paper 1- 5 markers

Question 1

Explain five properties that make water important for organisms

Answer 1

A metabolite in condensation/hydrolysis/ photosynthesis/respiration
A solvent so (metabolic) reactions can occur
High heat capacity so buffers changes in temperature
Large latent heat of vaporisation so provides a cooling effect
Cohesion (between water molecules) so supports columns of water (in plants)
Cohesion (between water molecules) so produces surface tension supporting (small) organisms

Question 2

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample

Answer 2

Lipid- Add ethanol then add water and mix, milky white emulsion
Non-reducing sugar- Do Benedict’s test and stays blue/negative, Boil with acid then neutralise with alkali, Heat with Benedict’s and becomes red/orange
Amylase- Add biuret (reagent) and becomes purple/violet/mauve/lilac, Add starch, test for reducing sugar/absence of starch

Question 3

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers

Answer 3

A condensation reaction joins monomers together and forms a (chemical) bond and releases water
A hydrolysis reaction breaks a (chemical) bond between monomers and uses water
e.g. amino acid and polypeptide, alpha glucose and glycogen
e.g. nucleotide and polynucleotide
Reference to a correct bond within a named polymer

Question 4

Compare and contrast the structure and properties of triglycerides and phospholipids

Answer 4

Both contain ester bonds
Both contain glycerol
Fatty acids on both may be saturated or unsaturated
Both are insoluble in water
Both contain C, H and O but phospholipids also contain P
Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group
Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t

Question 5

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 5

Glucose and galactose
Joined by condensation
Joined by glycosidic bond
Added to polypeptide in Golgi

Question 6

The diagram shows an image from an optical microscope of meiosis occurring in a flower bud of a flowering plant. W and Z are undergoing meiosis. Explain the appearance of W and Z

Answer 6

W has 4 cells / nuclei since it is at the (end of) 2nd division
Z has 2 cells/nuclei since it is at the (end of) 1st division
W shows haploid cells / cells containing n chromosomes
W contain half the mass of DNA of cells in Z

Question 7

Describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees

Answer 7

Use random sample of seeds (from each population)
Use (large enough) sample to be representative of whole population
Indication of what size was measured e.g. mass
Calculate a mean and standard deviation (for each population)
Use the (Student’s) t-test
Analyse whether there is a significant difference between (the means of) the two populations

Question 8

Describe the roles of iron ions, sodium ions, and phosphate ions in cells

Answer 8

Haemoglobin binds/associates with oxygen

Co-transport of glucose/amino acids
sodium moved out by active transport/Na – K pump
Creates a sodium concentration/diffusion gradient
Affects osmosis/water potential

Affects osmosis/water potential
Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides
Used in/to produce ATP
Phosphorylates other compounds (usually) making them more reactive
Hydrophilic/water soluble part of phospholipid bilayer/membrane

Question 9

The movement of substances across cell membranes is affected by membrane structure. Describe how.

Answer 9

Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances
Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances
Carrier proteins allow active transport
Channel/carrier proteins allow facilitated diffusion/co-transport
Shape/charge of channel / carrier determines which substances move
Number of channels/carriers determines how much movement
Membrane surface area determines how much diffusion/movement
Cholesterol affects fluidity/rigidity/permeability