This document provides an overview of the nitrogen and phosphorus cycles. It begins with the student's name, course details, and introduction to the topic. For nitrogen, it discusses the history of discoveries in the cycle. It then defines the steps of the cycle including nitrogen fixation, assimilation, ammonification, nitrification, denitrification, and sedimentation. For both nitrogen and phosphorus, it discusses biological and non-biological processes, important molecules and enzymes involved, and the impacts of human activity on accelerating the cycles.

1. ASSIGNMENT TOPIC:NITROGEN AND PHOSPHOROUS CYCLE
Name Hafiz M Waseem
ROLL NO. Mcf-1901171
Semester 2nd (E)
Department Zoology
Subject Ecology
Submitted to Dr.Nazish mazhar Ali
Submission date 31-04-2020

2. CONTENTS
Nitrogen cycle
History
Define
Steps
Biological nitrogen fixation
Non biological nitrogen fixation
Nitrogenase complex
Nodulin
 aerobic nitrogen fixation
Anearobic nitrogen fixation
Importance
Phosphores cycle
History
Function
Biological function
Importance
Uses
Empect of human activity
Cycle
Eutrafication
Human effect

3. Discovery of nitrogen cycle
 Wilfrath and Hellreigal first discovered the fact that legumes fix the
atmospheric nitrogen in the soil.
 The fixed N2 is directly consumed by cereals during crop-rotation.
 Beijerinck in 1922 first isolated the bacteria from the root nodules of
leguminous plants and named it Rhizobium leguminosarum.
Plants need
atmospheric
nitronen

4. Discovery of nitrogen cycle
 Later a large number of organisms were reported for their N2-fixing
capacity.
 The research workers of the Central Research Laboratory in the USA
first isolated an enzyme nitrogenase from the bacteria Closteridium
pasieurianum in the year 1960.
 Later, in 1966 Dilworth and Schollhorn discovered the activities of
nitrogenase in N2 fixation.

5. Introduction
 Nitrogen is abundantly present (78%) in the atmosphere.
 But green plants can not utilize the atmospheric N2 directly.
 Plants can take up N2 only from the soil.
 N2 present in the soil can be ultimately tracked back to the atmosphere.
 N2 is very important for plants, as it is a constituent of proteins, nucleic acids and a variety of
compounds.
 Mostly plants obtain N2 from the soil as nitrates and ammonium salts.
 As plants continuously absorb nitrate and ammonium salts, the soil gets depleted of fixed
nitrogen.

6. introduction
 Besides this the leaching effect of rain and denitrifying action of some bacteria lower the nitrogen content of
the soil.
 This loss is compensated by the processes of lightning and nitrogen fixation
 N2 is supplied in the form of fertilizers to agricultural crops.
 The crop rotation with cereals and legumes has been practiced for a long time to increase the N2 content of
the soil.
 This is done because legumes fix the atmospheric N2 in the soil.
Plants not break
triple bond
between2 nitrogen
Bacteria
breake 3 bont
by chemical

7. Define
 the process by which nitrogen is converted between its various chemical forms.
This transformation can be carried out through both
 biological and
 physical processes.
 The conversion of molecular N2 of the atmosphere is accomplished by 2
methods
1. Lightning or Atmospheric N2-fixation (or) Non-biological N2 fixation
2. Biological Nitrogen Fixation

8. Forms of Nitrogen : a) organic nitrogen as
ammonium (NH4+),
 nitrite (NO2-)
, nitrate (NO3-),
 nitrous oxide (N2O)
, nitric oxide (NO) or b)
 inorganic nitrogen as nitrogen gas (N2).
phytoplan
kton
Nitrogen
cycle in
water

9. Steps of nitrogen fixation
• Nitrogen cycle consists of the following steps
• 1. Nitrogen Fixation
• 2. Nitrogen assimilation
• 3. Ammonification
• 4. Nitrification and
• 5. Denitrification
• 6. Sedimentation

11. NITROGEN CYCLE IN WATER

12. Nitrogen fixation
The conversion of free nitrogen of atmosphere
into the biologically acceptable form or
nitrogenous compounds.
There are following ways to convert N2 into more
chemically reactive forms:
a) Biological Nitrogen fixation
b) Physiocochemical nitrogen fixation
c) Industrial nitrogen fixation

13. Nitrogen cycle in marine water

14. Physiocochemical or Non-biological nitrogen
fixation :• In this process, atmospheric nitrogen
• combines with oxygen (as ozone ) during lightning or
• electrical discharges in the clouds and produces different
• nitrogen oxides :

15. Non biological nitrogen fixation
 The nitrogen oxides get dissolved in rain water and on
 reaching earth surface they react with mineral
 compounds to form nitrates and other nitrogenous
 compounds :

