Practice Paper 2 (Cambridge International AS Biology)

Specimens can be measured using eyepiece graticules and stage micrometers.

Which of the following correctly describes the role of a stage micrometer?

A giant bacterium, Epulopiscium fishelsoni was discovered in 1985.

Which cell structure(s) would enable biologists to classify E. fishelsoni as a prokaryote?

A typical animal cell is surrounded by a cell membrane with a mean thickness of 8 nm, measured using electron microscopy.

A light microscope-generated image of the whole cell itself measures 5 cm across at a magnification of x1250.

Calculate the number of times wider the whole cell is than the thickness of its membrane.

A light microscope and an electron microscope were used to examine the contents of a plant cell.

The light microscope was used at two different magnification settings to produce the images shown in Fig .1. The electron microscope image is also shown in Fig.1

In all three images the field of view contained the same piece of biological material.

Fig.1

Suggest reasons for the differences in the appearance of the three images in Fig. 1.

Extract:

A light microscope and an electron microscope were used to examine the contents of a plant cell.

The light microscope was used at two different magnification settings to produce the images shown in Fig .1. The electron microscope image is also shown in Fig.1

In all three images the field of view contained the same piece of biological material.

Fig.1

Give two possible names of cell components that could be shown in Fig. 1.

Assume that the setup of the microscopes and sample preparation has been carried out to give the best possible view of the specimens under observation in each case.

Table 1 contains information on the percentage of total cell membrane found in some different cell organelles in liver cells and in pancreas cells.

Note that not all organelles have been included, so the totals do not add up to 100 %.

Table 1

Give three conclusions about the comparative activities of liver and pancreas cells that can be drawn from the data in Table 1.

Extract:

Table 1 contains information on the percentage of total cell membrane found in some different cell organelles in liver cells and in pancreas cells.

Note that not all organelles have been included, so the totals do not add up to 100 %.

Table 1

| Organelle in which membrane is found | Percentage of total cell membrane | | Liver cell | Pancreas cell | | Plasma membrane | 2 | 5 | | Rough ER | 35 | 60 | | Smooth ER | 16 | <1 | | Golgi apparatus | 7 | 10 | | Outer mitochondrial membrane | 7 | 4 | | Inner mitochondrial membrane | 32 | 17 | | Nuclear membrane | 0.2 | 0.7 |

Predict how the data in Table 1 would be different for:

(i) A prokaryotic cell.

(ii) A plant cell.

Table 2 contains information about the volume and surface area of liver and pancreas cells.

Table 2

Calculate the surface area to volume ratio for:

(i) Liver cells

(ii) Pancreas cells

Extract:

Table 1 contains information on the percentage of total cell membrane found in some different cell organelles in liver cells and in pancreas cells.

Note that not all organelles have been included, so the totals do not add up to 100 %.

Table 1

| Organelle in which membrane is found | Percentage of total cell membrane | | Liver cell | Pancreas cell | | Plasma membrane | 2 | 5 | | Rough ER | 35 | 60 | | Smooth ER | 16 | <1 | | Golgi apparatus | 7 | 10 | | Outer mitochondrial membrane | 7 | 4 | | Inner mitochondrial membrane | 32 | 17 | | Nuclear membrane | 0.2 | 0.7 |

The micrograph below shows a cell from the pancreas.

Fig. 1

(i) Identify one organelle visible in the micrograph that is not listed in Table 1.

(ii) Describe the role of the organelle identified in part (i).

Which carbohydrate would test positive for the Benedict’s test after acid hydrolysis, but negative before acid hydrolysis, has occurred?

Which of the statements above are not true?

The diagram shows a polypeptide of the protein glutenin, which has an important role in maintaining the strength and elasticity of bread dough.

What is the structure of glutenin and why?

Which property of water is paired with an incorrect physiological use?

Triglycerides are the main form of dietary lipids ingested by humans. They are digested by the enzyme lipase in the stomach.

Describe a biochemical test that could be performed to determine whether a sample of food contains triglycerides.

Extract:

The (ethanol) emulsion test:

• Mix the food sample with ethanol/alcohol;
• Then add water / pour into water;
• (If lipids are present) a white/milky emulsion forms;

Using your knowledge of the structure of triglycerides, explain the visual result of a positive test for the presence of lipids.

