Biology 5090/31 — October/November 2025

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Observations and Measurements · Experimental Contexts · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials · Planning Experiments and Investigations · Microscopy and Biological Drawing

Q115MMediumObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and Evaluation

Apple juice is made by cutting up and crushing apples. When apple tissue is cut up and crushed, it can become a darker colour and go brown.

You are going to investigate the effect of vitamin C on the colour change when apple is cut up and crushed.

You are provided with some apple tissue, $20\text{ cm}^3$ of vitamin C solution, $20\text{ cm}^3$ of distilled water, a glass rod and three large test-tubes.

Read through the following procedure carefully and decide how to label your test-tubes.

Do not carry out the procedure yet.

Label a large test-tube and use a clean syringe to add $5\text{ cm}^3$ of vitamin C solution.
Label a second large test-tube and use a clean syringe to add $5\text{ cm}^3$ of distilled water.
Label a third large test-tube and do not add any liquid.
Cut three cubes of apple each $1\text{ cm} \times 1\text{ cm} \times 1\text{ cm}$ . Ensure that each surface of the cubes is freshly cut. Do not include any skin or core.
Cut each cube into many small pieces. Take care to keep the pieces from each cube separate.
Add the pieces of one cube to the test-tube containing vitamin C solution.
Add the pieces of the second cube to the test-tube containing distilled water.
Add the pieces of the third cube to the test-tube with no added liquid.
Use a glass rod to gently crush the pieces of apple in the bottom of each test-tube.
Clean the glass rod in the rinsing water between using it in each test-tube.

(a)

When you have finished crushing the apple, observe the colour of the crushed apple in each test-tube.

11M

(i)

In Table 1.1, record your observations of the crushed apple at 0 minutes.

1M Similar

(ii)

Start timing.

Record the start time. ______

1M Similar

(iii)

Observe the colour of the crushed apple in each test-tube at 5, 10 and 15 minutes and record your observations in Table 1.1.

Table 1.1

time /minutes	colour of crushed apple in each test-tube
	vitamin C	distilled water	no added liquid
0
5
10
15

4M Similar

DifficultyMedium-Easy

Worked solution

Answer

time / minutes	vitamin C	distilled water	no added liquid
0	pale yellow	pale yellow	pale yellow
5	pale yellow	pale yellow	pale yellow
10	pale yellow	pale yellow	pale yellow
15	pale yellow	pale yellow	brown/dark yellow

Final answer

Table completed with colours at 5, 10 and 15 min; vitamin C same colour throughout; no added liquid brown/dark yellow by 15 min; distilled water same as vitamin C or intermediate.

Detailed explanation

Walkthrough

At each time (5, 10 and 15 minutes) look at each test-tube and record the colour of the crushed apple. The expected pattern is that the vitamin C tube stays the same colour throughout, the no-added-liquid tube becomes brown or dark yellow by 15 minutes, and the distilled water tube either stays the same as vitamin C or is intermediate between vitamin C and no added liquid. This is because the enzyme in the apple reacts with oxygen in the air; vitamin C prevents this reaction, while water reduces the amount of oxygen available.

Key Takeaways

A results table should have every cell filled with the observation.
The same colour description should be used for the same appearance.
The pattern of results supports the later conclusions about vitamin C and distilled water.

Common Mistakes

Leaving some cells blank.
Recording 'brown' for the vitamin C tube.
Recording different colours for the same tube at different times when the colour has not changed.
Writing a measurement (e.g. '5') instead of a colour.

Things to Be Careful About

The mark scheme requires a colour in all the 5, 10 and 15 minute cells.
Use consistent colour words so that 'same' is clear.
The no-added-liquid tube should be brown/dark yellow at 15 minutes; the distilled water tube should not be as brown as that.

Techniques used

record observations at intervalscompare colours across treatments over timecomplete a results table

(iv)

Using your observations in Table 1.1, state what can be concluded about the effect of vitamin C on the colour change when apple is cut up and crushed.

______

1M Similar

(v)

Using your observations in Table 1.1, state what can be concluded about the effect of distilled water on the colour change when apple is cut up and crushed.

