Biology 5090/42 — October/November 2025

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

questions

marks

minutes

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

Q111MMediumObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationPlanning Experiments and Investigations

Hydrogen peroxide is a harmful waste product in living cells. The enzyme catalase breaks down hydrogen peroxide into water and oxygen.

Some students investigated catalase in tissues from different plants. They used small filter paper discs. The filter paper discs were placed on the cut surface of plant tissues to absorb liquid from the cells. The liquid from the cells might contain catalase.

Fig. 1.1 shows how the students were able to tell if catalase was present in tissues from different plants.

Fig. 1.1

The students were given $2\text{ cm} \times 2\text{ cm} \times 2\text{ cm}$ cubes of tissue from three different plants labelled A, B and C, small filter paper discs and a beaker of hydrogen peroxide solution.

The students followed this procedure.

Cut the piece of plant tissue A in half.
Use forceps to place a filter paper disc onto a cut surface of plant tissue A, to absorb liquid from the cells.
After 1 minute, use forceps to pick up the filter paper disc from the cut surface of plant tissue A.
Drop the filter paper disc into the beaker of hydrogen peroxide solution and immediately start timing. The filter paper disc will sink to the bottom of the beaker.
Observe the filter paper disc until it reaches the surface of the hydrogen peroxide solution, then stop timing. If a filter paper disc does not float within 4 minutes (240 seconds) stop timing and record the time taken for the filter paper disc to reach the surface as >240.
Record the time taken, to the nearest whole second, for the filter paper disc to reach the surface of the hydrogen peroxide solution.
Use forceps to remove the filter paper disc from the beaker of hydrogen peroxide solution and place it in the waste container provided.
Rinse and dry the forceps.
Repeat the procedure two more times with filter paper discs on the same cut surface of plant tissue A.
Repeat all of the procedure for filter paper discs on plant tissue B and then again for plant tissue C.

Fig. 1.2 shows a student's notebook. The student has recorded their results to the nearest whole second. The result for the third filter paper disc on plant tissue A is missing from their notes.

Fig. 1.2

Fig. 1.3 shows the time taken for the third filter paper disc on plant tissue A to reach the surface.

Fig. 1.3

(a)

(i)

Complete the headings in Table 1.1.

Table 1.1

______	______
	disc 1	disc 2	disc 3	mean
A
B
C

1M Similar

DifficultyEasy

Worked solution

Answer

plant / tissue	time / s	disc 1	disc 2	disc 3	mean
A
B
C

Headings:

First blank (top left): plant (or tissue)
Second blank (top, above disc 1): time / s (or time taken for disc to float / seconds)

Final answer

plant / tissue; time / s

Detailed explanation

Walkthrough

The table is designed to record the results of an experiment comparing three plant tissues (A, B, C). The rows are labelled with the tissue names, so the first column header must identify what is in the rows: plant or tissue. The data being recorded is the time it takes for the filter paper disc to float. The mark scheme requires the unit, so the second header must be time / s (or time in seconds). Without units, the data is meaningless in a scientific context.

Key Takeaways

When completing a results table, the first column usually identifies the independent variable (here, the plant tissue type), and the subsequent columns record the dependent variable (time) with its units.

Common Mistakes

Forgetting the units in the header (e.g., writing just 'time' instead of 'time / s').
Writing 'mean' in the first column header.

Things to Be Careful About

The mark scheme explicitly states 'units required'. Always include units in the main column header for the data. 'plant' and 'tissue' are interchangeable here.

Techniques used

identify the independent variable for the table headerstate the dependent variable with correct units

(ii)

Enter the data from Fig. 1.2 and Fig. 1.3 into Table 1.1.

Calculate the mean times for the filter paper discs, from tissues A, B and C, to reach the surface. Record all the values to the nearest whole second.

4M Similar

DifficultyMedium-Easy

Worked solution

Answer

plant	time taken for disc to float / s
	disc 1	disc 2	disc 3	mean
A	10	10	9	10
B	21	16	20	19
C	> 240	> 240	> 240	> 240

Working:

Plant A, disc 3: Fig 1.3 shows 9.31 s. Rounded to nearest whole second = 9 s.
Mean A: $(10 + 10 + 9) / 3 = 9.67 \approx$ 10 s.
Mean B: $(21 + 16 + 20) / 3 = 57 / 3 =$ 19 s.
Plant C: No disc floated within 4 minutes (240 s), so all values are > 240 and the mean is > 240.

