Questions related to Biochemical Cycles

2. Question No 1

3. Q 1: Explanation

4. Question No 2

5. Explanation
 The main role of bacteria in carbon cycle
involves breakdown of organic compounds. Bacteria
decompose plant and animal bodies, replenish the
insufficient amount of Carbon dioxide required for
photosynthesis. Some Cyanobacteria are involved in
photosynthesis too, but photosynthesis is primarily carried
out by plants.

6. Question No 3

7. Explanation
 Cellulose degradation is carried out by the enzymes called
“cellulases”, responsible for the hydrolysis of
β-1, 4-linkages present in cellulose.
 Cellulases break down the cellulose molecule into
monosaccharides ("simple sugars") such as β-glucose, or shorter
polysaccharides and oligosaccharides.
 True cellulolytic organisms produce a multiple-enzyme system.
These multiple-enzyme systems act in synergy to bring effective
hydrolysis of cellulose. At least three different types of enzyme
activities are required for complete hydrolysis of this polymeric
substrate into its monomeric unit.
 Endoglucanase activity
 Exoglucanase activity (also called cellodextrinase or
cellobiohydrolase)
 β – glucosidases activity

8. Contd…
 Endoglucanases produce random internal cuts within
the amorphous region in the cellulose molecule,
yielding cello-oligosaccharides of various lengths and
thereby generating new chain ends.
 Exoglucanases act progressively on the reducing
and/or non-reducing ends producing either glucose,
cellobiose and/or cellooligosaccharides.
 These soluble cellodextrins and cellobiose are then
hydrolyzed by β-glucosidases to glucose.
 The three types of enzymes act in a coordinated
manner to hydrolyze cellulose.

9. Question No 4

10. Explanation
 Proteolytic bacteria are capable of hydrolyzing proteins, due to
producing extracellular proteinases. The most active
microorganisms responsible for elaborating the proteolytic
enzymes (proteinases and peptidases) are Pseudomonas,
Bacillus, proteus, Clostridium histolyticum, Micrococcus,
Alternaria, Penicillium etc.
 The breakdown of proteins is completed in two stages. In first
stage proteins are converted into peptides or polypeptides by
enzyme (proteinases) and in second stage polypeptides/peptides
are further broken down into amino acids by the enzyme
(peptidases).
Proteinases peptidases
 Proteins…………………….>peptides……………………>Amino acids

11. Question No 5

12. Explanation
Predation
 It is a widespread phenomenon when one organism
(predator) engulf or attack other organisms (prey).
 The prey can be larger or smaller than the predator and this
normally results in the death of the prey.
 Normally predator-prey interaction is of short duration. It
is a negative interaction.
 Examples of Predation:
 a. Protozoan-bacteria in soil: Many protozoans can feed
on various bacterial population which helps to maintain
the count of soil bacteria at optimum level.
 b. Bdellovibrio, Vamparococcus, Daptobacter, etc are
examples of predator bacteria that can feed on a wide range
of the bacterial population.

13. Parasitism
 It is a negative relationship in which one population (parasite)
get benefited and derive its nutrition from other population
(host) in the association which is harmed.
 The host-parasite relationship is characterized by a relatively
long period of contact which may be physical or metabolic.
 Some parasite lives outside the host cell, known as ectoparasite
while other parasite lives inside the host cell, known as
endoparasite.
 Examples of parasitism:
 a. Viruses: Viruses are an obligate intracellular parasite that
exhibits great host specificity. There are many viruses that
are parasite to bacteria (bacteriophage), fungi, algae, protozoa
etc.
 b. Bdellovibrio: Bdellavibrio is ectoparasite to many gram-
negative bacteria.


14. Commensalism
 It is a positive relationship in which one organism (commensal) in the
association is benefited while another organism (host) of the association is
neither benefited nor harmed.
 It is a unidirectional association and if the commensal is separated from the
host, it can survive. Examples of commensalism are:
 a. Non-pathogenic E. coli in the intestinal tract of humans:
E. coli is a facultative anaerobe that uses oxygen and lowers the O2
concentration in the gut which creates a suitable environment for obligate
anaerobes such as Bacteroides. E. coli is a host which remains unaffected
by Bacteroides.
 b. Flavobacterium (host) & Legionella pneumophila (commensal):
Flavobacterium excretes cystine which is used by L. pneumophila and
survives in the aquatic habitat.
 c. Association of Nitrosomonas (host) & Nitrobacter (commensal) in
Nitrification: Nitrosomonas oxidize Ammonia into Nitrite and
finally, Nitrobacter uses nitrite to obtain energy and oxidize it into Nitrate.