______

2M Similar

(vi)

You may have found difficulty in carrying out some of the instructions consistently which may have resulted in sources of error.

State one possible source of error and suggest how it could be overcome.

______

2M Similar

(b)

(i)

Use the universal indicator paper that has been provided to test and record the pH of the distilled water and the pH of the vitamin C solution.

distilled water pH ______
vitamin C solution pH ______

2M Similar

(ii)

When apple tissue is cut up and crushed, an enzyme comes into contact with oxygen in the air. In the presence of oxygen, the enzyme catalyses the reaction of a colourless molecule in the cells of the apple tissue to cause the change in colour.

Suggest how this might explain the effect of:

distilled water ______

vitamin C. ______

2M Similar

Q218MMedium-HardObservations and MeasurementsAnalysis, Conclusions and EvaluationExperimental ContextsUse of Techniques, Apparatus and MaterialsPlanning Experiments and Investigations

Yeast is used to produce bread. Flour is mixed with water and yeast to produce dough. The yeast breaks down starch in the flour to produce sugar. The yeast uses the sugar for respiration, giving off bubbles of carbon dioxide. The bubbles of carbon dioxide are trapped in the dough, making it increase in volume before it is baked.

(a)

Some students tested the effect of yeast in four doughs, each made from a different type of flour – wheat, rye, buckwheat and maize. The effect of the yeast in the dough was evaluated by measuring how much the dough increased in volume.

The same mass of each type of flour was mixed with the same volume of water and the same mass of yeast to form a dough. Four $100\text{ cm}^3$ measuring cylinders were labelled and dough was added to each. The volume of the dough in each of the cylinders was measured and recorded at 15-minute intervals. Some of the results are shown in Table 2.1.

10M

(i)

Fig. 2.1 shows the measuring cylinder with dough made from wheat flour after 30 minutes.

Fig. 2.1

Record the volume of the dough in Table 2.1.

1M Similar

(ii)

Complete Table 2.1 by calculating the total increase in volume of each dough after 45 minutes.

Table 2.1

time/minutes	volume of dough in measuring cylinder/ $\text{cm}^3$
	wheat flour	rye flour	buckwheat flour	maize flour
0	20	21	21	20
15	24	23	21	21
30		27	22	22
45	45	32	23	22
total increase in volume after 45 minutes	25

2M Similar

DifficultyMedium-Easy

Worked solution

Answer

time/minutes	wheat flour	rye flour	buckwheat flour	maize flour
total increase in volume after 45 minutes	25	11	2	2

(rye: $32-21=11$ ; buckwheat: $23-21=2$ ; maize: $22-20=2$ )

Final answer

rye 11, buckwheat 2, maize 2

Detailed explanation

Walkthrough

The total increase after 45 minutes is the final volume minus the starting volume for each flour. The wheat row shows the pattern: $45 - 20 = 25$ . Apply the same subtraction: rye $32 - 21 = 11$ ; buckwheat $23 - 21 = 2$ ; maize $22 - 20 = 2$ . Enter all three numbers so every cell of that row is filled — the first mark is for completing all three cells, the second for all three being correct.

Key Takeaways

Increase = final value − initial value; complete every required cell of a table.

Common Mistakes

The mark scheme states 'R if units in table' — writing cm³ in the cells loses the marks. Subtracting from zero instead of the time-zero volume; leaving a cell blank.

Things to Be Careful About

No units anywhere in the cells; use each flour's own starting volume, which differs slightly between flours.

Techniques used

calculate an increase in volumecomplete a results table

(iii)

On the grid draw a bar chart to show the total increase in volume of the four doughs after 45 minutes.

Fig. 2.2

4M Similar

(iv)

The students wanted to know why the effect of yeast in the four doughs varied.

Table 2.2 shows some of the biological molecules in the four flours.

Table 2.2

biological molecule	mass/ $\text{g}$ per $100\text{ g}$ flour
	wheat flour	rye flour	buckwheat flour	maize flour
starch	54.5	54.1	59.0	74.0
gluten (a protein)	8.9	3.1	0.0	0.0
fibre	10.6	13.7	10.4	4.3

Using Table 2.2, your bar chart and the information about the process of bread production, suggest and explain how these biological molecules affect the total increase in volume of bread dough.

