TOPIC 1.6

Question 1

What is mitosis for?

Answer 1

Growth
Asexual reproduction
Tissue
Embryonic development
(GATE)

Question 2

What is a haploid

Answer 2

Half set of chromosomes

Question 3

What is a diploid

Answer 3

Full set of chromosomes (one set from each parent)

Question 4

What is a centromere

Answer 4

Part of chromosome which links sister chromatids

Question 5

What are sister chromatids

Answer 5

Duplicated chromosomes attached by a centromere. When they split after anaphase, they are called chromosomes

Question 6

What is the role of centrioles

Answer 6

To organise spindle microtubules

Question 7

What are the phases of interphase?

Answer 7

G1, S, G2 and G0

Question 8

What happens during G1?

Answer 8

• increased volume in cytoplasm
• organelles produced
• proteins synthesised
  SA:Vo ratio decreases

Question 9

What happens during S?

Answer 9

Cell replicates all genetic material in its nucleus, so after mitosis both new cells have complete set of genes

Question 10

What happens during G2?

Answer 10

• increased volume of cytoplasm
• organelles produced
• synthesised proteins

Question 11

What is G0

Answer 11

A phase on interphase that occurs sometimes when the cell has left the cycle and stopped dividing. Entered after G1

Question 12

What is the difference between chromatin, chromosome and sister chromatid?

Answer 12

Chromatin refers to the DNA complex spread out in the nucleus of a cell. When a cell is getting ready to divide and the chromatin condenses, then they are called chromosomes. When chromosomes are replicated, each chromosome is called a sister chromatid. Divide, then called chromosomes again.

Question 13

What happens during prophase?

Answer 13

• chromosomes are supercoiled (chromatin is condensed)
• sister chromatids formed
• nucleolus breaks down, as well as nuclear membrane
• microtubules form on opposite poles of cell between centrosomes

Question 14

What happens during interphase

Answer 14

Preparing to divide
Mr - Metabolic reactions 
P - protein synthesis, allows cell to function 
O - organelles numbers are increased
D - DNA is replicated

Question 15

What happens during metaphase?

Answer 15

• Microtubules continue to grow and attach to centromeres on each chromosome (pair of sister chromatids)
• Sister chromatids attach to microtubules from different poles so they can separate
• Microtubules tested by shortening at centromere, if attachment is correct, chromosomes remain on an line up on equator of cell

Question 16

What happens during anaphase?

Answer 16

• Centromeres divide so sister chromatids can separate and be called chromosomes
• spindle microtubules pull them to opposite poles of the cell, so genetically identical nuclei can form

Question 17

What happens during telophase?

Answer 17

• Chromosomes pulled into MTOC so nuclear membrane can form around them
• Chromosomes uncoil (decondense to chromatin) and nuclear membrane forms around
• microtubule spindle fibres disappear
• cell is dividing and daughter cells enter interphase

Question 18

What is cytokinesis?

Answer 18

The division of the cytoplasm and therefore the cell. It begins before mitosis is completed.

Question 19

How does cytokinesis take place in animal cells?

Answer 19

• Plasma membrane is pulled inwards around equator of cell to form cleavage furrow.
• Accomplished using ring of contractile protein inside plasma membrane at equator
• when cleavage furrow reaches centre, cell is pinched apart

Question 20

How does cytokinesis take place in plant cells?

Answer 20

• Vesicles from Golgi are moved to equator where they fuse to form tubular structures across
• Structure and other vesicles merge to form two layers of plasma membrane
• become plasma membranes of two daughter cells
• cell plate continues to form until it meets the plasma membrane of the existing cell
• This completes division of the cytoplasm
• next vesicles deposit pectins by exocytosis to form middle lamella that links new cell walls
• Both daugter cells secrete cellulose to form new adjoining walls

Question 21

What are cyclin?

Answer 21

A group of proteins with the role of ensuring that tasks are performed at the right time and the cell only moves on to the next stage of the cycle when appropriate.

Question 22

How to cyclins work?

Answer 22

They bind to cyclin dependent kinases. The kinases become active and attach phosphate groups to other proteins to become active and carry out tasks specific to one of the phases of the cycle.

Question 23

Aim of cyclin

Answer 23

Cells cannot progress to the next stage of the cell cycle unless the specific cyclin reaches it threshold.

Question 24

What is a tumour?

Answer 24

An abnormal growth of tissue

Question 25

What is cancer?

Answer 25

A malignant tumour named after the part of the body where it develops

Question 26

What is a mutation

Answer 26

A change in an organism's genetic code which can result in cancer

Question 27

What are mutagens?

Answer 27

Agents that cause genetic mutations, not necessarily result in cancer

Question 28

What is carcinogen?

Answer 28

A mutation which causes cancer

Question 29

What is an oncogene?

Answer 29

A gene that tells cells when to stop dividing, control the cell cycle. If there is a mutation in oncogenes, this can cause uncontrolled division and tumours

Question 30

How do primary tumours develop?

Answer 30

Cancerous cells detach from primary tumour, some gain ability to penetrate. lymph/ blood vessels and circulate around the body, then invading tissues and divide uncontrollably to cause secondary tumours. This is called metastasis; the movement of cells from primary tumour to set up secondary tumours in other parts of body

Question 31

What is the evidence supporting endosymbiotic theory?

Answer 31

organelles like mitochondria and chloroplast have: - their own DNA (naked DNA in circular shape) - ribososmes similar to those in prokaryotes (70) - have double membrane - can only be produced by division of pre-existing mitochondria and chloroplasts

Question 32

Describe briefly the endosymbiotic theory

Answer 32

Suggests that the first eukaryotic cells came about when small prokaryotic cells/organisms were engulfed by larger prokaryotic cells. Instead of being consumed and digested, they smaller prokaryotic cells survived, and a symbiotic relationship was formed, in which the smaller cell provided the bigger prokaryotic cell with a characteristic that made the organism competitive in its environment, allowing the cell to reproduce and adapt with the cell it consumed as an organelle over time.

Question 33

Give an example of endosymbiotic theory

Answer 33

An aerobic prokaryote was engulfed by a larger anaerobic prokaryote. Instead of being digested, the aerobic prokaryote survived and provided the larger one with the ability to aerobically respirate, making it more competitive in its environment and forming a symbiotic relationship. The organism started reproducing by binary fission, and over time, the aerobic prokaryote became a part of the larger one. We now know this as the mitochondria.

Question 34

G0

Answer 34

Cell leaving the cell cycle, stops dividing