Cell Divison

Question 1

Not all multicellular organisms retain the ability to divide
What are they able to divide using instead?

Answer 1

Cell cycle

Question 2

Where does DNA replication occur during the cell cycle

Answer 2

Interphase

Question 3

Define mitosis

Answer 3

-Part of the cell cycle in which eukaryotic cells divide
- they produce 2 daughter cells
- each with identical copies of DNA produced by parent cell during DNA replication

Question 4

What are the 3 key stages of the cell cycle

Answer 4

• interphase -G1,S,G2
• nuclear division - mitosis - meiosis
• cytokinesis

Question 5

What is the G1 phase

Answer 5

Proteins r are synthesised for replication

Number of organelles & volume of cytoplasm increases,

Question 6

What is the s phase - synthesis

Answer 6

● DNA replicates semi-conservatively (S phase)
○ Leading to 2 chromatids (identical copies) joined at a centromere

Question 7

What is the G2 phase - gap phase 2

Answer 7

● Number of organelles & volume of cytoplasm increases, protein synth

Question 8

What is interphase known as

Answer 8

Resting phase

Question 9

What is nuclear divisor

Answer 9

It is mitosis -
Nucleus divides
To produce 2 nuclei with identical copies of DNA produced by parent cells

Question 10

What is cytokinesis

Answer 10

Cytoplasm and cell membrane divides
To form 2 new genetically identical daughter cells

Question 11

What are the 4 key stages of mitosis

Answer 11

• Prophase
• metaphase
  -anaphase
• telophase

Question 12

What are 4 key facts of mitosis

Answer 12

• One round of Divison
• genetically identical cells are made
• diploid Cells are made
  _ growth And repair

Question 13

What is an example of growth and repair in mitosis

Answer 13

Clonal expansion of B cells

Question 14

What is the difference between the cell cycle And mitosis

Answer 14

Cell cycle includes growth period between divisions
Mitosis is only 10% of the cell cycle and refers to nuclear division

Question 15

Outline what happens during the prophase

Answer 15

● Chromosomes condense, becoming shorter / thicker so visible
○ Appear as 2 sister chromatids joined by a centromere
● Nuclear envelope breaks down
● Centrioles move to opposite poles forming spindle network
- spindle fibers start to attach to chromosomes by their centromere

Question 16

Outline what happens during the metaphase

Answer 16

● Spindle fibres attach to chromosomes by their centromeres
● Chromosomes align along equator

Question 17

Outline what happens during anaphase

Answer 17

● Spindle fibres shorten / contract
● Centromere divides
● Pulling chromatids (from each pair) to opposite poles of cell

Question 18

Outline what happens in the telophase

Answer 18

● Chromosomes uncoil, becoming longer / thinner
● Nuclear envelopes reform = 2 nuclei
● Spindle fibres / centrioles break down

Question 19

What is the equation of mitoxic index

Answer 19

The number of cells in mitosis/ total number of cells X 100

Question 20

Define mitotic index

Answer 20

Proportion of cells in a population undergoing mitosis

Question 21

What does a higher proportion of mitotic index mean

Answer 21

More cells are undergoing all divisor

Question 22

True or false mitosis a controlled process

Answer 22

True

Question 23

Describe how tumours and cancers form

Answer 23

Mitosis is a controlled process so:
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumour = non-cancerous

Question 24

Suggest how cancer treatments control rate of cell division

Answer 24

● Some disrupt spindle fibre activity / formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents / slows mitosis
● Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis

Question 25

Behaviour of chromosomes In each stage of mitosis

Answer 25

Prophase: chromosomes highly condensed becoming more visible and centrosomes begin to separate
Metaphase: chromosomes line up along the equator
Anaphase: chromosomes move to opposite poles
Telophase: chromosomes uncoil and become Longer and thin and nuclear envelope forms around 2 daughter nuclei

Question 26

What is the division in prokaryotic cells

Answer 26

Binary fission

Question 27

What is the process of binary fission

Answer 27

• Replication of circular DNA And plasmids
  -division of cytoplasm to produce 2 daughter cells
  -each with a single copy of circular DNA and a variable number of copies of plasmids

Question 28

Why don’t viruses undergo cell division and what happens instead

Answer 28

-As they’re non-living
- they inject their nucleic acid into the host
Infected host cell replicates the virus particle
-

Question 29

Name the fixed poison occupied by a gene on a DNA molecule

Answer 29

Locus

Question 30

Describe how viruses replicate

Answer 30

1. 2. 3. Attachment proteins attach to complementary receptors on host cell
         Inject viral nucleic acid (DNA/RNA) into host cell
         Infected host cell replicates virus particles:
         a. Nucleic acid replicated
         b. Cell produces viral protein / capsid / enzymes
         c. Virus assembled then released