Cell cycle 2.3

Question 1

When does mitosis take place?

Answer 1

• it occurs during growth and repair or to replace a damaged cell.
  -Or during differentiation when cells become specialised.

Question 2

What is mitosis?

Answer 2

Mitosis in nuclear division.
( At the end of telophase, cytokinesis occurs where the cytoplasm divides and together with mitosis this is regarded as cell division.)

Question 3

What is the order of stages in mitosis?

Answer 3

Prophase, metaphase, anaphase, telophase.

Question 4

What happens in Prophase?

Answer 4

-The DNA supercoils and condesnses.
- The nuclear envelope breaks down.
-The centriols form spindles.

Question 5

What are chromatids?

Answer 5

one strand of the replicated chromosome pair that is joined to the other chromatid at the centromere

Question 6

What are centrioles?

Answer 6

Small structured made up of microtubules that are involved in the formation of spindle fibres.

Question 7

What happens in metaphase?

Answer 7

-The pairs of sister chromatids orientate themselves at the equator of the cell.
-Using their centromeres, each pair attach to the spindle threads.

Question 8

What happens in anaphase?

Answer 8

-The centromere divides or splits, separating the pairs of chromatids.
-The chromatids are drawn, centromere first, towards opposite poles of the cell.
- The chromatids cannot move on tbhier own= The rely on the microtubules of the spindles allow them to move.
- At thend the chromatids act as completley different enterties.

Question 9

What happens in telophase?

Answer 9

-The chromosomes reach the opposite poles on the spindle.
-The chromosomes uncoil and become long and thin.
-The nuclear envelope reform around each group of chromosomes.

Question 10

State what the cell cycle is and outline its stages.

Answer 10

Regulated cycle of division with intermediate growth periods.
1) interphase.
2)mitosis and meiosis.
3)Cytokinesis.

Question 11

Outline what happens during G1 in interphase.

Answer 11

G1- Is the time between the end of the previous round of mitotic cell division and the start of chromosome duplication. The cell assimilates ( takes in and understands the material), grows and develops.
In actively dividing cells G1 is very short- a matter of hours or days, but on other cells it can be months or even years.

Question 12

Outline what happens during S in interphase.

Answer 12

S- chromosomes replicates and become 2 sister chromatids joined at a centromere.

Question 13

Outline what happens during G2 in interphase.

Answer 13

G2- Organelles needed for division and synthesised - before a cell can divide it needs two of everything.

Question 14

Outline what happens during M in interphase.

Answer 14

M- nuclear division when cells are actively dividing.

Question 15

Outline what happens during C in interphase.

Answer 15

C- cytokinesis, the final stage of cell division when the new cells separate.

Question 16

What is the purpose of mitosis?

Answer 16

Produces two identical daughter cells for:
- Growth
-Cell replacement/ tissue repair
-asexual reproduction

Question 17

What are chromosomes?

Answer 17

is made up of a mass of coiled threads of DNA proteins.

Question 18

When and where do chromosomes become visible?

Answer 18

Supercoiling ( makes DNA more stable)

Question 19

What is a karyotype?

Answer 19

an individual set of chromosomes

Question 20

How is DNA packaged?

Answer 20

-The DNA wraps around histones to from a dense cluster of nucleosomes.
-These then interact to produce more coiling and then supercoiling to form the DNA you can see through the microscope in the nucleus of a dividing cell.
-In the supercoiled areas the genes are not available to be copied to make proteins.

Question 21

How often does the cell cycle occur?

Answer 21

In multicellular organism the cell cycle repeats very frequently in almost all cells during development. However, once the organism is mature, it may slow down or stop completely in some tissue.

Question 22

How is the cell cycle controlled?

Answer 22

The cell cycle is controlled by a number of chemical signals made in response to different genes. This control is brought about at a number of checkpoint where the cell cycle moves from one phase to the next.

Question 23

What are the control chemicals called in the cell cycle ?

Answer 23

cyclins

Question 24

What are cyclins?

Answer 24

These are small proteins that build up during interphase and are involved in the control of the cell by their attachment to enzymes called cyclin-dependant kinases.

Question 25

What does cyclin-dependant kinases (CDKs) do?

Answer 25

The CDK complex phosphorylates other proteins, changing their shape and bringing about the next stage in the cell cycle.

Question 26

What is CDKs?

Answer 26

are enzymes involved int the control of the cell cycle by phosphorylating other proteins, activated by attachment to cyclins.

Question 27

What do most diseases that are classed as cancer have in common?

Answer 27

cancer cells do not respond to the normal mechanisms that control cell growth- They divide rapidly to forma mass of abnormally growing cells called a tumour.

Question 28

What do malignant tumours do?

Answer 28

Split and release small groups of cells into blood and tissue fluid. They circulate and often lodge in different areas of the body, forming secondary tumours.

Question 29

Why is control of the cell lost?

