Glossary Bacteria micro-organisms that can cause decay and disease- Non-harmful bacteria are used in food industry Decay to go bad or rot away Dough a soft mixture of flour and water used to make bread Fungus a micro-organism such as yeast- A mushroom is also a fungus Germ a micro-organism that causes diseases Microbe another word for micro-organism Microorganism an organism that is too small to see, such as viruses, bacteria and fungi Mould a greenish micro-organism that can grow on old food or on cold wet places such as damp walls Vaccinate to protect someone against a disease by giving them a mild form of the disease Virus a micro-organism that can cause infectious diseases Yeast a fungus used to make bread Yoghurt a food made with milk and non-harmful bacteria 1
Transcript
Glossary
Bacteria micro-organisms that can cause decay and disease- Non-harmful bacteria are used in food industry
Decay to go bad or rot away
Dough a soft mixture of flour and water used to make bread
Fungus a micro-organism such as yeast- A mushroom is also a fungus
Germ a micro-organism that causes diseases
Microbe another word for micro-organism
Microorganism an organism that is too small to see, such as viruses, bacteria and fungi
Mould a greenish micro-organism that can grow on old food or on cold wet places such as damp walls
Vaccinate to protect someone against a disease by giving them a mild form of the disease
Virus a micro-organism that can cause infectious diseases
Yeast a fungus used to make bread
Yoghurt a food made with milk and non-harmful bacteria
Micro-organism is the term given to anything that is too small to see without the use of a microscope. Often when the term micro-organism or microbe is used we think mainly of bacteria and viruses- in other words, germs.
Microbes can cause diseases in human s which can then spread quickly from one person to another. When you have a cold, cover your mouth when you cough to help to make sure that the germs do not spread.
Microbes can reproduce very quickly in the right conditions. Many like warm and damp conditions.
Harmful micro-organisms
What diseases are caused by micro-organisms?
Many diseases are caused by micro-organisms but some are not. For example, scurvy is a disease caused by a lack of vitamin C in your diet
There are three main types of micro-organisms: viruses, bacteria and fungi.
Viruses
Viruses cause diseases like colds, flu and chicken pox. You can easily catch diseases like these from other people when they sneeze in the air. You should always try to sneeze into a handkerchief to avoid spreading diseases.
Bacteria
Bacteria cause diseases like food poisoning and diphtheria. They also cause conditions like boils and tooth decay.
Bacteria in your mouth feed on sugar in your food. They make substances called acids that can make holes in your teeth (tooth decay). The bacteria can also damage your gums and cause gum disease, which can make your teeth fall out. You need to brush your teeth twice a day to remove the bacteria from your teeth.
Fungi
Only some fungi are micro-organisms. These can cause conditions like athlete’s foot.
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Vaccinations
What are vaccinations?
People often have injections, called vaccinations, to stop them from getting diseases. When you are vaccinated you are injected with a vaccine. A vaccine contains dead or weak forms of the microorganism that causes a disease. The vaccine will not give you the disease, but your body makes chemicals called antibodies to destroy the micro-organisms in the vaccine. These antibodies then stay in your body, often for the rest of your life. If the real microorganism gets inside you, the antibodies are ready to destroy them.
You need a different type of antibody to destroy each type of micro-organism, which is why you need to have different vaccines for different diseases.
10- 14 years Rubella (given to girls if they have not already had the vaccine)
13 years Tuberculosis
You only get some diseases once because of antibodies. For example if you are ill with measles, your body makes antibodies to destroy the measles viruses. After a few days you start to get better because the antibodies have now been made. If measles viruses get into you again, the antibodies are ready there to destroy them.
However, diseases like colds are caused by many different viruses so you will always get these diseases!
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Decay
How does decay occur?
This food has gone mouldy! Mould is a micro-organism but there is so much of it here that you can see it.
As well as mould, there are many other micro-organisms that you cannot see, growing and reproducing on the food.
The micro-organisms feed on the food and turn it into other things, and this is called decay. This happens fastest when it is warm and damp. The micro-organisms can make you very ill with food poisoning.
Bacteria can float around in the air and land on food that is uncovered.
There are many ways in which we can preserve food to stop it going bad
1. Heat the food well to kill the bacteria. Then put it on a clean sealed container to stop any other bacteria landing on it.
2. Keep the food very cold. The cold does not kill the bacteria but it stops them from reproducing.
3. Dry the food out so that there is no water for the bacteria to live on.
4. Make any food that is going to be kept for a while very sugary, because bacteria cannot survive very strong sugar solutions.
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Useful decay
How can decay be useful?
Dead things, like leaves, don’t pile up in nature but disappear because micro- organisms feed on them. This is useful because the dead things contain substances called nutrients, which plants need to grow. When the dead things decay, the nutrients go into the soil.
Compost heaps
Gardeners often put vegetable peelings, leaves and grass clippings on a compost heap. Eventually the dead things decay to make compost, which gardeners put on the soil.
Landfill sites
Many manufactured things, like plastic and glass, don’t decay and can litter the environment. When we throw them away, they are dumped in huge landfill sites.
