SEMESTER 2 2012/13 BIOLOGY PRESENTATION BY: HUI SAAN LIM
Slide 3
The NitrogenCycleThe NitrogenCycle
Slide 4
Nitrogen Nitrogen is important to all life. There is an
abundant supply of nitrogen in the earth's atmosphere, nearly 79%
of the air is nitrogen. Nitrogen belongs to the 7 th element in the
periodic table. It is found in plants and animals. Nitrogen is
essential for the formation of amino acids in proteins.
Slide 5
How do plants and animals obtain nitrogen? Nitrogen is so
unreactive, it cannot be used directly by plants to make protein.
Most of the plants and animals cannot get the nitrogen they need
directly from the air, it must first be fixed to a usable form. We
depend on a special kind of bacteria that can absorb N 2 gas and
use it, which involves the conversion of nitrogen gas to
nitrates.
Slide 6
Nitrogen fixation Nitrogen can be fixed in three ways:
Atmospheric fixation This occurs spontaneously due to lightning;
only a small amount is fixed this way. Industrial fixation The
Haber process is used to make nitrogen fertilizers. Biological
fixation Nitrogen-fixing bacteria fix 60% of nitrogen gas.
Slide 7
Atmospheric fixation The enormous energy from lightning breaks
the nitrogen molecules and enables their atoms to combine with
oxygen in the air, forming nitrates. Precipitation carries nitrates
to the ground, where they can be assimilated by plants.
Slide 8
Industrial fixation (Habers process) Ammonia is produced in
industry : Under a high pressure of 200 atmospheres (atm) Extremely
high temperature of 600C The use of an iron catalyst Atmospheric
nitrogen and hydrogen can be combined to form ammonia (NH 3 ).
Slide 9
How the Haber Process works
Slide 10
Biological fixation About 60% of nitrogen fixation is done by
bacteria. There are two types of nitrogen fixing bacteria : Free
living bacteria Fix significant levels of nitrogen without the
direct interaction with other organisms Symbiotic bacteria
Aztobacter
Slide 11
Symbiotic Bacteria The plant provides sugars that are used by
nitrogen-fixing microorganism. The microbe provides nitrogen to the
host plant. Mutualism Rhizobium inhabit the roots of leguminous
plants, forming lumps or nodules where the nitrogen fixation takes
place. Rhizobium uses enzyme nitrogenase to convert N 2 to NH 4 +
using H + and ATP
Slide 12
Assimilation Uptake of nitrogen by plants The nitrates (NO 3 -
) and ammonia (NH 3 ) resulting from nitrogen fixation are used to
produce amino acids. Animals then ingest these algae and plants,
converting them into body organic compounds (eg. Protein)
Slide 13
Ammonification The initial form of nitrogen is organic. Soil
fungi and bacteria, convert the organic nitrogen back into ammonium
(NH 4 + ). Ammonification classically occurs in the soil, in an
aerobic environment. Once ammonification has been accomplished, the
next stage, nitrification, can occur.
Slide 14
Nitrification Most plants cannot utilize ammonium effectively,
and they require nitrate as their essential source of nitrogen
nutrition. Nitrification is a process conducted by a specialized
group of bacteria. Oxidation of ammonium compounds to nitrites and
then to nitrates by the nitrifying bacteria.
Slide 15
Nitrification.. Nitrification is a two stage process and each
stage is performed by a different group of bacteria. Oxidation of
ammonium to nitrite is a function carried out by ammonium oxidizing
bacteria. Nitrosococcus nitrosus, Nitrosospira briensis,
Nitrosovibrio and Nitrococcus
Slide 16
Nitrification Once nitrite is formed, it is rapidly oxidized
further to nitrate, by nitrite- oxidizing bacteria. Nitrospira
gracilis, Nirosococcus mobilis etc, and several fungi(e.g.
Penicillium, Aspergillus) The nitrates can then be taken in by
plants.
Slide 17
Nitrification Process
Slide 18
Denitrification Nitrates are reduced to nitrites and then to
nitrogen gas, completing the nitrogen cycle and replenishing the
atmosphere. Denitrifying bacteria: Thiobacillus denitrificans,
Micrococcus denitrificans, Pseudomonas aeruginosa, etc. Conditions
are anaerobic. Bacteria get the oxygen they need for respiration
from the breakdown of nitrates. Denitrification can be a harmful
process as fixed nitrogen is removed from the soil, making it less
fertile.
Slide 19
Slide 20
Nitrogen Cycle Overview
Slide 21
Slide 22
Video https://www.classzone.com/books/ml_science_share/
vis_sim/em05_pg20_nitrogen/em05_pg20_nitrogen.s wf
https://www.classzone.com/books/ml_science_share/
vis_sim/em05_pg20_nitrogen/em05_pg20_nitrogen.s wf
Slide 23
Questions 1. The relationship between Rhizobium and Legumes is
A. Competitive B. Parasitic C. Predator/ Prey D. Mutualistic
Slide 24
2. The industrial process by which ammonia is made from
nitrogen gas is called A. The Ammonia process B. The Haber process
C. Electrolysis
Slide 25
3. The conversion of nitrogen gas to nitrates by bacteria is
called A. Nitrification B. Nitrogen fixation C. Decay D.
Denitrification E. Excretion
Slide 26
Figure 4 shows the stages in biological nitrification. 8 (c)
(i) Give two ways in which ammonium ions can be produced.
1...................... 2............................ (2
marks)
