NSAA 2023 Biology S1

• A.The beetle and the fungus have a mutualistic relationship.
• B.The beetle and the tree have a mutualistic relationship.
• C.The fungus is a parasite on the beetle.
• D.The fungus is the primary producer that the beetle feeds on.
• E.The tree is the primary producer that the beetle feeds on.

Answer: A

Which of the following graphs could describe processes taking place in the leaf of an oak tree in the presence of light?

Graph 1 shows the rate of photosynthesis on the y-axis against temperature / °C on the x-axis. The curve starts at the origin, increases to a peak, and then decreases.

Graph 2 shows the mass of carbon dioxide used in the leaf on the y-axis against the time of day on the x-axis (0:00 to 24:00). The curve is high at the start and end of the day and dips to a minimum at midday (12:00).

Graph 3 shows the rate of photosynthesis on the y-axis against the distance from a light source on the x-axis. The curve starts high on the y-axis and decreases as the distance increases.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: B

The diagram shows the flow of energy in a year's growth of grass from 1 m² of grassland.
Energy flow is as follows: 3000 kJ is eaten by the cow. The cow loses 1020 kJ in breath, movement and heat loss, and 1860 kJ in faeces and urine. 120 kJ goes to the growth of the cow. 14800 kJ goes to decomposers from the grass. 3520 kJ is eaten by other herbivores.

Which of the following statements is/are correct?

1. 62% of the energy consumed by the cow is lost in faeces and urine.
2. The diagram illustrates all the main processes of carbon uptake and release in the carbon cycle.
3. 4% of the energy absorbed by the cells of the cow is used for growth.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: B

A Petri dish was filled with agar that had been mixed with starch. The agar is not digested by enzymes used in the experiment.

Four small wells were cut in the agar. Three were filled with different solutions. Well Y was filled with water to act as a control.

The dish was kept at 30 °C for 30 minutes. The surface of the agar was then washed with iodine solution, turning parts of it blue-black in the presence of starch.

The Petri dish was placed on a piece of graph paper, as shown in the diagram, to measure the clear areas around the wells. The area of each well should be considered negligible.

Which of the statements is/are correct?

1. The area of starch digested around well W is 4 times the area digested around well X.
2. Amylase could have been used in well W and protease could have been used in well X.
3. The solution put in well Z could have contained boiled enzyme.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: F

The diagram shows a bubble potometer at the start of an experiment.

The glass tube has an internal diameter of 1 mm.

After five minutes, one end of the air bubble had moved to the 4 cm mark on the scale.

Which row is correct?

• A.name of process being investigated: translocation, volume of water taken up / mm³: $\pi \times (0.5)^2 \times 10$
• B.name of process being investigated: translocation, volume of water taken up / mm³: $\pi \times (0.5)^2 \times 15$
• C.name of process being investigated: translocation, volume of water taken up / mm³: $2\pi \times (0.5) \times 10$
• D.name of process being investigated: translocation, volume of water taken up / mm³: $2\pi \times (0.5) \times 15$
• E.name of process being investigated: transpiration, volume of water taken up / mm³: $\pi \times (0.5)^2 \times 10$
• F.name of process being investigated: transpiration, volume of water taken up / mm³: $\pi \times (0.5)^2 \times 15$
• G.name of process being investigated: transpiration, volume of water taken up / mm³: $2\pi \times (0.5) \times 10$
• H.name of process being investigated: transpiration, volume of water taken up / mm³: $2\pi \times (0.5) \times 15$

Answer: F

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: D

A student viewed a bacterial cell using a microscope. The cell was measured with a microscope ruler as shown in the diagram. Each division on this ruler measures 2.5 µm.

The student made a drawing of this cell. The drawing was 5.0 cm in length and included the structures that the student expected to see.

Which row of the table gives the magnification of the student's drawing and one of the structures that should be included?

