Page 23 - Science Class 08

Proper es of Viruses Preserva on of Food

v They are non-cellular organisms which are We can save our food from various micro-
enclosed in a protec ve envelope. organisms by preserving it properly. There are
v The presence of spikes helps in a aching various methods by which we can preserve our
the viruses to the host cell. food.

v These viruses do not grow, neither respire v Refrigera on and Freezing : Low temp-
nor metabolize, but they reproduce. erature keeps the growth of microorganisms
under check which keeps the food fresh and
v They are surrounded with a protein coat –
safe for a few days. Freezing further lowers
capsid and have a nucleic acid core the temperature and stops the ac vi es of
comprising of DNA or RNA.
the microbes and thus the food can be
v They are considered both as living and preserved for many months.
non-living things. These viruses are inac ve v Pasteuriza on : This is the best method to
when they are present outside of host preserve the milk. Louis Pasteur invented
cells, but become ac ve within host cells.
this method. In this method, milk is heated
These viruses cause several infec ons and
to kill the bacteria, then it is cooled to
reproduce within the host cell by using the check the bacteria from growing. Then, it is
enzymes and raw materials.
stored at low temperature.
FOOD POISONING
v Adding Salt and Sugar : This method is
Food when not preserved properly is a acked used to preserve the fruits and vegetables.
by various microorganisms which make the Salt and sugar are used as preserva ve in
food poisonous and unfit for consump on. pickles, canned vegetables, in jam, jellies,
Various bacteria like salmonella and clostridium etc. Except salt and sugar, oil and spices are
rot the food and cause severe diges ve also used as preserva ves.
disease. Bacteria also spoil the milk which is v Sun Drying, Hea ng and Smoking : Food
not boiled. Similarly, various fungi grow on the items are dried to remove water contents
unpreserved food and make it unfit for
which checks the ac vi es of the microbes.
consump on. To save the food from these Similarly, hea ng and smoking is used to
micro-organims, we should preserve our food preserve fish, meat, etc. Vegetables are
properly.
dehydrated to preserve them for long
period.

Take a balloon and fill it with air. Release the air. Now, take a
cup of water and heat it. Add a packet of yeast and some sugar
to it and s r. Now, pour this mixture in a glass bo le. Shake
the bo le and you will see some bubbles in the bo le. Now,
a ach the balloon to the mouth of the bo le and keep it for
an hour. Slowly you will see the air rising in the balloon and
balloon standing up-right. Where does this air come from?
Yeast feed on sugar to produce carbon dioxide. This gas fills in
balloon and it stands up-right.

Science-8 23