Final answer

See table above

Detailed explanation

Walkthrough

First, extract the data from the notebook (Fig 1.2) and the stopwatch (Fig 1.3).

Plant A: Notebook has '10, 10'. The stopwatch (Fig 1.3) reads 9.31 SEC. The question asks to record to the nearest whole second, so 9.31 becomes 9. The rows for A are 10, 10, 9. Mean = $(10+10+9)/3 = 9.66...$ , which rounds to 10.
Plant B: Notebook has '21, 16, 20'. Mean = $(21+16+20)/3 = 57/3 =$ 19.
Plant C: Notebook says 'no disc floated at 4 minutes'. The procedure says if it doesn't float within 240 seconds, record as >240. So all three discs are > 240. The mean of values all greater than 240 is also > 240.

Key Takeaways

Always round raw data to the precision requested (nearest whole second here).
When calculating a mean, round the final answer to the same precision as the data if appropriate, or follow the mark scheme's rounding (9.67 rounds to 10).
Censored data (values exceeding the max time) should be recorded as >max_time, and the mean reflects this inequality.

Common Mistakes

Recording 9.31 instead of 9.
Calculating the mean for A as 9 (rounding down incorrectly) or 9.7.
Writing '0' or '4 minutes' for Plant C instead of '> 240'.

Things to Be Careful About

The stopwatch shows 9.31, but the instruction says 'nearest whole second'.
Plant C data is qualitative ('no disc floated'), but must be converted to the quantitative format used in the table (> 240).

Techniques used

read a digital stopwatch to the nearest whole secondcalculate a mean from three readingshandle censored data (>240s)

(iii)

Using the results in Table 1.1, state what you can conclude about catalase in plant tissues A, B and C.

tissue A ______

tissue B ______

tissue C ______

3M Similar

(b)

(i)

Suggest why the filter paper discs were left on the cut surfaces of the plant tissues for the same length of time.

______

2M Similar

(ii)

Suggest a suitable control for this investigation.

______

1M Similar

Q221MMedium-HardMicroscopy and Biological DrawingExperimental ContextsObservations and MeasurementsAnalysis, Conclusions and EvaluationPlanning Experiments and InvestigationsUse of Techniques, Apparatus and Materials

Lemna is a small green plant that floats on the surface of water in ponds and lakes. It consists of leaves which float and a root that hangs down in the water.

Fig. 2.1 shows a single plant that has four leaves. D and E indicate the maximum length of two of the plant's leaves.

Fig. 2.1

(a)

On Fig. 2.1, draw a straight line to join D and E. Measure the length of the line and record it.

______ $\text{mm}$

Calculate the actual maximum length of two of the plant's leaves and record it to the nearest whole number.

______

3M Similar

(b)

The population of this plant grows by each plant dividing into two smaller plants. These smaller plants then grow new leaves and divide again.

Some students decided to investigate the growth of Lemna plants. They placed six plants in a small beaker containing nutrients in distilled water (nutrient solution). They used a lamp to provide constant light.

12M

(i)

Suggest why the students added nutrients to the distilled water.

______

1M Similar

(ii)

The students decided to measure growth by counting the total number of leaves at the same time each day. At the start of the investigation there were 16 leaves in total on the plants.

Fig. 2.2 shows the beaker seen from above on day 4.

Fig. 2.2

Count the total number of leaves visible in Fig. 2.2 and enter the number in Table 2.1.

Table 2.1

time / days	total number of leaves
0	16
2	20
3	29
4
5	55
6	83
7	91

1M Similar

(iii)

On the grid, draw a line graph of the data shown in Table 2.1.

Join the points with ruled, straight lines.

grid

5M Similar

DifficultyMedium

Worked solution

Answer

Axes: Horizontal axis labelled time / days and vertical axis labelled total number of leaves.
Scales: Linear scales on both axes starting at 0 at the origin:
- $x$ -axis: 2 cm (1 major grid square) $= 1\text{ day}$ (from 0 to 7 or 8 days).
- $y$ -axis: 2 cm (1 major grid square) $= 20\text{ leaves}$ (from 0 to 100 leaves).
Plotting: All 7 points accurately plotted with small, neat crosses ( $\times$ $\times$ ) or encircled dots ( $\odot$ $⊙$ ):
- $(0, 16)$
- $(2, 20)$
- $(3, 29)$
- $(4, 42)$
- $(5, 55)$
- $(6, 83)$
- $(7, 91)$
Line: Points connected sequentially with clean, single ruled straight lines from point to point.

