What it shows
Slices of bread sealed in bags under different conditions show that mould grows fastest on damp bread in a warm place and hardly at all on dry bread or in the fridge. Mould is a fungus that grows from spores already present in the air.
The science
Mould spores float everywhere in the air and land on food. A spore grows only when it has moisture, warmth and food. Bread gives the food; a few drops of water give moisture; room temperature gives warmth. In the fridge the cold slows the chemical reactions inside the fungus, and dry bread gives no water, so growth stops. The fuzzy patches are threads (hyphae) and the black or green dots are new spores.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 4 slices of bread from the same packet
- 4 zip-lock bags
- A spoon of water
- A refrigerator, a warm shelf and a marker
- A hand lens (optional)
Safety
For this project: Seal the bags and never open them again; look through the plastic. Throw the sealed bags away at the end of the week. Anyone with asthma or a mould allergy should only watch. Wash hands after handling the bags.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Label the four bags: dry warm, damp warm, damp cold, dry cold.
Put one slice in each bag; sprinkle a teaspoon of water on the two damp slices.
Seal all four bags tightly and do not open them again.
Keep the two warm bags on a shelf in the room and the two cold bags in the fridge.
Every day look at each bag through the plastic and note the colour, size and number of mould patches.
Trace the patches on a square-ruled sheet to estimate their area in square centimetres.
After 7 days make a table and a bar chart of mould area for the four conditions.
Throw all four sealed bags into the dustbin without opening them.
What you should see
The damp warm slice is covered in grey, green or black fuzzy mould by day 4 to 7; the damp cold slice shows a little; the dry slices show almost none. Moisture and warmth together let mould grow.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is mould?
A fungus that grows from spores and feeds on food such as bread.
2Why do we keep food in the fridge?
Cold slows the growth of moulds and bacteria.
3Where did the mould come from?
From spores already in the air and on the bread.
4Why must the bags stay sealed?
Breathing in lots of mould spores can cause allergies or make some people ill.
Take it further
Compare bread with a preservative listed on the packet against bakery bread without one.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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