Answer 29

• Only about 15% of human cancers are caused by viral infection, which causes changes in the cells, effecting the control of the cell cycle and leading to cancer.
  -Most cancers result from mutation, which occur in the DNA of a normal body cell as it reproduces. ( several mutations may work together to increase the likelihood of cancer)

Question 30

How can a single mutation of proto-oncogene to an oncogene cause cancer?

Answer 30

Proto-oncogene code for proteins which stimulate the cell cycle. Oncogenes produce uncontrolled amount of stimulating proteins.

Question 31

How does a tumour cause cancer?

Answer 31

suppressor genes code for the production of chemicals which supress the cell cycle, acting as a break on the cell dividing

Question 32

How do genetic factors effect the risk of people getting cancer?

Answer 32

-some people are more likely to experience a mutation that will cause cancer.
-Some people are born with mutations that give them a very high risk of s specific disease.

Question 33

How do environmental factors effect the risk of someone getting cancer?

Answer 33

-Tar in cigarette smoke
-ionising radiation
-mutagens

Question 34

What is the mitotic index equation?

Answer 34

mitotic index = number of cells with visible chromosomes ÷ total number of cells

You can multiply the answer by 100 if you need to give the mitotic index as a percentage

Question 35

What is the mitotic index used for ?

Answer 35

used the study tumour growth in cancer patients- if there are a higher number of cells doing mitosis than there should be then there ma be something wrong.

Question 36

What do cells in interphase look like under a microscope?

Answer 36

Clearly defined nucleus and posses clearly visible condensed chromosomes.

Question 37

What do the cells look like in prophase under a microscope?

Answer 37

chromosomes condensed but more look like individual chromosomes( worms) and still confined to nuclear region.

Question 38

What do cells in metaphase look like under a microscope?

Answer 38

Chromosomes align along the equator of the cell

Question 39

What do cells in Anaphase look like under a microscope?

Answer 39

Two distinct clusters of chromosomes at apparent poles of the cell

Question 40

What does a cell in telophase look like under a microscope?

Answer 40

Two nuclear regions present with a single cell ( difficult to see because takes place alongside cytokinesis)

Question 41

In the core practical for observing mitosis, explain why the root tip had to be heated?

Answer 41

To break the tissue into individual cells.
- The Cellulose walls of the plant are held together by pectins such as calcium pectate.
- Treatment with hydrochloric acid breaks this down.

Question 42

In the core practical for observing mitosis, what effect will pressing the slides down have on the cells?

Answer 42

-It will separate the cells in the meristems tissue into a single layer.
-This makes it easier to see the chromosomes and identify the stages of division.

Question 43

In the core practical for observing mitosis, what information about the cells counts give you about each stage of mitosis.

Answer 43

The cell count shows the relative duration of each stage in the cell cycle. The longer a phase the more cell are likely to be going through that phase at any given time.

Question 44

What are the main differences between sexual and asexual reproduction?

Answer 44

Asexual=
- Single parent passes on its gene to offspring,
- No fertilisation occurs,
-Offspring are genetically identical to parent.
Sexual=
-Two parent give rise to offspring and pass on their genes,
-Fertilisation must occur,
-Offspring have a unique combination of both parents genes,
-Greater variation in species.

Question 45

What are the advantages of Asexual reproduction?

Answer 45

-Does not rely on a mate.
-Can give rise to a large number of offspring.

Question 46

What are the disadvantages of Asexual reproduction?

Answer 46

• The offspring are genetically identical to the parent organism.
  -If living conditions change in some way, or temperature or human intervention that can lead to total destruction of species.

Question 47

What are some strategies of asexual reproduction?

Answer 47

1) Producing spores
2)Regeneration
3)Producing buds
4)New plant structure

Question 48

How does asexual reproduction work through producing spores?

Answer 48

Sporulation involves mitosis and the production of asexual spores that are capable of growing into new individuals.
-These spores can usually survive in adverse conditions so easily spread over great distances.
- This type of asexual reproduction is most common in fungi and plants.

Question 49

How does asexual reproduction work through regeneration?

Answer 49

Fragmentation is a type of regeneration when some organisms can reproduce themselves asexually from fragments of their original body.

Question 50

How does asexual reproduction work through producing buds?

Answer 50

Reproductive budding is when there is an outgrowth from the parent organism that produces a smaller but identical individual, which eventually becomes detached from the parent and has an independent existence.
The new organism is produced purely by mitotic division.

Question 51

How does asexual reproduction work through New plant structure?

Answer 51

Vegetative propagation is a more sophisticated version of reproductive budding and occurs in flowering plants.
-A plant forms a structure that develops into a fully differentiated new plant, which is identical to the plant and eventually becomes independent.

Question 52

What does vegetative propagation often include and why is this important?

Answer 52

Often involves perennating organisms.
- These contain stored food from photosynthesis and can remain dormant int he soil to survive adverse conditions.
-They are often means of surviving from one growing season to the next.
- And it is easily exploited by gardeners and farmers to produce new plant.

Question 53

What is Parthenogenesis?

Answer 53

The process by which an unfertilised egg cell develops into anew individual- Sexual reproduction from one parent.