VMBO Year 2 · HAVO/VWO Years 2–3 · Ecology and sustainability · Section 6.2

Food relationships and cycles

Producers, consumers and decomposers

Plants make organic food by photosynthesis, using light energy, water and carbon dioxide. They also need minerals for growth. They are producers and often form the first feeding level in a food chain.

Animals obtain organic substances by eating and are consumers. Primary consumers eat producers; secondary consumers eat primary consumers. Higher-level consumers feed farther along a chain.

Not every organism is eaten alive. Detritivores and scavengers feed on dead material. Decomposers, including many bacteria and fungi, break organic material down further, releasing substances such as minerals, water and carbon dioxide.

Plants can use these substances again, forming matter cycles. Energy, unlike matter, is not continually recycled: it flows through ecosystems and is eventually dissipated as heat.

The water cycle

Water evaporates from seas, lakes, soils and other surfaces, and plants release water vapour. Condensation forms clouds, and water returns as precipitation.

Water moves through the ground and rivers towards seas. Animals take in water and release it again. These movements together form the water cycle.

The carbon cycle

Carbon occurs in atmospheric carbon dioxide. Plants take it up during photosynthesis and incorporate it into glucose and other organic substances.

Animals obtain carbon by eating. They use organic substances for fuel and building materials. Respiration by plants, animals and microorganisms releases carbon dioxide. Dead material and faeces pass carbon to decomposers, whose activity also returns carbon to the environment.

Biodegradable and non-biodegradable

Biodegradable material can be broken down by organisms. Plant and animal remains, bread crusts and many paper products are examples, depending on conditions.

Glass, metals, stone and most conventional plastics do not biodegrade in this way. They can persist for a long time, although some undergo other chemical or physical changes.

Plastic pollution

Large quantities of plastic enter the sea and accumulate in some regions. These are usually dispersed mixtures of debris rather than solid islands.

Sunlight and waves can fragment plastic into smaller pieces called microplastics. Animals may swallow them, and particles can move through food relationships. Humans are exposed through several routes, including food, water and air.

Plastic can harm wildlife physically, and some associated chemicals can be hazardous. The health effects of different microplastic exposures are still being investigated.