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Discover all the things influenced by microorganisms.

Perform experiments and examine characteristics of microorganisms.

Search for the places where you can encounter microorganisms. Meet the scientists who studied the microworld. Learn about the power of microorganisms!


from Learn e About th oMicr f o r e w Po ms! organis


Read interesting stories about invisible beings.


Nemanja Ristić Marica Kicušić Mladen Anđelković


the Microworld


Tatjana Mihajilov – Krstev

Learn e About th f Power o ganr o o r c i M isms!

from the Microworld Illustrations

Nemanja Ristić Marica Kicušić Mladen Anđelković


here is a wonderful world of small invisible organisms in nature. They live in their realms, have rulers and subjects; they work, rest, travel and wage wars in which they die and survive. Scientists have performed many experiments and they have discovered that these organisms are very powerful and important for the whole planet. Meet them the way the scientists do. You will see that exploration is interesting and exciting! If you wonder where to find them and what to do, look for the answers in this book. Various experiments with organisms from the invisible world are described in it along with the ways to handle them. Let us explore together!

Instructions on

How to Perform Experiments

Before You Start... 1. Plan precisely everything you will do during the experiment. 2. Gather everything you need for the experiment. 3. Think through whether or not you need help in performing the experiment.

4. Find a suitable place where you will conduct the experiment. 5. Make sure to have ample time for work. 6. Let no one distract you while you are working!

When you perform experiments with tiny invisible organisms, you must take care of hygiene. There are two reasons for doing so. 1. You do not want any of those organisms to spread on or inside your body. 2. You do not want the tiny organisms living inside you or on you to attack the ones you are investigating. You can maintain hygiene by washing your hands before and after work, and if it is necessary, by wearing surgical gloves and a protective mask. The equipment you will use must also be washed and wiped by alcohol. In order to ensure maximum safety, do not touch the organisms you are examining with your bare hands. After viewing the results, pack the containers in plastic bags and dispose of them in a dumpster. At the end, wash your hands thoroughly with soap and water.


Once You Get Started... 1. Be patient if an experiment requires more time than you expected. 2. Use the equipment that can hurt you (a razor blade, scalpel, scissors and the like) in the presence of an adult.

3. Be careful not to damage something. 4. Do not forget to write down your observations in a notebook. 5. Take photos of the phases of the experiment you think could be of use later. 6. After the experiment, do your best to clean the space in which you have worked.

Planning an experiment is very important. However, even with a good plan, mistakes can happen. That is normal. Every explorer makes mistakes sometimes. If that happens, think carefully, and then repeat the experiment. Everything will probably go well then.


The World of Invisible Beings


verywhere around us there are invisible beings. They are so tiny that it is impossible to see them with the naked eye, not even through the magnifying glass. But although we cannot see them, we know they exist. We perceive their presence in various ways. We call the tiny beings microorganisms, because the first part of the word denotes something very small, tiny. If you compared a microorganism to a grain of sand, you would see that the grain is much bigger than the microorganism. However small microorganisms may be, their influence is enormous. Here, just think:

• microorganisms made yogurt;

• microorganisms spoiled the ham and the cheese;

• microorganisms caused chickenpox;

• microorganisms decomposed the remaining part of the apple.


This is precisely why it is important to study well microorganisms and the way in which they are to be handled. And in order to study them, we must become detectives – the detectives for exploring the microworld.

A detective for microorganisms has many tasks:

• to find microorganisms; • to get to know how the microorganisms are built; • to find out if all small beings are the same or there are differences between them; • to find out whether or not they really are alive, that is, whether they are born, whether they grow and multiply; • to examine how they influence other organisms; • to examine how they influence the environment in which they live.

Detective work is hard. You must investigate, think, watch... That is why you must start with a good snack!


A Detective Snack Make a pizza and invite over for lunch all the people who could join you later in exploring the microworld. Carefully follow the recipe!

1. Stir beaten egg white with sour cream and a bit of parsley. Use the mixture to spread over the crust.

1. Recipe for the Pizza What you need:

• partially pre-baked pizza crust, cream cheese, sour cream, one egg, parsley, green olives, sausage, ham, cheese, onion, ketchup, peppercorns, oregano

10. Spread the cream

cheese over the crust’s edge, and sprinkle plenty oregano over the edge.

9. Add a few peppercorns.

11. Bake the pizza in the oven. 10

8. Add circles of

sliced ham.

3. Arrange several

olives on the crust.

4. Slice the sausage into

5. Arrange a few slices of onion.

elliptical pieces and put them on the pizza.

2. Make a small hollow

and put a yolk in it.

7. Place elliptical pieces of cheese here and there. 6. Draw a curved line with ketchup.


The Momentous 17th Century Discovery Your wish to see microorganisms would be of no use if Leeuwenhoek had not constructed the microscope. With the use of a few glass lenses through which light is refracted, the microscope magnifies the image of what is observed to many times its actual size.


Coarse Focus

Here is what is in the tube of the microscope! At one end of the tube, the one into which light comes, there is an objective, and in it, two or more lenses. At the other end, there is the eyepiece. There are several more lenses in it. The person watching something must set an eye right above the eyepiece and peer through the opening. Take a look at the other parts of the microscope and other things necessary for examination.


The source of light can be a small lamp or a mirror which catches the natural light. Using the light microscope, only thin objects can be examined, the ones through which light is transmitted. When an object is big, a thin piece needs to be cut from it. Microorganisms, however, are small enough to be seen in their entirety.




2. Microscopic Specimen Samples In order to observe microorganisms, it is necessary to make a microscopic sample. Get required material and follow the instructions.

What you need:

• a rectangular piece of glass which serves as a surface on which the observed specimen is placed (a slide), a thin square piece of glass used to cover the observed object (a cover glass or cover slip), a dropper (a pipette)


Everything you need for making samples can be bought at a lab supplies store


1. Take some water from a puddle using the dropper.

2. Express one drop

from the dropper on the middle of the slide.

3. Put the cover slip

over the drop, taking care that there are not any air bubbles left under the cover slip.

4. Absorb excess water around the cover slip with a tissue.

Using specimen samples made in this way, scientists study all that is visible only with a microscope.


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