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Helpful microbes
Some microbes are very helpful. We use some of them to help make food.
Yeast is a helpful microbe. It produces a gas that helps bread to rise. When making bread, the dough is left to rise until it has doubled in size.
Some animals, such as cows, have helpful bacteria inside their stomachs which help them digest plants.
Microbes can also be found in yoghurt- they help to give it that special taste.
Some people also like eating microbes which have been specially grown in cheese. This cheese is not mouldy, just tasty!
Bread and cheese
Bread
Yeast is a type of fungus that is used to make most types of bread. It feeds on sugar in the bread mixture (called dough) and makes bubbles of gas called carbon dioxide. These bubbles make the bread dough rise and it is then baked.
Cheese
Bacteria are used to make cheese. Milk is first heated to about 70 ºC for 16 seconds. This kills most of the bacteria in it, including any dangerous ones. Special bacteria are then added, which feed on the milk and turn it into a lumpy substance, a bit like watery cottage cheese.
The liquid (whey) is removed, leaving only the solid bits (curds). The curds are mixed with more bacteria and the cheese is pressed into shape. The cheeses are then left for a time to allow the bacteria to feed on the cheese and give it its flavour. Sometimes a special mould is added to make blue cheese.
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1. Which of the following are diseases? Underline the answers.
German measles tooth ache mumps
Cold chickenpox broken ankle
2. What is the name of the way of preventing diseases like smallpox?
3. Ali and Omar investigated bread. They placed it in a clear plastic bag and left it for 10 days. They observed it frequently and recorded what they saw.
Day 1 Day 4 Day 7 Day 10No mould Some very small bits of
1. Underline the foods that are made using micro-organisms
Yoghurt cake bread
Chocolate bars orange juice cheese
2. Make a list of foods that you eat and drink that have been preserved by these different methods
Freezing Drying Canning Pickling
3. Maya and Lulwa divided a ball of bread dough made with yeast into three equal sizes (by weight) and placed the dough balls in containers of the same shape and size. The height of the dough was the same in each container at the start. A piece was placed in:
a) A warm window sill
b) cool corridor
c) A cold fridge
They measured in millimetres how much the dough had risen in each container in 60 minutes.
Was this a fair test? .......................................................................................................................................
7. Where should a baker leave dough to rise quickly? ................................................................................
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1. Micro-organisms can be harmful and cause disease. Which of these complaints are caused by microorganisms? For each complaint, put a tick if it is caused by a microorganism, and put a cross if it is not caused by micro-organisms.
Complaint Tick or cross
A cold
A broken leg
A bruise
Chickenpox
Toothache
A nose bleed
A graze
2. Micro-organisms can also be useful, for example when they break down materials.
Which of these objects can be broken down by micro-organisms?
Object Tick or cross
Pile of leaves
Glass bottle
Vegetable peelings
Plastic bag
Grass cuttings
Dead bird
coins
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1. These pictures show the process of making yoghurt but they are in the wrong order. Rearrange them into the correct order.
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Choose the correct answer:
1. Micro-organisms cannot be seen without a
a. Microscope
b. Periscope
c. Telescope
2. Which of these is not true about micro-organisms?
a. They are all harmful
b. They feed and grow
c. They reproduce
3. What is yeast used for?
a. To cure chickenpox
b. To make bread rise
c. To make yoghurt
4. Why should cooked and uncooked foods be stored separately?
a. Because bacteria only like cooked food
b. Because bacteria only like uncooked food
c. To stop bacteria spreading from one to the other
5. Bacteria and viruses are both small types of micro-organisms. Which is smaller?
a. Bacteria
b. Viruses
c. They are both the same size
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There are a number of a different ways to preserve food. Read the explanations of the main methods of preserving food. Connect each explanation to its correct food picture.
Method How it works Example
CANNING
A. To stop the micro-organism from breeding, all water is removed from the food. When it is time to eat the food, water is added, making it swell up
SALTINGB. The liquid is heated enough to kill the microbes but not enough to change the taste.
DRYING
C. The food is cooled very quickly and stored at temperatures below 0°C. Micro-organisms will not multiply.
PASTEURIZATIOND. Acid is added to the food. This kills the micro-organisms and the food can be kept for a long time.
PICKLINGE. Adding a lot of salt to some foods also kills microbes. The salt draws water from them and they die.
FREEZING
F. The food is placed in a can and heated to kill the microbes. The cans are sealed so that no more micro-organisms can get inside.
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Year 6 students are doing an experiment about yeast. That’s what they did:
Step 1.They used 4 clean glass bottles.
Step 2.In the 1st bottle they added a teaspoon of sugar.
Step 3.In the 2nd bottle they added a teaspoon of yeast.
Step 4.In the 3rd bottle they added a teaspoon of sugar and a teaspoon of yeast.
Step 5.In the 4th bottle they added a teaspoon of yeast and 3 teaspoons of sugar.
Step 6.They added a cup of water to each of the bottles and gently shaked them.
Step 7.Afterwards, they immediately attached balloons to the tops of the bottles.
Step 8.They waited for 30 minutes.
1. What happened? Draw the balloons after 30 minutes.
