All cells arise from other cells

Question 1

What is mitosis?

Answer 1

A division of a cell that results in two daughter cells having an exact copy of the DNA of the parent cell.

Question 2

How does cell division take place?

Answer 2

Either by:
Mitosis - produces 2 daughter cells with the same number of chromosomes as the parent cell and each other.
Meiosis - produces 4 daughter cells, each with half the number of chromosomes of the parent cell.

Question 3

What is interphase?

Answer 3

The period following mitosis where the cell is not dividing.
It occupies most of the cell cycle.
Lots of cellular activity, including the replication of DNA.

Question 4

What are the four stages of mitosis?

Answer 4

Prophase
Metaphase
Anaphase
Telophase

Question 5

What is prophase?

Answer 5

The chromosomes shorten and thicken (condense) and become visible.
Centrioles move to opposite ends of the cell and spindle fibres develop from them.
Collectively, these are called spindle apparatus.
The nucleolus disappears and the nuclear envelope breaks down.
The chromosomes are left freely in the cytoplasm.
The chromosomes are drawn to the equator of the cell by the spindle fibres.

Question 6

What is metaphase?

Answer 6

The chromosomes are seen to be made up of 2 chromatids.
Each chromatid is an identical copy of DNA from the parent cell.
The chromatids are joined by the centromere.
The chromosomes are pulled along the spindle apparatus by the centromere and arrange themselves along the equator of the cell.

Question 7

What is anaphase?

Answer 7

The centromeres divide into two and the spindle fibres pull the individual chromatids apart.
The chromatids move to their respective poles and are now referred to as chromosomes.
The energy required is provided by the mitochondria, which gather around the spindle fibres.

Question 8

What is telophase?

Answer 8

The chromosomes reach their respective poles and become longer and thinner, finally disappearing completely, and leaving widespread chromatin.
The spindle fibres disintergrate and the nuclear envelope and nucleolus re-form.
The cytoplasm divides through cytokinesis.

Question 9

How does cell division happen in prokaryotic cells?

Answer 9

Binary fission:
The circular DNA molecule replicates and both copies attach to the cell membrane.
The plasmids also replicate.
The cell membrane begins to grow between the two DNA molecules and pinches inwards, dividing the cytoplasm in two.
A new cell wall forms between the two DNA, dividing the cell into two identical daughter cells.
They each have a single copy of the circular DNA and a variable number of copies of the plasmids.

Question 10

What is mitosis used for?

Answer 10

Growth
Repair
Reproduction

Question 11

Which cells have a cell cycle?

Answer 11

Cells that do not divide continuously but undergo a regular cycle of division separated by periods of growth.

Question 12

What is the first stage of the cell cycle?

Answer 12

Interphase - it occupies most of the cycle (about 90%).
It is sometimes known as the resting place as no division takes place.

Question 13

What is the second stage of the cell cycle?

Answer 13

Nuclear division - when the nucleus divides either into two or four.

Question 14

What is the third stage of the cell cycle?

Answer 14

Cytokinesis - the cytoplasm divides to produce two or four new cells.

Question 15

How long is the cell cycle?

Answer 15

Complete cell cycle length varies between organisms.
Typically, a mammalian cell takes about 24 hours, 90% of which is interphase.

Question 16

What is cancer?

Answer 16

A group of diseases caused by a growth disorder of cells.
It is the result of damage to the genes that regulate mitosis and the cell cycle.
This leads to uncontrollable growth and division of cells.
The cells can reject apoptosis (the cell naturally killing itself) and keep mutliplying.

Question 17

What are tumours?

Answer 17

A group of abnormal cells that develop and constantly expand.

Question 18

When are tumours cancerous?

Answer 18

When they develop from benign to malignant.

Question 19

What are malignant tumours?

Answer 19

They grow rapidly
Less compact
More likely to be life-threatening

Question 20

How is cancer often treated?

Answer 20

It often involves killing dividing cells by blocking part of the cell cycle.
The cell cycle is disrupted and cell division, and hence, cancer growth ceases.

Question 21

How is the cell cycle disrupted?

Answer 21

Drugs - chemotherapy - prevent the DNA from replicating.
Inhibits the metaphase stage of mitosis by interfering with spindle formation.

Question 22

What is the disadvantage with chemotherapy?

Answer 22

They also disrupt the cell cycle of normal cells.
For example, hair-producing cells, that divide rapidly, are also vulnerable to damage, and therefore hair loss is frequent in cancer patients.

Question 23

What is the advantage with chemotherapy?

Answer 23

The drugs are more effective against rapidly dividing cells.
Cancer cells have very fast rate of division, so are damaged to a greater degree than normal cells.

Question 24

How do mutations affect mitosis?

Answer 24

A mutation to one of the genes controlling mitosis causes uncontrolled mitosis.
The mutant cells are usually structurally and functionally different.
Most mutated cells die.
But those that survive are capable of dividing to form clones of themselves and form tumours.

Question 25

What is cell specialisation?

Answer 25

Cells are specialised to perform specific functions.
Depending on their function, cells have developed to have more or less of certain cells.