Questions at end of AS paper 2

Question 1

Describe the roles of iron ions, sodium ions, and phosphate ions in a cell ( 5 marks )

Answer 1

Iron ions
- Haemoglobin binds with oxygen

Sodium ions
- Co-transport of glucose
- Because sodium moved out by
active transport
- Creates a sodium concentration
gradient
- Affects osmosis

Phosphate ions
- Affects osmosis
- Joins nucleotides
- Used to produce ATP
- Phosphorylates other
compounds
- Water soluble part of
phospholipid

Question 2

The movement of substance across cell membranes is affected by membrane structure. Describe how (5 marks)

Answer 2

• Phospholipid bilayer allows movement of non-polar substances
• Phospholipid bilayer prevents movement of polar substances
• Carrier proteins allow active transport
• Channel/ carrier proteins allow faciliatated diffusion
• Shape of channel/ carrier determines which substances move
• Membrane surface area determines how much diffusion
• Cholesterol affects fluidity

Question 3

Explain five properties that make water important for organisms (5 marks)

Answer 3

• A metabolite in condensation
• A solvent so metabolic reactions can occur
• High specific heat capacity so buffers changes in temperature
• Large latent heat of vapourisation so provides a cooling effect
• Cohesion between water molecules so supports columns of water
• Cohesion between water molecules so produces surface tension supporting small organims

Question 4

Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue (6 marks)

Answer 4

• Homogenise to break open cells
• Filter to remove debris
• Cold solution to prevent enzyme activity
• Solutions with equivalent water potential to prevent osmosis
• Buffered solution to stop enzyme denaturing
• Centrifuge at lower speed so nuclei in pellet move to bottom

Question 5

Describe the role of organelles in the production and release of enzymes by animal cells (5 marks)

Answer 5

• DNA in nucleus codes for enzyme
• Ribosome produces enzyme
• Rough endoplasmic reticulum transports enzyme
• Mitochondria produce ATP
• Golgi apparatus modify enzymes
• Vesicles move to cell surface membrane

Question 6

Describe the structure of ATP.
Outline how named enzymes break down and resynthesise ATP (4 marks)

Answer 6

• Ribose, Adenine, and 3 phosphates
• ATP to ADP + Pi by ATP hydrolase in hydrolysis
• ADP + Pi to ATP by ATP synthase
• In condensation reaction

Question 7

Describe how the quaternary protein is formed from its monomers (5 marks)

Answer 7

• Amino acids joined by peptide bonds
• By condensation reactions
• Secondary structure is formed by hydrogen bonding
• Tertiary structure formed by interactions between R groups
• Quaternary structure contains more than 1 polypeptide

Question 8

Describe the structure of DNA and the structure of a chromosome (6 marks)

Answer 8

• Polymer of nucleotides
• Nucleotide consists of deoxyribose, phosphate, and a nitrogenous base
• Phosphodiester bonds between nucleotides
• DNA double helix held by hydrogen bonds
• Hydrogen bonds between adenine, thymine and cytosine and guanine
• DNA associated with histones
• Chromosome consists of 2 chromatids joined at a centromeme

Question 9

Other than mutations, describe and explain the other processes that result in increase in genetic variation within a species (4 marks)

Answer 9

• Independent segregation of homologous chromosomes
• Crossing over between homologous chromosomes
• Random fertilisation of gametes
• Produces new combinations of alleles

Question 10

Define gene mutation and explain how a gene mutation can have:
- No effect on an individual
- A positive effect on an individual (4 marks)

Answer 10

(Definition of gene mutation)
1. Change in the base/nucleotide (sequence of
chromosomes/DNA);
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid
sequence may not change);
OR
Mutation is in an intron (so amino acid sequence
may not change);
4. Does change amino acid but no effect on tertiary
structure;
5. (New allele) is recessive so does not influence
phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively
changes the properties (of the protein)
OR
Results in change in polypeptide that positively
changes a named protein;
7. May result in increased reproductive success
OR
May result in increased survival (chances);