This document outlines nutrient cycles, including the carbon, nitrogen, and water cycles, highlighting the processes of nutrient recycling essential for living organisms. It details how nutrients like carbon and nitrogen are transformed and used by plants and animals, alongside the different stages of each cycle, such as decomposition, nitrification, and evaporation. Additionally, it explores the impact of human activities like deforestation and fossil fuel burning on these cycles and discusses the importance of various forms of nitrogen fixation.

1. Nutrient Cycles
UNIT FIVE, LESSON 5.6
BY MARGIELENE D. JUDAN

2. LESSON OUTLINE
Recycling Nutrients
Carbon Cycle (Oxygen to Carbon Dioxide Cycle)
Nitrogen Cycle
Water Cycle

3. Nutrients are important components of
living organisms. These nutrients take
various forms:
Water (H2O), oxygen (O2), carbon
dioxide (CO2), nitrogen (N2),
phosphorus (P)

4. But in order for them to be used again,
they need to be recycled.
In order to be recycled, organisms must
return these nutrients to the Earth (soil).

5. Recycling Nutrients
1. Decomposition
2. Excretion
3. Perspiration and Evapotranspiration
4. Respiration

6. 1. Decomposition
As organisms die,
decomposers return
their nutrients to the
soil to be recycled.

7. 2. Excretion
H2O and N2 are returned
to the soil through urine.
P is returned to the earth
in the form of feces.

8. 3. Perspiration and
Evapotranspiration
When animals perspire, their
sweat evaporates and
becomes vapor.
Plants release water through
evapotranspiration
(evaporation in plants)
Vapor goes to the atmosphere
(not to the soil)

9. 4. Respiration
Animals respire by
taking O2 from the
environment and
release CO2.
(O2 → CO2)
Plants respire by
taking CO2 to release
O2. (CO2 → O2)

10. CARBON CYCLE (O2 to CO2 Cycle)
The element carbon is the present in all living
organisms.

11. 1. Carbon enters the atmosphere as carbon dioxide from
respiration and combustion.

12. 2. Carbon dioxide is absorbed by producers to
make carbohydrates in photosynthesis.

13. 3. Animals feed on the plant passing the carbon compounds along the food
chain. Most of the carbon they consume is exhaled as carbon dioxide
formed during respiration. The animals and plants eventually die.

14. 4. The dead organisms are eaten by decomposers and the carbon in their
bodies is returned to the atmosphere as carbon dioxide. In some
conditions decomposition is blocked. The plant and animal material may
then be available as fossil fuel in the future for combustion.

18. 1. Carbon enters the
atmosphere as carbon
dioxide from respiration and
combustion.
CO2

19. CO2
2. Carbon dioxide is
absorbed by producers to
make food and oxygen via
photosynthesis. Oxygen is
inhaled.
O2
Via photosynthesis

20. 3. Animals feed on
the plant, passing the
carbon compounds
along the food chain.

21. 4. Most of the carbon they
consume is exhaled
as carbon dioxide
formed during respiration.
CO2

22. 5. The animals and
plants eventually die.

23. 6. The dead organisms are
eaten by decomposers and
the carbon in their bodies is
returned to the atmosphere
as carbon dioxide.
CO2

24. 7. The cycle repeats. In some
conditions decomposition
is blocked. The plant and
animal material may then be
available as fossil fuel in the
future for combustion.
CO2

25. Another activity that contributes to the release
of CO2 is deforestation. When trees are cut,
the CO2 stored in them are released into the
atmosphere.
Burning of fossil fuels and deforestation
are two human activities that have increased
the carbon dioxide content of the atmosphere
in the past hundred years.

26. This results in rise of atmospheric
pressure.
The greater the pressure, the greater
the temperature.
Thus, a phenomenon called global
warming.

27. NITROGEN CYCLE
Abundant in air (78% of the volume of Earth’s
atmosphere).
Because N2 is unreactive, it cannot be used
directly by plants to make protein. Only
nitrates are useful to plants, so we are
dependent on other processes to convert
nitrogen to nitrates in the soil.