16. Industrial nitrogen fixation
Haber-Bosch process.
Under great pressure, at a temperature of 600 temperature
and with the use of an iron catalyst, hydrogen and atmospheric
nitrogen can be combined to form ammonia (NH3) in the

17. Biological Nitrogen fixation
 some symbiotic bacteria , blue-green algae and some free-living bacteria are
able to fix nitrogen as organic nitrogen.
e.g
symbiotic bacteria : Rhizobium symbiotic
 blue-green algae : species of Nostoc, Anabaena , etc
 free-living bacteria : Azotobacter, Clostridium, Derxia,
Rhodospirillium, etc
Sym
bioti
c
relat
ions
hip

18. Biological Nitrogen fixation
Nitrogen assimilation : In this process ,
Inorganic nitrogen in the form of
 nitrates ,
nitrites , and
ammonia
It is absorbed by the green plants via their
roots and then it is converted into
nitrogenous organic compounds.
Nitrates are first converted into ammonia
which combines with organic acids to form
aminoacids . Aminoacids are used in the
systhesis of
proteins,
 enzymes,
 chlorophylls,
 nucleic acids, etc.

19. Biological Nitrogen fixation
Ammonification :
 It is the process of releasing ammonia by
certain microorganisms utilizing organic
compounds derived from the dead organic
remains of plants and animals and excreata
of animals .
The microorganisms especially involved are
actinomycetes,
 bacilli ( Bacillus ramosus , B. vulgaris, B.
mesenterilus )

20. Nitrification :
 Nitrification is a process of enzymatic oxidation of ammonia to nitrate by
certain microorganisms in soil and ocean.
Nitrosomonas ammonia to nitrites
 (NO2Nitrobacter oxidation of the nitrites into nitrates (NO3-).

21. 6. Sedimentation :
Sometimes , nitrates of soil are locked up in the rocks while they are
washed down to the sea or leached deeply into the earth along with
percolating water.This phenomena is known as sedimentation.

22. Nitrogenase complex
Nitrogen is a highly un reactive molecule, which generally requires red-hot Mg
for its reduction.
 But under physiological temperature, N2 is made into its reactive form by an
enzyme catalyst, nitrogenase.
 The research workers of Central Research Laboratory first isolated the enzyme
from the bacteria C. pasieurianum.
 They are the bacteria inhabiting the soil; they prefer anerobic environment for
their proper growth and development.

23. Nitrogenase complex
The researchers prepared the extract of these bacteria and searched for the N2
reducing property of the extract.
 The extract converts N2 into NH3.
 The researchers also used radio active labelled N15 in its molecule. Since
then, Dilworth & Schollhorn et al (1966) have discovered that the enzyme
nitrogenase reduces not only the N2 into NH3 but also acetylene into ethylene.
 The ethylene is measured by using gas chromatographic methods.

24. groups of inhibitors which inhibit the activity
of Nase
 1. Classical inhibitors: include diff kinds of substrates which compete for the
Nase against N2
 Eg: Cyclopropane, HCN, Nitrogen azide, CO are competitive inhibitors
2. Regulatory inhibitors: O2 and ATP N itself inhibits the Nase axn.

25. Rol of protein in nase activity
Nase also requires some globular pro for its normal N reducing activity.
 2 types of proteins participates in Nase activity namely legHbs & nodulins.
 1. Leghaemoglobins: Heme protein- facilitates the free diffusion of O2 from the
cytoplasm – it creates anaerobic environment for the axn of Nase.
–1st isolated from the root nodules of legumes.

27. Nodulin
Another globular protein found in the root nodules of plants infected with
Rhizobium.
 It is produced before the root nodule starts to fix the N from the atmosphere.
 Facilitates the proper utilization of NH3 released during N fixation. Induces
activation of a no of enzymes like uricase, glutamine synthetase, ribokinase

28. Aerobic nitrogen fixation
 The aerobic mos produce carbohydrates
especially polysaccharides.
 PSs hinder the free diffusion of O2 into cells.
 PSs pretect the Nase against the oxidizing
property of O2.
 Thus the PS permit the Nase activity in
aerobic micro organisms.
 The aerobic mos also have some adaptations
for the protection
of Nase against the damaging agencies in the
cell.

29. Important adaptation
 Enzyme protein association
 Rapid respiratory metabolism
 Association with rapid oxygen consumers
 Association with acid lovers
 Time specific Nase activity
 Protection through colonization of bacteria
 Special separation of the N2 fixing system

30. Anaerobic nitronen fixation
 Anaerobic microbes actively reduce N into NH3
 This NH3 is widely used in the metabolism of plants.
 In general, Nase is denatured when it is exposed to the O2 present in the
atmosphere
 But the Nase of Closteridium shows high rate of tolerance of O2.
 So the organisms like Closteridium fix N2 even under aerobic condition.
 Microbes ---fix N2 -----in association with the root

31. Symbiotic nitrogen fixation
 Microbes ---fix N2 -----in association with the roots of higher plants.(
symbiotic N2 fixers).
They fix the N2 either under aerobic / anerobic
 Eg: Rhizobium leguminosarum, R. japonicum, R.trifolli, etc,
 They invade the roots of leguminous plants and nonleguminous
plants like Frankia, Casurina etc, for their growth & multiplication
 After the establishment of symbiotic association, they start to fix the
atmosphere N in the soil.

