paper 1/AS

Question 1

Describe how you would test for presence of a lipid in a sample of food.

Answer 1

1. Add ethanol, then add water;
2. White (emulsion shows lipid);

Question 2

A fat substitute cannot be digested in the gut by lipase. Suggest why.

Answer 2

1. (Fat substitute) is a different/wrong
   shape/not complementary;
   OR
   Bond between glycerol/fatty acid
   and propylene glycol different (to
   that between glycerol and fatty
   acid)/no ester bond;
2. Unable to fit/bind to (active site of)
   lipase/no ES complex formed;

Question 3

Describe how a fish undergoes inspiration

Answer 3

• Fish opens its mouth
• Floor of the buccal cavity is lowered
• Volume inside buccal cavity increases
• Decreases pressure inside the buccal cavity
• Pressure is now higher outside of the mouth so water flows into the buccal cavity to reach equilibrium.

Question 4

Pieces of leaf tissue examined using an optical microscope were very thin. Explain why this was important

Answer 4

Single/few layer(s) of cells;
So light can pass through;

Question 5

Other than the distribution of stomata, state and explain 2 xerophytic features of the leaves a xerophyte may have.

Answer 5

1. Hairs so ‘trap’ water vapour
   and water potential gradient
   decreased;
2. Stomata in pits/grooves so
   ‘trap’ water vapour and water
   potential gradient decreased;
3. Thick (cuticle/waxy) layer so
   increases diffusion distance;
4. Waxy layer/cuticle so reduces
   evaporation/transpiration.
5. Rolled/folded/curled leaves so
   ‘trap’ water vapour and water
   potential gradient decreased;
6. Spines/needles so reduces
   surface area to volume ratio;

Question 6

Suggest 2 reasons why rate of water uptake by a plant may not be the same as rate of transpiration

Answer 6

1. Water used for support/turgidity
2. Water used in photosynthesis
3. Water used in hydrolysis
4. Water produced in respiration

Question 7

Suggest how widening of blood vessels can reduce ventricular blood pressure

Answer 7

1. Larger lumen/volume (of blood vessels)
2. Reduces blood pressure (in blood vessels)
3. Less friction/resistance (in blood vessels)

Question 8

Ammonification is one process in which microorganisms add ammonium ions to soil.
Describe another process carried out by microorganisms which adds ammonium ions to soil.

Answer 8

1. Protein / amino acids broken down (to ammonium ions / ammonia);
   Accept: nucleic acids / RNA / DNA / urea / any named nitrogen containing compound as an alternative to protein / amino acids
2. By saprobionts / saprobiotic (microorganisms).
   Neutral: decomposers

Question 9

Give the formula for pulmonary ventilation. What is it?

Answer 9

Pulmonary ventilation (dm3min-1) = tidal vol (dm3) x ventilation rate (min-1)

Volume of air moved into the lungs in 1 min at rest

Question 10

Give the formula for cardiac output. What is it?

Answer 10

Cardiac output (mlmin-1) = Stroke vol (ml) x Heart rate (bpm)

Volume of blood pumped by one ventricle in 1 min at rest

Question 11

What is lung volume measured using and give the different definitions of terms to describe lung volumes

Answer 11

Measured using spirometer.

Tidal vol = Vol of air inspired when at rest
Tidal lung capacity = Total vol of air contained in the lung after max. inhalation
Vital capacity = Max. vol of air a person can expel from the lungs after a max. inhalation in one breath
Residual vol = vol of gas remaining in the lungs at the end of maximal exhalation

Question 12

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some
of these cells have membranes with a carrier protein called NHE3.

NHE3 actively transports one sodium ion into the cell in exchange for one proton
(hydrogen ion) out of the cell.

Use your knowledge of transport across cell membranes to suggest how NHE3
does this.

Answer 12

1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion
   and/or proton across the membrane);

Question 13

Some proteases are secreted as extracellular enzymes by bacteria.

Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment.

Explain your answer.

Answer 13

1. To digest protein;
2. (So) they can absorb amino acids for
   growth/reproduction/protein synthesis/synthesis
   of named cell component;
   OR
   (So) they can destroy a toxic substance/protein;

Question 14

Describe how presentation of a virus antigen leads to the secretion of an antibody
against this virus antigen.

Answer 14

1. Helper T cell/TH cell binds to the antigen (on
   the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B
   cell;
3. B cell clones
   OR
   B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;

Question 15

Explain three ways in which an insect’s tracheal system is adapted for efficient gas
exchange.

