What is ecology? Ecosystems and food chains
Ecology is the study of living things and the places they live in. A group of living things plus their surroundings is an ecosystem: a pond, a forest, a farm or even a puddle.
- Producers: plants and algae. They make food using sunlight (photosynthesis).
- Consumers: animals that eat others. Herbivores eat plants; carnivores eat animals; omnivores eat both.
- Decomposers: bacteria and fungi that break down dead things and return nutrients to the soil.
- Food chain: plant → rabbit → fox. Many chains linked together make a food web.
- Non-living parts: light, water, temperature and soil also shape what can live there.
Energy flow: the 10% rule
Energy comes from the Sun and moves along the food chain in one direction only.
- Trophic level: a step in a chain (producer, herbivore, carnivore...).
- 10% rule: only about 10% of the energy at one level reaches the next. The rest is used for moving, growing and staying warm, or lost as heat.
- Example: 1000 J in plants → 100 J in herbivores → 10 J in carnivores.
- Why it matters: food chains rarely have more than 4 or 5 steps, and there are very few top predators.
Biogeochemical cycles
Unlike energy, matter is recycled. Atoms of carbon, nitrogen, water and phosphorus move between living things (bio), air, water and rocks (geo) as different chemicals.
- Carbon cycle: plants take CO₂ in photosynthesis; animals and plants release it in respiration; decay and burning also release it.
- Water cycle: evaporation, clouds, rain, rivers and back to the sea.
- Nitrogen cycle: bacteria turn nitrogen from the air into forms plants can use; other bacteria return it to the air.
- Phosphorus cycle: moves slowly from rocks to soil to plants to animals and back; it has almost no gas stage.
- Human effect: burning fuels adds extra CO₂ and fertilisers add extra nitrogen and phosphorus, which can upset the cycles.
Energy resources and renewables
An energy resource is anything we use to get useful energy.
- Non-renewable: coal, oil, natural gas, uranium. They took millions of years to form and will run out. Burning fossil fuels adds CO₂ and warms the planet.
- Renewable: sunlight, wind, flowing water, plant material (biomass) and heat from the earth. Nature refills them quickly.
- Good points of renewables: almost no CO₂ while running, local, and cheaper each year.
- Challenges: sun and wind are not constant, so we need storage and a smart grid; panels and dams need land and care for nature.
- Smart use: saving energy (LED lamps, good insulation) is the cheapest "new" source.
New materials
New materials are designed to have exactly the properties a job needs.
- Composites: two materials joined (for example carbon fibre in plastic). Strong and light, used in planes, bicycles and wind-turbine blades.
- Smart materials: change when heat, light or electricity changes (glasses that darken in sunlight).
- Nanomaterials: made of very tiny parts, a few billionths of a metre across, with special properties.
- Bio-based and biodegradable materials: made from plants, they can break down after use.
- Choosing wisely: ask about strength, weight, cost, safety and what happens at the end of life (reuse, recycle or rot).
Key formulas and definitions
- Producer → herbivore → carnivore = a food chain
- 10% rule: energy at next level ≈ 0.10 × energy at this level
- Biogeochemical cycle = matter moving between living things, air, water and rocks
- Renewable = refilled by nature quickly; non-renewable = used up much faster than it forms
- Composite = two or more materials combined to get better properties
- Energy flows (one way); matter cycles (round and round)
Worked examples
1. Plants in a field capture 5000 J of energy. How much reaches the carnivore (third level)?
Herbivore: 10% of 5000 = 500 J. Carnivore: 10% of 500 = 50 J.
2. Why can a forest feed many rabbits but only a few foxes?
Each step passes on only about 10% of the energy. Plants have the most energy, rabbits get a tenth of it, and foxes get a tenth of the rabbits' share, so only a few foxes can be fed.
3. Give one good point and one challenge of solar power.
Good: it adds almost no carbon dioxide while running and the sunlight is free. Challenge: it works only in daytime, so we need batteries or other power at night.
Common mistakes
- Thinking energy is recycled like matter. Energy flows one way and ends up as heat; matter is recycled.
- Thinking decomposers are not important. Without them nutrients stay locked in dead bodies.
- Thinking renewable means no effect on nature. Dams, panels and farms for biofuel still need land and care.
- Thinking 10% of energy is lost. It is 10% that is passed on; about 90% is used or lost.