unit 1 past paper questions Flashcards
A student carried out the Benedict’s test. Suggest a method, other than
using a colorimeter, that this student could use to measure the quantity of
reducing sugar in a solution.
Filter and dry (the precipitate);
Accept: correct reference to evaporation after filtration
Find mass/weight;
Use of a colorimeter in this investigation would improve the repeatability of
the student’s results.
Give one reason why.
Quantitative
OR
(Color change is) subjective;
Accept: accurate/precise
Standardizes (the) method;
Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.
Cellulose is made up of β-glucose (monomers) and glycogen is
made up of α-glucose (monomers);
Cellulose molecule has straight chain and glycogen is
branched;
Cellulose molecule has straight chain and glycogen is coiled;
glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has
only 1,4- glycosidic bonds;
Explain the difference in the structure of the starch molecule and the
cellulose molecule shown in the diagram above.
Starch formed from α-glucose but cellulose formed from β-glucose;
Position of hydrogen and hydroxyl groups on carbon atom 1
inverted.
Describe the structure of glycogen.
Polysaccharide of α-glucose;
OR
polymer of α-glucose;
(Joined by) glycosidic bonds
OR
Branched structure;
Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage
molecule.
Insoluble (in water), so doesn’t affect water potential;
Branched / coiled / (α-)helix, so makes molecule compact;
OR
Branched / coiled / (α-)helix so can fit many (molecules) in
small area;
Polymer of (α-)glucose so provides glucose for respiration;
Branched / more ends for fast breakdown / enzyme action;
Large (molecule), so can’t cross the cell membrane
Describe the induced-fit model of enzyme action and how an enzyme acts
as a catalyst.
Substrate binds to the active site/enzyme
OR
Enzyme-substrate complex forms;
Accept for ‘binds’, fits
Active site changes shape (slightly) so it is complementary to
substrate
OR
Active site changes shape (slightly) so
distorting/breaking/forming bonds in the substrate;
Reduces activation energy;
A competitive inhibitor decreases the rate of an enzyme-controlled
reaction.
Explain how.
Inhibitor similar shape to substrate;
Reject same shape
Accept ‘complementary to active site’
Fits/binds to active site;
Prevents/reduces enzyme-substrate complex forming;
Describe how a peptide bond is formed between two amino acids to form a
dipeptide.
Condensation (reaction) / loss of water;
Accept each marking point if shown clearly in
diagram.
Between amine / NH2 and carboxyl / COOH;
Describe how the structure of a protein depends on the amino acids it
contains.
Structure is determined by (relative) position of amino acid/R
group/interactions;
Accept for ‘interactions’, hydrogen bonds / disulfide
bridges / ionic bonds / hydrophobichydrophilic
interactions
Primary structure is sequence/order of amino acids;
Secondary structure formed by hydrogen bonding (between amino
acids);
Accept alpha helix/β-pleated sheet for ‘secondary
structure’
Tertiary structure formed by interactions (between R groups);
Accept for ‘interactions’, hydrogen bonds / disulfide
bridges / ionic bonds / hydrophobichydrophilic
interactions
Creates active site in enzymes
Explain how the active site of an enzyme causes a high rate of reaction.
Lowers activation energy;
Induced fit causes active site (of enzyme) to change shape;
(So) enzyme-substrate complex causes bonds to form/break;
The secondary structure of a polypeptide is produced by bonds between
amino acids.
Describe how.
Hydrogen bonds;
Accept as a diagram
Reject N - - - C / ionic / disulfide bridge / peptide
bond
Between NH (group of one amino acid) and C=O (group);
OR
Forming β pleated sheets / α helix;
The secondary structure of a polypeptide is produced by bonds between
amino acids.
Describe how.
Different sequence of amino acids
OR
Different primary structure;
If candidate assumes proteins are the same, accept
effect of different pH/ temperature
Forms ionic / hydrogen / disulfide bonds in different places;
Compare and contrast the processes by which water and inorganic ions enter cells.