Final answer

Line graph plotted with time on x-axis and total number of leaves on y-axis, points joined with ruled straight lines

Detailed explanation

Walkthrough

To score full marks on a 5090 line graph:

Orientation & Labels: Put the independent variable on the $x$ -axis (time / days) and the dependent variable on the $y$ -axis (total number of leaves). Units must be included as given in the table.
Scale: Scales must be linear (evenly spaced) and make good use of the grid (using at least half of the grid area in both directions). Values must be indicated at the origin (0 on both axes).
- For $x$ : 0 to 7 days fits well at 2 large squares per day.
- For $y$ : 0 to 100 leaves fits well at 1 large square per 20 leaves (or 2 large squares per 20 leaves depending on orientation).
Plotting: Mark all seven points with clear, precise crosses ( $\times$ ) or circled dots ( $\odot$ ) to within $\pm 0.5\text{ mm}$ (half a small square).
Line connection: The question explicitly states: "Join the points with ruled, straight lines." Use a ruler to draw straight line segments between consecutive data points. Do not extrapolate beyond day 7 or before day 0.

Key Takeaways

Always check whether the prompt asks for a "smooth line/curve" or "ruled, straight lines". Here, straight lines connecting points are required.

Common Mistakes

Drawing a freehand curve when asked for ruled straight lines.
Omitting the origin value or units on axes.
Extrapolating the line beyond the plotted points.

Things to Be Careful About

Ensure the point at day 4 uses the value 42 determined in part (b)(ii).

Techniques used

plot a line graphchoose linear scaleslabel axes with unitsjoin points with ruled lines

(iv)

Use your graph to estimate the total number of leaves that would have been present on day 1. Show your working on your graph.

total number of leaves on day 1 = ______

2M Similar

(v)

Predict the shape of the graph after day 7 if the investigation continues for another six days. Explain your answer.

prediction ______

explanation ______

2M Similar

(vi)

Suggest one other method that the students could use to measure the growth of Lemna.

______

1M Similar

(c)

Plan an investigation to determine the effect of different concentrations of a nutrient solution on the growth of Lemna. Use the same method of counting the number of leaves that the students used in their investigation for measuring growth.

6M Similar

DifficultyMedium-Hard

Worked solution

Answer

Independent variable: Prepare at least three (e.g. 5) different concentrations of nutrient solution (e.g. $0\%$ , $25\%$ , $50\%$ , $75\%$ , and $100\%$ ).
Controlled variables:
- Keep the volume of nutrient solution the same in each container (e.g. $100\text{ cm}^3$ ).
- Start each container with the same number of Lemna plants/leaves (e.g. 6 plants / 16 leaves).
- Keep the temperature constant (e.g. using a thermostatically controlled room or water-bath at $20\,^\circ\text{C}$ ).
- Keep the light intensity constant (e.g. same distance from the same lamp, constant illumination).
Dependent variable & procedure: Place the plants into each solution and count and record the total number of leaves at regular intervals (e.g. every day at the same time for 7 days).
Repetition: Repeat the experiment at least twice more for each concentration (minimum 3 trials per concentration) and calculate the mean number of leaves for each concentration.
Data processing: Compare growth across the different concentrations by calculating the percentage increase in leaf number or the growth rate (leaves per day), or by plotting a graph of leaf count against nutrient concentration.

Final answer

See working

Detailed explanation

Walkthrough

To obtain full marks (6 marks) in a Cambridge 5090 planning question, structure the response clearly covering all key experimental design areas:

Independent Variable: State a clear range of at least three different concentrations of nutrient solution (e.g., $0\%$ , $25\%$ , $50\%$ , $75\%$ , $100\%$ or $0.1\text{ M}$ , $0.2\text{ M}$ , $0.3\text{ M}$ ).
Control of Confounding Variables (Constants): Name specific variables to control:
- Same volume of solution (e.g. $50\text{ cm}^3$ in each beaker).
- Same initial number of plants/leaves in each beaker.
- Same temperature (e.g. room temperature $20\,^\circ\text{C}$ ).
- Same light intensity (constant light from a lamp at a fixed distance).
Dependent Variable & Method: State what is measured and how: count the number of leaves at regular intervals (e.g. daily at the same time) over a specified duration (e.g. 7 days).
Reliability & Repeats: Specify repeating each concentration at least twice more (3 trials total) and calculating a mean.
Analysis / Comparison: Describe how to compare the results to determine the effect of concentration (e.g. calculate percentage increase in leaves, calculate rate of leaf production, or plot a graph of mean leaf number against concentration).

