All cells arise from other cells (3)

Question 1

What is the cell cycle?

Answer 1

cycle of division with intermediate growth periods

Question 2

What are the 3 stages of the cell cycle?

Answer 2

1) interphase
2) mitosis/meiosis (nuclear division)
3) cytokinesis (cytoplasmic division)

Question 3

What are the 3 stages of the interphase?

Answer 3

G1
S
G2

Question 4

What happens in the G1 stage?

Answer 4

cell synthesises proteins for replication, e.g. tubulin for spindle fibres, and cell size doubles

Question 5

What happens in the S stage?

Answer 5

DNA replicates so chromosomes consist of 2 sister chromatids joined at a centromere

Question 6

What happens in the G2 stage?

Answer 6

organelles divide

Question 7

Why does the cell cycle not occur in some cells?

Answer 7

because after differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have the ability to divide

Question 8

What is the result of mitosis?

Answer 8

produces 2 genetically identical daughter cells

Question 9

What is the purpose of mitosis?

Answer 9

(produces 2 genetically identical daughter cells) for:
- growth
- cell replacement/tissue repair
- asexual reproduction

Question 10

What are the 4 stages of mitosis?

Answer 10

1) prophase
2) metaphase
3) anaphase
4) telophase

Question 11

What are the 3 steps of the prophase?

Answer 11

1) chromosomes condense, becoming visible (can see X shape of 2 sister chromatids joint at the centromere)
2) centrioles move to opposite poles of cell and mitotic spindle fibres form
3) nuclear envelope and nucleolus break down so chromosomes become free in cytoplasm

Question 12

What happens during the metaphase?

Answer 12

sister chromatids line up at cell equator and are attached to mitotic spindle fibre by their centromeres

Question 13

What are the 2 steps of the telophase stage?

Answer 13

1) chromosomes decondense, becoming invisible again
2) new nuclear envelopes form around each set of chromosomes so there are 2 new nuclei, each with 1 copy of each chromosome

Question 14

What are the names and colours of 2 dyes that bind to chromosomes?

Answer 14

toluidine blue (blue)
acetic orcein (purple-red)

Question 15

What are the 3 steps of the anaphase stage?

Answer 15

1) spindle fibres contract so centromeres divide
2) sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles of cell
3) spindle fibres break down

Question 16

What does the anaphase require?

Answer 16

energy from ATP hydrolysis

Question 17

Which stage of mitosis requires energy from ATP hydrolysis?

Answer 17

anaphase

Question 18

What does the anaphase look like in a diagram?

Answer 18

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Question 19

What are the 3 steps of the procedure for the root tip squash experiment?

Answer 19

1) prepare temporary mount of root tissue
2) focus an optical microscope on the slide and count total number of cells in the field view and number of cells in a mitosis stage
3) calculate the mitotic index

Question 20

What is the mitotic index?

Answer 20

proportion of cells undergoing mitosis

Question 21

What are the 4 steps on how to prepare a root tip mount?

Answer 21

1) place root in hydrochloric acid to halt cell division and hydrolyse middle lamella
2) strain root tip with a dye that binds to chromosome
3) macerate tissue in water using mounted needle
4) use mounted needle at 45 degrees to press down coverslip and obtain a single layer of cells and avoid trapping air bubbles

Question 22

Why is only the root tip use when calculating a mitotic index?

Answer 22

• meristematic cells at root tip are actively undergoing mitosis
• cells further from root tip are elongating rather than dividing

Question 23

What are tumour suppressor genes?

Answer 23

genes that code for proteins to trigger apoptosis/slow cell cycle

Question 24

What is apoptosis?

Answer 24

programmed death of damaged cells

Question 25

What are proto-oncogenes?

Answer 25

genes that code for proteins to stimulate cell cycle to progress from 1 stage to the next

Question 26

How do cancer treatments control rate of division?

Answer 26

disrupt cell cycle:
- prevent DNA replication
- disrupt spindle formation which inhibits metaphase and anaphase

Question 27

What is one issue with cancer treatments?

Answer 27

can also damage healthy cells

Question 28

How can mutations to tumour suppressor genes cause cancer?

Answer 28

• no production of a protein needed to slow the cell cycle
• disruption to cell cycle causing uncontrolled cell division which leads to a tumour

Question 29

How can mutations to proto-oncogenes cause cancer?

Answer 29

• form permanently-activated oncogenes
• disruption to cell cycle causing uncontrolled cell division which leads to a tumour

Question 30

What are the 4 steps on how prokaryotic cells replicate via binary fission?

Answer 30

1) DNA loop replicates, both copies stay attached to cell membrane, plasmids replicate in cytoplasm
2) cell elongates, separating the 2 DNA loops
3) cell membrane contracts and septum forms
4) cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids

Question 31

What are the 4 steps on how a virus replicates?

Answer 31

1) attachment proteins attach to receptors on host cell membrane
2) enveloped viruses fuse with cell membrane or move in via endocytosis and either release DNA/RNA into the cytoplasm or inject the DNA/RNA
3) host cell uses viral genetic information to synthesis new viral proteins/nucleic acid
4) components of new viral particle assemble

Question 32

What happens to new viral particles which leave host cell?

Answer 32

they either bud off and use cell membrane to form envelope or cause lysis of host cell

Question 33

Why is it difficult to develop effective treatments against viruses?

Answer 33

they replicate inside living cells so it’s difficult to kill them without killing host cell

Question 34

What is one issue with viruses?

Answer 34

it’s difficult to develop effective treatment against them