Rot that feeds the world

Science · Organisms & Life Processes · ages 15-16

Name ______________________ Date ____________

What do decomposers return to the soil?
- Carbon dioxide for leaves
- Nitrates for roots
- Sunlight for warmth
Which organisms are the decomposers?
- Bacteria and fungi
- Worms and insects only
- Green plants and algae
Which set lists the four decay dials?
- Light, sound, colour, shape
- Rain, wind, snow, hail
- Warmth, moisture, oxygen, surface area
Why must a compost heap be turned regularly?
- It adds air for decomposers
- Turning keeps the heap cool
- Turning chops the scraps smaller
Why does milk last longer in a fridge?
- Cold strengthens the milk skin
- Cold slows enzymes so decay slows
- Fridges add preservatives to milk
Two identical apple cores lie in a dry shed and a damp garden. Which rots faster, and why?
- Both rot at the same speed
- The shed one, since dryness feeds fungi
- The garden one, since moisture carries decomposer enzymes
A gardener chops stalks finely, waters the heap and turns it weekly. Why does this exact trio work?
- It buries all the carbon forever
- It scares pests away from the heap
- Surface, moisture and oxygen all rise, so respiration runs at full pace
A student seals food in an airtight jar and claims decay stops since germs are trapped. What is the error?
- Sealed jars always speed decay up
- Decay slows from missing oxygen but the claim overstates it, since some microbes manage without air
- Jars poison decomposers directly

Answer key

For grown-ups. Fold this page away before handing over the rest.

Nitrates for roots · Minerals go back to soil while carbon returns to air.
Bacteria and fungi · Bacteria and fungi digest dead matter and recycle nutrients.
Warmth, moisture, oxygen, surface area · Each dial feeds or starves decomposer respiration.
It adds air for decomposers · Packed middles run out of air, and turning refills it.
Cold slows enzymes so decay slows · Slow enzymes mean slow respiration and slow rot.
The garden one, since moisture carries decomposer enzymes · Water is a decay dial, so the damp core rots first.
Surface, moisture and oxygen all rise, so respiration runs at full pace · Three dials turned high together give the fastest rot.
Decay slows from missing oxygen but the claim overstates it, since some microbes manage without air · Low oxygen throttles most decay yet never guarantees zero.