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Nature^81

Plant and
animal remains
are broken down
by decomposers

DECOMPOSING PEACH 3

A peach rots as it is broken down

by fungi and bacteria. Organisms

like these that break down other

organisms are called decomposers.

Carbon

compounds

enter soil in dead

plant and animal

remains

Animals take

in carbon

compounds

from plants

Decomposers
give off carbon
dioxide during
respiration

Plants extract carbon
dioxide from air during
photosynthesis

Plants and animals

give off carbon dioxide

during respiration

FOOD CHAIN

In any ecosystem, species eat and are eaten

by other species. A food chain is a simple

pathway that connects up to six species by

what they eat. It describes the route

followed by energy and nutrients as they

are passed from organism to organism.

CARBON CYCLE 1

All organisms, including these

African savanna species, need

carbon to build their bodies. The

carbon cycle ensures that carbon

is recycled and never runs out.

WHAT IS THE NITROGEN CYCLE?

Plants take up nitrogen-containing chemicals, called

nitrates, from the soil. Animals obtain nitrogen by

eating plants, or animals that eat plants. Bacteria

release the nitrogen in dead plant and animal matter,

allowing it to be returned to the soil. Nitrogen is an

important part of proteins that cells need to survive.

WHAT PART DO BACTERIA

AND FUNGI PLAY IN THE CARBON CYCLE?

Certain fungi and bacteria, called decomposers, play a

key role. They break down, or decompose, the remains

of dead organisms. This releases carbon dioxide back

into the air, where it can be re-used by plants.

HOW ARE PLANTS INVOLVED IN THE WATER CYCLE?

Most rainwater flows to the sea along rivers, but some

is taken up by plant roots. Water evaporates from

plant leaves back into the air. Like water evaporated

from the sea, it rises into the air, and falls as rain.

WHAT IS A FOOD WEB?

The community within an ecosystem can contain

thousands of species. Each species may be part of two

or more food chains. The interconnected network of

food chains in an ecosystem is called a food web. It

includes producers that make their own food by

photosynthesis, consumers that eat plants or animals,

and decomposers that break down dead organisms.

WHY ARE THERE FEWER PREDATORS THAN PREY?

Predators are fewer in number than prey because they

are higher up the food chain. In a food chain, an

organism passes on only part of the energy it receives

from food. With less energy, each level in a food

chain supports fewer individuals than the one below it.

Top consumer is grey seal that

eats herrings

Secondary consumers are

herrings that eat copepods

Primary consumers are copepods
that eat marine phytoplankton

Producers are marine

phytoplankton that are single-

celled and plant-like

4 PYRAMID OF ENERGY

This energy pyramid shows the

levels of a marine food chain

with four links. Each step

up represents a decreasing

amount of energy. At

each step in a food

chain, some energy is

lost and some energy

is passed on.

Beetles eat

worms

Plants are food for

many animals, and

for decomposers

such as fungi

Carbon dioxide

in atmosphere

NUTRIENT CYCLES

Organisms take chemical nutrients, such

as carbon, nitrogen, and water, from their

surroundings. They then return or recycle

them when they respire (breathe) or die.

Fungi and

bacteria feed

on plant

matter

Badgers

eat plants and

small animals,

such as worms,

beetles, and

moles

Moles feed on

beetles and

other insects

1 FOOD WEB

This simplified woodland food

web includes producers (plants),

consumers (animals), and

decomposers (fungi).

Worms feed on

dead plant and

animal matter

Garden snails feed

on plants

FIND OUT MORE. Animals 96–97 • Feeding 98 • Fungi 86 • Human Impact 64–65 • Micro-organisms 85 • Plants 88–89