Cell division and stem cells

Question 1

Where are chromosomes found?

Answer 1

In the nucleus of every cell.

Question 2

When are chromosomes visible?

Answer 2

Only when the cell is about to divide.

Question 3

What are chromosomes made out of?

Answer 3

DNA (deoxyribonucleic acid)

Question 4

What are genes?

Answer 4

Genes are sections of DNA that control the features of an organism.

Question 5

How many chromosomes are there in humans?

Answer 5

46 chromosomes (23 pairs, 23 from each parent).

Question 6

Are the pairs in meiosis identical?

Answer 6

They are not identical because the form of the gene (called an allele) can vary.

Question 7

What are xy and xx chromosomes?

Answer 7

Male and female.

Question 8

What are the sex determining chromosomes?

Answer 8

Pair number 23.

Question 9

What does cell division result in?

Answer 9

In multicellular organisms, it results in growth, repair, replacement of old or damaged cells and tissues.

Question 10

What is mitosis?

Answer 10

Where one cell (the mother cell) divides to form 2 new (daughter) cells. The daughter cells are genetically identical to the mother cell because the chromosomes replicate themselves and one copy is passed into each of the new 2 cells.

Question 11

In mitosis, is the number of chromosomes in the mother and daughter cells the same?

Answer 11

Yes, both have equal chromosomes.

Question 12

When does meiosis occur?

Answer 12

It only occurs when sex cells (gametes) are formed.

Question 13

What is meiosis?

Answer 13

Although the DNA and chromosomes duplicate like mitosis, 4 new cells are formed instead of 2, and each cell receives half a set of chromosomes. (23 each)

Question 14

Do the pairs of cells in meiosis form identically?

Answer 14

The chromosomes have pairs that are not identical because during the process meiosis the gametes get one chromosome from each pair. The new cells in meiosis are therefore not identical.

Question 15

Why is mitosis carefully regulated?

Answer 15

Mitosis is carefully regulated to allow time for cells to grow and become specialised. Sometimes this control fails, mitosis gets out of control and the cells produce cancerous tumours.

Question 16

What are the 4 main points regarding mitosis?

Answer 16

• Occurs in all body cells except those forming gametes.
• Daughter cells are genetically identical.
• 2 daughter cells are formed.
• Daughter cells have a full set of chromosomes.

Question 17

What are the 4 main points regarding meiosis?

Answer 17

• Occurs only in gamete-forming cells.
• Daughter cells are genetically different.
• 4 daughter cells are formed.
• Daughter cells have half sets of chromosomes.

Question 18

What is an embryo?

Answer 18

Undifferentiated clumps of cells that have not yet specialised. The can turn into any cell.

Question 19

What happens when a cell differentiates?

Answer 19

They can only form cells similar to themselves.

Question 20

What are stem cells?

Answer 20

The undifferentiated cells in the embryo.

Question 21

What can stem cells do?

Answer 21

Grow them into different types of cell that can be used to repair or replace damaged tissue.

Question 22

What are the advantages to stem cell therapy?

Answer 22

• They could be used to treat diseases such as cancer and type 1 diabetes, which affect or kill millions of people.
• They can be used to repair damaged damaged tissue, such as brain damage or spinal cord injuries which can result in paralysis.

Question 23

What are the objections to stem cell therapy?

Answer 23

• Any embryo has the potential to develop into a human being, and so the process destroys life. However, the embryos used are those rejected during fertility treatment, so even if they were not used they would never get the chance to develop.
• Some people are worried that embryos might be created specifically to produce stem cells, so it would be like ‘farming’ human beings (but this is not a current issue, rather one to consider in the future).

Question 24

What are alternatives to stem cell therapy?

Answer 24

• Stem cells can be found in adults (bone marrow). These cells are in mature tissues but have not lost the ability to differentiate into different cells. The issue is they cannot develop into as many types of cells as embryos can.
• Stem cells can be collected from the umbilical cord at birth. These could be useful in treating that same baby later in life as the cells would be genetically identical to its own cells and so would not be attacked by its own immune system.

Question 25

What are meristems?

Answer 25

Stem cells within plants. They are found in the growing areas of a plant in shoots and roots. They can be used to cultivate new plants, but have no medical uses.

Question 26

Why is Gregor Mendels theory not representative of most phenotypes?

Answer 26

Most phenotypes are the result of multiple genes

Question 27

State the term used to refer to competition between 2 different species.

Answer 27

Interspecific competition

Question 28

State the term used to refer to competition between members of the same species.

Answer 28

Intraspecific competition