Key Takeaways

A complete experimental plan must specify: IV (range of $\ge 3$ values), DV (measurement method and time intervals), CVs (at least 2 specific variables kept constant), Replicates (repeat and mean), and Data Analysis.

Common Mistakes

Providing fewer than 3 concentrations.
Stating "repeat to avoid errors" rather than "repeat and calculate mean to improve reliability".
Forgetting to control key abiotic variables like light intensity and temperature.

Things to Be Careful About

The prompt specifies using the same method of counting leaves as the original investigation, so make sure leaf counting is explicitly described as the measurement method.

Techniques used

plan an investigationidentify independent, dependent and controlled variablesdescribe repeat trials and data processing

Q38MMediumUse of Techniques, Apparatus and MaterialsMicroscopy and Biological DrawingExperimental Contexts

Fig. 3.1 is a photomicrograph of cells from a plant epidermis that have been treated so that some of the cells are plasmolysed.

Fig. 3.1

(a)

State three items of apparatus that you would need to use to observe the actual cells shown in the photomicrograph.

______
______
______

3M Similar

(b)

Make a large drawing of the two cells labelled X and Y as they appear in Fig. 3.1.

3M Similar

DifficultyMedium

Worked solution

Answer

Clear, continuous outlines drawn with a sharp pencil, with no shading, stippling, or ruled lines.
Large drawing measuring at least $100\text{ mm}$ across cells X and Y combined, showing the two cells touching each other along their shared/adjacent boundary.
Accurate structural detail showing:
- The upper right wall of cell X and lower left wall of cell Y drawn as approximately straight and parallel lines.
- The shrunken cytoplasm/protoplast drawn inside plasmolysed cell Y, leaving a clear gap between the cytoplasm and the cell wall, while the cytoplasm of cell X fills the cell up to the cell wall.

Final answer

Large drawing of cells X and Y measuring at least 100 mm across, drawn with clear continuous lines, no shading, and correct structural details showing plasmolysis in Y.

Detailed explanation

Walkthrough

When creating a biological drawing from a photomicrograph:

Line Quality and Technique: Use a sharp HB pencil to draw crisp, continuous, single lines. Do not sketch with overlapping strokes, do not use a ruler for biological outlines, and strictly avoid any shading, cross-hatching, or stippling.
Size and Proportion: The combined width of the two cells drawn must be at least $100\text{ mm}$ (spanning more than half the available drawing space). The cells must be drawn in contact with each other, sharing a common boundary region.
Structural Details:
- Cell X is non-plasmolysed: its cytoplasm/protoplast occupies the entire volume enclosed by the outer cell wall.
- Cell Y is plasmolysed: its cytoplasm has shrunk into a rounded mass, pulled away from the rigid cell wall, leaving an empty region between the protoplast and the wall.
- The outer boundaries between adjacent cells in this tissue (specifically the upper right edge of cell X and the lower left boundary of cell Y) are approximately straight and parallel.

Key Takeaways

Biological drawings must follow strict rules: sharp continuous lines, minimum size, no shading, and faithful representation of cellular morphology.
In plasmolysed plant cells, the cell wall maintains its shape while the cell membrane and cytoplasm pull away towards the center.

Common Mistakes

Adding pencil shading to represent dark/tinted cytoplasm (strictly penalized in biological drawings).
Drawing fuzzy, sketchy, or broken outlines.
Drawing cell Y without its outer cell wall boundary, or forgetting the shrunken cytoplasmic mass inside.

Things to Be Careful About

Ensure the drawing exceeds the specified size threshold (minimum $100\text{ mm}$ across).

Techniques used

make a biological drawing adhering to standard conventionsrepresent relative sizes, shapes, and positions of adjacent cells

(c)

Describe how you would treat cells from a plant epidermis so that they become plasmolysed.

______

2M Similar