B2 Cell Divison

Question 1

What do chromosomes do?

Answer 1

Chromosomes carry genes that contain instructions for making new cells, organs, and tissues.

Question 2

Define gene

Answer 2

A small packet of information that controls a characteristic (or part of it) of your body.

Question 3

How many pairs of chromosomes do we have?

Answer 3

23 pairs = 46 chromosomes

Question 4

Where are chromosomes found?

Answer 4

In the nucleus of cells

Question 5

How many chromosomes do gametes have?

Answer 5

23 chromosomes (1 per pair)

Question 6

Why is mitosis needed?

Answer 6

For growth and replacement of cells (e.g. at the site of a wound, during production of RBS in bone marrow, during growth spurts etc…)

Question 7

How does the length of the cell cycle vary during: baby development (before birth), childhood, and after puberty?

Answer 7

Baby development before birth: Short
Childhood: Fairly rapid
After puberty: Slows down

Question 8

Summarise the stages of the cell cycle (3 stages)

Answer 8

1) Cells grow bigger, increase mass to carry out normal cell activities. Cells replicate their DNA to form two copies of each chromosome. Cells increase the amount of sub-cellular structures (e.g mitochondria, ribosomes) {Longest Stage}.
2) Mitosis: One set of chromosomes is pulled to each end of the cell and the nucleus divides.
3) Cytoplasm and cell membrane divide to form two identical daughter cells.

Question 9

Why is cell division by mitosis important?

Answer 9

It’s important in the growth and development of multicellular organisms.

Question 10

Define DNA

Answer 10

A unique molecule which makes up our chromosomes

Question 11

Define stem cells

Answer 11

An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type.

Question 12

What happens as an organism develops?

Answer 12

Cells differentiate to form different types

of cells.

Question 13

When do animal cells become specialised?

Answer 13

In animals, most cells become specialised in early life.

Question 14

What happens when a cell becomes specialised?

Answer 14

Some of its genes have been switched on; others have turned off. The cell acquires different sub-cellular structures to carry out specific functions.

Question 15

Describe the restriction of cell division in mature animals

Answer 15

In mature animals, cell division is mainly restricted to repair and replacement.

Question 16

How do specialised cells divide and what are the restrictions of specialised cells dividing?

Answer 16

Specialised cells can divide by mitosis; they can only form the same sort of cell (e.g muscle cells divide to form more muscle cells).

Question 17

List 2 examples of cells which can’t divide and describe how they are replaced

Answer 17

Red blood cells and skin cells can’t divide so they are replaced by adult stem cells.

Question 18

Can nerve cells divide? If not, how are they replaced?

Answer 18

Nerve cells can’t divide, once differentiated and they can’t be replaced by stem cells. Therefore, damaged nerve cells usually aren’t replaced.

Question 19

How does plant cell differentiation differ from animal cell differentiation?

Answer 19

Plant cells can differentiate throughout their lives.

Question 20

Where are undifferentiated cells formed (plants)?

Answer 20

At the meristems (active regions of stems and roots).

Question 21

What happens at the meristems?

Answer 21

Mitosis continuously happens at the meristems. The cells grow and elongate before they differentiate.

Question 22

Describe how plant cells can redifferentiate

Answer 22

Plant cells can move from one part of a plant to another, where it can redifferentiate and become a different cell.

Question 23

Explain how a piece of leaf tissue can produce identicall plant clones

Answer 23

1) In right conditions, a plant cell will become unspecialised and undergo mitosis many times.
2) Undifferentiated cells will produce more cells by mitosis.
3) These cells will then differentiate to form tissues.

Question 24

What does an egg and sperm cell form?

Answer 24

A zygote (single new cell)

Question 25

How is an embryo formed?

Answer 25

When the zygote divides and becomes a hollow ball of cells - the embryo

Question 26

Where are embryonic stem cells taken from?

Answer 26

The inner cells of the ball (embryo) are embryonic stem cells.

Question 27

Where, in the human body, is there a good source of adult stem cells?

Answer 27

Bone marrow

Question 28

List 2 conditions stem cells may be able tohelp

Answer 28

Paralysis and diabetes

Question 29

Stem cells from meristems can be used to make clones of mature parent plants quickly. List reasons this is helpful (5 reasons)

Answer 29

• Can produce large numbers of plants reliably and safely.
• Can save rare plants from extinction.
• Produce large population of plants for scientific research.
• Horticulture: produce large numbers of plants for sale.
• Agriculture: produce large numbers of plants with special features (e.g disease resistance).

Question 30

How do embryonic stem cells differ from adult stem cells?

Answer 30

Embryonic stem cells can differentiate into any type of cell; adult stem cells can only differentiate into related types of cells.

Question 31

Cons of embryonic stem cells

Answer 31

• Religious beliefs: can’t accept interference with human reproduction.
• Progress in therapies involving embryonic stem cells has been slow, difficult, and expensive.
• Difficult to persuade embryonic stem cells to differentiate into other types of cells.
• Divide and grow rapidly: could potentially cause cancer.

Question 32

Cons of adult stem cells

Answer 32

• May be infected with viruses which could transfer infections to the patient.
• If used to treat an unrelated person, could trigger an immune response: patient would have to take immunosuppresant drugs to stop the body rejecting the cells.
• A lot of money and time is being wasted on stem cell research.

Question 33

Pros of using stem cells

Answer 33

• Scientists have found embryonic stem cells in the umbilical cord blood of babies and in the ammiotic fluid that surrounds the fetus: can overcome ethic problems.
• Scientists are finding ways to grow adult stem cells, due to limited range: avoids ethic problems and have been used to treat forms of heart disease and grow organs such as tracheas.

Question 34

What is the area of stem cell research known as?

Answer 34

Therapeutic cloning

Question 35

What happens in therapeutic cloning?

Answer 35

An embryo is produced with the same genes as the patient so the stem cells produced are not rejected.