Page 17 - Science Class 08
P. 17
Their Discovery manure that is used in them. Though most of
Needless to say, discoveries and researches the microbes are beneficial for the soil, others
regarding microbes could be possible only a er are harmful too. Let us perform an experiment
the invent of the microscope as they could not to observe microbes in a sample of pond water.
be seen with the naked eyes. Development of
electronic microscope has helped further the
scope of study regarding microbes. These Take some water from a pond and bring it
scien fic inven ons have belied the belief that home. Sieve it through a piece of fine cloth.
all microbes are harmful. It has become clear Observe carefully what is le on the piece of
that only certain microbes are harmful while cloth. You will see some mud in general but
most of them are useful. also some small organisms moving inside it.
The sieved water will look fairly clean.
For example:
Take a clean piece of glass and place it on
v Soil bacteria fix the nitrogen of the air for
the table. Put a big drop of the sieved water
the good of plants.
on it and spread it on the glass piece.
v Microbes help in preparing curd, cheese, Observe this water through a magnifying
aroma, pickle, wine, vinegar and tobacco. glass. You will see s ll nier organisms
v Microbes are u lised in the prepara on of dar ng about in it.
an bio cs and also in sewage disposal.
MICROBE-CULTURE
HABITATS OF MICROBES
Microbe-culture means rearing microbes for
Microbes can exist in all types of habitats. They carrying out study or for some other purposes.
are generally single-celled but some mes they
It can be done providing a suitable medium
occur in chains of cells. They can be easily
that includes the presence of factors like
collected from air and water especially when acidity, oxygen, temperature and alkalinity.
they are in impure condi on. Microbes are of
A suitable medium is generally prepared in the
nearly 20000 species though only a few of
laboratory. It is called potato dextrose agar
them have been discovered.
(PDA).
Bodies of animals and human beings also make
It is prepared as follows :
good habitats for microbes. The body-surface,
nose, mouth, throat and diges ve canal of each Take 200 grams of healthy potato tubers and
animal and human being are all inhabited by wash them properly. Cut them into pieces and
microbes. They are among the normal flora boil them ll they become so . Crush them
(plants) and are a part of the environment. into a paste and let is cool down. Now, add 500
ml dis lled water to the paste. Take 20 gram of
Some microbes enter the bodies of animals
agar gel and boil it separately in 500 ml water.
and human beings and cause various diseases.
Mix the boiled gel and the paste. The PDA
They are called pathogenic microbes. Faeces of
mixture is ready. It can be used to rear
a sick person and some insects are major
microbes.
habitats of microbes. From there, they reach to
foods and contaminate them. Cul vated fields Yeast extract can be used for this purpose also.
also contain innumerable microbes due to the It is made using yeasts and carbohydrates.
Science-8 17