15. Ammensalism (Antagonism)
 When one microbial population produces substances that are
inhibitory to other microbial population then this inter population
relationship is known as Ammensalism or Antagonism. It is a negative
relationship.
 The first population which produces inhibitory substances are
unaffected or may gain competition and survive in the habitat while
other populations get inhibited. This chemical inhibition is known as
antibiosis.
 Examples of the antagonism (amensalism):
 a. Lactic acid produced by lactic acid bacteria in the vaginal
tract: Lactic acid produced by many normal floras in the vaginal tract
is inhibitory to many pathogenic organisms such as Candida albicans.
 b. Skin normal flora: Fatty acid produced by skin flora inhibits many
pathogenic bacteria in the skin
 c. Thiobacillus thiooxidans: Thiobacillus thioxidant produces
sulfuric acid by oxidation of sulfur which is responsible for lowering pH
in the culture media which inhibits the growth of most other bacteria.

16. Question No 6

17. Explanation
What is a Lichen?
A lichen is not a single organism; it is a
stable symbiotic association between a
fungus and algae and/or cyanobacteria.
Lichen fungi require carbon as a food
source; this is provided by their
symbiotic algae and/or cyanobacteria,
that are photosynthetic. The lichen
symbiosis is thought to be a mutualism,
since both the fungi and the
photosynthetic partners, called
photobionts, benefit. The photobiont
may be an alga and/or cyanobacteria,
both of which can produce simple sugars
by photosynthesis.

18. Question No 7

19. Explanation
 “Biofertilizers are substances that contain microorganisms, which
when added to the soil increase its fertility and promotes plant
growth.”
 Bacteria, fungi, and algae are some of the beneficial
microorganisms that help in improving the fertility of the soil.
 Types of Biofertilizers
 Symbiotic Nitrogen-Fixing Bacteria- Eg: Rhizobium
 Loose Association of Nitrogen-Fixing Bacteria (Symbiotic:
do not develop an intimate relationship with plants)-
Eg: Azospirillum
 Symbiotic Nitrogen-Fixing Cyanobacteria/Blue-Green algae
 Free-Living Nitrogen-Fixing Bacteria- They are saprotrophic
such as Clostridium beijerinckii (Anaerobe), Azotobacter
(Aerobe), etc.

20. Question No 8

21. Explanation
 These are natural compounds that contain micro-organisms to
enrich soil fertility to increase crop yield and plant growth.
Microbial inoculants like bacteria, algae, and fungi can be used
in biofertilizers.
 The biofertilizers having algae as an inoculant in them are
known as algal biofertilizers.
Benefits of algal fertilisers
Algal fertilisers could not only help in improving soil fertility through
the increase of soil carbon and nitrogen, and through the aggregation
of soil particles to improve soil structure. They also
secrete extracellular polymeric substances which help bind soil
particles together, as well as help soil overcome conditions of water
stress.

22. Question No 9

24. Question No 10

25. Explanation
 Denitrification is the microbial process of reducing
nitrate and nitrite to gaseous forms of nitrogen,
principally nitrous oxide (N2O) and nitrogen (N2).
Nitrogen Cycle

26. Question No 11

27. Explanation
 Sulfur-containing proteins are degraded into their constituent
amino acids by the action of a variety of soil organisms. The
sulfur of the amino acids is converted to hydrogen sulfide
(H2S) by another series of soil microbes.
 Steps:
 In the sulfur cycle, microbes degrade organic sulfur
compounds, such as amino acids to release H2S, which can be
oxidized by Thiobacillus to sulfate. This ion can be assimilated
into amino acids by plants and bacteria or reduced by
Desulfovibrio to hydrogen sulfide. H2S is used by
photoautotrophic bacteria as an electron donor to synthesize
carbohydrates. The sulfur-containing by-product of this
metabolism is elemental sulfur.

28. Sulfur Cycle

29. Question No 12

30. Explanation
 Escherichia coli (E. coli) are enteric bacteria classified
in the family Enterobacteriaceae, more recently named
Enterobacteriales. It is a commensal normally found in
the intestinal tract of humans and warm-blooded
animals and is involved in various intestinal and extra-
intestinal infections as an opportunistic pathogen.

31. Question No 13

32. Explanation
 Denitrification is the reverse process of nitrification.
 The overall process of denitrification as follows:
Nitrate……….>Nitrite……> Nitrous oxide…….>Nitrogen
gas
 The most important denitrification bacteria are
Thiobacillus denitrificans, Micrococcus denitrificans
and species of Pseudomonas, Bacillus, Achromobacter,
Serratia, Paracoccus denitrificans etc.

