The big idea: An organism's ecological niche is its role in an ecosystem — not just where it lives, but how it lives.
Abiotic conditions
- The abiotic conditions the organism can tolerate
Food and energy
- How it obtains its food and energy
Interactions
- Its interactions with other species
Conditions for survival: To survive, an organism must live somewhere that provides the conditions for survival its niche requires — for example the right temperature, enough light, and enough oxygen.
- Ecological niche
- An organism's role in its ecosystem: the abiotic conditions it can tolerate, how it obtains its food and energy, and its interactions with other species.
- Habitat
- The physical place where an organism lives. (Its niche is what it DOES there — a habitat is the address, the niche is the job.)
- Conditions for survival
- The environmental conditions an organism needs to stay alive and function — for example a suitable temperature, light, water and, for many organisms, oxygen.
- Abiotic factor
- A non-living, physical or chemical feature of the environment, such as temperature, light intensity, pH, salinity or dissolved oxygen.
- Biotic factor
- A condition created by other living organisms, such as food supply, predators or competitors.
| Type of condition | What it means | Examples |
|---|---|---|
| Abiotic | A non-living, physical or chemical feature of the environment | Temperature, light intensity, pH, dissolved oxygen, salinity, water availability |
| Biotic | A condition created by other living organisms | Availability of food, predators, competitors, mates, disease |
Habitat vs niche: A useful hook: the habitat is the address (where it lives), and the niche is the job (what it does and what conditions it needs).
Two species can share the same habitat but still have different niches, because they use the conditions and resources differently.
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How this is tested: Questions ask you to name a condition for survival, define key terms, or read a tolerance graph.
What the questions ask
- Paper 1B State / Describe: given an organism (such as an obligate-aerobe seaweed), name one environmental condition it needs to survive
- The strongest answer is dissolved oxygen, because the organism cannot respire without it
- A common Paper 1A point: distinguish abiotic from biotic conditions, or define the ecological niche as an organism's role
- Paper 1B / Paper 2 data: a tolerance graph — deduce whether an organism could survive at a stated value of an abiotic factor
IB-style question — a condition an obligate aerobe needs
A species of seaweed living in a coastal rock pool is an obligate aerobe. State one environmental condition the seaweed needs to survive, and explain why. [2]
How to score both marks
- State the condition. The seaweed needs dissolved oxygen in the water.
- Explain why. As an obligate aerobe, it must carry out aerobic respiration, which requires oxygen to release energy — without oxygen it cannot respire and would die. (Mark 1: (dissolved) oxygen. Mark 2: needed for aerobic respiration / cannot survive without it.)
Final answer
Dissolved oxygen — as an obligate aerobe the seaweed must respire aerobically, and aerobic respiration requires oxygen to release the energy it needs to survive.
Why this scores full marks: The answer names a specific abiotic condition (oxygen) and then links it to the organism's biology (it is an obligate aerobe, so it needs oxygen for respiration).
A vague answer like 'water' or 'a good environment' would not score — the question wants a named condition tied to why the organism needs it.
Exam tips
- Read the organism's description: 'obligate aerobe' is a strong hint that the required condition is OXYGEN.
- Always pair the condition with a reason (oxygen → for aerobic respiration) when the command term is 'explain'.
- An abiotic condition is non-living (oxygen, temperature, light); food and predators are biotic — don't mix them up.