OCR A Level Biology A Unified Biology June 2019 question paper H420/03

Identify the cellular components shown at A and B.

The real size of the line between C and D on Fig. 1.1 is 1.4 × 10⁻⁶ m.

Calculate the magnification that was used to produce the image in Fig. 1.1.

Give your answer to 2 significant figures.

Fig. 1.2 shows a student’s drawing of another sago pondweed cell, which was observed under a light microscope. The student used a sharp pencil but did not label the drawing.

Describe two other ways in which the drawing could be improved.

The student stained a sago pondweed sample to improve the contrast between cellular components when viewed under a microscope.

The student used the following procedure to stain the sample:

• Use forceps to place the sample on a glass slide.

• Use a pipette to place two drops of the stain in the centre of the sample.

• Carefully lower a cover slip onto the sample, ensuring that the cover slip is parallel with the slide as it is lowered.

Describe two improvements the student should make to their staining procedure.

Sago pondweed has evolved many adaptations to its aquatic environment. Three such adaptations are described below.

Explain the advantage of each adaptation.

Adaptation 1: No waxy cuticle

Adaptation 2: Stem tissue that contains air spaces

Adaptation 3: A thin, flexible stem

Fig. 2.1 shows a naked mole rat, Heterocephalus glaber.

The naked mole rat is a mammal. However, it has several features that are unusual for mammals.

Naked mole rats regulate their temperature in a way that is different from most mammals.

Some features of thermoregulation in naked mole rats are listed below:

• They live in complex underground tunnel systems, which tend to have a stable temperature of 30–32 °C. However, sometimes the environmental temperature can increase or decrease outside this range.

• In experiments that examine environmental temperature changes, the core body temperature of naked mole rats remains close to that of the environmental temperature.

• When tunnel temperature increases they often move to cooler parts of the tunnel system.

• When tunnel temperature decreases they often lie together in large groups.

Outline two ways in which thermoregulation in naked mole rats is different from thermoregulation in most mammals.

In humans, when core body temperature falls below 35 °C, positive feedback causes this decrease in core body temperature to continue. This process is known as hypothermia.

Explain how positive feedback could accelerate the process of hypothermia.

Mammals, including naked mole rats, have temperature receptors that play a role in thermoregulation.

The table below lists four statements about mammalian temperature receptors.

Write either ‘true’ or ‘false’ in the empty boxes to indicate whether each statement is true

Use the information in Fig. 2.2 to suggest why naked mole rats do not feel pain when exposed to acid.

Explain how a pain receptor is an example of a transducer.

Fig. 2.3 shows the relationship between body mass and lifespan in a range of mammal

Describe the relationship between body mass and lifespan shown in Fig. 2.3.

What conclusion can you draw from Fig. 2.3 about the lifespan of naked mole rats in comparison to other mammals?

Naked mole rats can survive without oxygen for up to 18 minutes. This is several times longer than other mammals of a similar size.

The following information might help to explain how naked mole rats can survive without oxygen for a long time:

• In normal glycolysis, the enzymes needed to convert glucose to triose phosphate may be inhibited by lactate.

• Naked mole rats can use fructose as a respiratory substrate.

• Fructose is converted to triose phosphate.

• Triose phosphate can then enter the glycolysis pathway.

Suggest why the use of fructose allows naked mole rats to survive without oxygen for a long time.

Suggest one other aspect of the physiology of naked mole rats that explains how they are able to survive without oxygen for a long time.

Icefish live in very cold water.

Icefish contain biological molecules that allow them to tolerate cold temperatures.

Adaptations can be grouped into three general categories.

Which category of adaptation is represented by cold-tolerant molecules?

Suggest and explain two improvements that would increase the validity of the students’ investigation.

Suggest appropriate units to use to represent the rate of enzyme activity in this investigation.

The students recorded the temperature that produced the fastest reaction rate in each of the five replicates. These results are shown in Table 3.

One of the students made the following statement:

I think the mean is a more accurate measure than the median or mode for these results.

Evaluate the student’s statement.

The students wanted to know whether there was a difference between the reaction rates of the two forms of trypsin at 30 °C.

They performed a statistical test on the mean of the five replicates for human trypsin and the five replicates for icefish trypsin.

Suggest the most appropriate statistical test for the students to use and explain why this test is appropriate.

It is possible to manufacture antibodies to treat certain diseases. These are known as synthetic antibodies.

DNL-Fab3, shown in Fig. 4.2, is an example of a synthetic antibody.

State two conclusions that can be drawn from Fig. 4.2 about the differences between the way DNL-Fab3 functions and the functioning of normal antibodies.

All organisms exchange gases with their environment.

Beet armyworm larvae eat a variety of plants, including tomato plants.

Scientists wanted to investigate how effective a chemical called methyl jasmonate was in stopping beet armyworm larvae from eating plants. They sprayed tomato plants with different concentrations of methyl jasmonate and recorded the final biomass of the plants.

The results are shown in Fig. 5.1.

applied to plants (mmol dm^–3)

Fig. 5.1

The scientists wrote the following hypothesis:

Plants use methyl jasmonate as a defence against herbivory.

What additional information do the scientists need to confirm their hypothesis?

Suggest one valid conclusion it is possible for the scientists to draw from the results in Fig. 5.1.

Bacteria and fungi can be used to make food for human consumption. The use of microorganisms in food production creates fewer ethical issues than the use of animals.

On an industrial scale, microorganisms can be cultured using either batch fermentation or continuous fermentation.

The table below lists statements about industrial culturing of microorganisms.

Place ticks (✓) in the table to indicate whether each statement applies to batch or continuous fermentation.

A student carried out a different serial dilution to estimate the size of another bacterial population.

The serial dilution resulted in four colonies developing on an agar plate.

Explain why the student’s estimation of this bacterial population is likely to be inaccurate.

Some microorganisms can be used by humans in industry. Some microorganisms are pathogenic.

Pathogenic microorganisms are transmitted in various ways.

Complete the following passage about the transmission of pathogenic microorganisms using the most appropriate terms.

Some pathogens are carried between host organisms by animals, which are often insects.

These animals suffer no symptoms of the disease and are known as........

Other pathogens, such as P. infestans that causes potato blight, produce reproductive structures

called........, which can be carried on air currents to infect other hosts.