______

3M Similar

DifficultyMedium

Worked solution

Answer

Gluten (a protein) has an effect: its amounts match the pattern of total volume increase — wheat has the most gluten ( $8.9\text{ g}$ ) and the largest increase, rye less gluten and a smaller increase, and buckwheat and maize have none and the smallest increases.
The dough with the largest volume increase trapped more bubbles of carbon dioxide (gluten forms a stretchy network that holds the gas in).
Starch and fibre have little or no effect: they do not match the volume differences (maize has the most starch yet one of the smallest increases).

Final answer

Gluten amount matches the volume-increase pattern; more gluten traps more carbon dioxide bubbles; starch and fibre do not match the differences.

Detailed explanation

Walkthrough

'Suggest' means reason from the data, not recall. Compare the three molecules in Table 2.2 against the bar chart:

Starch: maize has by far the most starch (74.0 g per 100 g) but one of the smallest volume increases (2 cm³), while wheat with less starch has the biggest increase. So starch does not explain the pattern.
Fibre: rye has the most fibre but only a middling increase — again no match.
Gluten: wheat 8.9 g → 25 cm³; rye 3.1 g → 11 cm³; buckwheat 0 → 2 cm³; maize 0 → 2 cm³. This ordering matches the bar chart perfectly, so gluten is the molecule responsible. Biologically, gluten forms an elastic protein network in dough that traps the carbon dioxide bubbles made by respiring yeast, so more gluten means more gas held and a greater rise.

Key Takeaways

To identify which factor causes a pattern, check whether its values rise and fall in step with the results; a factor whose values contradict the pattern can be eliminated.

Common Mistakes

Saying 'starch is broken down to sugar so it causes the rise' without noticing maize contradicts this; describing the gluten effect without linking it to trapping carbon dioxide bubbles; giving observations ('wheat rose most') without the explanation the question demands.

Things to Be Careful About

All three marking points are needed: gluten matches the pattern (+), the mechanism is trapping CO₂ bubbles (+), and starch/fibre are excluded because they do not match (+). Each point needs both halves joined by '+' in the scheme.

Techniques used

correlate data across two tables and a graphsuggest an explanation matching a patternidentify which variable explains the differences

(b)

Describe how you would show that each of the four flours contained starch.

______

2M Similar

(c)

The students made more dough from wheat flour, yeast and water.

Using this dough, plan an investigation based on the method in 2(a) to determine the effect of temperature on the increase in volume of dough at temperatures between $20\,^\circ\text{C}$ and $80\,^\circ\text{C}$ .

Predict your expected results.

investigation plan ______

expected results ______

6M Similar

DifficultyMedium-Hard

Worked solution

Answer

Investigation plan

Make the dough and divide it equally between several $100\text{ cm}^3$ measuring cylinders.
Use at least three different temperatures between $20\,^\circ\text{C}$ and $80\,^\circ\text{C}$ , e.g. $20\,^\circ\text{C}$ , $50\,^\circ\text{C}$ and $80\,^\circ\text{C}$ .
Place each cylinder in a water-bath at its temperature.
Keep everything else the same: same mass of flour, yeast and water, same initial volume of dough.
Measure the volume of dough at stated time intervals (e.g. every 15 minutes up to 45 minutes).
Calculate the increase in volume at 45 minutes for each temperature.
Repeat each temperature at least three times and calculate the mean increase in volume.
Plot a graph of mean total volume increase (y-axis) against temperature (x-axis).

Expected results
The volume increase will increase as temperature increases up to an optimum (around $40\,^\circ\text{C}$ ), then increase much less / decrease at higher temperatures as enzymes denature above the optimum.

Final answer

See working — plan with at least three temperatures in water-baths, controlled variables, repeats and mean, graph of volume increase against temperature; prediction: volume increase rises with temperature to an optimum then falls/levels off.