• A.magnification of the student's drawing: $2.5 \times 10^{-4}$, structure that should be included: cell wall
• B.magnification of the student's drawing: $2.5 \times 10^{4}$, structure that should be included: nucleus
• C.magnification of the student's drawing: $4.0 \times 10^{-1}$, structure that should be included: cell wall
• D.magnification of the student's drawing: $4.0 \times 10^{-1}$, structure that should be included: nucleus
• E.magnification of the student's drawing: $4.0 \times 10^{3}$, structure that should be included: cell wall
• F.magnification of the student's drawing: $4.0 \times 10^{3}$, structure that should be included: nucleus
• G.magnification of the student's drawing: $2.0 \times 10^{4}$, structure that should be included: cell wall
• H.magnification of the student's drawing: $2.0 \times 10^{4}$, structure that should be included: nucleus

Answer: E

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: F

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: A

The diagram shows a flow chart representing the hormonal activity associated with the menstrual cycle.
The key indicates a minus sign for a negative feedback loop and a plus sign for a loop in which an ovarian hormone stimulates the release of a second hormone from the pituitary gland.
The flowchart shows: hypothalamus releases GnRH, which acts on the anterior pituitary. Anterior pituitary releases hormone 1 and hormone 2. Hormone 1 acts on the ovarian follicle, which releases hormone 3. Hormone 2 acts on the ovarian corpus luteum, which releases hormone 4. Hormone 3 has positive feedback on the anterior pituitary. Hormone 4 has negative feedback on the hypothalamus and anterior pituitary. There are also negative feedback loops from the anterior pituitary to the hypothalamus, and from hormone 2 to the anterior pituitary.

Which of the following statements about the menstrual cycle is/are correct?

1. Hormone 1 stimulates follicle maturation and the release of hormone 3 from the ovarian follicle.
2. Hormone 4 maintains the uterus lining.
3. At the end of the menstrual cycle the levels of hormone 1 and hormone 2 will reach their highest point and then decrease, leading to menstruation.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: E

A scientist was investigating the effect of substrate concentration on lipase enzyme activity

Two test tubes were set up:
• one containing a sample of full-fat milk mixed with an alkaline solution, and a pH indicator
• one containing lipase

The pH indicator turned the alkaline milk sample pink.

Both tubes were incubated in a water bath set to an optimum temperature for lipase until the contents had reached this temperature.

The scientist then added the lipase to the tube with the milk sample and measured the time taken for the indicator to turn colourless. This colour change was caused by an increase in concentration of one of the products of the reaction.

Further samples of the milk were diluted, and added to the same quantity of alkaline solution and pH indicator, to produce another six different substrate concentrations, and the experiment was repeated. All other variables were kept constant.

The scientist found that each substrate concentration caused the pH indicator to change to colourless in a different length of time. The results of the reaction in all seven tubes were plotted on a graph.

Which option correctly identifies the shape of the graph of the results, the limiting factor during the experiment and an explanation for the change in colour of the pH indicator?

• A.Graph shows time taken increasing with substrate concentration. Limiting factor is substrate concentration. Indicator changes due to an increase in pH.
• B.Graph shows time taken increasing with substrate concentration. Limiting factor is substrate concentration. Indicator changes due to a decrease in pH.
• C.Graph shows time taken increasing with substrate concentration. Limiting factor is temperature. Indicator changes due to an increase in pH.
• D.Graph shows time taken increasing with substrate concentration. Limiting factor is temperature. Indicator changes due to a decrease in pH.
• E.Graph shows time taken decreasing with substrate concentration. Limiting factor is substrate concentration. Indicator changes due to an increase in pH.
• F.Graph shows time taken decreasing with substrate concentration. Limiting factor is substrate concentration. Indicator changes due to a decrease in pH.
• G.Graph shows time taken decreasing with substrate concentration. Limiting factor is temperature. Indicator changes due to an increase in pH.
• H.Graph shows time taken decreasing with substrate concentration. Limiting factor is temperature. Indicator changes due to a decrease in pH.

