Soil micro ornanism beneficial and harmful role

1. Soil Biota
By Dr. Kamini Roy

2. Soil organism
Soil flora Soil fauna
Soil macroflora Soil microflora Soil macrofauna Soil microfauna
e.g. Roots of the higher plants e.g. Bacteria , Fungi ,
Actinomicetes etc
e.g. Earthworms ,Moles
,Ants etc.
e.g. Protozoa, Nematodes,
By Dr. Kamini Roy

3. Bacteria
The bacteria are of two types.
(a) Autotrophic bacteria: These bacteria manufacture their food by using very simple
inorganic substances. Autotrophic bacteria oxidise ammonia, nitrate, sulphur, manganese,
iron, carbon monoxide, hydrogen and methane, so that plant can utilize these substances.
(b) Heterotrophic bacteria: These bacteria depend upon organic matter or living body
for their food. They bring about mineralization of organic matter through hydrolysis and
oxidation and release nitrogen, phosphorus and other nutrients in forms available to plants.
They also fix atmospheric nitrogen in the soil.
By Dr. Kamini Roy

4. Autotrophic bacteria: These bacteria manufacture their
food by using very simple inorganic substances. Autotrophic
bacteria oxidise ammonia, nitrate, sulphur, manganese, iron,
carbon monoxide, hydrogen and methane, so that plant can
utilize these substances.
A. True
B. False
By Dr. Kamini Roy

5. SOIL FUNGI
Root hairs
Vesicles
arbuscules
These are non-green plant (no chlorophyll); thus, they cannot
manufacture their own food and so they depend on others for their
food.
They decompose the organic matter in form available to the
plants. Many antibiotics are derived from fungus
By Dr. Kamini Roy

6. Actinomycetes
Actinomycetes are soil microorganisms. They are a type of bacteria, but they
share some characteristics with fungi that are most likely a result of convergent
evolution due to a common habitat and lifestyle.
Actinomycetes are transitional between bacteria and fungi.
By Dr. Kamini Roy

7. • Actinomycetes are soil microorganisms. They are a type of bacteria,
but they share some characteristics with fungi that are most likely a
result of convergent evolution due to a common habitat and lifestyle
• A. True
• B. False
By Dr. Kamini Roy

8. One of the most notable characteristics of the actinomycetes is their ability to produce
antibiotics.
 Streptomycin, neomycin, erythromycin and tetracycline are only a few examples of these
antibiotics.
Streptomycin is used to treat tuberculosis and infections caused by certain bacteria and
neomycin is used to reduce the risk of bacterial infection during surgery.
 Erythromycin is used to treat certain infections caused by bacteria, such as bronchitis,
pertussis (whooping cough), pneumonia and ear, intestine, lung, urinary tract and skin
infections.
Antibiotics Produced by Actinomyces
By Dr. Kamini Roy

9. • Algae
Algae can make their own nutrients through photosynthesis.
They contain chlorophyll and therefore, they manufacture their own food.
The main groups of algae are: 1. green 2. blue-green 3. yellow-green and 4.
diatoms.
Algae are also capable of performing nitrogen fixation.
By Dr. Kamini Roy

10. • Algae can make their own nutrients through photosynthesis
• A. True
• B. False
By Dr. Kamini Roy

11. Types :
Algae can be split up into three main groups: the Cyanophyceae, the Chlorophyceae and
the Bacillariaceae.
The Cyanophyceae contain chlorophyll A, which is the molecule that absorbs sunlight and uses
that energy to make carbohydrates from carbon dioxide and water and also pigments that
make it blue-green to violet in color.
The Chlorophyceae usually only have chlorophyll A & B in it which makes it green,
and the Bacillariaceae contain chlorophyll as well as pigments that make the algae yellow-
green or brown in color.
By Dr. Kamini Roy

12. Protozoa
Protozoa are eukaryotic organisms that were some of the first microorganisms
to reproduce sexually.
Soil protozoa feed either on soil organic matter or on bacteria, thus, regulating
the number of the bacteria in the soil.
By Dr. Kamini Roy

13. Nematodes
They live in soil & water and cause diseases
in many crops e.g. rice, tomato `
By Dr. Kamini Roy

14. • Nematodes live in soil & water and cause diseases in many crops e.g.
rice, tomato
A. True
B. False `
By Dr. Kamini Roy

15. Function or Role of soil microorganisms
(I) Beneficial function of soil microorganisms
The beneficial roles of soil microorganisms are:
(A) Change and decomposition of organic matter
(i) Ammonification. The change of organic nitrogenous compounds into ammonia is
called ammonification. It occurs as a result of action of enzymes produced by
microorganism in the presence of air.
Protein Polypeptides amino acids ammonia
By Dr. Kamini Roy

16. (ii) Nitrification.
The conversion of ammonia to nitrate (NO3) is known as nitrification. Autotrophic
bacteria performed this transformation. It is an aerobic process.
Nitrosomonas Nitrobacter
NH3 N02 NO3
Ammonia Nitrite Nitrate
By Dr. Kamini Roy

