What happens to a leaf that falls to the ground and nobody picks up?
Your guess
Pick one before you read on. It is fine to be wrong.
By the end you can
Explain how fungi, bacteria and worms break down dead things
Make a compost heap and record what rots first
A forest drops leaves every year. Animals die too. Yet the ground is never buried deep in dead things. Something is clearing them away. Watch the cycle build up.
Draw it first
Dead things are recycled
1 Plants make food from light. Animals eat the plants, or each other.
2 Plants and animals die, and leaves and waste fall. These are the remains.
3 Decomposers feed on the remains and break them down.
4 This puts nutrients into the soil. Plants take them up and grow.
Decomposers are living things that break down dead plants, dead animals and waste. Nutrients are the simple substances that plants need from the soil, such as those in a rotted leaf.
The decomposers are fungi and bacteria. A fungus sends fine threads into a dead thing and soaks up food from it. Bacteria are microbes. They live on every surface and feed on dead things too.
Worms and woodlice help in a different way. They are detritivores. They eat dead leaves and tear them into small pieces. Small pieces have more surface, so fungi and bacteria can reach more of the leaf.
Decomposers break things down. Detritivores eat dead things and make small pieces.
See it three ways
With things
Look under dead leaves on the ground. You may see a worm or a woodlouse eating them.
As a picture
In words
Not every food chain starts with a living plant. A dead leaf can feed a worm, and a worm can feed a bird.
Decomposers are living things, so they need the same as other living things: warmth, water and air. Food goes bad fast on a warm, damp day. It lasts longer when it is kept cold or dried.
Decay is fastest when it is warm and damp.
Compost is rotted plant waste. Gardeners and farmers make it in a heap. The decomposers turn the waste into dark, crumbly soil that is full of nutrients. You can make a small heap and watch.
Layers of plant waste and soil. Put in plant waste only, because meat and bones attract rats.
Try it
Make a compost pot
You need: a pot, tin or box with a few holes in the bottom, damp soil, a fruit peel, a leaf, a piece of paper and a small stick, gloves, or water and soap for your hands.
Be safe: Wear gloves, or wash your hands well afterwards. Do not put your face near mould. Do not eat or taste anything from the pot. Use plant waste only.
Half fill the pot with damp soil. Bury the peel, the leaf, the paper and the stick in four places. Mark each place with a pebble.
Keep the soil damp, not wet. Put the pot in a warm place out of the rain.
Every few days, dig gently at each place. Look, then cover it again.
Write down the day each thing has rotted. Put the numbers in a table.
What you will see: Most often the peel rots first, then the leaf, then the paper. The stick takes longest, because wood is tough. Decomposers work on soft things first.
If you cannot try it, this is what happens.
This ring is the cycle again. The same nutrients are used by plant after plant, because decomposers return them to the soil.
Decomposers close the ring. Plants that die go straight to the remains too.
A wrong idea many people have
Dead things just disappear.
Why it feels right: A fallen leaf is gone after a few weeks.
The test that breaks it: Turn over the leaves on the ground. Under the top ones they are in bits. Below that is dark, crumbly soil from the leaves that fell before.
What is true: Nothing disappears. Decomposers change dead things. Some of the matter goes into the air as gas. The nutrients go back into the soil, where plants use them.
Key words
decomposers
fungi and bacteria that break down dead things.
nutrients
simple substances that plants take from the soil to grow.
detritivores
animals such as worms and woodlice that eat dead leaves in small pieces.
compost
rotted plant waste that makes good soil.
Back to your guess
The answer is C: Living things break it down. Some goes into the air as gas, and the nutrients go into the soil.
Fungi and bacteria feed on the dead leaf and break it down. Some of it goes into the air as gas. The nutrients go back into the soil, and plants use them to grow.
Check yourself
Try each one before you look. A wrong answer tells you where to go next.
Which living things are the decomposers?
See the answer
Fungi and bacteria
Fungi soak up food from dead things, and bacteria feed on them. Together they break dead things down.
If you chose A: They help by eating dead leaves into small pieces. The breaking down of those pieces is done by fungi and bacteria. Go to S3.2.5.
If you chose B: Grass makes food from light and rabbits eat grass. Neither breaks down dead things for nutrients. Go to S3.2.5.
What do worms and woodlice do to a dead leaf?
See the answer
They eat it and tear it into small pieces.
Small pieces have more surface, so fungi and bacteria can work faster. These animals are detritivores.
If you chose A: Worms and woodlice are a big help. They tear leaves into small pieces, so fungi and bacteria can reach more of each leaf. Go to S3.2.5.
If you chose C: Only green plants make food from light. Worms and woodlice are animals and have to eat. Go to S3.2.5.
Where do the nutrients go when a dead leaf is broken down?
See the answer
Into the soil, where plants take them up
Decomposers put nutrients back in the soil. Plants take them in through their roots and use them to grow.
If you chose A: Nothing disappears. What the leaf was made of is changed into nutrients that stay in the soil. Go to S3.2.5.
If you chose B: Some gas goes into the air, but the nutrients plants need stay in the soil. Go to S3.2.5.
Which of these will rot last in a compost pot?
See the answer
A small stick
Wood is tough, so decomposers need much longer. Soft things such as peels and leaves go first.
If you chose B: A peel is soft and rots first. Decomposers work fastest on soft things. Go to S3.2.5.
If you chose C: A soft leaf rots quite fast. A tough thing takes much longer. Go to S3.2.5.
The chart shows how many days each thing took to rot. How many more days did the stick take than the paper?
See the answer
32 days
The stick took 60 days and the paper took 28. 60 − 28 = 32.
If you chose A: That is the time the stick took altogether. The question asks how many more days than the paper, so take the paper's time away. Go to S3.2.5.
If you chose C: You have added the two times. To find how many more, subtract the smaller from the larger. Go to S3.2.5.
From an earlier chapter
About how much of the energy in food passes on to the next animal in a chain?
See the answer
About a tenth
An animal uses most of its food for living and loses much as heat. About a tenth passes on.
If you chose A: Animals use most of the energy to live, and lose much as heat. Far less than all passes on. Go to S3.2.4.
If you chose B: It is much less than half. A rough rule is about a tenth. Go to S3.2.4.
Keep it
Copy this into your exercise book.
Decomposers are fungi and bacteria. They break down dead things and put nutrients back in the soil. Worms and woodlice tear dead leaves into small pieces. Decay is fastest when it is warm and damp.
Draw: Draw a ring of five boxes: plants, animals, remains, decomposers, soil. Draw arrows round the ring.