Answer: F

Even when sufficient oxygen is available, yeast will respire anaerobically using glucose as a substrate. However, if its source of glucose runs out and oxygen is available, yeast can switch to using ethanol as a substrate, which it uses to respire aerobically.

A sample of yeast was added to 100 cm³ glucose solution in an open flask.

The contents of the flask were monitored over 32 hours and the results are shown in the graph.
The graph shows that from 0 to about 12 hours, glucose concentration decreases, while ethanol and yeast concentration increase. After 12 hours, glucose is depleted, and ethanol concentration starts to decrease, while yeast concentration continues to increase at a slower rate.

Which of the following statements are correct?

1. Carbon dioxide would be produced in the flask at all times throughout the observation period, regardless of whether the yeast was respiring aerobically or anaerobically.
2. The yeast was respiring using ethanol as the only substrate for 22 hours.
3. The yeast started respiring anaerobically from the start of the observation period.
4. The yeast used an average of 4 g glucose per hour for the first 10 hours.

• A.1, 2 and 3 only
• B.1, 2 and 4 only
• C.1, 3 and 4 only
• D.2, 3 and 4 only
• E.1, 2, 3 and 4

Answer: A

The diagram represents part of the carbon cycle.
The diagram has a central box labelled 'plants'. Arrow 3 points to 'plants'. Arrow 6 points away from 'plants'. Arrow 4 points from 'plants' to another box. Other arrows (1, 2, 5, 7) connect other unlabelled boxes in the cycle.

Which of the arrows represent processes resulting in at least one organic product (contains carbon and hydrogen)?

• A.3 only
• B.4 only
• C.5 and 6 only
• D.1, 2 and 7 only
• E.3, 5 and 6 only
• F.1, 2, 3 and 4 only
• G.3, 4, 5 and 6 only
• H.1, 2, 3, 4, 5, 6 and 7

Answer: G

In an experiment, 8 identical cubes of potato were each weighed and placed in a different test tube.

Each of the test tubes contained a different concentration of sodium chloride solution. All other conditions were kept the same throughout the experiment.

After 30 minutes, the potato cubes were removed from the test tubes and weighed, and the percentage change in mass was calculated.

The graph of percentage change in mass versus concentration of sodium chloride / mol dm⁻³ is shown. The line graph shows that as concentration increases, the percentage change in mass decreases, crossing the x-axis (0% change) at a concentration of 0.3 mol dm⁻³.

Which of the following statements is/are correct?

1. The initial concentration of sodium chloride inside the potato cubes must be 0.3 mol dm⁻³.
2. Osmosis involves the diffusion of water molecules from a solution of high solute concentration to one of low solute concentration.
3. In this experiment, the rate of osmosis is fastest at a sodium chloride concentration of 0.8 mol dm⁻³.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: D

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: E

The family tree shows the inheritance of an autosomal recessive genetic condition.

Key:
- male without condition (unfilled square)
- female without condition (unfilled circle)
- female with condition (filled circle)

The pedigree shows unaffected parents having four children: an unaffected female (1), an unaffected male (2), an affected female (3), and an unaffected male (4).

Which of the following statements is/are correct for this family?

1. If one cheek cell is collected from each individual, the overall ratio of X chromosomes to Y chromosomes will be 3.67:1.
2. The probability of individual 2 and individual 3 having the same alleles on their X chromosomes is 100%.
3. The probability of individual 2 and individual 3 having the same genotype for the condition is 50%.

(Assume no mutations.)

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: B

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: E

The graph shows the change in the pressure in the space X between the wall of the thorax and the lungs (as shown in the diagram) during one complete breathing cycle.

The graph shows pressure in space X on the y-axis against time in seconds on the x-axis. One full cycle takes 4 seconds. The pressure drops from t=0 to t=1.5s and then rises from t=1.5s to t=4s.

Which of the following statements is/are correct?

1. The person is breathing out between 0 and 1.5 seconds.
2. The diaphragm is relaxing between 2 and 3 seconds.
3. The rate of breathing is 15 breaths per minute.

(Assume the person continues breathing at the same rate.)

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: G