Seeds are a good source of lipids. They also contain starch which serve as a food source for the growing plant embryo during germination.

Outline the biological test that can be used to confirm the presence of starch.

Proteins are macromolecules composed of many amino acids.

(i) Two amino acids are represented in the diagram in Fig.1. Complete the diagram to show how the two amino acids react together to form a dipeptide.

Fig.1

(ii)State what is represented by R₁ and R₂ in Fig.1.

Amylose and cellulose are polysaccharides.

Fig. 2 shows the structure of part of a cellulose molecule.

Fig. 2

With reference to Fig. 2, state how the structure of a cellulose molecule differs from the structure of an amylose molecule.

Extract:

Amylose and cellulose are polysaccharides.

Fig. 2 shows the structure of part of a cellulose molecule.

Fig. 2

With reference to Fig. 2, state how the structure of a cellulose molecule differs from the structure of an amylose molecule.

How the structure of a cellulose molecule differs from the structure of an amylose molecule is...

Any two of the following:

• Cellulose is a linear/straight chain polymer whereas amylose is a helical molecule;
• In cellulose β-glucose is present whereas α-glucose is present in amylose OR β-1:4 glycosidic bonds are present in cellulose whereas α-1:4 glycosidic bonds are present in amylose;
• (In cellulose) β-glucose monomers are arranged rotated 180° to each other;

Cellulose is the main component of plant cell walls.

Explain why cellulose is suitable as a component of plant cell walls.

People suffering from anaemia are generally lacking in dietary iron. It is recommended that they consume more red meat and green leafy vegetables to increase the iron levels in their blood.

Explain why one of the symptoms of anaemia would be fatigue.

At high altitudes, the partial pressure of oxygen in the air is substantially lower than at sea level. This means that the partial pressure of oxygen in the bloodstream is also much lower at high altitudes compared to at sea level. The partial pressure of oxygen at sea level is about 14.0 kPa, while at 10 000 metres above sea level it is about 4.0 kPa. Table 1 shows the percentage saturation of haemoglobin at different partial pressures of oxygen.

Table 1

With reference to Table 1, calculate the percentage decrease in the percentage saturation of haemoglobin as you travel from sea level to 10 000 metres above sea level.

Show your working.

Compare the different chemical elements found in proteins and carbohydrates.

Enzymes called proteases are able to break proteins down and they are often added to biological washing powders to remove protein-based stains from clothes.

Explain how these enzymes are able to break proteins down.

Suggest and explain one advantage to ecosystems of solid water (ice) being less dense than liquid water.

Fig. 1 shows a water molecule with its bond angle labelled as 104.49°.

Fig. 1

The bond angle that would be expected in a molecule of this shape would usually be larger, around 109°.

Use information in Fig. 1 to suggest why water's bond angle is less than that of the expected geometric shape of a water molecule.

Water reaches its maximum density of 1 000 kg m^-3 at 4 °C, while the density of ice is 917 kg m^-3.

Density can be calculated using the formula:

Density = mass ÷ volume

Use the formula provided to calculate the percentage volume expansion that occurs when 1 000 kg of water freezes from 4 °C to below its freezing point.

State your answer to the nearest whole number.

The following equation shows a reversible reaction:

In this reaction, which row best describes what is occurring?

In the graph, Z represents the relationship between the initial rate of reaction of an enzyme and the concentration of its substrate under optimal conditions and without an inhibitor.

Which curve would represent the same experiment carried out in the presence of a low concentration of a non-competitive inhibitor?

A student wanted to investigate the effect of enzyme concentration on the rate of a reaction. The student made a serial dilution of a 10% amylase solution. He had three test tubes for each of the different concentrations of amylase that contained 2 cm³ of starch solution.

After incubating both amylase and starch solutions for 10 minutes at 40°C, he mixed 1 cm³ of the different amylase solutions with the starch solution in the relevant test tubes. The student removed samples from the mixtures at 1 minute intervals and tested for the presence of starch using iodine solution. He recorded the time taken for all the starch to be digested by the amylase.

His results are presented in Table 1

Table 1

(i)State the conclusion that can be drawn from these results.

