DPS-Modern Indian School, Doha Qatar
Subject: Biology
Notes
Class VIII
Topic : Micro organism
Sub topic:Algae , Protozoa and Fungi
Q-1) Write the economic importance of Algae.
Ans. Algae are useful in many waysIn MedicineWe obtain antibiotic Chlorellin for Chlorella
In Industry-i) Agar obtained from red algae is used in food industry.
ii) Algin obtained from Brown algae is used in cosmetics and medicine.
iii) They are sources of iodine, sodium and potassium.
iv) Iodine is obtained from Kelp.
In Agriculture-i) Used as manure in fields as rich source of nitrogen and
potassium.
ii) Nostoc and Anabena helps in Nitrogen Fixation.
As food and fodder- i)Red alga Pyrophyra is used as food in China and
Japan.
ii) Chondrus is used in puddings and jellies.
iii) Chlorella is very rich in proteins and vitamins and is a potential
source of food
iv) Green algae is consumed as food by fishes.
v) Sea weed such as Laminaria is used as fodder for sheep and cattle.
Q-2) How algae can be harmful to us?
Ans. Algae can be harmful in following ways*Algal Bloom- Since algae grow rapidly they can cover the entire water
surface and make it unfit for consumption.
*Algae like Chrococcus and Oscillatoria produces toxins affecting
nervous system on direct or indirect consumption by animals and
humans.
Q-3) Mention the harmful and useful effects of Protozoa.
Ans. Protozoa are useful to us in following ways
Some protozoa
are important link in aquatic food chain as they eat algae and in
turn eaten up by other organisms.

Since some are
Saprophytic help in degradation of waste and sewage.

They are used
as research material for many biological activities.
Harmful effects - Protozoa can also prove to be harmful to us as
they cause many diseases like Amoebic dysentery, malaria etc.
USEFUL FUNGI
1. In Medicine:
 Antibiotic penicillin is obtained from the fungus Penicillium notatum
 Antibiotic griseofulvin is obtained from the fungus Griseofulvum.
2.
In Industry:
(i)
In brewery and bakery:
 The fungus yeast is used extensively in wine(brewery) and
bread(bakery) industries.
 Both these industries are based on fermentation activity of
yeast. Fermentation is the anaerobic respiration(breaking down
of food in the absence of oxygen) of these organisms.
 Of the two products of yeast fermentation, alcohol is the
industrial product in brewery.
 In bakery, carbon dioxide causes the dough to rise and makes
the bread light and spongy.
(ii)
In cheese industry:
 Various species of Penicillium are used for the preparation of
cheese of various grades and flavours.
(iii) Vitamins:
 Yeast is an important source of vitamin B-complex.
(iv)
Preparation of organic acids:
 Fermentation properties of several fungi are utilized for the
manufacture of oxalic acid, citric acid, etc.
3. In Agriculture:
Fungi decompose the dead bodies of plants, animals and their wasteproducts.
Products obtained after decomposition then escape into the air and the soil.
The soil thus get enriched with humus and becomes fertile.
4. As Food:
(i)
Some fungi are edible.
(ii)
examples:-Morchella, Agaricus(mushroom),Ramaria, Clavaria,
Plurotus
Yeast is used in the preparation of idli and dosa.
HARMFUL FUNGI
1. Fungi causes skin diseases such as athlete’s foot, ringworm or
eczema in human beings.
(For rest of the diseases caused in human beings by fungi,please
refer to page 22,Table 2.1)
2. Fungi spoil food due to fermentation and make it unfit for
consumption.
3. Fungi damage stored food, books, paper, fabrics, leather and shoes
particularly during the rainy season.
4. Fungi like Puccinia and Ustilago cause rusts and smuts in
cereals.
(For rest of the diseases caused in plants by fungi,please refer to
page 22,Table 2.2)
5. Amanita even though a very beautiful fungus, it is poisonous to
eat.
Sub topic : Food Preservation
Q-4) What do you understand by the term "Food Preservation"? What
are the 2 basic approaches in Food preservation?
