2. Aim: to explore the carbon and nitrogen cycles
Objectives
 Describe how energy flows in an ecosystem
 Illustrate the carbon and nitrogen cycles
 Explain how human activity is affecting carbon
emissions

4. Trophic Levels
 Energy moves from one organisms to another
when it is eaten
 Each step in this transfer of energy is known as a
trophic level
 The main trophic levels are producers and consumers

5. Food Chains
 The energy flow from one trophic level to the other
is know as a food chain
 A simple food chain shows how energy is
transferred from the sun through living organisms.
 It involves one organism at each trophic level
 Producers (e.g. plants)
 Primary Consumers
 Secondary Consumers
 Tertiary Consumers

6. Food Chain

7. Food Web
 Most animals eat more than JUST one organism
 So in any ecosystem food chains connect to form a
food web
 Food webs are more complex and involve lots of
organisms

8. Food web
Identify trophic levels

9. Ecological Pyramid
 At each trophic level energy is used and waste material
produced
 So there is less energy available for transfer at each
stage and a food pyramid is formed

11. Carbon cycle

13. Atmospheric
Carbon Dioxide

14. Atmospheric
Carbon Dioxide
Plants use carbon
dioxide to make their
food (photosynthesis)

15. Atmospheric
Carbon Dioxide
Plants use carbon
dioxide to make their
food (photosynthesis)
Green plants are
eaten by animals

16. Atmospheric
Carbon Dioxide
respiration
Plants use carbon
dioxide to make their
food (photosynthesis)
Green plants are
eaten by animals

17. Atmospheric
Carbon Dioxide
respiration
Plants use carbon
dioxide to make their
food (photosynthesis)
green plants are
eaten by animals
dead remains of plants and
animals

18. Atmospheric
Carbon Dioxide
respiration
Plants use carbon
dioxide to make their
food (photosynthesis
green plants are
eaten by animals
dead remains of plants
and animals
decay by fungi
and bacteria

19. Plants use carbon
 Carbon is pulled from the atmosphere by plants and used
for the process of photosynthesis
 used to make organic molecules (carbohydrate, proteins
and fats)
• The carbon becomes part of the plant (stored food).

20. Animals eat plants
 When organisms eat plants, they digest the organic
compounds and use these products for their own
purposes.
 All leaving organisms carry out respiration breaking
down food substances to release energy. This also
produces carbon dioxide which returns to the
atmosphere.

21.  When plants and animals die, most of their bodies are
decomposed by fungi and bacteria. They break down
organic compounds via respiration to carbon dioxide
and carbon atoms are returned to the atmosphere.
 Some are not decomposed fully and end up in deposits
underground (oil, coal, etc.). Humans burn these fuels
releasing carbon dioxide into the atmosphere.

22. Carbon Cycle Diagram
Carbon in Atmosphere
Decomposers
break down dead Plants use carbon
things, releasing to make food
carbon to
atmosphere and Plants and
soil animals die
Fossil fuels are
Animals eat
burned; carbon
plants and take
is returned to Bodies not in carbon
atmosphere decomposed —
Carbon slowly after many
released from these years, become part
substances returns of oil or coal
to atmosphere deposits

23. Carbon in Oceans
 Additional carbon is stored in the ocean.
 Many animals pull carbon from water to use in
shells, etc.
 Animals die and carbon substances are
deposited at the bottom of the ocean.
 Oceans contain earth’s largest store of carbon.

24. Human Impact
 Fossil fuels release carbon stores very slowly
 Burning anything releases more carbon into
atmosphere — especially fossil fuels
 Increased carbon dioxide in atmosphere increases
global warming
 Fewer plants mean less CO2 removed from
atmosphere

26. Greenhouse Gases
The greenhouse effect is
causing the Earth to warm up.
This is causing climate
change and melting of
the polar ice caps, this
It is due to increasing could lead to flooding.
amounts of greenhouse
gases, such as carbon Burning fuels is a
dioxide, water vapour and major cause of this
methane. increase.
Video

27. Nitrogen cycle

29. Nitrogen (N2) in atmosphere
Amino acids
Assimilation and proteins in
plants and animals Nitrogen
by plants
fixation
Denitrifying
bacteria Detritus
Nitrogen-fixing
bacteria in root
Nitrates nodules of legumes
(NO3–)
Detritivores
Nitrogen-fixing
Decomposition bacteria in soil
Nitrogen
fixation
Ammonium (NH4+)

30. The largest single source of nitrogen is in the atmosphere.
Nitrogen (N2) makes up 79% of
our air!
But living organisms cannot use
this form directly

31. There are 4 phases in the cycle:
 Nitrogen fixation = NH3/NH4+
 Decay = decomposing organic nitrogen into NH4+
 Nitrification = converting NH4+ to NO2 to NO3
 Denitrification = converting NO3 into N2
Micro-organisms play an important part in this cycle!