Answer 15

1. Tracheoles have thin walls so short
   diffusion distance to cells;
2. Highly branched/large number of
   tracheoles so short diffusion distance to
   cells;
3. Highly branched/large number of
   tracheoles so large surface area (for gas
   exchange);
4. Tracheae provide tubes full of air so fast
   diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that
   moves out (into tissues) during exercise
   so faster diffusion through the air to the
   gas exchange surface;
   OR
   Fluid in the end of the tracheoles that
   moves out (into tissues) during exercise
   so larger surface area (for gas exchange);
6. Body can be moved (by muscles) to move
   air so maintains diffusion/concentration
   gradient for oxygen/carbon dioxide;

Question 16

Explain the advantages of lipid droplets and micelle formation

Answer 16

1. Droplets increase surface areas (for lipase / enzyme action);
2. (So) faster hydrolysis / digestion (of triglycerides / lipids);
3. Micelles carry fatty acids and monoglycerides to membrane / to (intestinal epithelial) cell;

Question 17

Explain the role of the heart in formation of tissue fluid

Answer 17

1. Contraction of VENTRICLE(s) produces high blood / hydrostatic pressure;
2. (This) forces water (and some dissolved substances) out (of blood capillaries);

Question 18

Explain how the chromosome number is halved during meiosis

Answer 18

1. Homologous chromosomes (pair);
2. One of each (pair) goes to each (daughter) cell / to opposite poles;

Question 19

Define species richness

Answer 19

Number of different species in a COMMUNITY (not population)

Question 20

Suggest how increase of temperature causes increased release of red pigment in beetroot cells

Answer 20

(2 max)
1. Damage to (cell surface) membrane;
2. (membrane) proteins denature;
3. Increased fluidity / damage to the phospholipid bilayer;

Question 21

Describe how to use an eyepiece graticule to determine the mean diameter of stomata

Answer 21

1. Measure (each stoma) using eyepiece graticule;
2. Calibrate eyepiece graticule against stage micrometer / ruler / graph paper;
3. Take a number of measurements (to calculate a mean); !

Question 22

Describe how change in number produced to result in one extra chromosome

Answer 22

1. In meiosis;
2. Homologous chromosomes / sister chromatids
   do not separate; - Accept non-disjunction

Question 23

Describe the cohesion-tension theory of water transport in the xylem

Answer 23

1. Water lost from leaf because of transpiration / evaporation of water (molecules) / diffusion from mesophyll / leaf cells;
   OR
   Transpiration / evaporation / diffusion of water (molecules) through stomata / from leaves;
2. Lowers water potential of mesophyll / leaf
   cells;
3. Water pulled up xylem (creating tension);
4. Water molecules cohere / ‘stick’ together by
   hydrogen bonds;
5. (forming continuous) water column;
6. Adhesion of water (molecules) to walls of
   xylem;

Question 24

If a dipeptide alone is added to a dipeptide under neutral conditions in a laboratory, the peptide bond does not break down.
Explain why the bond is able to break down in the human body but not in the laboratory. (2)

Answer 24

• The human body contains enzymes (which are not present in the laboratory)
• These catalyse the hydrolysis reaction that breaks the bond/increases the rate at which the bond is broken down.

Question 25

Describe how the students would have prepared a microscope slide to view the cells in this root tip (after its been incubated in dilute hydrochloric acid and rinsed with cold water). (4)

Answer 25

- The student could have placed the root tip on the microscope slide and cut 2mm / a small section from the very tip of it. - Then used a mounted needle to break the tip open and spread the cells out thinly. - Then added a few drops of stain (eg: ethano-orcein or toluidine blue O) and left for few mins - Then place cover slip gently over cells and push down firmly between thumb and forefinger

Question 26

Give 2 pieces of evidence that can be given from chromosomes to prove a cell is undergoing mitosis. Explain your answer.

Answer 26

1. The (individual) chromosomes are visible because they have condensed; 2. (Each) chromosome is made up of two chromatids because DNA has replicated; 3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;

Question 27

Compare and contrast the structure and properties of triglycerides and phospholipids. (5)

Answer 27

1. Both contain ester bonds (between glycerol and fatty acid); 2. Both contain glycerol; 3. Fatty acids on both may be saturated or unsaturated; 4. Both are insoluble in water; 5. Both contain C, H and O but phospholipids also contain P; 6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group; 7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region; 8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Question 28

State and explain advantages and disadvantages to a farmer replanting hedges on her farmland.

Answer 28

Advantages - Greater (bio)diversity so increase in predators of pests OR Increase in predators of pests so more yield/income/less pesticides/less damage to crops OR Increase in pollinators so more yield/income OR May attract more tourists/subsidies to their farm so more income (from diversification); Disadvantages - Reduced land area for crop growth/income OR Greater (bio)diversity so increase pest population OR Increase pest population so less yield/less income/(more) need for pesticides/(more) damage to crops OR Increased (interspecific) competition so less yield/income OR More difficult to farm so less income;

Question 29

Suggest and explain one way in which the leaf growth of xerophytic plants would be different from the leaf growth of sunflowers

Answer 29

- Low/slow growth; - Due to smaller number/area of stomata (for gas exchange); OR - Growth may continue at lower water potentials; - (Due to) adaptations in enzymes involved in photosynthesis/metabolic reactions;

Question 30

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.

Answer 30

1.  Filter and dry (the precipitate); Accept: correct reference to evaporation after filtration 2.  Find mass/weight;

Question 31

Nuclear Pore Complexes (NPCs) control the passage of substances in and out of the nucleus. Cells from mutant plants with reduced NPC function were centrifuged. The cells from mutant plants produced a smaller pellet containing ribosomes, compared to cells from non-mutant plants. Explain why.

Answer 31

- Ribosomes are made in the nucleolus - Nucleolus is found within the nucleus - If there was reduced function of the NPCs, then fewer ribosomes could pass through the nuclear pore into the cytoplasm