be taken.

Question 20

what is cancer and how is it caused ?

Answer 20

cancer is when cells start to divide uncontrollable and this is caused by a mutation in the genes that control cell division and that cause cells to divide out of control.

Question 21

what mutagenic agents can cause these mutations for cancer to produce occur ?

Answer 21

ionising radiation from UV rays and carcinogenic chemicals such as found in cigarettes.

Question 22

how are cancer cells different to body cells ?

Answer 22

cancer cells are dofferent as they will either die from apoptosis or can be destroyed from the immune system when recognised as a foreign cell.

Question 23

how does a cancer form ?

Answer 23

when cancer cells pass all the checkpoints in cell division and despite having a damaged DNA are still not recognised as foreign by the immune system , they will continue to divide uncontrollably and they start to layer ontop of eachother forming a tumour. Tumours damage the surrounding tissue and the organs that they may grow, causing blockages , leading to cancer.

Question 24

why do tumours suffer from low oxygen levels ?

Answer 24

they have their own blood supply however their blood supply can not satisfy the tumours oxygen demand due to the high rate of cell division occuring.

Question 25

name the 2 different types of tumours

Answer 25

.malignant
.benign

Question 26

what is a malignant tumour ?

Answer 26

Malignant tumour grows rapidly and will invade other tissues and organs causing blockages and damage to the organs and it can also be life threatening.

Question 27

what is a benign tumour ?

Answer 27

Benign tumours grow slowly and do not invade other tissues or organs and are usually not life threatening.

Question 28

how are cancer treatments made to work ?

Answer 28

they target the cells cell cycle and try to stop it.
eg : chemotherapy prevents the synthesis of the enzyme required for DNA replication . this stopes the cell cycle at the S phase and the DNA can not be replicated so the cell division can not occur.