32. Nitrogen Fixation
• The enormous energy of lightning breaks nitrogen molecules
apart and enables the nitrogen atoms to combine with
oxygen forming nitrogen oxides (N2O)
• Nitrogen oxides dissolve in rain, forming nitrates (NO3)
• Nitrates (NO3) are carried to the ground with the rain.
N
N O
(N2O)
(NO3)

33. Lightning “fixes” Nitrogen!
N
N O
Nitrogen combines
with Oxygen
Nitrogen oxides forms
(N2O)
Nitrogen oxides
dissolve in rain and
(NO3) change to nitrates
Plants use nitrates to
grow!

34. Industrial Fixation NN
H
Under great pressure, at a N
H3
temperature of 600
Industrial Plant combines
ºC, and with the use of a nitrogen and hydrogen
catalyst, atmospheric
nitrogen (N2) and
hydrogen are combined Ammonia is formed
to form ammonia (NH3). (NH3)
Ammonia can be used as
a fertiliser.
Ammonia is used as a fertilizer in soil

35. Biological Fixation
 Some bacteria, including Rhizobium, live in the soil or
within root nodules of legumes (peas, beans and clover)
 These bacteria are anaerobic and use enzymes to convert
nitrogen gas (N2) to ammonium ions (NH4+)
 The plants supply the bacteria with energy and nutrients
in return of nitrogen fixation (mutualism)

36. Symbiotic Relationship Legume plants
Bacteria
Bacteria live in the roots of
N
legume family plants and
provide the plants with
ammonium (NH4) in exchange
NH3
for the plant’s carbon and a
protected home.
N
Roots with nodules
where bacteria live
Nitrogen changes into
ammonium

37. Decay
 Animals acquire their amino acids when they eat plants.
 When animals and plants die their remains are used as
food by micro-organisms such as bacteria and fungi.
 Decomposers convert the nitrogen back into ammonia
(NH3)
Decomposers convert organic nitrogen
to ammonia (NH3) Ammonia (NH3) is used by
some plants
Ammonia (NH3) is
stored in soil.

38. Nitrification
• Living in the soil are nitrifying bacteria.
• First, Nitrosomonas bacteria combine ammonia with oxygen to
form nitrites.
• Then another group of nitrifying bacteria, Nitrobacter, convert
nitrites to nitrates which green plants can absorb and use!
Nitrifying bacteria in soil combine
ammonia with oxygen
Ammonia changes to nitrites
Nitrifying bacteria in soil convert
Nitrates nitrites to nitrates
Ammonia Nitrites
(NH3) (NO2) (NO3)
Plants absorb nitrates and
grow!

39. ATMOSPHERE
N2
Amino
acids
N2 Nitrogen-fixing
bacteria
NH4+
Soil NH4+ NO3–
(ammonium) (nitrate)
Nitrifying
bacteria
Ammonifying
bacteria
Organic
material Root
Figure 32.13

40. Denitrification
 Denitrification converts nitrates (NO3) in the soil to
atmospheric nitrogen (N2) which is returned to the air.
 Denitrifying bacteria live deep in soil and in aquatic
sediments where conditions make it difficult for them to
get oxygen
Denitrifying bacteria live (NO3) (N2)
deep in soil and use
nitrates as an alternative Nitrogen in
to oxygen making a atmosphere closes the
byproduct of nitrogen gas. nitrogen cycle!

42. Acid Rain
Human activity have doubled
the amount of fixed nitrogen
entering the nitrogen cycle in
just 100 years Manufacture and use of
nitrogen
fertilisers, combustion of
Climate change, acid fossil fuels and forest
rain, the acidification of burning
soils and loss of soil
nutrients, and the
acidification of streams
and lakes. Kills fish, damages trees and
buildings.
Video