(ii) Explain the importance of having three test tubes for each of the different concentrations of amylase.

Extract:

A student wanted to investigate the effect of enzyme concentration on the rate of a reaction. The student made a serial dilution of a 10% amylase solution. He had three test tubes for each of the different concentrations of amylase that contained 2 cm³ of starch solution.

After incubating both amylase and starch solutions for 10 minutes at 40°C, he mixed 1 cm³ of the different amylase solutions with the starch solution in the relevant test tubes. The student removed samples from the mixtures at 1 minute intervals and tested for the presence of starch using iodine solution. He recorded the time taken for all the starch to be digested by the amylase.

The student judged the colour change of the iodine solution by eye.

Describe a more accurate method that the student could use to determine when all the starch had been digested.

Extract:

A student wanted to investigate the effect of enzyme concentration on the rate of a reaction. The student made a serial dilution of a 10% amylase solution. He had three test tubes for each of the different concentrations of amylase that contained 2 cm^3^ of starch solution.

After incubating both amylase and starch solutions for 10 minutes at 40°C, he mixed 1 cm^3^ of the different amylase solutions with the starch solution in the relevant test tubes. The student removed samples from the mixtures at 1 minute intervals and tested for the presence of starch using iodine solution. He recorded the time taken for all the starch to be digested by the amylase.

The student repeated the investigation described in part a) but incubated the starch and amylase solution at 60°C.

Suggest and explain the possible outcome of this investigation.

Extract:

A student wanted to investigate the effect of enzyme concentration on the rate of a reaction. The student made a serial dilution of a 10% amylase solution. He had three test tubes for each of the different concentrations of amylase that contained 2 cm³ of starch solution.

After incubating both amylase and starch solutions for 10 minutes at 40°C, he mixed 1 cm³ of the different amylase solutions with the starch solution in the relevant test tubes. The student removed samples from the mixtures at 1 minute intervals and tested for the presence of starch using iodine solution. He recorded the time taken for all the starch to be digested by the amylase.

Identify two variables that must be controlled during the investigation described in part a).

The enzyme catalase catalyses the following reaction:

H₂O₂ → O₂ + H₂O

A student studied the action of catalase by measuring the volume of oxygen released from the reaction solution using a gas syringe. They recorded the volume of oxygen every 60 seconds over 15 minutes.

The results of the experiment are shown in Fig. 1 below:

Fig. 1

Calculate the initial rate of reaction shown in Fig. 1.

Extract:

The enzyme catalase catalyses the following reaction:

H2O2 → O2 + H2O

A student studied the action of catalase by measuring the volume of oxygen released from the reaction solution using a gas syringe. They recorded the volume of oxygen every 60 seconds over 15 minutes.

The results of the experiment are shown in Fig. 1 below:

Fig. 1

The student wanted to investigate the effect of temperature on the rate of reaction of catalase. They did so by repeating the experiment using water baths kept at 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C.

(i) The data from Fig. 1 was taken from the experiment carried out at 30°C.

Sketch a line onto the Fig. 1 graph to predict the outcome of the experiment at 60 °C.

(ii) Explain the shape of your line from part (i).

Extract:

The enzyme catalase catalyses the following reaction:

H2O2 → O2 + H2O

A student studied the action of catalase by measuring the volume of oxygen released from the reaction solution using a gas syringe. They recorded the volume of oxygen every 60 seconds over 15 minutes.

The student wanted to investigate the effect of temperature on the rate of reaction of catalase. They did so by repeating the experiment using water baths kept at 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C.

State three factors that the student would need to consider when designing the experiment described in (a) and (b) to ensure valid results.

Extract:

The enzyme catalase catalyses the following reaction:

H2O2 → O2 + H2O

A student studied the action of catalase by measuring the volume of oxygen released from the reaction solution using a gas syringe. They recorded the volume of oxygen every 60 seconds over 15 minutes.

The student wanted to investigate the effect of temperature on the rate of reaction of catalase. They did so by repeating the experiment using water baths kept at 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C.

Catalase is an enzyme found in human body cells, such as liver cells, and plays an important role in metabolism.

Predict what you would expect the student's results to show about the effect of temperature on catalase activity.