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
- Phosphorykates 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