32. Effect of field effect of nitrogen fixation
 1. Soil moisture:- moderate( ↑ and ↓ moisture of the soil reduce the rate
of N fixation in soil)
 2. Effect of Drought:- the increased water deficiency causes decrease in
the conc of legHb in the root nodules. (↓N fixation)
 3. Oxygen tension:- ↑ O2 tension in the soil causes ↓ in the rate of N
fixation by microbes.
 4. Effect of the pH of the soil solution:
 An ↑ in the soil salinity ↓ the rate of N fixation.
 5. Light intensity:- In photosynthetic microbes, light induces a high rate of
Photosynthesis resulting in high rate of N fixation.
 During N fixation, the microbes

34. Phosphorus history
Phosphorus was discovered
by Hennig Brand at 1669 in
Germany. Origin of name:
from the Greek word
"phosphoros" meaning
"bringer of light"
Brand kept his process
a secret, phosphorus
was discovered
independently in 1680
by an English chemist,
Robert Boyle.

35. Phosphorus used
White Phosphorus is used
in some explosives,
including rockets. This
caused an uproar because of
safety concerns.
Red Phosphorus is used
in match heads. You can
see the texture of a match
head next to the matches.
Fertilizer; Phosphorus is
known for being
essential to DNA and to a
lesser extent fertilizer

36. Importance of phasphoras
 It is an essential nutrient for plants and animals.
 It is a part of DNA-molecules and
RNA-molecules, molecules that store
energy (ATP and ADP)
 It is also a building block of certain
parts of the human and animal body,
such as the bones and teeth.

37. function of phosphoras
 Ecological Function
 Phosphorus is an essential nutrient for
plants and animals.
 Limiting nutrient for aquatic
organisms.
Forms parts of important lifesustaining
molecules that are very
common in the biosphere.

38. Biological Function
 The primary biological
importance of phosphates is as a
component of nucleotides, which
serve as energy storage within cells
(ATP) or when linked together, form
the nucleic acids DNA and RNA..

39. Phosphorous cycle
The biogeochemical cycle that describes the
movement of phosphorus through
the lithosphere, hydrosphere, and biosphere.
Unlike many other biogeochemical cycles,
the atmosphere does not play a significant
role in the movement of phosphorus, because
phosphorus and phosphorus-based
compounds are usually solids at the typical
ranges of temperature and pressure found
on Earth.

42. phosphorous cycle
1. Reservoir –
erosion transfers phosphorus to
water and soil; sediments and
rocks
that accumulate on ocean floors
return to the surface as a result of
uplifting by geological processes
2. Assimilation –
plants absorb inorganic PO4
(phosphate) from soils; animals
obtain organic phosphorus.
3. Release –
plants and animals release
phosphorus when they
decompose;
animals excrete phosphorus in
their
waste products

43. Effect of human activity on phosphoras cycle
We remove large amounts of phosphate
from the earth to make fertilizer.
We reduce phosphorous in tropical soils
by clearing forests.
We add excess phosphates to aquatic
systems from runoff of animal wastes and
fertilizers. (causes eutrophication)

44. Eutrafication

45. Phosphoras cycle
When rocks high in
phosphorus are exposed to
water, the rock weathers
out and goes into solution
2. Autotrophs absorb this
phosphorus and use it in
many different ways,
3. Then the plant is eaten
by a heterotroph and
obtains phosphorus from
the plant
4. Then the phosphate
leaves the body, and
decomposers move the
phosphorus into the soil or
water then another plant
will absorb this
phosphorus.

47. Human Impacts on the Phosphorus Cycle
 Like nitrogen, increased use of fertilizers increases phosphorus runoff into our
waterways
and contributes to eutrophication.
 Humans have greatly influenced the P cycle by mining P, converting it to fertilizer, and
by shipping fertilizer and products around the globe.
 Transporting P in food from farms to cities has made a major change in the global P
cycle.
 Waters are enriched in P from farms run off, and from effluent that is inadequately
treated
before it is discharged to waters.
 Natural eutrophication is a process by which lakes gradually age and become more
productive and may take thousands of years to progress.
 Cultural or anthropogenic eutrophication, however, is water pollution caused by
excessive plant nutrients, which results in excessive growth in algae population