IB Biology HL Theme A: Unity and diversity questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Medium16 marks

A student investigated the effect of water availability on seed germination. Five dishes were used for each treatment, with 20 seeds in each dish. Each dish contained filter paper and the same type of water. The dishes were kept at the same temperature and light conditions. After 72 hours, a seed was counted as germinated if its radicle had emerged. At 20 mL, the seeds were fully submerged; at the other volumes, the filter paper was moist but the seeds were not submerged.

Water added / mL	Number of seeds germinated out of 100
0	0
2	38
5	82
10	86
20	42

(a)

Calculate the difference in germination percentage points between the 10 mL and 20 mL treatments.

[2]

(b)

Describe the relationship between water added and germination.

[3]

(c)

Explain why germination was absent without added water but high in the 5 mL and 10 mL treatments.

[3]

(d)

Explain how water acts as a transport medium from roots to leaves in a seedling, including one adaptation of xylem for this role.

[3]

(e)

The syllabus statement is that water is the medium for life. Using the results and your biological knowledge, explain how water can be essential as a medium without increasing water volume always increasing germination. Refer to the environment in which the first cells originated and to a role of water in present-day cells.

[5]

Question 2

Paper 2Easy4 marks

Figure 1 shows the number of possible DNA base sequences for strands of different lengths.

(a)

Use Figure 1 to state the number of possible DNA base sequences for a strand of four nucleotide positions.

[1]

(b)

Use the pattern in Figure 1 to explain how a short DNA molecule can store a large amount of information.

[1]

(c)

Explain how complementary base pairing, based on hydrogen bonding, allows genetic information to be replicated and expressed.

[2]

Question 3

Paper 2Easy6 marks

A research group summarized its estimates for the ages of the first living cells and the last universal common ancestor (LUCA) in Figure 1. The estimates are ranges in Ga, where 1 Ga is one billion years before the present. The estimate for the first living cells was based on fossilized evidence in ancient seafloor hydrothermal-vent precipitates; the estimate for LUCA was based on conserved sequences from genomic analysis.

(a)

Using Figure 1, state the estimated age range for each of the first living cells and LUCA.

[2]

(b)

State the interval in which the two estimates overlap.

[1]

(c)

State what the fossilized evidence in ancient seafloor hydrothermal-vent precipitates indicates.

[1]

(d)

State what conserved sequences from genomic analysis indicate about LUCA.

[1]

(e)

Using Figure 1, state what the age estimates show about the time scale over which life has been evolving.

[1]

Question 4

Paper 2Medium16 marks

A student makes a temporary mount of leaf epidermal cells and examines it using a light microscope. At the objective used, a length of 100 μm on a stage micrometer spans 40 eyepiece graticule divisions. One cell has a width of 24 eyepiece graticule divisions. A printed image of the same cell has a width of 6.0 mm. Assume that the printed image has not been resized.

(a)

Calculate the actual length represented by one eyepiece graticule division.

[2]

(b)

Calculate the actual width of the cell and the magnification of the printed image. State the length on the printed image of a scale bar representing 10 μm.

[5]

(c)

A fluorescent stain is used to make cell boundaries visible. To locate protein R, a fluorescently labelled antibody against R is used. Describe how immunofluorescence reveals the location of R and distinguish it from the use of the fluorescent stain.

[3]

(d)

In a further test, 100 cells were scored according to the location of the strongest detectable fluorescence signal.

Preparation	Plasma membrane (%)	Cytoplasm (%)	No detectable signal (%)
Fluorescently labelled antibody against R	70	25	5
Fluorescently labelled non-specific antibody	6	7	87

Assess the claim that protein R is located exclusively at the plasma membrane, using the data.

[3]

(e)

Another team wants to investigate the internal surfaces of cell membranes and the detailed structure of a protein complex while preserving it close to its native state. Outline how electron microscopy and its developments can be used to address these aims.

[3]

Question 5

Paper 2Medium4 marks

A culture of Escherichia coli containing bacteriophage lambda was monitored. At 40 min, the culture conditions were changed. Figure 1 shows the measured concentrations of intact bacterial cells and free lambda particles.

