NSAA 2020 Section 1, Part D (Biology questions)

Which of the following cells do not contain mitochondria?

1. bacterial cells
2. embryonic stem cells
3. mature red blood cells
4. potato cells

Which of the following could lead to phenotypic variation between a father and his son?

1. time spent in sunlight
2. their genomes
3. their diets

The diagram shows part of the carbon cycle.

Which row identifies the correct descriptions for boxes P, Q, R and S?

(Each option gives the box for ${\text{CO}}_2$ in the atmosphere, then for carbon-rich compounds in animals, in decomposers and in plants.)

A section of double-stranded DNA contains 4500 base pairs. 10% of the bases present are adenine.

Which of the following statements is/are correct?

1. There are 450 thymine bases present.
2. 40% of the bases present are cytosine.
3. There are 3600 guanine bases present.

Pepsin and trypsin are both protease enzymes found in the human digestive system.

The graph shows how the activity of both enzymes varies with pH.

In the human digestive system:

1. pepsin is most active in the stomach.
2. trypsin would be inactive in the stomach.
3. pepsin could be a substrate for trypsin.
4. pepsin is most active at low acidity and trypsin most active at high acidity.

Which statements are correct?

The diagram shows two human gametes, cell P and cell Q, fusing to form cell R.

Cell P carries an additional copy of one of its chromosomes so that it has one more chromosome than cell Q.

Cell R divides to form two cells S and T.

S and T grow into two separate individuals.

Using this information, which row shows the correct number of chromosomes in the nucleus of cell R and in the nucleus of cell T?

(Each option gives the number for cell R, then for cell T.)

SCID is an inherited condition in humans.

In one type of SCID, the white blood cells are unable to make the functional enzyme ADA, which is necessary for these cells to divide by mitosis during an immune response.

Scientists have developed a gene therapy treatment whereby a gene is inserted into the DNA of stem cells taken from the bone marrow of a person with this condition. These cells can then be returned to the body of the person, and can divide and differentiate into white blood cells. If this gene therapy is successful, the number of white blood cells should increase significantly.

Which of the following statements correctly describe(s) how this method of gene therapy might work to help a person with this type of SCID?

1. Genetically altered stem cells differentiate into white blood cells that are able to produce functional ADA.
2. Genetically altered stem cells can differentiate into gametes so that offspring will not inherit SCID.
3. The sequence of the bases in the DNA of the white blood cells, derived from the genetically altered stem cells, has changed.

The table shows concentrations of substances in blood entering and leaving three different organs of a person:

- kidney
- small intestine
- chambers of the right side of the heart

The blood sample was taken 10 minutes after the person had eaten a carbohydrate-rich meal.$$\begin{array}{ccccccc}\text{organ}& {\text{glucose in / mg dm}}^{-3}& \text{oxygen in / arbitrary units}& {\text{urea in / mg dm}}^{-3}& {\text{glucose out / mg dm}}^{-3}& \text{oxygen out / arbitrary units}& {\text{urea out / mg dm}}^{-3}\\ 1& 9.0& 65& 3.0& 9.0& 65& 3.0\\ 2& 9.0& 85& 3.0& 9.0& 70& 2.4\\ 3& 9.0& 85& 3.0& 12.0& 70& 3.0\end{array}$$("in" is the concentration in blood entering the organ, "out" the concentration in blood leaving it.)

Which row in the following table identifies the organs?

(Each option gives organ 1, then organ 2, then organ 3.)

The table shows information about a human genetic condition called sickle cell anaemia and an infection called malaria. Both sickle cell anaemia and malaria can be fatal.$$\begin{array}{ccc}\text{genotype}& \text{phenotype}& \text{comment}\\ \text{MM}& \text{does not show sickle cell anaemia}& \text{can be infected with malaria}\\ \text{Mm}& \text{does not show sickle cell anaemia}& \text{shows resistance to malaria}\\ \text{mm}& \text{shows sickle cell anaemia}& \text{shows more resistance to malaria than Mm}\end{array}$$Which of the following statements is/are correct?

1. In areas without malaria, human populations are likely to have a low number of people with the m allele.
2. In areas with malaria, only those individuals that are heterozygous will be able to pass on their alleles to the next generation.
3. Presence of malaria has caused a mutation of the M allele to the m allele leading to an increased chance of survival in the heterozygous state.

Which of the following could be a result of the addition of a large amount of organic material into a slow flowing river?

1. A decrease in biodiversity in the river.
2. A reduction in the oxygen concentration gradient between the air and the water.
3. An increase in the size of at least one aquatic population.

The graph shows the mass of product produced over time for an enzyme-controlled reaction in two different conditions, X and Y. All other variables were kept constant.

Which of the following could be correct for this graph?

1. Condition X is a higher pH than condition Y.
2. Condition X has less substrate supplied than condition Y.
3. Condition X is a lower pH than condition Y.
4. Condition X has more substrate supplied than condition Y.

