B13

Question 1

Meiosis

Answer 1

1) cell grows and DNA replicates
2) First division is when each chromosome pulled to each end
3) cytoplasm and cell membrane divide to form two new cells, each with one set of chromosomes
4) Second division so copy of each chromosome pulled to each end of the cell

5)cytoplasm and cell membrane divide again forming 4 genetically DIFFERENT gametes
Half the no. of chromosomes from parent cell

Question 2

ASEXUAL(mitosis)

• aphids
• Mexican hap-plants
• bacteria
• cells of the body

Answer 2

ADVANTAGES:
Faster
Less energy needed
One parent needed

DISADVANTAGES:
No genetic variety
No evolution through natural selection
More likely to die in changes to environment

Question 3

SEXUAL(meiosis)

• human gametes = sperm and egg
• plant gametes = pollen and egg

🧚🏻‍♀️Opposite of mitosis card so just memorise one of them🧚🏻‍♀️

Answer 3

ADVANTAGES:
Genetic variety
May survive when changes to environment

DISADVANTAGES:
Need to find partner
Slower
Fewer offspring

Question 4

Meiosis & Mitosis comparison

Answer 4

Meiosis: Mitosis:
4 genetically different 2 identical cells

Cells divide twice One division

Gametes with half no. Same no. of chromosomes
Of chromosomes

Sexual Asexual

Question 5

DNA

Answer 5

• polymer made up of two strands forming a double helix

- contained in structures called chromosomes found in the nucleus(2)

Question 6

Human Genome:

Memorise spec reference

Answer 6

• search for genes linked to different types of diseases
• understanding and treatment of inherited disorders
• tracing human migration patterns from the past

Question 7

Nucleotide= Base

Enzyme= Protein

Answer 7

A — T

C — G

Sequence of three—amino acid—protein

Question 8

DNA 
Transcription 
Translation 
Protein
(6 marks)

Answer 8

• template is produced from the DNA in a nucleus
• template leaves the nucleus and binds to surface of the ribosome
• a carrier molecule with an amino acid attached which is complementary to the template attaches
• different carrier molecules keep bringing specific amino acids adding to the growing chain
• protein chain detaches and folds into correct shape

Question 9

Explain how mutation could cause an enzyme to not work
(4 marks)

Diagram usually given

Answer 9

1) incorrect base sequence
2) incorrect amino acid sequence
3) incorrect protein made
4) active site changed
5) enzyme no longer fits the substrate

Question 10

Chromosomes

Answer 10

Human Body = 23 pairs

22 = control characteristics

1 = determines sex

Female= XX 
Male= XY

Question 11

Genetic Screening

Cystic fibrosis

Answer 11

ADVANTAGES:
Greater chance of having child without cystic fibrosis
Cystic fibrosis not passed onto future generations
Child with CF difficult/expensive to bring up

DISADVANTAGES:
 Operation dangers
 Cruel to embryos
 Cost of procedure
 Possible damage to embryos