cell division

Question 1

define a gene

Answer 1

a specific section of DNA that codes for the production of one specific protein

Question 2

how many chromosomes does each human somatic cells contain?

Answer 2

46 chromosomes
23 pairs

Question 3

why is it somatic cells in all multicellular organisms must be able to divide and reproduce cells

Answer 3

so that:
- damaged and old cells are replaced
- tissues and organs can be replaced
- tissues and organs can grow
- the organism itself can grow

Question 4

explain stage 1 of the cell cycle

Answer 4

Cell growth and replication:
- cell increases in size
- DNA is replicated so that there is twice as much DNA present
- number of organelles such as the mitochondria and ribosomes are also doubled

Question 5

explain stage 2 of the cell cycle

Answer 5

mitosis:
- Chromosomes are lined up in the middle of the cell
- half of the chromosomes are pulled to each side
- 2 nuclei form within the cell
- the cytoplasm, organelles + cell membrane and nuclei are split to form 2 new daughter cells which are genetically identical

Question 6

describe 1 difference between 1 daughter cells

Answer 6

one has ring-shaped plasmids

Question 7

Bacteria divide when conditions are favourable. Give 2 examples of favourable conditions for bacterial growth

Answer 7

• few toxins
• enough space

Question 8

a cell has a mean division time of 20 minutes. How many cells will it produce in an hour?

Answer 8

60/20= 3
2^3 = 8 cells

Question 9

a single cel divides to produce 32 cells in 2.5 hours. What is the mean division time in minutes?

Answer 9

2.5h/5 = 30 minutes

Question 10

what is a stem cell?

Answer 10

an undifferentiated cell

Question 11

where does asexual reproduction occur?

Answer 11

bacteria, some plants, and some animals

Question 12

explain asexual reproduction

Answer 12

• involves mitosis
• involves only one parent
• does not involve the fusion of gametes
• does not result in the mixing of genetic information
• produces genetically identical offspring

Question 13

where does sexual reproduction occur?

Answer 13

animals

Question 14

what do reproductive organs include in meiosis?

Answer 14

• testes + ovaries in animals
• anthers and ovaries in flowering plants

Question 15

what happens when a cell divides to for gametes in meiosis?

Answer 15

• copies of genetic information are made
• the cell divides twice to form four gametes, each with a single set of chromosomes
• which are haploid
• all gametes are genetically different from each other

Question 16

compare mitosis and meiosis

Answer 16

1. (mitosis) produces genetically identical cells
   (meiosis) produces genetically unique cells
2. (mitosis) results in diploid cells
   (meiosis) results in haploid cells
3. (mitosis) takes place throughout an organisms lifetime
   (meiosis) takes place only at certain times in an organism’s lifetime
4. (mitosis) asexual reproduction
   (meiosis) sexual reproduction

Question 17

advantages of sexual reproduction

Answer 17

• produces genetically varied offspring: advantage because if the environment changes variation give some individuals a survival advantage by allowing natural selection
• natural selection can be speeded up by humans in selective breeding to increase food production

Question 18

advantages of asexual reproduction

Answer 18

• only one parent needed
• more time + energy efficient as parent doesn’t need to find a mate
• faster than sexual reproduction
• many genetically identical offspring can be produced when conditions are favourable