Cell Cycle Exam Revision (ch4)

Question 1

Why do cells replicate?

Answer 1

Growth/Development, maintain and repair tissues, reproduce (unicellular organisms)

Question 2

Exponential Growth +example

Answer 2

Cells double each cycle. Formula C=2n (C=total cells, n=divisions)
Eg. Bacteria can divide every 20 minutes

Question 3

Define Binary Fission

Answer 3

Binary fission is a type of asexual reproduction used by prokaryotic cells (like bacteria), where a single parent cell divides into two genetically identical daughter cells.

Question 4

Features of Binary Fission

Answer 4

Occurs in prokaryotes (no nucleus), Simple and fast process, No need for a mate (asexual), Produces clones (same DNA as parent)

Question 5

Steps Of Binary Fission

Answer 5

DNA replication – Circular chromosome and plasmids are copied.
Cell elongation – DNA moves to opposite ends.
Cytokinesis – Cell membrane pinches inward.
Separation – Two identical cells are formed.

Question 6

Interphase

Answer 6

The stage where the cell grows, duplicates its DNA, and prepares for division.

Question 7

Mitosis

Answer 7

The process where the nucleus divides, separating duplicated chromosomes into two identical nuclei.

Question 8

Cytokenisis

Answer 8

The division of the cytoplasm that results in two separate, genetically identical daughter cells.

Question 9

Interphase Subphases:G1

Answer 9

G1 (Gap 1) – Cell grows, synthesises proteins, organelles replicate

Question 10

Interphase Subphases:S

Answer 10

DNA replicates, forming sister chromatids

Question 11

Interphase Subphases:G2

Answer 11

Final preparations, cytosol grows, proteins for mitosis are made

Question 12

Interphase Subphases:G0

Answer 12

Cell rests; may be:
Quiescent – Can re-enter cycle (e.g. liver cells)
Terminally differentiated – Permanent exit (e.g. neurons)

Question 13

Mitosis: Prophase, Metaphase

Answer 13

Prophase – Chromosomes condense, spindle fibres form, nuclear membrane breaks down
Metaphase – Chromosomes align at equator, spindle fibres attach to centromeres

Question 14

Mitosis: Anaphase, Telophase

Answer 14

Anaphase – Centromeres split, chromatids pulled to poles, cleavage furrow forms

Telophase – Spindle fibres break down, nuclei reform, chromosomes de-condense

Question 15

Cytokinesis Plant v Animal

Answer 15

Animals: Cleavage furrow splits cell into two
Plants: Cell plate forms, then splits cell due to rigid wall
Result: Two genetically identical daughter cells

Question 16

What do the Checkpoints do and where are they located

Answer 16

Occur at G1, G2, and Metaphase
Detect errors – cell repairs or undergoes apoptosis if needed

Question 17

Apoptosis

Answer 17

Controlled, programmed cell death
Removes damaged/unwanted cells

Question 18

Function Of Apoptosis

Answer 18

Eliminates faulty cells
Shapes body structures (e.g. finger separation, tail loss in tadpoles)

Question 19

Apoptosis

Answer 19

Intrinsic (Mitochondrial), Trigger: Internal stress or DNA damage
Mitochondria release cytochrome c
Activates caspase enzymes → cell death
Extrinsic (Death Receptor), Trigger: External signals (e.g. immune response)
Death receptors activate caspases

Question 20

Stages of Apoptosis

Answer 20

Caspase enzymes activated (cytochrome c involved), Cell contents break down, Cell and nucleus shrink, Membrane blebbing, apoptotic bodies form, Apoptotic bodies engulfed by phagocytes

Question 21

Necrosis

Answer 21

Necrosis is the uncontrolled death of a cell caused by injury or damage, where the cell swells, bursts, and releases its contents, often leading to inflammation and damage in surrounding tissues.

Question 22

Too much apoptosis

Answer 22

Causes the loss of healthy cells, especially in the brain, and is linked to diseases like. cause: Alzheimer’s, Parkinson’s, Huntington’s

Question 23

To Little apoptosis

Answer 23

Damaged cells aren’t removed, allowing them to divide uncontrollably and form tumours, increasing the risk of cancer.

Question 24

Tumor Benign v Malignant

Answer 24

Benign: Do not spread, slow-growing
Malignant: Invasive, spread to other tissues (cancerous)

Question 25

Factors effecting apoptosis

Answer 25

Mutations (e.g. p53, BRCA1/BRCA2) Chemical: tobacco, air pollution Physical: UV rays, X-rays Biological: viruses

Question 26

Define Stem Cells

Answer 26

Undifferentiated cells Can self-renew and differentiate into specialised cell types

Question 27

Stem Cell Potencys

Answer 27

Totipotent – Can become any cell (e.g. zygote) Pluripotent – Can become many cell types (e.g. embryonic stem cells) Multipotent – Limited to certain types (e.g. blood stem cells → WBC, RBC, platelets)

Question 28

Zygote

Answer 28

Fertilised egg

Question 29

Morula

Answer 29

A morula is a solid ball of 16–32 cells formed by the early divisions of a fertilised egg before it develops into a blastocyst.

Question 30

Gastrula

Answer 30

Forms 3 germ layers: Ectoderm – Skin, nervous system, eyes Mesoderm – Muscles, bones, blood Endoderm – Lungs, digestive system, bladder