How is water recycled in nature, and how do nutrients get returned to the soil?
Describe the water cycle and the role of decomposers in recycling nutrients, and explain why recycling in nature matters
A clear answer to the N(T) Science point on recycling in nature. The stages of the water cycle, how decomposers return nutrients to the soil, and why these natural cycles matter.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
This dot point wants you to describe how water is recycled in nature through the water cycle, and how nutrients are returned to the soil by living things called decomposers. You should also explain why these natural cycles matter. The big idea is that nature reuses its materials over and over: water keeps moving between the sea, the air and the land, and the nutrients in dead plants and animals are returned to the soil to be used again. Nothing is wasted.
The answer
Why nature recycles
Nature does not make new water or new nutrients; it reuses the same ones again and again. Two important examples are the water cycle, which keeps water moving around, and nutrient recycling, which returns the goodness from dead things back to the soil. The energy that drives much of this comes from the Sun.
The water cycle
The water cycle is the way water moves between the sea, the air and the land. It has these main stages:
- Evaporation: the Sun heats water in the sea, lakes and rivers, turning it into water vapour (a gas) that rises into the air.
- Condensation: high up, the air is cooler, so the water vapour cools and turns back into tiny droplets, forming clouds.
- Precipitation: when the droplets join and grow heavy, they fall back to the ground as rain (or snow or hail).
- Collection and run-off: the water that falls collects in rivers and lakes and flows back to the sea, and the cycle starts again.
So the same water is used over and over: it evaporates, forms clouds, falls as rain, and flows back to the sea. Plants take up some of this water from the soil, and people use it too.
Decomposers and nutrient recycling
When plants and animals die, the useful nutrients (minerals) are locked inside their dead bodies. Decomposers are living things, mainly bacteria and fungi, that break down this dead material and waste.
As decomposers break down dead leaves, dead animals and waste, they return the nutrients to the soil. Living plants can then take up these nutrients through their roots and use them to grow. In this way the same nutrients are recycled: plant to animal to dead material to soil to plant again.
Why these cycles matter
These natural cycles keep the world working:
- The water cycle keeps supplying fresh water (as rain) to the land, which plants, animals and people all need.
- Nutrient recycling keeps the soil rich, so plants can keep growing. Without decomposers, dead material would pile up and the nutrients would stay locked away, so the soil would slowly run out and plants would grow poorly.
Recycling in nature means materials are never used up; they are constantly reused.
Examples in context
Example 1. Dew and rain on a normal day. Overnight, water vapour in the cooler air condenses into tiny droplets of dew on the grass, and on other days clouds form and bring rain. Both are everyday signs of the water cycle: water moving from vapour to liquid and back, supplying the moisture that plants and animals depend on.
Example 2. A compost heap in a garden. A compost heap is nutrient recycling in action. Gardeners pile up dead leaves and vegetable scraps, and decomposers like bacteria and fungi break them down into rich compost. Spreading that compost on the soil returns the nutrients, so new plants grow well. Nature's recycling is put to work.
Try this
Cue. Name the stage of the water cycle where the Sun turns sea water into vapour. This stage is evaporation.
Cue. State what decomposers do and name two examples. Decomposers break down dead plants and animals and return their nutrients to the soil; examples are bacteria and fungi.
Cue. Explain why the soil would lose its nutrients if there were no decomposers. Dead material would pile up with its nutrients locked inside, so the nutrients would not return to the soil and it would slowly run out, making plants grow poorly.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marksThe water cycle moves water around between the sea, the air and the land. (a) Name the process where the Sun turns sea water into water vapour. (b) Name the process where water vapour cools to form clouds. (c) Name the way water falls from clouds back to the ground. (d) State where the energy for the water cycle comes from.Show worked answer →
(a) The Sun turning sea water into water vapour is called evaporation.
(b) Water vapour cooling to form clouds (tiny water droplets) is called condensation.
(c) Water falling from clouds back to the ground is called precipitation (rain, and also snow or hail).
(d) The energy for the water cycle comes from the Sun.
What markers reward: evaporation for sea to vapour, condensation for vapour to clouds, precipitation (rain) for falling water, and the Sun as the energy source for the whole cycle.
Original3 marksWhen a dead leaf falls to the ground it slowly rots away. (a) Name the type of living thing that breaks down dead material. (b) Explain why this rotting is useful for plants. (c) State what would happen to the soil if nothing broke down dead material.Show worked answer →
(a) The living things that break down dead material are decomposers (such as bacteria and fungi).
(b) The rotting is useful because decomposers break down the dead material and return its nutrients (minerals) to the soil, where living plants can take them up again to grow.
(c) If nothing broke down dead material, dead plants and animals would pile up, and the nutrients locked inside them would not be returned to the soil, so the soil would slowly run out of nutrients and plants would grow poorly.
What markers reward: naming decomposers (bacteria and fungi), explaining that they return nutrients to the soil for plants, and that without them dead material would pile up and the soil would lose its nutrients.
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