2.9.1Inquiry Process

Habitats — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 92 of 160

📚 IB Biology HL Hub / Topical Revision

0%read

Part 1 of 4Describing a Habitat

A habitat is described by where it is and by what kind of ecosystem it is.

Habitat

The place where an organism lives, which supplies the food, shelter and physical conditions that the species needs to survive and reproduce.

Community

All the populations of different species living together in one habitat;
- a single habitat therefore contains many species interacting with one another.

Location

A habitat can be named by where it is on Earth, for example a polar habitat at the Arctic or Antarctic, a coastal strip or a mountain slope.

Ecosystem type

A habitat can also be named by its general type,
- such as grassland, desert, wetland or woodland,
- and the same type may occur on several continents.

Abiotic setting

Non-living conditions such as light, temperature, water, salinity, pH and oxygen define a habitat and decide which species can live there.

Description used	Example habitat	What it tells you
Geographical location	Arctic polar habitat	Where on Earth the habitat is found
Ecosystem type	Grassland (prairie or savannah)	The general structure and dominant plants
Both together	North American grassland	Location and ecosystem type combined

Marram Grass on Sand Dunes

Challenges

Dune sand drains quickly, the air is dry and windy, salt spray is common and nutrients are scarce,
- so water is hard to obtain and easy to lose.

Rolled leaves

Rolling the leaf traps a pocket of humid air inside and reduces the surface exposed to wind,
- so the water vapour gradient out of the leaf is smaller.

Sunken stomata and hairs

Stomata sit in pits lined with tiny hairs that trap water vapour, raising local humidity and slowing the loss of water by evaporation.

Thick waxy cuticle

A waterproof layer on the outer surface of the leaf greatly reduces evaporation through the epidermis itself.

Xerophyte

A plant adapted to survive in dry conditions;
- marram grass is a standard example because several features all reduce transpiration.

Challenges

Mangrove swamps are tropical coastal habitats often flooded by sea water,
- so they combine high salinity, little fresh water and very low oxygen in the mud.

Aerial roots

Parts of the root system rise above the water or mud so that tissues can take in oxygen for aerobic respiration,
- which submerged roots cannot do.

Red mangrove

Prop roots support the tree in soft mud, and root cells exclude salt so that fresh water can be taken up without losing water by osmosis.

Black mangrove

Pneumatophores grow upwards out of waterlogged soil to collect air, and salt taken up is excreted through salt glands on the leaves.

Osmotic risk

Sea water has a higher solute concentration than root cells, so unprotected roots would lose water by osmosis instead of gaining it.

Feature	Marram grass	Mangrove
Main problem	Water shortage	Salt and lack of oxygen
Key adaptation	Rolled leaf, sunken stomata	Aerial roots, salt exclusion or excretion
Overall effect	Reduces water loss	Allows respiration and water uptake

Habitat The place where an organism lives.
Community All the populations of different species living together in one habitat.
Abiotic factor A non-living part of the environment, such as temperature, light or salinity.
Xerophyte A plant adapted to survive in dry conditions.
Pneumatophore A root that grows upwards out of waterlogged soil to take in air.

Confusing a habitat with a niche or an ecosystem; a habitat is simply where an organism lives.
Writing that marram grass has no stomata; it has stomata, but they are sunken in pits that trap humid air.
Saying mangroves absorb salt water freely; red mangroves exclude salt and black mangroves excrete it.
Describing adaptations without linking each one to the abiotic factor that selects for it.

Last updated: 28 October 2026