Detailed explanation

Walkthrough

The planning question rewards hitting every category the scheme lists, and it lists eight points for five marks plus one for the prediction, so cover them all:

Dependent variable: increase in volume of dough, measured as in 2(a) — divide the dough equally between cylinders, read volumes at fixed intervals, calculate the increase at 45 minutes.
Independent variable: temperature, with at least three stated values strictly within 20–80 °C (e.g. 20, 50, 80 °C). Values outside the range score nothing.
How to control temperature: water-baths set at each temperature.
Controlled variables: same masses of flour, yeast and water, same starting volume — anything that would itself change gas production must be held constant.
Reliability: repeat each temperature at least three times and calculate a mean.
Presentation: plot total volume increase (y-axis) against temperature (x-axis).
Prediction: yeast respiration is catalysed by enzymes, so rate rises with temperature up to an optimum near 40 °C, then falls sharply as enzymes denature above it — so volume increase rises then drops (or stops rising) at high temperatures.

Key Takeaways

A scoring plan names what is measured, how, at least three values of the independent variable within the stated limits, the variables kept constant, repeats with a mean, and how results will be displayed. Predictions about enzyme reactions follow the temperature–activity curve.

Common Mistakes

Giving temperatures outside 20–80 °C; using only two temperatures; forgetting the water-baths; predicting a rise with no mention of the fall beyond the optimum; plotting temperature on the y-axis; omitting repeats and a mean.

Things to Be Careful About

The scheme caps the plan at 5 marks and gives 1 for the prediction — write both sections clearly under their headings. State the temperatures explicitly; 'different temperatures' alone does not score point 2.

Techniques used

plan an investigation varying temperatureidentify variables to controlpredict enzyme activity against temperature

Q37MMediumExperimental ContextsObservations and MeasurementsMicroscopy and Biological Drawing

A student investigated a plant that had some stems with flowers and some stems with no flowers. The student picked one leaf from a stem with flowers and one leaf from a stem with no flowers. Fig. 3.1 shows the two leaves.

Fig. 3.1

(a)

(i)

Complete Table 3.1 to compare the size and shape of the leaves.

Table 3.1

feature of leaf	leaf from stem with flowers	leaf from stem with no flowers
size
shape

2M Similar

DifficultyMedium-Easy

Worked solution

Answer

feature of leaf	leaf from stem with flowers	leaf from stem with no flowers
size	large / larger	small / smaller
shape	longer than wide / pointed oval shape / just 1 point at tip	widest at base / three pointed sections

Final answer

See working

Detailed explanation

Walkthrough

The question asks for a comparison of the size and shape of two leaves. The critical detail here is the magnification label beneath each photograph. The leaf from the stem with flowers is shown at $\times 1$ (actual size), while the leaf from the stem with no flowers is shown at $\times 2$ (twice actual size).

Size: Although the right leaf appears roughly the same height as the left leaf in the photograph, it is magnified twice as much. Therefore, its actual size is about half the height of the left leaf. The leaf from the stem with flowers is larger in actual size, and the leaf from the stem with no flowers is smaller.

Shape:

The left leaf (flowers) is an unlobed, pointed oval or lanceolate shape. It is longer than wide, with just one point at the tip.
The right leaf (no flowers) is palmately lobed (ivy-like). It is widest at the base, with three (or more) pointed sections (lobes) radiating outwards.

Key Takeaways

Always check for magnification labels on photographs before comparing sizes. An object magnified $\times 2$ that looks the same size as an object at $\times 1$ is actually half the size in reality.
Use precise biological terminology for shapes (e.g., 'unlobed', 'palmately lobed', 'lanceolate', 'longer than wide').

Common Mistakes

Ignoring magnification: Stating that the right leaf is larger because it looks bigger in the photograph. This is a classic trap.
Vague shape descriptions: Saying 'one is round, one is spiky'. The mark scheme requires specific descriptors like 'longer than wide' or 'widest at base'.
Confusing the columns: Putting the description of the left leaf in the right column.

Things to Be Careful About

The mark scheme accepts 'large/larger' and 'small/smaller' for size. Do not just write 'big' and 'small'; comparative terms are expected when comparing two items.
Give exactly the number of points required. The table has two rows (size and shape), so provide one clear point for each column in each row.