28. NITROGEN CYCLE
These processes are:
1. action of nitrogen-fixing bacteria
2. action lightning

29. NITROGEN CYCLE TERMS
Nitrogen fixation – process by which free nitrogen
(N) in air is converted to other chemical forms
usable to plants
Nitrification – process of converting ammonia to
nitrite, then nitrite to nitrate
Denitrification – process of converting nitrate to
nitrogen gas

31. 1. Nitrogen gas is converted to nitrate compounds by nitrogen-fixing
bacteria in soil or root nodules. Lightning also converts nitrogen gas
to nitrate compounds. The Haber process converts nitrogen gas into
ammonia used in fertilizers. Ammonia is converted to nitrates
by nitrifying bacteria in the soil.

32. NITROGEN CYCLE
Some nitrogen-fixing bacteria
live free in soil and water. The
most important is a bacterium
called rhizobium, which
inhabits the root nodules of
leguminous plants – a group
of soybeans, peanuts, and
peas. This is a form of
mutualism.

33. NITROGEN CYCLE
The nitrogen then becomes ammonia (NH3). But
still, NH3 is still unusable to most plants, so it still
needs to be converted.
Nitrifying bacteria do this in a process called
nitrification (process of converting ammonia to
nitrite, then nitrite to nitrate).
Nitrogen > ammonia > nitrite > nitrate

34. 2. Plants absorb nitrates from the soil and use these to build
up proteins. The plant may be eaten by an animal, and its
biomass used to produce animal protein.

35. 3. Urea and egested material is broken down by decomposers.
This results in nitrogen being returned to the soil as ammonia.

36. 4. Decomposers also break down the bodies of dead organisms
resulting in nitrogen being returned to the soil as ammonia.

37. 5. Higher only: In some conditions denitrifying bacteria in the soil
break down nitrates and return nitrogen to the air. This is usually
in waterlogged soil. Improving drainage reduces this effect, making
the soil more fertile.

38. NITROGEN CYCLE
The ammonia (NH3) is converted back to nitrogen
by denitrifiers or denitrifying bacteria in a process
called denitrification (process of converting nitrate
to nitrogen gas). Lightning and other forms of
combustion also play a vital role in nitrogen fixation
to form nitrates. The cycle repeats.
Ammonia/nitrite/nitrate > nitrogen

39. NITROGEN CYCLE
Nitrogen > Ammonia > Nitrite > Nitrate >
Ammonia/Nitrite/Nitrate > Nitrogen
Nitrogen fixation Nitrification
(usable form)
(released back into the soil
when an organism dies)
Denitrification
Decomposition

40. THE WATER CYCLE
Constitutes 60-96% of
the weight of living
things.
Differs from the other cycle
because here, water remains
unchanged unlike in other
cycles (ex. In carbon cycle,
carbon takes the form of CO2)

41. Water Cycle Steps
1. Evaporation – liquid to gas
2. Condensation – gas to liquid
3. Precipitation – water falls back to the ground either
as rain, snow, or hail
These three are the main processes of the water cycle

42. Water Cycle Steps
4. Surface Runoff – much of the water that return to
Earth as precipitation runs off the surface of the land,
and flows down hill into streams, rivers, ponds, and
lakes. Small streams flow into larger streams, then
into rivers, and eventually the water flows into the
ocean.
Surface runoff is an important part of the water cycle
because, through surface runoff, much of the water returns
again to the oceans, where a great deal of evaporation
occurs

43. Water Cycle Steps
5. Infiltration – process where rain water soaks into the
ground, through the soil and underlying rock layers,
Some of this water ultimately returns to the surface at
springs or in low spots downhill. Some of the water
remains underground and is called groundwater. As
the water infiltrates through the soil and rock layers,
many of the impurities in the water are filtered out.
This filtering process helps clean the water.

44. Water Cycle Steps
6. Transpiration – process where plants remove water
through its stomata in the leaves. This is the process
of evaporation in plants (also called
evapotranspiration).

45. THE WATER CYCLE
The next slide is a
picture summary of the
water cycle. Try to trace
the processes
mentioned.

47. Quiz tomorrow (20 items = 25 pts)
Carbon Cycle, Nitrogen Cycle, and Water Cycle; pp. 165-167
Memorize especially the forms of nutrients, ways of recycling
nutrients, and the 4 main steps of the Carbon Cycle.
In the nitrogen cycle, understand esp. the different conversion
processes (nitrogen fixation, nitrification, denitrification)
Memorize esp. the 6 steps in the water cycle.

48. Sources:
Science Links 7
http://www.bbc.co.uk/schools/gcsebitesize/science/add_gatew
ay_pre_2011/greenworld/recyclingrev1.shtml
http://www.mbgnet.net/fresh/cycle/concepts.htm