CYCLES OF THE
ENVIRONMENT
4 CYCLES THAT MAINTAIN
HOMEOSTASIS IN THE ENVIRONMENT
Our Environment’s
Homeostasis
 Atoms of carbon, hydrogen, nitrogen,
oxygen and phosphorous make up living
organisms (CHNOPS)
 This matter AND energy recycles
through ecosystems.
Matter & Energy Transfer
through Environment
Food Chain
Food Web
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…
Food Chain & Energy
Pyramid
Food Chain
Energy Pyramid
Quaternary-4th
Tertiary-3rd
Secondary-2nd
Primary-1st
Producer
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.
Energy Loss at Trophic Levels
 90% of Energy is used
by the organism for:
 Breathing /Respiraton
 Reproduction
 Homeostasis
 Movement/Interaction
with other orgs.
4 Cycles of an
Environment

1.
2.
3.
4.
They include:
Water Cycle
Carbon Cycle
Nitrogen Cycle
Phosphorous Cycle
Water Cycle
3 states of Matter
1. liquid (water or
precipitation),
2. solid (ice, snow)
3. Gas (atmosphere)
WATER CYCLE
Water Cycle Flow
1. Water begins cycle through ecosystem
when plants absorb water through
roots.
2. Animals drink water or get it indirectly
w/food they consume.
3. Animals and plants respire giving off
water vapor (Transpiration).
Water cycle (continued)
4. Organisms lose water through
excretion.
5. Water (liquid, solid or gas) recycles into
lakes, streams, rivers, oceans via the
groundwater.
Carbon cycle
1. Carbon found in environment as a gas
(CO2) in atmosphere and oceans.
2. CO2 moves to water and plants.
3. 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.
CARBON CYCLE
4. Org. obtain carbon when they consume
producers or other consumers.
5. Respiration and decay return carbon to
the atmosphere (gas).
6. Carbon also returns to atmosphere in
large amounts as CO2 when fossil fuels
are burned.
Carbon Cycle
Nitrogen Cycle - Land
1. N2 makes up 78%
of air.
2. Living things cannot
use Nitrogen in
atmospheric form.
Nitrogen moves through
the food web.
Nitrogen cycles as
matter and energy
transfer through the
food web.
Nitrogen Fixation Methods
Conversion of atmospheric N2 into reactive
compounds such as:
1.
2.
3.
4.
5.
6.
Biological Fixation
Abiotic Fixation
Denitrification
Assimilation
Nitrification
Ammonification
Nitrogen Forms
=
BADANA
Nitrogen Compounds





N2 – Nitrogen
NO2 – nitrogen oxide or nitrite
NO3-Nitrous oxide or nitrate
NH3 – Ammonia
NH4 - Ammonium
Nitrogen Cycles
1. Abiotic Fixation
a. 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).
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.
2. Biological Fixation
a. 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.
Soybeans and Chickpeas
Chick Peas
Soy Beans
2. Biological Fixation
(cont)
c. 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.
2. Biological Fixation
(Cont)
d. 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.
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
Soybeans
72.7
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
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)
2. Biological Fixation
(cont)
d. To promote sustainable soil fertility, it is
beneficial to use these legume crops
w/other plants such as corn.
e. Corn depletes the available N2 in soil
quickly.
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.
Nitrifying Bacteria
3. Nitrification
 NH3 is oxidized to nitrite ions (NO2¯) and
then to nitrate ions (NO3¯).
 Bacteria, Nitrosomas. oxidizes NH3 to
NO2.
 (NH3 + 1.5 O2 + Nitrosomonas → NO2+ H2O + H)
 NO2- + 0.5 O2 + Nitrobacter → NO3-
3. Nitrification
 Bacteria, Nitrobacter, oxidizes NH3 to
NO3.
 NH3 + O2 → NO2− + 3H+ + 2e−
 NO2− + H2O → NO3− + 2H+ + 2e−
4. Assimilation-Plants
a. Nitrates (NO3¯) are
commonly
assimilated (taken
in/absorbed) by
plants through their
root hairs.
4. AssimilationHeterotrophs
b. Heterotrophic
organisms cannot
readily absorb N2 as
plants do, so N2 is
acquired through
foods they/we eat.
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
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.
5. Ammonification
6. Denitrification
a. Nitrates (NO3¯) are
reduced to N2 and
are lost / returned to
the atmosphere.
b. 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.
Phosphorous cycle
Phosphorous Cycle
2 ways: Short-term and Long Term
A. Short-term
1. Plants use P from soil in body tissues.
2. Animals get phosphorous fr eating
plants.
3. When animals die, they return the
P to the environment.
Phosphorous Cycle
 Long Term Phosphorous Cycle
1. Phosphates washed into the oceans b/c
part of rock compounds.
2. After millions of years, rock layers wash
off and P b/c part of the environment.