17. (iii) Decomposition to simple products.
The more common simple products resulting from the activity of the soil microorganisms
are as follows:
Carbon: CO2, CO3
--, HC03
-, elemental carbon
Sulphur: S, H2S, SO3
--, SO4+, CS2
Phosphorus: H2PO4
-
, HPO4
--
Others: H2O,O2, H2, H+,OH-, K+,Ca++, Mg++ etc.
By Dr. Kamini Roy

18. (iv) Mineralization of organic sulphur.
Autotrophic bacteria (sulphur bacteria) oxidised sulphur into sulphate form.
Enzymic
S + 2O2 SO4
--
Sulphur Oxygen Oxidation Sulphate
(v) Mineralization of organic phosphorus.
Organic phosphorus compounds are mineralized by the action of microorganism into inorganic
phosphorus.
Microorganism
Organic phosphorus H2PO4
- or HPO4
--
available phosphorus
By Dr. Kamini Roy

19. (B) Fixation of atmospheric nitrogen.
The conversion of elemental nitrogen to readily available form by nitrogen-fixing
microorganisms is called biological nitrogen-fixation. The microorganisms fixing atmospheric
nitrogen in the soil is known as 'bio-fertilizers'.
The nitrogen-fixing microorganisms are: (I) Bacteria (II) Algae
By Dr. Kamini Roy

20. • The conversion of elemental nitrogen to readily available form by
nitrogen-fixing microorganisms is called biological nitrogen-fixation
• A. True
• B. False
By Dr. Kamini Roy

21. (1) Bacteria.
There are two main groups of bacteria which fix atmospheric nitrogen; symbiotic and
non-symbiotic.
(i) Symbiotic nitrogen-fixing bacteria: This group of bacteria (Rhizobium) fixes
nitrogen in association with leguminous plants, called symbiotic bacteria.
The Rhizobium bacteria living in the root of leguminous plants. They take their food
from the leguminous plants and absorb nitrogen from the atmosphere. They
produce nitrogenous compound and supply to the leguminous host plants.
Both the legume (pulse) crop and bacteria are benefited by this association, known as
'symbiosis'.
By Dr. Kamini Roy

22. Species name Group name Leguminous crops
Rhizobium leguminosarum Pea group All types of pea, lentil, bean
R. japonicum Soyabean group Soyabean
R. phaseoli Phaseolus group Kidney and garden beans
R. trifoli Clover group White clover
R. meliloti Alfalfa group Lucerne
By Dr. Kamini Roy

23. (ii) Non-symbiotic nitrogen fixing bacteria.
Azotobacter and Clostridium work independently of any host crop.
Azotobacter is an aerobic nitrogen-fixing bacteria and thrives well in
neutral soil. It is susceptible to a deficiency of phosphate.
Clostridium is anaerobic and fixing less amount of nitrogen than
Azotobacter
By Dr. Kamini Roy

24. (2) Algae.
Most algae are chlorophyll bearing organisms. Blue-green algae are capable of fixing
atmospheric nitrogen to the soil.
The main genus of algae which fix nitrogen are Anabaena, Nostoc and Cylindrospermum.
They prefer usually neutral or slightly alkaline soil.
In water-logged rice field, algae grow well and fix about 20-30 kg nitrogen per hectare.
By Dr. Kamini Roy

25. • Most algae are chlorophyll bearing organisms. Blue-green algae are
capable of fixing atmospheric nitrogen to the soil.
• A. True
• B. False
By Dr. Kamini Roy

26. (3) Mycorrhizae (Myco =fungus; rhiza =root).
Mutually beneficial association between certain fungi and roots of higher plants is called
mycorrhizae (fungus roots). By this symbiotic association, fungi get sugars and organic
exudates from the roots of higher plant. In return, the fungi provide several essential
nutrients to the plant.
Mycorrhizae are divided into two types: ectomycorrhiza and endomycorrhiza. The
endomycorrhiza group are called vesicular-arbuscular mycorrhizae (VAM) increase the
uptake of phosphorus, enhance resistance against drought and certain root-infecting
fungus.
By Dr. Kamini Roy

27. (II) Harmful role of soil microorganism
There harmful effects of microorganisms are:
(a) denitrification,
(b) development of plant diseases
(c) formation of toxic compounds and
(d) competition for nutrients
By Dr. Kamini Roy

28. (a) Denitrification.
The conversion of soil nitrate into gaseous nitrogen or nitrous oxide is known as denitrification. It
is an anaerobic process performed by bacteria belonging to genera Pseudomonas,
Micrococcus and Bacillus. Water-logging in rice fields will increase nitrogen losses due to
denitrification. Nitrate fertilizers, therefore, should not be applied in rice fields.
Pseudomonas/Bacillus
NO3 (Nitrate) NO2 (Nitrites) N2 (N gas)
By Dr. Kamini Roy

29. (b) Development of plant diseases.
The blight disease of rice, apple and pear is caused by bacteria. Fungi cause
more serious damage to crop plants. e.g. smuts and rusts of cereal crops and
late blight of potatoes.
By Dr. Kamini Roy

30. (c) Formation of toxic compounds.
Under anaerobic conditions toxic substances such as methane, hydrogen sulphide are formed
due to improper decomposition of organic matter.
(d) Competition for nutrients.
Competition for plant nutrients between microorganisms and crop plants is quite high. So
plants get insufficient nutrients for their growth.
By Dr. Kamini Roy