1. CYCLES OF THE ENVIRONMENT
4 CYCLES THAT MAINTAIN HOMEOSTASIS IN THE ENVIRONMENT

2. Our Environment’s Homeostasis
Atoms of carbon, hydrogen, nitrogen, oxygen and phosphorous make up living
organisms (CHNOPS)
This matter AND energy recycles through ecosystems.

3. Matter & Energy Transfer through Environment
Food Chain
Food Web

4. Cycling Maintains Homeostasis
Food chains, food webs and energy pyramids → energy gained or used in one direction in ecosystem.
Matter, in form of nutrients, moves through org. at each trophic level.
Trophic Levels include: producer, lst order consumer, 2nd order consumer…

5. Food Chain & Energy Pyramid
Quaternary-4th
Tertiary-3rd
Secondary-2nd
Primary-1st
Producer

6. Energy Flow in an Ecosystem
Each step in a food
chain represents a transfer of energy & materials.
Energy is lost at each level = only 10% is transferred to next trophic level.

7. Energy Loss at Trophic Levels
90% of Energy is used by the organism for:
Breathing /Respiraton
Reproduction
Homeostasis
Movement/Interaction with other orgs.

8. 4 Cycles of an Environment
They include:
Water Cycle
Carbon Cycle
Nitrogen Cycle
Phosphorous Cycle

9. Water Cycle 3 states of Matter
1. liquid (water or precipitation),
2. solid (ice, snow)
3. Gas (atmosphere)

10. WATER CYCLE

11. Water Cycle Flow
Water begins cycle through ecosystem when plants absorb water through roots.
Animals drink water or get it indirectly w/food they consume.
Animals and plants respire giving off water vapor (Transpiration).

12. Water cycle (continued)
Organisms lose water through excretion.
Water (liquid, solid or gas) recycles into lakes, streams, rivers, oceans via the
groundwater.

13. Carbon cycle 1. Carbon found in environment as a gas
(CO2) in atmosphere and oceans.
2. CO2 moves to water and plants.
Photosynthesis is major player in CC.
a. P.S. combines carbon dioxide and water.
b. P.S. changes molecules fr low energy to high energy.

14. CARBON CYCLE
Org. obtain carbon when they consume producers or other consumers.
Respiration and decay return carbon to the atmosphere (gas).
Carbon also returns to atmosphere in large amounts as CO2 when fossil fuels are burned.

15. Carbon Cycle

16. Nitrogen Cycle - Land N2 makes up 78% of air.
Living things cannot use Nitrogen in
atmospheric form.

17. Nitrogen moves through the food web.
Nitrogen cycles as matter and energy transfer through the food web.

18. Nitrogen Fixation Methods
Conversion of atmospheric N2 into reactive compounds such as:
Biological Fixation
Abiotic Fixation
Denitrification
Assimilation
Nitrification
Ammonification
Nitrogen Forms =
BADANA

19. Nitrogen Compounds N2 – Nitrogen NO2 – nitrogen oxide or nitrite
NO3-Nitrous oxide or nitrate
NH3 – Ammonia
NH4 - Ammonium

20. Nitrogen Cycles

21. 1. Abiotic Fixation
High energy fixation w/ lightning & cosmic radiation. Accounts for 10% of nitrate in N2 cycle. Occurs when…
1. N2 combines w/O2 to form nitrogen oxides such as NO and NO2
2. Carried to Earth’s surface in rainfall as
nitric acid (HNO3 or acid rain).

22. Legumes…you say?
A legume is any of the thousands of plant species in the legume family, Leguminosae.
Legumes have seed pods that, when ripe, split along both sides.

23. 2. Biological Fixation Completed by living orgs such as
soil aerobic bacteria (needs O2) and anaerobic bacteria (chemosynthesis w/o O2).
b. Symbiotic bacteria (Rhizobium) found in roots of legumes such as clover, alfalfa, soy beans and chick peas assists in bio fix.

24. Soybeans and Chickpeas

25. 2. Biological Fixation (cont)
How does this happen?
c1. Roots of legumes, bacteria split the nitrogen atoms into two free nitrogen atoms which combine with hydrogen to form ammonia, NH3.
c2. Any excess nitrogen leftover from ammonification (NH3) not used by the plant are returned to the soil.

26. 2. Biological Fixation (Cont)
Some bacteria freely fix nitrogen, without splitting the N2 atom, in soil such as:
1. Aerobic bacteria, Azotobacter
2. Anaerobic bacteria, Clostridium
3. Photosynthetic Cyanobacterium fix
nitrogen in aquatic environments.

27. Major agricultural crops produced in the United States in 2000 (excluding root crops, citrus, vegetable, etc).
Crop
Harvested Area (million acres)
Cash Receipts from Sales ($ billion)
Corn (grain)
72.7
15.1
Soy-beans
12.5
Hay
59.9
3.4
Wheat
53.0
5.5
Cotton
13.1
4.6
Sorghum (grain)
7.7
0.82
Rice
3.0
1.2

28. 2. FYI: Benefits of N2 Fix
Since its introduction into Nigeria in 1908, soybean (Glycine max. (L) Merrill) has been grown primarily as a sole crop (Ogunwolu, 1991) yet it has been shown to be able to fix atmospheric nitrogen up to 417 kg N ha-1
(LaRue and Patterson, 1981)

29. 2. Biological Fixation (cont)
To promote sustainable soil fertility, it is beneficial to use these legume crops w/other plants such as corn.
Corn depletes the available N2 in soil quickly.

30. 3. Nitrification
Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms)…see next 2 slides—caused by Bacteria.

31. Nitrifying Bacteria

32. 3. Nitrification
NH3 is oxidized to nitrite ions (NO2¯) and then to nitrate ions (NO3¯).
Bacteria, Nitrosomas. oxidizes NH3 to NO2.
(NH O2 + Nitrosomonas → NO2- + H2O + H)
NO O2 + Nitrobacter → NO3-

34. 3. Nitrification Bacteria, Nitrobacter, oxidizes NH3 to NO3.
NH3 + O2 → NO2− + 3H+ + 2e−
NO2− + H2O → NO3− + 2H+ + 2e−

35. 4. Assimilation-Plants
Nitrates (NO3¯) are commonly assimilated (taken in/absorbed) by plants through their root hairs.

36. 4. Assimilation-Heterotrophs
b. Heterotrophic organisms cannot readily absorb N2 as plants do, so N2 is acquired through foods they/we eat.

37. 4. Assimilation (cont) c. Plants are base of food chain.
d. N2 is already assimilated into their tissue & will continue to pass from one organism to another.
Food Chain

38. 5. Ammonification
a. Host of decomposing microorganisms such as bacteria & fungi breaks down nitrogenous wastes & organic matter found in animals and dead plants.
b. It is converted to inorganic NH3 for absorption by plants as ammonium ions (NH4).
c. Decomposition rates affect the level of nutrients available to primary producers.

39. 5. Ammonification

41. 6. Denitrification
Nitrates (NO3¯) are reduced to N2 and are lost / returned to the atmosphere.
Facultative anaerobes in anaerobic conditions break down the NO3’s.
c. Ex: Farmers w/waterlogged fields and high-clay content are vulnerable to losing the available nitrogen for their crops.

42. Phosphorous cycle

43. Phosphorous Cycle 2 ways: Short-term and Long Term A. Short-term
Plants use P from soil in body tissues.
Animals get phosphorous fr eating plants.
When animals die, they return the
P to the environment.

44. Phosphorous Cycle Long Term Phosphorous Cycle
Phosphates washed into the oceans b/c part of rock compounds.
After millions of years, rock layers wash off and P b/c part of the environment.