IB Biology 2025 · Theme B · Form and function

B4.1 Adaptation to environment. Practice questions with markscheme.

45 original IB-style questions on B4.1, written from the 2025 guide: 19 multiple-choice, 15 short-answer, 6 data-based, 3 extended-response part, 2 drawing. Below is a 22-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

8 statements at SL and HL.

B4.1.1SL / HL Habitat as the place in which a community, species, population or organism lives
B4.1.2SL / HL Adaptations of organisms to the abiotic environment of their habitat
B4.1.3SL / HL Abiotic variables affecting species distribution
B4.1.4SL / HL Range of tolerance of a limiting factor
B4.1.5SL / HL Conditions required for coral reef formation
B4.1.6SL / HL Abiotic factors as the determinants of terrestrial biome distribution
B4.1.7SL / HL Biomes as groups of ecosystems with similar communities due to similar abiotic conditions and convergent evolution
B4.1.8SL / HL Adaptations to life in hot deserts and tropical rainforest

In the bank for B4.1

19 multiple-choice
15 short-answer
6 data-based
3 extended-response part
2 drawing
0 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

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The practice paper

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Biology · topic quiz

Standard level · topic practice, not an exam format

35 minutes22 marks

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Covers B4.1 Adaptation to environment

Name:

Which combination of abiotic conditions is required for (hard) coral reef formation?

[1]

Deep, cold, nutrient-rich upwelling water
Shallow, warm, clear water with normal salinity
Any tropical water, whatever its depth
Brackish estuary water with high turbidity

Which sampling method is most suitable for investigating how plant species' abundance changes with distance from a lake shore?

[1]

Quadrats at regular intervals along a transect
A single large quadrat placed at the shore
Mark–release–recapture of the plant species
Counting every plant in the whole study area

The Atlantic puffin (Fratercula arctica) nests in colonies of several thousand pairs and feeds on shoals of small fish. Which row correctly identifies the geographical location and the physical location that would be given in a description of the habitat of this species?

[1]

Geographical location: burrows dug in grassy slopes at the top of sea cliffs; physical location: coasts and islands around the North Atlantic Ocean
Geographical location: coasts and islands around the North Atlantic Ocean; physical location: burrows dug in grassy slopes at the top of sea cliffs
Geographical location: coasts and islands around the North Atlantic Ocean; physical location: the shoals of small fish in the surface waters where it feeds
Geographical location: a colony of several thousand breeding pairs on one island; physical location: burrows dug in grassy slopes at the top of sea cliffs

A class wanted to use a transect to find out whether the distribution of a moss species is correlated with light intensity. Their teacher insisted that the transect be laid in a semi-natural woodland rather than in a nearby landscaped park. Suggest why the woodland is more suitable for this investigation than the park.

[3]

The chart shows the biome that develops under different combinations of mean annual temperature and mean annual precipitation. Each shaded region represents one biome. The upper edge of the chart slopes because cold air holds less water vapour, so very high precipitation occurs only where it is warm. Point X marks the climate of a lowland site near the equator.

(a)Identify the biome expected at site X.[1]

(b)State the two abiotic factors used to predict the biome in this chart.[1]

(c)Compare and contrast the climates of tundra and hot desert.[2]

(d)Explain why temperate forest rather than temperate grassland develops at 12 °C when precipitation is above 110 cm per year.[2]

(e)Outline two adaptations of plants living in hot deserts.[2]

Students laid a 32 m transect across a salt marsh, starting at the edge of a tidal creek and running inland. At five stations along the transect a 1 m × 1 m quadrat was placed and the percentage cover of glasswort (Salicornia europaea) and of sea lavender (Limonium vulgare) was estimated. At each station a conductivity sensor was pushed into the mud at three points inside the quadrat to measure the salinity of the soil water. The readings are shown in the table.

Station	Distance from creek / m	Salinity reading 1 / g dm⁻³	Salinity reading 2 / g dm⁻³	Salinity reading 3 / g dm⁻³	Glasswort cover / %	Sea lavender cover / %
1	0	34	36	35	70	0
2	8	29	30	31	55	5
3	16	22	25	22	30	40
4	24	16	17	18	10	60
5	32	9	11	10	0	35

(a)Calculate the mean salinity of the soil water at station 3.[1]

(b)Describe the relationship between soil-water salinity and the percentage cover of glasswort.[2]

(c)Suggest one reason for taking three salinity readings inside each quadrat rather than one.[1]

(d)State one abiotic variable, other than salinity, that the students could have measured with a sensor at each station.[1]