Techniques used

compare physical features of specimensinterpret magnification labels to infer actual size

(ii)

Suggest what the student needs to do to be certain that the two leaves they picked are representative of the leaves on the two types of stem.

______

2M Similar

(b)

In the space below, make a large drawing of the leaf from the stem with no flowers as it appears in Fig. 3.1.

3M Similar

DifficultyMedium

Worked solution

Answer

The drawing must meet the following criteria to earn full marks:

Conventions: Drawn with a sharp pencil using continuous lines, with no shading, no ruled lines, and no overlapping text.
Size and Proportion: A correct leaf shape drawn with a minimum height of 80 mm.
Specific Detail: Must include a notch in the right lobe at the base.
Vein/Branch Detail: Must show at least 3 side branches (one to each lobe) radiating from the top of the petiole.
Petiole: The petiole (leaf stalk) must be drawn as a double line.

Final answer

Large labelled drawing of the palmately lobed leaf from the stem with no flowers

Detailed explanation

Walkthrough

This is a biological drawing question on Paper 3 (Practical Test). The candidate is asked to draw the leaf from the stem with no flowers (the right-hand leaf in Fig 3.1). This leaf is palmately lobed, resembling an ivy leaf, with three to five pointed lobes.

1. Drawing Conventions (1 mark):
5090 is extremely strict about drawing style. The candidate must use a sharp pencil (not a pen or soft pencil). Lines must be continuous (no jagged or broken lines). There must be no shading, stippling, or cross-hatching. There must be no ruled lines (rulers are not allowed for drawing the specimen itself, only for label lines). Text from the question or other labels must not overlap the drawing.

2. Size and Proportion (1 mark):
The drawing must be large. The mark scheme specifies a minimum height of 80 mm. The proportions must accurately reflect the photograph: the leaf is wider at the base and tapers to pointed lobes. The candidate must not just trace the photo; they must redraw it to scale on the exam paper.

3. Specific Structural Detail (1 mark):
This is where candidates often lose marks. The mark scheme explicitly requires:

A notch in the right lobe at the base (look closely at the base of the right-hand leaf in Fig 3.1; there is a distinct indentation where the right lobe meets the central lobe).
At least 3 side branches (veins or minor stems) radiating from the top of the petiole (the point where the leaf stalk meets the leaf blade), with one going to each lobe.
The petiole (the leaf stalk at the bottom) must be drawn as a double line (two parallel lines), not a single thick line.

Key Takeaways

Biological drawings are not art; they are scientific records. Conventions (sharp pencil, continuous lines, no shading) are non-negotiable and earn marks.
Minimum size is mandatory. An 80 mm minimum height is a hard requirement; a smaller drawing loses the size/proportion mark.
Read the mark scheme for specific details. Examiners look for very specific features (like the notch or the double-line petiole) that candidates might overlook if they just draw a generic 'ivy leaf'.

Common Mistakes

Using shading or cross-hatching: This is the most common error. Biological drawings must be clean line art.
Drawing the petiole as a single line: The mark scheme explicitly requires a double line for the petiole.
Missing the notch: The indentation at the base of the right lobe is a key identifying feature of this specific leaf variation and must be included.
Overlapping text: Label lines or text from the question covering the drawing invalidates the conventions mark.
Drawing the wrong leaf: The question asks for the leaf from the stem with no flowers (the lobed one), not the unlobed one.

Things to Be Careful About

Label lines: If you add labels, use straight, un ruled lines that do not cross each other or the specimen. However, this question does not explicitly ask for labels in the text, though the mark scheme description implies a complete drawing. Stick to the explicit criteria in the mark scheme.
Precision: The notch and side branches are small details. Use a sharp pencil and take your time to include them.
Paper orientation: Ensure the leaf is oriented correctly (petiole at the bottom, lobes pointing up/outwards) as shown in the photograph.

Techniques used

apply drawing conventions for biological specimensmaintain correct proportions and minimum size requirementsinclude specific structural details required by the mark scheme