The table shows the concentration of potassium ions in several different locations.$$\begin{array}{cc}\text{location}& \text{concentration of potassium ions}\\ \text{bacterial cell cytoplasm}& 30{\text{ mmol dm}}^{-3}\\ \text{mammalian blood plasma}& 4000\mu {\text{mol dm}}^{-3}\\ \text{mammalian heart cell cytoplasm}& 1.0\times 10^2{\text{ mmol dm}}^{-3}\\ \text{sea water}& 3.0\times 10^4\mu {\text{mol dm}}^{-3}\\ \text{yeast cell cytoplasm}& 300{\text{ mmol dm}}^{-3}\end{array}$$Which of the following statements is/are correct?

1. A mammalian heart cell needs energy from respiration in order to obtain more potassium ions from blood plasma.
2. If a yeast cell is placed in sea water then it will lose potassium ions by osmosis.
3. There is no concentration gradient for potassium ions between a bacterial cell and sea water.

The abundance of a plant species in a habitat can be measured in different ways:

- the density (the number of that plant species per ${\text{m}}^2$)
- the frequency (the number of quadrats in which the plant species occurs)

The abundance of a plant species in a $100{\text{ m}}^2$ area of grassland was measured. The diagram below represents this area of grassland. Each black circle represents one individual of the plant species in this area of grassland.

Two different size quadrats were used to sample the area:

- large quadrat ($50\text{ cm}\times 50\text{ cm}$)
- small quadrat ($10\text{ cm}\times 10\text{ cm}$)

The area is sampled randomly, first using 10 large quadrats and then a second time using 10 small quadrats.

Which of the following statements is/are correct?

1. The overall density in the grassland calculated from sampling with either size quadrat will always be the same.
2. The overall density in the grassland calculated from sampling will always be 1 plant per ${\text{m}}^2$.
3. The frequency obtained using the small quadrat will always be lower than that obtained with the large quadrat.

A student investigated the endothermic reaction of photosynthesis in pondweed. The student set up the apparatus as shown in the diagram.

The experiment was left for 5 minutes and the distance moved by the gas bubble along a capillary tube of 2 mm diameter was recorded. Using these values, the rate of gas production is $2\pi {\text{ mm}}^3$ per minute.

Which row of the table is correct?

(Each option gives the total distance moved by the gas bubble during the experiment in mm, the reason why the reaction is described as endothermic, and the observation if the light source was moved further from the pondweed.)

The placenta is an organ that develops during pregnancy. One function of the placenta is to allow the exchange of gases between the mother and the developing foetus.

The diagram represents the maternal and foetal blood flow between P and Q in a section of the placenta of a healthy small mammal. The concentration of oxygen in both maternal and foetal blood was measured at regular distances along this section.

Which graph illustrates the concentration of oxygen in both maternal and foetal blood between P and Q?

(The six graphs A to F are shown in the second figure, with a key: solid line maternal capillary, dashed line foetal capillary. Each option below describes its graph.)

The diagram shows the changes in the volume of the ventricles, and the ECG trace that accompanies those changes, during two consecutive heart beats.

Which row is correct about the events happening at X, Y and Z?

(Each option gives where blood is being pumped into at X, whether the valves between atria and ventricles are open or closed at Y, and which chambers of the heart are contracting at Z.)

Three different methods, X, Y and Z, of controlling pathogens in the human body are compared in the table.$$\begin{array}{ccccc}\text{method of controlling the pathogen}& \text{affects bacterial pathogens}& \text{affects viral pathogens}& \text{requires the movement of human cells to have an effect}& \text{uses a molecule released from human cells}\\ \text{X}& \text{yes}& \text{yes}& \text{yes}& \text{no}\\ \text{Y}& \text{yes}& \text{no}& \text{no}& \text{no}\\ \text{Z}& \text{yes}& \text{yes}& \text{no}& \text{yes}\end{array}$$Which row in the following table is correct?

(Each option gives the description of method X, then of method Y, then of method Z.)

Catalase is an enzyme found inside plant and animal cells. When catalase is added to hydrogen peroxide, bubbles of oxygen gas are formed.

Red blood cells were placed into either water or plasma, and were placed in the dark.

Plant cells were placed into either water or $0.5{\text{ mol dm}}^{-3}$ sucrose solution, and were placed in the dark.

Assume that hydrogen peroxide and catalase do not cross the cell surface membrane.

Which row shows the results when hydrogen peroxide was added?

(Each option states whether oxygen bubbles will form when hydrogen peroxide is added to red blood cells in plasma, to plant cells in a $0.5{\text{ mol dm}}^{-3}$ sucrose solution, to red blood cells in water, and to plant cells in water.)

The three family trees show the inheritance of three different genetic conditions, each controlled by one gene with one dominant and one recessive allele.

In which of the family trees must the male parent be heterozygous?

(Assume that no new mutations occur and that the genes are not found on the X chromosome.)

In rabbits, there are two alleles concerned with dark pigment in the fur:

- the dominant allele, B, for black colour
- the recessive allele, b, for brown colour

Two male black rabbits of unknown genotype each mated with a different female brown rabbit.

What is the expected proportion of brown offspring if both male rabbits are heterozygous, and what is the expected proportion of brown offspring if only one male rabbit is heterozygous?

(Each option gives the expected proportion of brown offspring if both male rabbits are heterozygous, then if only one male rabbit is heterozygous.)