Our Environment
Ecosystem: Components and Food Chains
An ecosystem is a self-contained unit in which living organisms interact with one another and with their non-living surroundings. A forest, a pond, a lake and a crop field are examples. An ecosystem has two kinds of components:
- Biotic (living) components — all the living organisms, grouped by how they obtain food: producers (green plants, which make food), consumers (animals, which eat others) and decomposers.
- Abiotic (non-living) components — physical factors such as sunlight, temperature, air, water and soil.
Consumers are further classified by what they eat: herbivores (primary consumers, eat plants), carnivores (secondary/tertiary consumers, eat other animals) and omnivores (eat both). Decomposers — bacteria and fungi — break down dead plants and animals and return the nutrients to the soil, so the same materials can be used again. Without decomposers, dead matter would pile up and nutrients would not be recycled.
A food chain is a sequence showing who eats whom, through which energy and nutrients pass — for example, grass → grasshopper → frog → snake → eagle. Each step is a trophic level. In nature, organisms usually eat more than one kind of food, so many food chains are linked together to form a food web.
Biotic components are grouped by how they get food.
- Producers — green plants.
- Consumers — animals (e.g. deer, lion).
- Decomposers — bacteria and fungi.
Decomposers recycle nutrients.
- They break down dead organisms.
- They return nutrients to the soil so producers can use them again, keeping nature's cycle going.
The chain starts with the producer.
- Producer: grass.
- The deer eats the producer, so it is the primary consumer (first consumer level).
Key Points
- An ecosystem has biotic (producers, consumers, decomposers) and abiotic (sunlight, water, air, soil) components.
- Decomposers (bacteria, fungi) recycle nutrients from dead matter.
- A food chain shows who eats whom (grass → grasshopper → frog → snake); each step is a trophic level.
- Linked food chains form a food web.
Flow of Energy and Trophic Levels
The energy that drives almost every ecosystem comes from the Sun. Producers (green plants) capture a small part of the Sun’s energy by photosynthesis and store it as chemical energy in food. This energy then flows from one trophic level to the next as one organism eats another.
An important feature of this energy flow is that it is one-way (unidirectional) — energy passes from the Sun to producers to consumers, and is lost as heat at each step; it does not flow back. At each step a lot of energy is used up by the organism for its life processes and lost to the surroundings as heat.
This gives the ten per cent law (given by Lindeman): on average, only about 10% of the energy available at one trophic level is passed on to the next; the other ~90% is lost. For example, if producers have 10,000 J of energy, herbivores get about 1000 J, the next carnivores about 100 J, and so on.
Because so much energy is lost at each step, food chains are usually short (rarely more than 4–5 levels) — there simply isn’t enough energy left to support many more levels. This is also why there are far fewer top carnivores than producers in an ecosystem.
Energy moves in one direction only.
- It flows from the Sun to producers to consumers.
- At each step it is lost as heat and does not return to the previous level.
Apply the ten per cent law.
- Only about 10% passes to the next level.
- 10% of 20,000 J = 2000 J.
Energy decreases sharply at each step.
- About 90% of energy is lost at every level.
- After a few levels too little energy is left to support another level.
Key Points
- Energy flows from the Sun → producers → consumers; it is unidirectional and lost as heat at each step.
- Ten per cent law: only ~10% of energy passes to the next trophic level.
- Heavy energy loss keeps food chains short (4–5 levels) and top carnivores few.
Environmental Problems: Ozone and Waste Management
Human activity is harming the environment, and two important problems are ozone depletion and the growing amount of waste.
The ozone layer is a layer of ozone gas (O₃) high up in the atmosphere. It is very important because it absorbs the harmful ultraviolet (UV) rays of the Sun, which can cause skin cancer, eye damage and harm to crops and other living things. The ozone layer is being damaged (depleted) by man-made chemicals called CFCs (chlorofluorocarbons), once used in refrigerators, air conditioners and spray cans. To protect the ozone layer, the world agreed (in the Montreal Protocol) to stop making CFCs.
Waste management: the materials we throw away are of two kinds. Biodegradable wastes are broken down by decomposers (e.g. food scraps, paper, cotton, leaves). Non-biodegradable wastes are not broken down by natural processes and remain for a very long time (e.g. plastics, glass, metals, many chemicals); they pollute the land and water and harm living things. Managing waste involves: reducing the waste we produce, reusing items, recycling materials, and disposing of waste safely — including segregating (separating) biodegradable and non-biodegradable waste before disposal. Caring for the environment in these ways protects the ecosystems that all life depends on.
Ozone shields us from UV rays.
- It absorbs the Sun's harmful ultraviolet (UV) rays, protecting living things.
- It is damaged by CFCs (chlorofluorocarbons).
Biodegradable wastes are broken down by decomposers.
- Biodegradable: vegetable peels, paper.
- Non-biodegradable: plastic bottle, glass.
The two need different handling.
- Biodegradable waste can be composted or broken down naturally.
- Non-biodegradable waste can be sent for recycling or safe disposal, instead of polluting.
Key Points
- The ozone layer absorbs harmful UV rays; it is depleted by CFCs (banned by the Montreal Protocol).
- Biodegradable wastes are broken down by decomposers (food, paper); non-biodegradable wastes are not (plastic, glass, metal).
- Manage waste by reduce, reuse, recycle and segregating waste before disposal.