(e)Explain the distribution of sea lavender along the transect, using the concepts of limiting factor and range of tolerance.[3]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
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Markscheme BbB-EAAAAAIAABQAOre_

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. B4.1.5 [1]

B: reef-building corals need light for their zooxanthellae (shallow, clear), warmth (~23–29 °C), stable marine salinity and carbonate for their skeletons;

2. B4.1.3 [1]

A: a (belt) transect with systematic quadrats captures change along an environmental gradient; mark–recapture is for mobile animals;

3. B4.1.1 [1]

B: the geographical location is the region of the world where the species is found (North Atlantic coasts and islands) and the physical location is the kind of place it occupies within that region (burrows in cliff-top grassland); A reverses the two; C gives the food supply, which is part of the niche, as the physical location; D describes a population, not a place, as the geographical location;

4. B4.1.4 [3 max]

a semi-natural habitat has been influenced by humans (e.g. by past management / felling) but is dominated by wild species, whereas a park is dominated by planted / cultivated species, OWTTE;
in the park, where plants grow is decided by people (planting, mowing, weeding, watering), so distribution would not reflect the plant's tolerance of abiotic conditions;
in the woodland the moss has established itself where conditions allow, so any correlation between its distribution and light intensity is more likely to reflect a real (causal) relationship, OWTTE;
management of the park (e.g. mowing, fertilizer, irrigation) would change other variables at the same time as light, confounding the investigation;

Accept any three. Do not accept "the woodland has more moss" without a reason.

5. B4.1.6

(a) [1]
- tropical rainforest;
(b) [1]
- (mean annual) temperature and (mean annual) precipitation / rainfall;
Both needed for the mark.
(c) [2 max]
- both have low precipitation compared with forest biomes (desert below about 50 cm per year; tundra mostly below about 100 cm);
- tundra has very low mean temperatures (below about −5 °C) whereas desert is warm to hot (above about 5 °C);
- desert can occur over a wider range of temperatures than tundra;
Accept any two; at least one similarity and one difference for full marks.
(d) [2 max]
- trees need more water than grasses to support their large biomass / transpiration from a large leaf area;
- with sufficient rainfall trees outcompete grasses for light by growing taller;
- temperature is suitable for either, so water is the limiting factor that determines which community persists;
Accept any two.
(e) [2 max]
- thick waxy cuticle / few or sunken stomata to reduce transpiration;
- water storage tissue in stems or leaves (succulence);
- leaves reduced to spines / small leaves to reduce surface area;
- deep or very widespread roots to obtain water;
- CAM metabolism / stomata open at night;
- vertical stems or reflective surfaces to reduce heat absorption;
Content pivot. Accept any two.

6. B4.1.4, B4.1.3

(a) [1]
- 23 (g dm⁻³);
Accept 23.0. Units not required.
(b) [2 max]
- glasswort cover increases as salinity increases / positive correlation;
- cover is greatest (70 %) at the highest salinity (35 g dm⁻³, at the creek edge) and zero at the lowest salinity (10 g dm⁻³);
- the change is (roughly) steady along the transect / no clear optimum within the range measured, OWTTE;
Do not accept "glasswort decreases with distance" alone, as the question asks about salinity.
(c) [1]
- salinity varies within the quadrat / a single reading may not be representative, so a mean is more reliable, OWTTE; OR to identify anomalous readings / reduce the effect of random error in the sensor readings, OWTTE;
Do not accept "to make it more accurate" without a reason.
(d) [1]
- (soil / air) temperature; OR light intensity; OR soil pH; OR soil moisture / water content; OR dissolved oxygen (of the soil water);
Mark the first answer only. Do not accept biotic variables such as cover of other plants.
(e) [3 max]
- salinity is a limiting factor for sea lavender / the adaptations of sea lavender give it a range of tolerance for salinity;
- sea lavender is absent (or almost absent) at stations 1 and 2 because salinity above about 30 g dm⁻³ is beyond the upper limit of its tolerance, OWTTE;
- cover is greatest at station 4 (17 g dm⁻³) which is near the optimum salinity for the species;
- cover is lower at station 5 even though salinity is lower, so another factor (e.g. competition from less salt-tolerant plants / lower tidal flooding / drier soil) limits it there, OWTTE;
- glasswort tolerates higher salinity than sea lavender, so the two species have different ranges of tolerance and occupy different parts of the marsh;
Content pivot. Accept "zone of intolerance" and "zone of stress" language. Do not accept explanations based only on distance without reference to an abiotic variable.