(a)

Using Figure 1, identify the viral cycle most consistent with each interval, 0–40 min and 40–80 min. Support each choice with one feature of the graph.

[2]

(b)

Explain how lambda DNA is maintained during the first interval, and state two ways in which the bacterial host supports phage production during the second interval.

[2]

Question 6

Paper 2Hard16 marks

Two bacterial lineages, A and B, reproduce by binary fission. They can be distinguished by an inherited feature unrelated to gene marker M. At the start of an investigation, M was detected in all sampled A colonies and none of the B colonies. A mixed culture contained both lineages; a control culture contained B only. At each time point, 100 colonies of each lineage were sampled and tested for M.

(a)

State two features of the biological species concept used to decide whether populations belong to the same species.

[2]

(b)

Describe the change in the percentage of lineage B colonies carrying M in the mixed culture over the 30 generations.

[2]

(c)

Suggest the most likely explanation for the appearance of M in lineage B, using all three series in Figure 1.

[3]

(d)

Two populations, P and Q, of another organism reproduce only asexually. Explain why the biological species concept cannot establish whether P and Q are the same or different species.

[3]

(e)

A student concludes that A and B must be one biological species because they share M after mixing, and that P and Q must be different species because they cannot interbreed. Assess these two conclusions, using Figure 1 and the biological species concept.

[6]

Question 7

Paper 2Easy5 marks

A botanical team reviewed a classification in which flowering plant species A and B were grouped together because their flowers have a similar shape. The team compared the same 12-base region of DNA in the three species.

Species pair	Number of base differences
A and B	12
A and C	2
B and C	10

(a)

Identify the pair with the most similar DNA sequences.

[1]

(b)

Does the DNA evidence support classifying A and B as the closest relatives among these three species? Justify your answer using one comparison from the table.

[2]

(c)

Suggest why classification based on flower shape could have been misleading.

[2]

Question 8

Paper 2Easy6 marks

Researchers record the percentage of beetles in a population with an inherited pale-colour characteristic.

Generation	Beetles with pale colour / %
1	32
5	47

One adult beetle develops greater leg-muscle mass through repeated exercise. This change is not passed to its offspring.

(a)

Calculate the increase in the percentage of beetles with pale colour from generation 1 to generation 5, in percentage points.

[2]

(b)

State what is meant by evolution.

[2]

(c)

Explain why the change in leg-muscle mass in the adult beetle does not count as evolution.

[2]

Question 9

Paper 2Hard16 marks

Ecologists surveyed the same twelve 1 ha woodland plots in 2012, 2018 and 2024. Expert teams used the same method, visited at the same time of year and spent the same amount of time surveying each plot. The table shows the numbers of individuals recorded for six native bird species. A zero indicates that no individuals of that species were recorded.

Species	2012	2018	2024
A	40	50	70
B	30	24	12
C	20	14	4
D	10	7	2
E	8	5	0
F	2	0	0

A citizen-science portal also collected observations in the surrounding landscape. A record is one submitted sighting, not a count of unique species. The portal did not use fixed observer-hours or fixed locations, and sightings were not independently checked.

Year	Records submitted	Contributors	Habitat types sampled
2012	1 200	80	3
2024	5 100	600	9

Other estimates for the same landscape were:

Measure	2012	2024
Human population	42 000	59 000
Native woodland remaining / ha	1 200	780
Woodland converted to agriculture or settlement since 2012 / ha	0	420
Plots occupied by an invasive alien plant / 12	1	7

(a)

Calculate the percentage change in recorded bird species richness between 2012 and 2024.

[2]

(b)

Describe how species richness and evenness changed in the bird survey between 2012 and 2024.

[3]

(c)

State one benefit of citizen-science observations and explain why the increase in portal records alone does not establish an increase in biodiversity.

[4]

(d)

A conservation group concludes that biodiversity in this landscape is recovering and that any decline in the bird survey was caused solely by human population growth. Evaluate whether the data support these conclusions.

[7]

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