Unit 2 - All Cells Arise From Other Cells

Question 1

What is a chromosome?

Answer 1

A chromosome is 1 DNA molecule folded into a condensed form, wrapped around histone proteins in eukaryotes.

Question 2

Following DNA replication what is a chromosome made from?

Answer 2

They’re made of 2 genetically identical sister chromatids. The chromatids are attached at the centromere.

Question 3

What is the definition of homologous chromosomes?

Answer 3

They have the same genes, but may have different alleles.

Question 4

What are diploid cells?

Answer 4

Cells with homologous pairs of chromosomes.

Question 5

What are haploid cells?

Answer 5

Cells with only 1 copy of each homologous pair of chromosomes.

Question 6

Example of a haploid cell?

Answer 6

Gamete cells.

Question 7

When can cells no longer divide?

Answer 7

One a cell is specialised and fully differentiated it cannot divide, but unspecialised calls can divide.

Question 8

What are the 3 main stages of the cell cycle?

Answer 8

1) Interphase
2) Mitosis
3) Cytokinesis

Question 9

What is interphase?

Answer 9

Interphase is the time when the cell is NOT dividing. During interphase the following events take place:
-New proteins are synthesised
-DNA replicates
-New organelles are made
The individual chromosomes are not visible during interphase, instead you can see the chromatin in the nucleus.

Question 10

Photo of a cell during interphase?

Question 11

What is mitosis?

Answer 11

The process which the cell undergoes to produce 2 genetically identical daughter cells.

Question 12

Why is mitosis important?

Answer 12

1) It allows the organism to grow.
2) Allows organisms to replace cells in order to repair tissues.
3) Results in genetically identical cells.
4) Asexual reproduction in some organisms.

Question 13

What are the 4 stages of mitosis?

Answer 13

Prophase, Metaphase, Anaphase and Telophase.

Question 14

What happens during prophase?

Answer 14

1) The nuclear membrane breaks down.
2) Centrioles move to the poles of the cell and make spindle fibres.
3) The chromosomes condense and become visible. Each chromosome is made up of 2 sister chromatids joined at the centromere.

Question 15

Photo of a cell during prophase?

Question 16

What happens during metaphase?

Answer 16

1) Spindle fibres attach to the centromere of each chromosome.
2) The chromosomes are moved to the equator (middle) of the cell by spindle fibres.

Question 17

Photo of a cell during metaphase?

Question 18

What happens during anaphase?

Answer 18

1) The centromere divides.
2) The spindle fibres contract, sister chromatids are pulled apart to the opposite poles of the cell.

Question 19

Photo of a cell during anaphase?

Question 20

What happens during telophase?

Answer 20

1) Chromosomes have reached the poles and the spindle fibres break down.
2) A new nuclear membrane forms around each group of chromosomes.
3) The chromosomes un-condense and begin to form chromatin again.

Question 21

Photo of a cell during telophase?

Question 22

What happens during cytokinesis?

Answer 22

The cytoplasm divides, producing 2 genetically identical daughter cells.

Question 23

What is mitosis controlled by?

Answer 23

It is controlled by certain genes.

Question 24

What leads to the formation of tumours and cancer?

Answer 24

If a mutation occurs in these genes, this causes uncontrolled cell division, which leads to the formation of tumours and cancer.

Question 25

Characteristics of cancerous cells?

Answer 25

-They divide uncontrollably.
-They have a shorter cell cycle.
-They divide more often.
-They’re unspecialised and have no function.

Question 26

How can tumours cause harm?

Answer 26

By damaging organs or blocking blood vessels to organs.

Question 27

How do cancer treatments work?

Answer 27

They mainly work by targeting parts of the cell cycle to prevent the cell from dividing. For example, these drugs may stop:
-DNA replication (disrupts interphase)
-Spindle formation/spindle contraction (prevents metaphase/anaphase)
-Cytokinesis

Question 28

What’s a side effect of cancer treatments?

Answer 28

They do not always distinguish tumour cells from healthy cells, so they also kill some normal body cells that are dividing, causing side effects.

Question 29

Why do treatments target tumour cells more?

Answer 29

Because tumour cells divide more frequently than normal cells.

Question 30

What is the process called that prokaryotic cells replicate by?

Answer 30

Binary fission.

Question 31

What are the steps of binary fission?

Answer 31

1) The circular DNA and the plasmids replicate.
2) The copies of circular DNA move to separate poles of the cell.
3) The cytoplasm divides to produce 2 daughter cells.
4) Each cell contains a single copy of the circular DNA but a variable number of plasmids.

Question 32

Why do viruses use a specific host cell to replicate?

Answer 32

Because viruses are non-living and acellular, so they don’t undergo cell division.

Question 33

How do viruses replicate?

Answer 33

1) The virus attachment proteins binds to a specific complementary receptor protein on a specific host cell.
2) The viral DNA/RNA is injected into the host cell.
3) The host cell uses the viral DNA/RNA and its own ribosomes and enzymes to synthesise viral proteins.
4) The viral particles are formed and released from the host cell.

Question 34

Why are viruses hard to treat with drugs?

Answer 34

They’re hard to treat with drugs because they replicate inside the cells where the drug is unable to bind them.

Question 35

How do calculate the length of a certain stage of mitosis?

Answer 35

(Number of cells in certain stage divided by total number of cells) multiplied by 100.

Question 36

What is the formula for mitotic index?

Answer 36

Number of cells undergoing mitosis (visible chromosomes) divided by total number of cells. Always give your mitotic index answer as a decimal. ONLY convert it to a percentage of the question asks you to!