3.2Chapter 3: Microorganisms and Decomposers

Microorganisms are our friends — Alhussan Biology - Stage 7 Revision Notes & Topical Questions

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3.2 Microorganisms are our friends — Food Production and Biotechnology — Alhussan International Academy — Biology (Stages 7–9) notes: Describe how bacteria and fungi are used to make foods and other useful products.Number — scientists estimate there are 5 million trillion bacteri…

Fermentation
Beer and wine
Milk sources
Fresh cheese
Matured cheese
Competition

Section 1 of 9Useful microorganisms

1Number

Number scientists estimate there are 5 million trillion bacteria on Earth, more than the stars in the Universe.

2Roles

Roles some microorganisms cause disease or make food rot, but many are useful.

3Biotechnology

Biotechnology the use of living organisms, or substances made by them, to make products.

4History

History people have used microorganisms to make foods for thousands of years, before anyone knew they existed.

5Methods

Methods bacteria and fungi work by respiring or by producing enzymes.

Section 2 of 9Yeast: bread, beer and wine

Yeast

Yeast a single-celled fungus that respires and grows fast when given sugar, warmth and air.

Fermentation

Fermentation yeast respiring without oxygen: glucose → ethanol + carbon dioxide.

Bread

Bread yeast is mixed into the dough and ferments the sugar.
The carbon dioxide forms bubbles that make the dough rise and give a light texture.
Baking makes the bubbles bigger, kills the yeast and evaporates the ethanol.

Beer and wine

Beer and wine yeast ferments sugars from barley or grapes, and the ethanol is the useful product.

Section 3 of 9Bacteria: yoghurt

Heat the milk to kill unwanted microorganisms, then cool it to about 40 °C.

Add a starter culture of bacteria such as Lactobacillus.

Keep the mixture warm for several hours while the bacteria feed on the sugar (lactose) in the milk.

The bacteria make lactic acid by fermentation.

The acid makes the milk proteins clump together, solidifying the milk and giving the sharp, tangy taste.

Milk sources

Milk sources milk from camels, cows, goats, horses and sheep can be used.

Keeping

Keeping the bacteria and the acid stop other bacteria growing, so yoghurt keeps for longer.

Section 4 of 9Bacteria: cheese

1Process

Process cheese is made by the reaction of bacteria with milk.
The bacteria make lots of lactic acid, so the milk separates into solid curds and liquid whey.

2Fresh cheese

Fresh cheese the curds may be mixed with seasoning and herbs and used fresh.

3Matured cheese

Matured cheese curds may be mixed with salt and other bacteria, pressed and left to dry for weeks, months or years.
Extra enzymes and moulds are added for certain types.

Section 5 of 9Microorganisms and medicine

Competition

Competition microorganisms battle each other for territory on skin, food or soil and make poisons to destroy their enemies.

Antibiotics

Antibiotics medicines that stop bacteria growing or kill them, curing the infectious diseases they cause.

Penicillin

Alexander Fleming noticed in the early 20th century a clear area around a mould growing on his bacteria cultures.
A substance from the mould stopped the bacteria growing and became known as penicillin.
It was the first antibiotic and has saved millions of lives.

Other antibiotics

Other antibiotics streptomycin and chloramphenicol come from bacteria.

How they work

How they work antibiotics target bacterial structures such as cell walls.
They do not work against viruses and do not harm human cells.

Section 6 of 9Microorganism factories

Product	Microorganism	Use
Antibiotics such as penicillin	Penicillium mould	Kill bacteria
Human insulin	Genetically modified bacteria	Treating diabetes
Biofuels (ethanol, biogas)	Yeast, bacteria	Renewable fuel
Mycoprotein (Quorn)	Fungus	Meat-free protein

Fermenters

Fermenters huge metal tanks in which the microorganisms grow.
The insulin is separated from the microorganisms and the liquid they grew in.

Advantages

Advantages microorganisms grow and reproduce rapidly, use cheap waste as food and need little land.

Section 7 of 9Controlling conditions in food production

Hygiene

Hygiene equipment is sterilised so unwanted microorganisms do not compete with useful ones or spoil the product.

Temperature

Temperature lactic acid bacteria work best at about 40 °C and yeast prefers about 30 to 35 °C.
If it is too low the microorganisms work slowly.
If it is too high their enzymes are denatured and they die.

Acidity

Acidity it is tested because too much or too little acid affects flavour and safety.

Section 8 of 9Key terms

Term	Meaning
Biotechnology	The use of living organisms or their products to make useful things.
Fermentation	Respiration without oxygen, producing ethanol and carbon dioxide in yeast.
Lactic acid	The acid made by bacteria that thickens milk into yoghurt.
Antibiotic	A medicine that stops bacteria growing or kills them.
Fermenter	A huge tank in which microorganisms are grown.
Curds and whey	The solid and liquid parts of milk separated during cheese making.