2020 paper 2 Flashcards
(37 cards)
Suggest and explain how the interaction between the muscles labelled in Figure 1
could cause the pupil to constrict (narrow).
- Circular muscle contracts; 2. Radial muscle relaxes;
The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail. Do not refer to colour vision in your answer.
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
- (Cones send) separate (sets of) impulses to brain;
Calculate the area of the fovea as a percentage of the area of the retina. The area of a circle is πr2. Use π = 3.14 in your calculation.
Show your working.
[2 marks]
- Correct answer of 0.6 (%) = 2 marks;;
The retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night. Do not refer to rhodopsin in your answer.
- High (visual) sensitivity;
- Several rods connected to a single neurone;
- Enough (neuro)transmitter to reach/overcome threshold
Steroid hormones are hydrophobic.
Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane.
- Lipid soluble;
2. (Diffuse through) phospholipid (bilayer);
In the cytoplasm, testosterone binds to a specific androgen receptor (AR). An AR is a protein.
Suggest and explain why testosterone binds to a specific AR.
- Has a (specific) tertiary structure/shape; 2. (Structures are) complementary;
The binding of testosterone to an AR changes the shape of the AR. This AR molecule now enters the nucleus and stimulates gene expression.
Suggest how the AR could stimulate gene expression.
- (AR is) a transcription factor; 2. Binds to DNA/promoter;
3. (Stimulates) RNA polymerase;
What can you conclude from the data in Table 1?
- With 16 or fewer than 16 (repeats the association) is significant;
- With 17 or more than 17 (repeats the association) is not significant;
- With 16 or fewer than 16 (repeats) there is less than a 5% or less than 0.05 probability of being due to chance
OR
With 17 or more than 17 (repeats) there is more than a 5% or more than 0.05 probability of being due to chance
OR
Explanation of a probability value e.g. 0.30 is a 0.30 or 30% probability of being due to chance; - With 16 or fewer than 16 (repeats) reject the null hypothesis
Other than the thermometer, explain how two features of the calorimeter shown in Figure 2 would enable a valid measurement of the total heat energy released.
- Stirrer distributes heat (energy);
- Insulation/space/air reduces loss/gain of heat
OR
Insulation/space/air reduces conduction/convection; - Water has high (specific) heat capacity;
The volume of water in the calorimeter was 100 cm3
The increase in temperature recorded was 15.7 °C
4.18 J of energy are needed to increase the temperature of 1 cm3 of water by 1 °C Use this information to calculate the heat energy released in kJ per g of biomass. Show your working.
3.28 / 3.3 (kJ g−1) = 2 marks;;
In natural ecosystems, most of the light falling on producers is not used in photosynthesis
Suggest two reasons why.
- (Light is) reflected;
- (Light is) wrong wavelength;
- (Light) misses chlorophyll/ chloroplasts/photosynthetic tissue;
- CO2 concentration or temperature is a limiting factor.
The light absorbed by chlorophyll is used in the light-dependent reaction. Name the two products of the light-dependent reaction that are required for the
light-independent reaction.
- ATP;
2. Reduced NADP;
Calculate the number of cells in the culture after 24 hours. Give your answer in standard form.
Show your working.
Correct answer of 1.31/1.3 × 108
Explain the banding pattern shown in Figure 3.
- Light/I band only actin;
- H zone/band only myosin;
- Darkest/overlapping region actin and myosin;
Use the information provided to describe how you could produce a calibration curve for creatinine.
Do not include details on the use of glassware in your answer.
- Use (distilled) water and creatinine solution to produce dilutions (series);
- Addition of (creatinine-)detecting solution (to each solution);
- Using a known/specified/constant volume of a solution (e.g. diluted creatinine solution);
- Record absorbance/transmission of solution/s using a colorimeter;
- Plot dilution/concentration of (creatinine) solution against absorbance/transmission;
Describe how you would determine the concentration of creatinine in a urine sample
using your calibration curve.
- Use same volumes of solutions as used in producing (calibration curve)
OR
Add (creatinine-)detecting solution (to urine); - Read off (creatinine) concentration against absorbance/transmission (value) obtained;
Describe the sequence of events involved in transmission across a cholinergic synapse.
Do not include details on the breakdown of acetylcholine in your answe
- Depolarisation of presynaptic membrane;
- Calcium channels open and calcium ions enter (synaptic knob);
3 (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter;
4 Acetylcholine/neurotransmitter diffuses across (synaptic cleft); - (Acetylcholine attaches) to receptors on the postsynaptic membrane;
- Sodium ions enter (postsynaptic neurone) leading to depolarisation;
Mutation is one cause of genetic variation in organisms. Give two other causes of genetic variation.
- Crossing over;
- Independent segregation/assortment (of homologous chromosomes);
- Random fusion of gametes
OR
Random fertilisation;
Name the relationship between the two alleles that code for flower colour.
Codominance
A dwarf, pink-flowered plant was crossed with a heterozygous tall, white-flowered plant.
Complete the genetic diagram to show all the possible genotypes and the ratio of
phenotypes expected in the offspring of this cross.
- ttCRCW and TtCWCW;
- TtCRCW, TtCWCW, ttCRCW and ttCWCW ;
- Tall pink, tall white, dwarf pink, dwarf white, and ratio 1 : 1 : 1 : 1;
A population of this species of plant contained 9% of red-flowered plants.
Use the Hardy–Weinberg equation to calculate the percentage of pink-flowered plants in this population.
Show your working.
. Correct answer of 42% = 2 mark
Calculate how many times greater the mean growth rate per day was using 37.5 g potassium nitrate than using 37.5 g ammonium sulfate.
Assume the mean biomass of the spinach plants at the start of the investigation was
0.5 g per pot.
1.375 / 1.3746 / 1.38 / 1.4
Using all the information, evaluate the effect on plant growth of adding the different
fertilisers to the soil.
- Potassium nitrate most effective and chicken manure least effective;
- All fertilisers more effective than control;
- No increase (in growth) with potassium nitrate above 30g;
- Ammonium sulfate (shows) small/gradual increase after 30g;
- Chicken manure effectiveness decreases after 45g
OR
Chicken manure effectiveness decreases at 60g;
6 Fertiliser/s provide nitrogen source for protein; - No statistical test (to determine if differences are significant);
- Only shows (results for) spinach;
The scientist determined the dry mass of the spinach plants. First, he heated each sample at 80 °C for 2 hours.
Suggest what the scientist should do to ensure that he has removed all the water from
the sample.
- Weigh and heat;
2. (Until) mass is constant;