Cell Division

Question 1

Why do cells divide by mitosis?

Answer 1

• to produce additional cells during growth

- to produce replacement cells

Question 2

What is a malignant tumour?

Answer 2

• the tumour grows and can spread to healthy tissue
• some malignant tumour cells can get int the bloodstream and circulate to other parts of the body
• malignant cells invade healthy tissues and form secondary tumours
• dangerous and potentially fatal

Question 3

How do chemicals and radiation cause tumours?

Answer 3

• chemical carcinogens: e.g. in tobacco or asbestos have been linked to lung cancer. interferes with normal cell functions, causing cells to divide uncontrollably and form a tumour
• ionising radiation: such as UV and x-rays

Question 4

When does a new cell have two sets of chromosomes?

Answer 4

• when gametes fuse at fertilisation
• the organism inherits genes from both parents
• this is how sexual reproduction produces variation
• this cell repeatedly divides by mitosis to form many cells

Question 5

What do cells in reproductive organs divide to form and by which process?

Answer 5

• gametes

- meiosis

Question 6

Describe the stages of mitosis

Answer 6

• in a cell that is not dividing, the DNA is spread out in long strings
• if a cell gets a signal to divide, DNA is replicated, to form X-shaped chromosomes.
• Each chromosome condenses, becoming shorter and thicker. the nuclear envelope (membrane) disappears
• the chromosomes line up at the centre of the cell and the cell fibres pull them apart
• membranes form around each of the sets of chromosomes, becoming the nuclei of the two new cells
• the cytoplasm divides, produces two daughters cells, each containing the same chromosomes

Question 7

How many copies of each chromosome do gametes have?

Answer 7

• only one copy of each chromosome

- this is so that it can combine with the sex cell of the mother and father

Question 8

When do organisms’ cells differentiate?

Answer 8

• as an organism develops, cells differentiate to form different kinds of cells
• animal: cells usually differentiate at an early stage. in mature animas, cell division is mainly restricted to repair and replacement
• plants: retain the ability to differentiate throughout life

Question 9

What are chromosomes made from?

Answer 9

• long DNA molecules

Question 10

Why are some people against stem cell research?

Answer 10

• human embryos shouldn’t be used for experiments as each one is a potential human life
• scientists should concentrate more on finding and developing other sources of stem cells, so embryos will not have to be used

Question 11

What is mitosis?

Answer 11

• when a cell reproduces itself by splitting to form two genetically identical cells

Question 12

What is therapeutic cloning?

Answer 12

• an embryo would be produced with the same genes as the patient, so the embryo would not be rejected by the patient’s body

Question 13

How do bone marrow transplants treat some blood diseases?

Answer 13

• e.g. sickle cell anaemia

- bone marrow contains stem cells that can turn into new blood cells to replace the faulty old ones

Question 14

What form does the nucleus contain genetic material?

Answer 14

• in the form of chromosomes

Question 15

What are alleles?

Answer 15

• different versions of the same gene

- gives different versions of a characteristic

Question 16

Where are stem cells found in humans?

Answer 16

• in early human embryos: they have the potential to turn into any kind of cell
• in the bone marrow in adults: they aren’t as versatile and can only turn into certain types of cell

Question 17

What happens when cells divide in an abnormal and uncontrolled way

Answer 17

• it forms a tumour that could be benign or malignant

Question 18

Where does meiosis occur in humans?

Answer 18

• only in the reproductive organs

Question 19

What is a gene?

Answer 19

• a gene is a short section of DNA.

- Each gene codes for a specific protein by specifying the order in which amino acids must be joined together.

Question 20

What is differentiation?

Answer 20

• differentiation is the process by which a cell changes to become specialised for its job

Question 21

How many pairs of chromosomes does a human cell nucleus contain?

Answer 21

• 23 pairs

Question 22

What do chromosomes carry?

Answer 22

• genes

- each chromosome carries a large number of genes

Question 23

What is a benign tumour?

Answer 23

• the tumour grows until there is no more room
• the cells stay where they are and don’t invade other tissues
• isn’t normally dangerous

Question 24

What are stem cells?

Answer 24

• these are undifferentiated cells that can develop into different types of cell, depending on what instructions they’re given

Question 25

What is cancer caused by?

Answer 25

• it is caused by body cells dividing out of control

Question 26

Describe meiosis

Answer 26

• DNA duplication occurs. each chromatid of a chromosome is an exact copy of the other chromatid
• In the first division in meiosis, the chromosome pairs line up in the centre of the cell
• the pairs are then pulled apart, so each new cell only has one copy of each chromosome
• some of the father’s chromosomes and some of the mother’s go into each new cell
• in the second division, the chromosomes line up again in the centre of the cell. the arms of the chromosomes re pulled apart
• you get four gametes each with only a single set of chromosomes in it

Question 27

Why are some people for stem cell research?

Answer 27

• patients who already exist and are suffering are more important than the rights of embryos
• embryos used in research are usually unwanted ones from fertility clinics which would have probably been destroyed

Question 28

How can embryonic stem cells help?

Answer 28

• they can be extracted from human embryos and grown
• e.g. make beating heart muscle cells in sick people
• insulin- producing cells for diabetics
• nerve cells for paralysed people with spinal injuries