Ecosystems — Biotic and Abiotic Factors
In 2019, BOM recorded that an 18-month drought cut rainfall across NSW by 40% — within weeks, biotic populations like kangaroo grass and platypus both crashed as the abiotic water supply dried up.
Printable Worksheets
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Q1 · Picture a patch of bush near your house. List four living things and four non-living things in that patch.
Q2 · If it stopped raining for six months in that patch, name two living things that would suffer and explain why.
● Know
- What an ecosystem is (community of living things + their non-living environment + interactions)
- The difference between biotic and abiotic factors
- Named NSW ecosystem examples (Sydney Harbour, Blue Mountains, Great Barrier Reef)
● Understand
- Why an ecosystem is not just the living things — the non-living environment matters too
- How biotic and abiotic factors interact (e.g. trees change soil moisture, soil pH limits what plants grow)
- Why removing one factor can change the whole ecosystem
● Can do
- Sort factors in a given ecosystem into biotic vs abiotic
- Describe one biotic-abiotic interaction in a NSW ecosystem
- Predict an effect when one abiotic factor changes
- Ecosystem
- Biotic factor
- Abiotic factor
- Habitat
- Community
- A non-living part such as sunlight or soil
- Living things + non-living environment + interactions
- All the species living together in an area
- A living or once-living part of an ecosystem
- The specific place a species lives
Stand in a patch of Australian bush and look around: some things are alive (the gum tree, the ant, the lichen on the rock) and others are not (the sunlight, the soil, the wind, the temperature) — and every living thing depends on both groups. Biotic factors are alive (or were once). Abiotic factors are non-living physical or chemical parts of the environment.
| Biotic factors (living / once-living) | Abiotic factors (non-living) |
|---|---|
| Gum trees, banksias, grasses | Sunlight |
| Kangaroos, possums, kookaburras | Temperature |
| Ants, worms, spiders | Rainfall / water availability |
| Fungi, bacteria, lichens | Soil type and pH |
| Fallen logs, dead leaves | Salinity (how salty the water is) |
| Algae and seaweed | Wind, air, atmospheric gases |
Quick rule: ask "is this alive or was it ever alive?" If yes → biotic. If no → abiotic. A fallen gum leaf is biotic (it was alive). A rock is abiotic (never alive).
A kangaroo is a factor. Sunlight is an factor. The pH of the soil is . A fallen gum leaf is still classed as because it was once alive.
Wrong: "A fallen leaf is abiotic because it isn't moving." A fallen leaf came from a living tree, so it counts as biotic. Biotic includes things that were once alive.
Right: Biotic means alive or once alive. Fallen leaves, fossils and timber all count as biotic factors.
Wrong: "An ecosystem is just the plants and animals living in a place." This leaves out the soil, water, sunlight and temperature — the abiotic factors that the living things depend on.
Right: An ecosystem includes both the community of living things and their non-living environment, plus the interactions between them.
Wrong: "Bacteria and fungi don't count — they're too small." Microbes are very much alive. Bacteria in the soil and fungi on a fallen log are some of the most important biotic factors in any ecosystem.
Right: Microbes (bacteria, fungi, protists) are biotic factors. Without them, dead matter would not be recycled and the ecosystem would collapse.
NSW has some of the most varied ecosystems in the world. Here are three you may know:
- Sydney Harbour — a marine/estuarine ecosystem. Biotic: seahorses, oysters, mangrove trees, dolphins, plankton. Abiotic: salt water, tides, sunlight, dissolved oxygen, sandy seafloor.
- Blue Mountains eucalypt forest — a sclerophyll forest. Biotic: gum trees, banksias, lyrebirds, kangaroos, fungi, ants. Abiotic: sandstone soil (low nutrients), seasonal rainfall, cool temperature, sunlight filtered through the canopy.
- Great Barrier Reef — a tropical coral reef. Biotic: coral polyps, parrotfish, clownfish, sea turtles, algae. Abiotic: warm shallow seawater (~26 °C), sunlight, salinity, dissolved gases.
Each ecosystem has its own mix of biotic and abiotic factors that fit together. Change one factor and the whole system shifts.
The word "ecosystem" exists because biotic and abiotic factors are constantly affecting each other. Some examples from a Blue Mountains eucalypt forest:
- Sunlight (abiotic) → gum trees (biotic): trees use sunlight for photosynthesis to make food.