33. Question No 14

34. Explanation
 Mycorrhizae literally means
“fungus root”. Mycorrhizae
are a symbiotic association
between plant roots and fungi.
Their major role is to enhance
nutrient and water uptake by
the host plant by exploiting a
larger volume of soil than roots
alone can do. In this
relationship, plants provide
food to the fungi and in return,
the fungi absorb water and
nutrients from the soil and
give it back to the plant.

35. Question No 15

36. Explanation
 Amensalism is a type of biological interaction where
one species causes harm to another organism without
any cost or benefits to itself. It can be seen as a form of
interaction or competitive behaviour among other
organisms.

37. Question No 16

38. Explanation
 Anabaena is a nitrogen-fixing cyanobacterium that is
symbiotically associated with the water fern Azolla and
are together found in rice fields.
 In this relationship, the cyanobacterium receives
carbon and nitrogen sources from the plant in
exchange for fixed nitrogen.

39. Question No 17

40. Explanation
 Legumes are able to form a symbiotic relationship with nitrogen-
fixing soil bacteria called rhizobia. The result of this symbiosis is
to form nodules on the plant root, within which the bacteria can
convert atmospheric nitrogen into ammonia that can be used by
the plant.

41. Question No 18

42. Explanation
 Nitrobacter play an important role in the nitrogen
cycle by oxidizing nitrite into nitrate in soil and
marine systems.
 Unlike plants, where electron transfer in
photosynthesis provides the energy for carbon
fixation, Nitrobacter uses energy from the oxidation of
nitrite ions.
 Nitrifying bacteria present in soil convert ammonia
into nitrates. Ammonia is changed to nitrites by nitrite
bacteria, e.g., Nitrosomonas, Nitrosococcus which is
then oxidised to nitrate by nitrate bacteria,
e.g., Nitrocystis, Nitrobacter.

43. Question No 19

44. Explanation
 Ammonification is the process where microscopic
organisms like bacteria or other types of decomposing
organisms, break down nitrogen-containing chemicals
from dead organic matter, into simple substances like
ammonia.

45. Question No 20

46. Explanation
 The process which is used to remove Carbon dioxide
from the air is photosynthesis.
 Plants and photosynthetic algae and bacteria use
energy from sunlight to combine carbon dioxide (C02)
from the atmosphere with water (H2O) to form
carbohydrates. These carbohydrates store energy.
Oxygen (O2) is a byproduct that is released into the
atmosphere. This process is known as photosynthesis.
 carbon dioxide + water + sunlight -> carbohydrate +
oxygenCO2 + H2O + sunlight -> CH2O + O2

47. Question No 21

48. Explanation
 Free-living (nonsymbiotic) and non-free-living
(symbiotic) bacteria are both capable of fixing
nitrogen.
 Cyanobacteria, Azotobacter, and Clostridium are a few
examples of non-symbiotic or free-living bacteria.

49. Question No 22

50. Explanation
 A protease (also called a peptidase, proteinase, or
proteolytic enzyme) is an enzyme that catalyzes
proteolysis, breaking down proteins into smaller
polypeptides or single amino acids, and spurring the
formation of new protein products.
 Cleavage of protein means breaking the peptide bond
with an enzyme known as Protease. Other than
proteases there are two more pancreatic enzymes in
the small intestine for breaking proteins into amino
acids are chymotrypsin and trypsin.

51. Question No 23

52. Explanation
 Rhizobium is a genus of Gram-negative soil bacteria that fix
nitrogen. Rhizobium species form an endosymbiotic nitrogen-
fixing association with roots of (primarily) legumes and other
flowering plants.
 The bacteria colonize plant cells to form root nodules, where
they convert atmospheric nitrogen into ammonia using the
enzyme nitrogenase.
 The ammonia is shared with the host plant in the form of
organic nitrogenous compounds such as glutamine.
 The plant, in turn, provides the bacteria with organic
compounds made by photosynthesis.

53. Question No 24

54. Explanation
 VAM or Vesicular-arbuscular mycorrhiza is formed by
the symbiotic relationship between certain fungi and
angiosperm roots.
 VAM fungi are mycorrhizal species of fungus that live
in the roots of different higher-order plants.
 VAM is a type of endo mycorrhizae.

55. Question No 25

56. Explanation
 Bradyrhizobium is a slow-growing N2 fixing bacterial
species.
 Bradyrhizobium species are Gram-negative bacilli
(rod-shaped) with a single subpolar or polar flagellum.
They are common soil-dwelling micro-organisms that
can form symbiotic relationships with leguminous
plant species where they fix nitrogen in exchange for
carbohydrates from the plant.
 They are capable of using ethanol as a sole source of
carbon and energy for growth.

57. Thank You