Adaptation to environment — IB Diploma Biology SL
Habitats, adaptations to abiotic factors, ranges of tolerance, coral reef conditions and the biomes set by temperature and rainfall. IB Biology B4.1.
Revision notes
5 short notes, in the order of the specification. Each one in short:
A habitat is the place in which a community, species, population or organism lives. Organisms have adaptations to the abiotic conditions of their habitat: marram grass survives dry, shifting sand dunes with rolled leaves and deep rhizomes, and red mangrove survives salty, waterlogged mud with stilt roots, lenticels and salt-excluding roots.
A range of tolerance is the span of values of an abiotic factor within which a species can survive. Abiotic variables such as temperature, light, soil pH, salinity and oxygen act as limiting factors: outside the range of tolerance a species cannot survive, so the distribution of plants and animals follows these variables, which transects can measure.
Coral reefs form only in shallow, clear, warm water of normal ocean salinity and slightly alkaline pH. Reef-building corals contain photosynthetic algae called zooxanthellae, so they need enough light, which limits water depth and requires clear water, and they build skeletons of calcium carbonate, which needs pH high enough for carbonate ions to be available.
A biome is a group of ecosystems with similar communities due to similar abiotic conditions and convergent evolution. Temperature and rainfall are the abiotic factors that determine terrestrial biome distribution: for any given pattern of the two, one natural ecosystem type is likely to develop, such as tropical forest where it is hot and wet all year.
Organisms in hot deserts are adapted to conserve water and cope with heat, while rainforest organisms are adapted to high rainfall, competition for light and life in trees. The saguaro cactus stores water and uses CAM photosynthesis, the dromedary camel tolerates rising body temperature, and the kapok tree has buttress roots to support it in shallow soil.
Exam questions
7 exam-style questions (22 marks), each with its mark scheme.
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17 cards: flip them, mark what you knew, and practise the rest.
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The whole of ecosystems (form and function) on one page, so you can see where this subtopic fits.
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Quick check questions
Define habitat.
Show answer
The place in which a community, species, population or organism lives.
Why does marram grass roll its leaves?
Show answer
To trap humid air around the stomata on the inner surface, reducing transpiration.
Name two factors needed for coral reef formation.
Show answer
Any two: shallow water, clear water, warm temperature, normal seawater salinity, slightly alkaline pH.
Which two abiotic factors mainly determine terrestrial biome distribution?
Show answer
Temperature and rainfall.
Why do mangrove stilt roots have lenticels?
Show answer
The waterlogged mud is anoxic, so oxygen diffuses into the roots from the air through lenticels.
Frequently asked questions
What is the difference between a habitat and a niche?
A habitat is the place where an organism, population, species or community lives, such as a sand dune. A niche is the role of a species in its ecosystem, including how it obtains food and all the biotic and abiotic interactions that affect its growth, survival and reproduction. Several species can share a habitat but not a niche.
How is marram grass adapted to sand dunes?
Marram grass rolls its leaves so the stomata, which sit in pits among hairs on the inner surface, are surrounded by humid air, reducing transpiration. A thick waxy cuticle covers the outer surface. Long roots and vertical rhizomes reach deep water and grow upwards when sand buries the plant.
What conditions do coral reefs need to form?
Coral reefs need shallow, clear water so light reaches the photosynthetic zooxanthellae in the corals. The water must also be warm, best at about 23 to 29 °C, of normal seawater salinity and slightly alkaline, so that carbonate ions are available for building calcium carbonate skeletons. That is why reefs are found mainly in shallow tropical seas.
What is a range of tolerance in ecology?
A range of tolerance is the span of values of an abiotic factor, such as temperature or soil pH, within which a species can survive. Within it there is an optimum range where the species is most abundant, with zones of physiological stress on either side. Beyond the limits, in the zones of intolerance, the species is absent.
Why do similar biomes occur on different continents?
Similar biomes occur wherever temperature and rainfall patterns are similar, because those conditions lead to the same natural ecosystem type. Unrelated species there face the same selection pressures, so convergent evolution gives them similar adaptations, such as the water-storing spiny stems of American cacti and African spurges in hot deserts.
Written and checked against the IB Biology SL specification · Updated October 2026