Ans. The treatment of perishable food material for longer retention of
their nutritive value and prevention of spoilage is called Food
Preservation.
The 2 basic approaches in all type of food preservation methods area)Bacteriocidal method: Here microbes causing spoilage are fully
eliminated Eg. Cooking, Canning, Bottling etc.
b) Bacteriostatic method : Here the conditions that are not suitable for the
growth and development of microbes are created in the food item.
Eg. Salting, Pickling etc.
Q-5) Discuss the various methods of Food Preservations.
Ans .Various methods of food preservations are-
a.Dehydration- Here the food items are dehydrated by removing water
from the so that microbes cannot grow. Eg. Sun drying of fish, vegetables
etc.
b. Preservation by adding salt and sugar-(Bacteriostatic method)
Excess of salt and sugar (68%) also curbs the growth of microbes in food
item. Eg. Preservation of raw mangoes, Amla (Goose berry)etc. by
salting.
C. Presevation by Oil and Vinegar: ( Bacteriostatic method)
Oil and vinegar also prevent spoilage as they create conditions
unfavourable for the growth of microbe.Eg. Pickles
d. Deep FreezingBelow 0 C enzymes become inactive which inhibits bacterial growth. So
food items like fruits and vegetables can be stored for longer time with
their nutritive value intact.
e. Chemical PreservationChemicals like Sodium Benzoate and Potassium metabisulphite are
added to the food items like jams,squashes etc. to prevent spoilage.
f. Irradiation (Bacteriocidal method)
food items are exposed to radiation like gamma rays or X-rays which
completely destroys harmful germs and food can be stored for a longer
time.
g. Canning-( Bactericidal method)
Canning is done for cooked stuff which is stored in sterilized tin
container.
h. Bottling (Bacteriocidal method )
Milk is mainly stored by this method after pasteurization. Pasteurization
is the process of heating at about 70 C and then sudden drop of
temperature at 20 C which kills most of the microbes.
i.Vaccum dryingMilk is preserved by this process where it is converted into milk powder
by removing moisture content from it.
Q-6) What are the advantages of food preservation?
Ans. i) It prevents the food from being spoiled by the action of enzymes
and micro organisms.
ii) It increases the storage period of food material.
iii) It helps in obtaining the off season food material.
iv) It makes the transportation of food material easier.
Q-7) What do you mean by Nitrogen fixation? What are 3 natural
methods of Nitrogen fixation?
Ans. The process of converting atmospheric nitrogen into compounds of
nitrogen which can be easily absorbed by the plants is called Nitrogen
fixation.
Following are the 3 natural methods of nitrogen fixationi)Fixation by Bacteria- Rhizobium bacteria present in the root nodules of
leguminous plants fix the nitrogen.
ii) Fixation by Blue-Green algae- Blue Green algae like Nostoc and
Anabena can help in Nitrogen Fixation. This is known as Biological
fixation. Eg. In Paddy fields
iii) Fixation by Lightning- During lightning, Nitrogen reacts with Oxygen
to form Nitrogen oxide which gets dissolved in rain water to form nitric
acid. The nitric acid formed reacts with alkalis present in the soil to form
nitrates which are absorbed by the plants.
Q-8) Draw Nitrogen Cycle and write steps involved in Nitrogen cycle.
Ans.( Diagram of Nitrgen Cycle to be done in Note book as per the
instructions by the teacher)
Steps involved in Nitrogen Cycle are1)Nitrogen present in the atmosphere is fixed by various methods i.e.
Natural and Artificial methods like Rhizobium, Lightning, fertilizers etc.
2) Nitrates are absorbed by plants from soil and converted into proteins.
3) Nitrogen in the form of plant protein goes to animals when they are
eaten up by animals and converted to animal protein.
4) When plants and animals die the putrefying bacteria and fungi in soil
decompose the protein to ammonia. This process is known as
ammonification.
5)Ammonia is converted to nitrites by Nitrosomonas and then to Nitrates
by Nitrobacter. This process is known as Nitrification.
6) Some of the nitrates are converted back into nitrogen which is released
in the air by denitrifying bacteria called Pseudomonas. This process is
called denitrification.