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
Habitats and adaptations
- B4.1.1What a habitat is
- B4.1.2A grass adapted to sand dunes
- B4.1.2A tree adapted to mangrove swamps
Tolerance and distribution
- B4.1.3Abiotic variables and distribution
- B4.1.4Range of tolerance
- B4.1.4 · Application of skillsSampling along a transect
- B4.1.4 · Application of skillsReading transect data
Coral reefs and biomes
- B4.1.5Conditions for coral reefs
- B4.1.5Why corals need light
- B4.1.6Climate decides the biome
- B4.1.7Six biomes
- B4.1.7Convergent evolution
Hot deserts and tropical rainforests
- B4.1.8A desert plant: the saguaro
- B4.1.8CAM photosynthesis
- B4.1.8A desert animal: the kangaroo rat
- B4.1.8Rainforest plants: kapok and cacao
- B4.1.8A rainforest animal: the sloth
B4.1 Adaptation to environment: summary
Habitat
- Where it lives: geographical, physical location, ecosystem type.
- Example: Lebanon cedar, rocky slopes 1300–3000 m.
Adaptations
- Marram grass: rolled leaves, sunken stomata, hairs, cuticle.
- Red mangrove: prop roots, lenticels, aerenchyma, salt filtering, vivipary.
Tolerance
- Optimum → stress → intolerance, for each factor.
- Transect: quadrats and sensors at intervals; correlation, not cause.
Coral reefs
- Shallow, clear, 23–29 °C, normal salinity, pH about 8.1.
- Zooxanthellae need light; they feed the coral.
Biomes
- Temperature + rainfall predict the biome.
- Six biomes; convergent evolution makes them alike worldwide.
Deserts and rainforests
- Saguaro (CAM, stored water); kangaroo rat (metabolic water).
- Kapok buttresses, cacao drip tips; sloth claws and algae.
Key terms
- Habitat
- the place in which a community, species, population or organism lives.
- Adaptation
- an inherited feature that suits an organism to its habitat.
- Abiotic variable
- a non-living factor, such as temperature, light or pH.
- Range of tolerance
- the values of a factor over which a species can survive.
- Limiting factor
- a factor whose value restricts where a species can live.
- Transect
- a line along which samples are taken at intervals.
- Biome
- ecosystems with similar communities due to similar abiotic conditions.
- Convergent evolution
- similar features evolving in unrelated organisms.
- Zooxanthellae
- single-celled algae living in coral tissue.
- CAM
- taking in CO₂ at night and using it by day, saving water.
Sample exam questions
Three of the 40 multiple-choice questions for B4.1. Try each one before opening the answer.
Question 1. What is a habitat?
- The role of a species in its ecosystem
- The place where a species lives
- All the organisms living in an area
- A group of similar ecosystems
Show the answer
Answer: B. A habitat is the place in which a community, species, population or organism lives.
Question 2. In marram grass, the stomata lie in grooves lined with hairs. What is the effect of this?
- More carbon dioxide diffuses in.
- The stomata open only at night.
- Water vapour is kept near the stomata.
- Salt is excreted through the hairs.
Show the answer
Answer: C. Hairs and grooves keep humid air near the stomata, reducing the gradient for water loss.
Question 3. Ecosystems in northern Canada and in Siberia are both tundra, although many of their species differ. Why are they the same biome?
- They have the same species in both regions.
- They are linked by migrating animals.
- Similar climates produce similar communities.
- They lie on the same line of longitude.
Show the answer
Answer: C. Similar abiotic conditions select similar plant forms, so the communities are alike.
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 B4.2)
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.