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
Accept aquaporins (for water) and ion channels
- Contrast: ions can move against a concentration gradient by active transport
Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm.
Polar molecule;
- Acts as a (universal) solvent;
OR
- (Universal) solvent;
- (Metabolic) reactions occur faster in solution;
OR
- Reactive;
- Takes place in hydrolysis / condensation / named reaction;
explain five properties that make water important for organisms.
A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
2. A solvent so (metabolic) reactions can occur
3. High heat capacity so buffers changes in temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5. Cohesion (between water molecules) so supports columns of wate
Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
iron ions
- Haemoglobin binds/associates with oxygen
Sodium ions - Co-transport of glucose/amino acids (into cells);
- (Because) sodium moved out by active transport/Na – K pump;
- Creates a sodium concentration/diffusion gradient;
- Affects osmosis/water potential;
Phosphate ions
- Affects osmosis/water potential;
Accept 5. OR 6. – not both
- Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
- Used in/to produce ATP;
Reject ‘energy produced’ - Phosphorylates other compounds (usually) making them more reactive;
Give two ways in which the hydrolysis of ATP is used in cells.
- To provide energy for other reactions/named process;
Reject ‘produce’ energy - To add phosphate to other substances and make them more reactive/change their shape;
ATP is useful in many biological processes. Explain why.
Releases energy in small / manageable amounts
2. (Broken down) in a one step / single bond broken immediate energy compound / makes energy available rapidly;
2. Accept easily broken down
3. Phosphorylates / adds phosphate makes (phosphorylated substances) more reactive / lowers activation energy;
3. Do not accept phosphorus or P on its own
4. Reformed / made again;
Give two ways in which the hydrolysis of ATP is used in cells.
To provide energy for other reactions/named process;
Reject ‘produce’ energy
To add phosphate to other substances and make them more
reactive/change their shape;
ATP is an energy source used in many cell processes. Give two ways in
which ATP is a suitable energy source for cells to use.
Releases relatively small amount of energy / little energy lost as
heat;
Key concept is that little danger of thermal death of
cells
Releases energy instantaneously;
Key concept is that energy is readily available
Phosphorylates other compounds, making them more reactive;
Can be rapidly re-synthesised;
Is not lost from / does not leave cells.
The new antibiotic is safe to use in humans because it does not inhibit the
ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase
is inhibited.
Human ATP synthase has a different tertiary structure to
bacterial ATP synthase
OR
Human ATP synthase has a different shape active site to
bacterial ATP synthase
OR
Antibiotic cannot enter human cells/mitochondria
OR
Antibiotic not complementary (to human ATP synthase)
Explain five properties that make water important for organisms.
A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
High (specific) heat capacity so buffers changes in temperature; .
Large latent heat of vaporisation so provides a cooling effect (through
evaporation);
Cohesion (between water molecules) so supports columns of water
(in plants)
(theory)’.
Cohesion (between water molecules) so produces surface tension
supporting (small) organisms;
Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm.
Polar molecule;
Acts as a (universal) solvent
3. (Universal) solvent;
4. (Metabolic) reactions occur faster in solution;
OR
5. Reactive;
6. Takes place in hydrolysis / condensation / named reaction
Describe the roles of iron ions, sodium ions, and phosphate ions in cell
Sodium ions
Co-transport of glucose/amino acids (into cells);
(Because) sodium moved out by active transport/Na – K pump;
Creates a sodium concentration/diffusion gradient;
Affects osmosis/water potential;
Phosphate ions
Affects osmosis/water potential;
Accept 5. OR 6. – not both
Joins nucleotides/in phosphodiester bond/in backbone of
DNA/RNA/in nucleotides;
Used in/to produce ATP;
Reject ‘energy produced’
Haemoglobin binds/associates with oxygen
OR
Haemoglobin transports/loads oxygen;
