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Answers
Answer:
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Explanation:
Microorganisms are small
A microorganism is a living organism that is so tiny it can only be seen with the aid of a microscope.
Consider that the largest human cells are about the diameter of a human hair. Bacteria cells are one-hundredth the size of a human cell and viruses are much, much smaller again. If you imagine that a single virus was the size of an adult human, a bacterium (single cell) would be over 10 storeys high by comparison. A bacterium next to a human cell is like a tiny boat next to a big ship. Hundreds of thousands of bacteria could fit onto a pinhead.
Friend and foe
The main microorganisms in and on our bodies are protozoa, algae, fungi, bacteria and viruses. Most microorganisms are beneficial, for example, there are microorganisms in our large intestine that synthesise vitamins and allow them to be absorbed into the bloodstream. However, a tiny minority are pathogens (disease-causing agents). These pathogens, often called germs or bugs, are a threat to all life forms.
Let’s take a closer look at bacteria, viruses and parasites.
Answer:
Y ou have seen several kinds of
plants and animals. However,
there are other living organisms
around us which we normally cannot
see. These are called microorganisms
or microbes. For example, you might
have observed that during the rainy
season moist bread gets spoilt and its
surface gets covered with greyish white
patches. Observe these patches through
a magnifying glass. You will see tiny,
black rounded structures. Do you know
what these structures are and where do
these come from?
2.1 Microorganisms
Activity 2.1
Collect some moist soil from the
field in a beaker and add water to
it. After the soil particles have
settled down, observe a drop of
water from the beaker under a
microscope. What do you see ?
Activity 2.2
Take a few drops of water from a
pond. Spread on a glass slide and
observe through a microscope.
Do you find tiny organisms moving
around?
These observations show that water
and soil are full of tiny organisms,
though not all of them fall into the
category of microbes. These
microorganisms or microbes are so
small in size that they cannot be seen
with the unaided eye. Some of these,
such as the fungus that grows on bread,
can be seen with a magnifying glass.
Others cannot be seen without the help
of a microscope. That is why these are
called microorganisms or microbes.
Microorganisms are classified into
four major groups. These groups are
bacteria, fungi, protozoa and some
algae. Some of these common
microorganisms are shown in
Figs. 2.1 - 2.4.
Viruses are also microscopic. They,
however, reproduce only inside the cells
of the host organism, which may be a
bacterium, plant or animal. Some of the
viruses are shown in Fig. 2.5. Common
ailments like cold, influenza (flu) and
most coughs are caused by viruses.
Serious diseases like polio and chicken
pox are also caused by viruses.
Diseases like dysentery and malaria
are caused by protozoa(protozoans)
whereas typhoid and tuberculosis (TB)
are bacterial diseases.
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