WRONG Qs LAST PUSHHHHHHHHH

Question 1

Describe the role of calcium ions and ATP in the contraction of a myofibril (7 marks):

Answer 1

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites))

Question 2

Ways in which ATP is a suitable energy source for cells to use (5 marks)

Answer 2

1. Releases relatively small amounts of energy
2. Releases energy instantly
3. Phosphorylated other compounds making them more reactive
4. Can be rapidly re synthesised
5. Not lost/ doesn’t leave cells

Question 3

What processes increase genetic variation in meiosis?

Answer 3

1. Independent segregation of homologous chromosomes M1
2. Crossing over of non-sister chromatids P1
3. Random fertilisation after meiosis

Question 4

What process causes a difference in the number of chromosomes?

Answer 4

• chromosome non-disjunction
• chromosomes fail to separate in meiosis= 1 extra copies or no copies of a particular chromosome
• e.g. Down’s syndrome= 47 instead of 46 as 3 copies of chromosome 21

Question 5

What is a homologous chromosome

Answer 5

• pairs of matching chromosomes in diploid organisms with one inherited form each parent
• share the same length, centromere position and gene sequence (loci) but may have different alleles (variations) for those genes

Question 6

What’s the difference between a sister and non-sister chromatid?

Answer 6

• sister chromatids= genetically identical copies of a single chromosome
• non sister chromatids= from homologous chromosomes (one maternal one paternal) that are not identical

Question 7

Describe the process of crossing over (4 marks)

Answer 7

1. Occurs in prophase/ metaphase 1 in meiosis
2. Non-sister chromatids of each pair become twisted around eachother
3. Creates tension and chiasmata breaks so sections of non-sister chromatids break off
4. Then rejoin with chromosomes of homologous partner which results in new combinations of alleles of chromatids= genetic variation

Question 8

Formula to work out number of chromosome combinations after meiosis:

Answer 8

2^n
- n= number of homologous chromosome pairs- in humans this would be 23 as 46 (diploid)/ 2= 23 (haploid)

Question 9

Formula to work out number of chromosome combinations after fertilisation:

Answer 9

(2^n)^2
- n= number of homologous chromosome pairs
- ^2= number of gametes
- in humans would be (2^23)^2

Question 10

What is a translocation mutation?

Answer 10

A section of one chromosome is separated and added onto another chromosome (not a homologous pair)

Question 11

2 similarities between diffusion and osmosis (2 marks):

Answer 11

1. Substances move down a concentration gradient
2. Do not use energy from respiration

Question 12

Where is ADH secreted?

Answer 12

The posterior pituitary gland

Question 13

Two symptoms as a result of a decrease in ADH:

Answer 13

1. Dehydration
2. Increase in volume of urine
3. Paler urine

Question 14

Describe the effect of ADH on the collecting duct of the kidneys (2 marks)

Answer 14

1. Stimulates addition of channel proteins into membrane
2. Increases permeability to water