- Gum trees (biotic) → soil (abiotic): fallen leaves rot and add nutrients to the soil; tree roots break up the rock.
- Rain (abiotic) → kangaroos (biotic): rain grows grass; kangaroos eat the grass.
- Kangaroos (biotic) → soil (abiotic): kangaroo droppings add nutrients to the soil.
- Temperature (abiotic) → all biotic: if it gets too hot or too cold, most species cannot survive.
Notice the arrows go both ways. Living things change their non-living environment, and the non-living environment limits which living things can survive there.
Some abiotic factors are so important that they decide what can live in a place at all. We call these limiting factors.
- In the desert, water is the limiting factor — very few species cope with so little rain.
- In the deep ocean, sunlight is the limiting factor — no light means no photosynthesis, so no plants.
- In a mangrove swamp, salinity is limiting — most plants die in salty mud, so only specialists like mangroves grow there.
- In the Antarctic, temperature is limiting — most species can't survive year-round cold.
When an abiotic factor is the limiting one, removing or changing it dramatically reshapes the ecosystem.
Imagine every gum tree is cut down in a patch of Blue Mountains bush. Predict TWO abiotic factors in that patch that would change, and explain why. Write 1–2 sentences, then reveal.
How close was your prediction?
Excellent — you saw the link from biotic (trees) to abiotic (light, moisture).
Good thinking — the key is that living things change the non-living environment too.
At the start of the lesson you were asked: if you cut down every gum tree in a patch of bush, what happens to the soil, the wind and the air temperature?
Now you know about biotic and abiotic factors, write your full answer. Which abiotic factors change when the trees are gone, and how does that affect the biotic (living) parts of the ecosystem?
Q1. Define "ecosystem" in your own words, and give one biotic factor and one abiotic factor from any NSW ecosystem of your choice. (3 marks)
Q2. For a Blue Mountains eucalypt forest, list FOUR biotic factors and FOUR abiotic factors. (4 marks)
Q3. A farmer clears a paddock by removing all the native trees. Explain TWO ways the abiotic environment of that paddock will change, and how those abiotic changes will then affect the biotic factors that can live there. (4 marks)
Answers
▾MCQ 1
C — Soil pH is a chemical property of the non-living soil, so it is abiotic. A kookaburra (A) and a soil bacterium (D) are alive (biotic). A fallen gum leaf (B) was once alive, so still counts as biotic.
MCQ 2
D — An ecosystem includes both the community of living things AND the non-living environment, plus their interactions. Answers A, B and C each leave out part of the system.
MCQ 3
A — A coral polyp is a living animal, so biotic. Salinity (B), temperature (C) and sunlight (D) are all non-living, so abiotic.
MCQ 4
B — Removing the trees lets much more sunlight reach the ground and stops the trees from holding moisture in the soil, so soil moisture drops and ground-level sunlight rises. A is the opposite direction; C is unlikely (rocks don't change pH from tree removal); D is wrong because living things do change their abiotic environment.
MCQ 5
C — A limiting factor is the abiotic factor that most decides which species can live in an area. Water in deserts, sunlight in the deep ocean, salinity in mangroves and temperature in Antarctica are all classic limiting factors.
Short Answer 1
Model answer: An ecosystem is a community of living things together with the non-living environment they interact with. For example, in Sydney Harbour a biotic factor is an oyster, and an abiotic factor is the salty seawater. Both are essential to the harbour ecosystem. Award 1 mark for definition mentioning living + non-living, 1 for a correct biotic example, 1 for a correct abiotic example.
Short Answer 2
Model answer: Biotic: gum trees, kangaroos, kookaburras, fungi (or lyrebirds, banksias, ants, bacteria). Abiotic: sandstone soil, rainfall, temperature, sunlight (or wind, pH, air, rocks). 1 mark for any 2 correct biotic, 1 for all 4 biotic, 1 for any 2 correct abiotic, 1 for all 4 abiotic.
Short Answer 3
Model answer: When the trees are removed, sunlight reaching the ground will increase (no canopy to block it) and soil moisture will decrease (no roots holding water, more evaporation from bare soil). These abiotic changes mean shade-loving plants like ferns, and moisture-loving small invertebrates, can no longer survive — they die or move out. Sun-loving grasses and dry-adapted insects move in, completely changing which biotic species live in the paddock. 1 mark for each of: two abiotic changes named, link from abiotic change to biotic effect (×2).