IB Biology · Theme B: Form and function · SL and HL
B4.1 Adaptation to environment
A one-page summary of B4.1 Adaptation to environment, the key terms to know, and sample exam questions with answers. For the full lesson, open the illustrated revision slides or practise in the app.
Guiding questions
How are the adaptations and habitats of species related?
What causes the similarities between ecosystems within a terrestrial biome?
What B4.1 covers
Habitat, adaptation and tolerance
- B4.1.1A habitat is a place, not a role
- B4.1.2Marram grass rolls its leaves to keep water in
- B4.1.2Mangroves solve the opposite problem
- B4.1.3Where a species lives tracks the abiotic conditions it can take
- B4.1.4One curve, three zones
- B4.1.4 · Application of skillsProving the curve means going outside
Marine conditions and terrestrial biomes
- B4.1.5A coral reef needs several conditions to line up at once
- B4.1.5The reef itself is built by a partnership
- B4.1.6Two numbers predict which biome forms
- B4.1.7A biome is a climate, not a location
- B4.1.7Unrelated deserts, the same solution
Life at the extremes: desert and rainforest
- B4.1.8In the desert, water comes from food, not drinking
- B4.1.8A cactus opens its stomata when it's dark
- B4.1.8A rainforest tree needs a wider base than its roots can give it
- B4.1.8A pointed leaf tip sheds water fast
B4.1 Adaptation to environment: summary
Habitat & adaptation
- Habitat = where; niche = how.
- Marram grass (dune) vs mangrove (mud) — opposite stresses.
Tolerance & distribution
- Bell curve: optimum → stress → intolerance.
- Transect correlates species with an abiotic variable.
Coral reefs
- Warm (23–29°C), clear, low-nutrient, stable pH.
- Zooxanthellae mutualism builds the reef.
Biomes
- Temperature + precipitation predict biome.
- Same biome, unrelated continents = shared climate.
Convergent evolution
- Cactus ≈ euphorbia: no shared ancestor, shared pressure.
Desert & rainforest
- Desert: metabolic water, CAM photosynthesis.
- Rainforest: buttress roots, drip-tip leaves.
Key terms
- Habitat
- The physical place where a community, species, population or organism lives.
- Niche
- The functional role an organism plays in its ecosystem, distinct from where it lives.
- Adaptation
- An inherited trait that improves survival and reproduction in a specific habitat.
- Range of tolerance
- The span of an abiotic factor's values within which an organism can survive.
- Limiting factor
- The abiotic variable that most restricts a species' distribution or performance.
- Zooxanthellae
- Photosynthetic dinoflagellates living in coral tissue, supplying sugars in exchange for shelter.
- Biome
- A group of ecosystems with similar communities due to similar abiotic conditions.
- Convergent evolution
- Unrelated organisms independently evolving similar traits under similar pressures.
- CAM photosynthesis
- Opening stomata at night to fix CO₂ into malate, minimising daytime water loss.
- Vivipary
- A propagule germinating while still attached to its parent plant.
Sample exam questions
Three of the 40 multiple-choice questions for B4.1. Try each one before opening the answer.
Question 1. Which term refers to the specific place where a population of a species lives?
- Niche
- Habitat
- Ecosystem
- Biome
Show the answer
Answer: B. Habitat is the physical location where an organism, population, or species lives, distinct from niche (role) or ecosystem (biotic + abiotic).
Question 2. Rolled leaves in marram grass (Ammophila arenaria) mainly reduce water loss by
- trapping a pocket of still, humid air inside the roll
- increasing the leaf surface area exposed to wind
- preventing all gas exchange with the atmosphere
- allowing stomata to open only at night
Show the answer
Answer: A. The rolled shape encloses a humid air space that reduces the water vapour concentration gradient between the leaf interior and outside air, slowing transpiration.
Question 3. The gut of a termite is inhabited by cellulose-digesting protists. For these protists, the termite’s gut is a
- community
- ecosystem
- population
- habitat
Show the answer
Answer: D. The termite gut provides the physical environment (habitat) in which the protists live.
Linking questions
Questions that connect B4.1 to other parts of the course, the kind that come up in Paper 2.
- Explain how the salt exclusion mechanism in mangrove roots relies on the selective permeability of cell membranes. (see B2.1)
- Outline how the mutualism between corals and zooxanthellae illustrates a symbiotic relationship within a community. (see C4.1)
- Discuss the role of abiotic factors in defining the realized niche of a species, with reference to the range of tolerance. (see C4.1)
Practise B4.1
Study notes, every question and full markschemes for B4.1 are in the app with Pro. Two lessons are completely free to try: A1.1 Water and B1.1 Carbohydrates and lipids.