Principles of Ecology:
Matter, Energy, and Life
Chapter 2
1

Outline:
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Food Webs
Ecological Pyramids
Biogeochemical Cycles
2

Sunlight
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Solar energy that reaches the earth’s surface is in, or near, the visible light wavelengths.

Drive photosynthesis.
More than half of the incoming sunlight may be reflected or absorbed by atmospheric clouds, dust, or gases.

Short wavelengths are filtered out by gases in the upper atmosphere.
3

Photosynthesis and Respiration
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Photosynthesis
6H
2
O + 6CO
2
+ sun  C
6
H
12
O
6
(sugar) + 6O
2
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Cellular Respiration
C
6
H
12
O
6
+6O
2
 6H
2
O + 6CO
2
+ energy
4

Energy Exchange
5

Energy and Matter in the Environment
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Species - All organisms genetically similar enough to breed and produce live, fertile offspring in nature.
Population - All members of a species that live in the same area at the same time.
Biological Community - All populations living and interacting in an area.
Ecosystem - A biological community and its physical environment ( water, mineral resources,air, sunlight etc.)
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Much of ecology is concerned with understanding the ways energy and matter move through an ecosystem
In an ecosystem, there is interaction between the biotic and abiotic factors.
The study of an ecosystem involves how energy flows from one sytem to another.
An open ecosystem is a system in which animals can move from one area to another without a boundary (energy also moves)
A closed ecosytem does not allow cross over ( energy does not move)
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Food Chains, Food webs & Trophic Levels
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Photosynthesis provides all the energy for all ecosytems.
One of the major property of an ecosystem is productivity ( amount of biomass) in a given area in a given time.
Photosynthesis is called as the primary productivity in an ecosystem.
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Food Webs and Trophic Levels
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Productivity refers to the amount of biomass produced in a given or during a given time.

Primary Producers – organisms who photosynthesize e.g plants
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Consumers – organisms who do not photosynthesize, they get their energy by eating other organisms.
Food Webs are series of interconnected food chains in an ecosystem.Some consumers feed on single sps., others have multiple food sources (Fig 2.13).
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Ecological Food Chain
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Trophic Levels
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An organism’s feeding position in an ecosytem is called as trophic level.
Organisms can also be identified by the kinds of food they consume:

Herbivores – cows eat plants.

Carnivores – lion eat animals.
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Omnivores - man eat plants and animals.

Detritivores – ants & beetles eat detritus ( litters)

Decomposers - bacteria and fungi breakdown complex organic matter into simpler compounds.
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Note position of each organism in this food chain:
A corn plant ( primary producer) is eaten by a grasshopper ( primary consumer)
Chicken (secondary consumer )eats the grasshopper
Man ( tertiary consumer ) (top carnivore)eats the chicken
Fungi and bacteria ( decomposers) feed on dead decaying matter.
Energy is transferred from corn plants to man and when man dies, body decays and the decomposers break down complex compounds to simpler ones releasing the energy…food chain
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Trophic Levels
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Ecological Pyramids
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Most ecosystems have huge number of primary producers supporting a smaller number of herbivores, supporting a smaller number of secondary consumers.
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Second law of thermodynamics ( a certain amount of energy is lost / dissipated)
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Ecosystems are not 100% efficient.
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E.g A prairie dog when eating grasses does not digest all the plant parts efficiently. Moreover energy is also lost when he is running …moreso when a carnivore eats him…he does not eat the flesh completely..energy is lost in the ecosystem.
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Ecological Pyramids
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BIOGEOCHEMICAL CYCLES
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Hydrological Cycle

Most of earth’s water is stored in the oceans, but solar energy continually evaporates this water, and winds distribute water vapor around the globe.

Water that condenses over land surfaces, in the form of rain, snow or fog supports all terrestrial ecosystem.
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Living organisms emit the moisture to the atmosphere through respiration and perspiration.
Eventually this moisture re- enters the atmosphere or enters lakes and streams and ultimately to the oceans.
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Hydrologic Cycle
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Carbon Cycle
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Carbon serves a dual purpose for organisms:

Carbon is a structural component of organic molecules (C
6
H
12
O
6, sugar)

Chemical bonds provide metabolic energy.

The carbon cycle begins with photosyntheric organisms that take up
(CO
2, carbon dioxide) to form starch.

Starch is taken up by several organisms, digested in stomach and simple sugars get broken down to simpler ones (CO
2 energy).
, H
2
0 &
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Carbon cycle ( Contd.)
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Sugar molecules either undergo respiration and releases carbon in the form of C0
2.
Simple sugar can also form large organic molecules such as cellular structrure of the cells.
When the body decay carbon returns to nature.
Dead decaying woods return their carbon after bacteria and fungi feed on them.
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Fossil fuel (e.g coal and oil) , their carbon atoms are not retuned to soil until they are burnt.
Calcium carbonate (CaCO
3
) building structure for many coral reefs also contribute to the carbon cycle.
Limestones deposit in nature are biologically formed from CaC0
3.
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Carbon Cycle
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The Nitrogen cycle
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Several organic molecules contain nitrogen
Amino acids, peptides and proteins are large organic molecules that living organisms need for their existence.
Nitrogen is a very important nutrient for living things.
Nitrogen is a primary component of many household ( Ammonia and other detergents) and agriculture fertilizers.
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Nitrogen Cycle ( Cont.)
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Nitrogen makes up about 78% of the air, but plants cannot use N
2 molecule in air.
, the stable diatomic

Plants acquire nitrogen through nitrogen cycle.
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Nitrogen-fixing bacteria( live in roots of legumes) and blue-green algae) are highly organised to fix nitrogen of the atmosphere to Ammonia ( N
2 to NH
3
)

They combine hydrogen of atmosphere with Nitrogen and form Ammonia( NH
3
)
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The nitrogen cycle( Contd.)
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Other forms of bacteria combine atmospheric oxygen ( O
2
) with Ammonia and form nitrites( NO
2
).
Other forms of bacteria convert nitrites to nitrates (NO
3
),which green plants can absorb and use.
After plants cells absorb nitrates, these nitrates are reduced to Ammonia (NH
3
).
Ammonia in plants are used to make amino acids which is used as building blocks to form protein( a polypetptide chain made up of several amino acids)
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Nitogen cycle (cont.)
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Nitrogen enters the environment in many ways:
Plants and animals die.
Fungi and bacteria decay dead organisms, releasing the ammonia which is converted back to nitrates .
Animals produce urine which is contain nitrogenous compounds .
Denitrifying bacteria breaks down nitrate s to nitrogen ( N
2
) and nitrous oxide ( N
2
O), gases released to atmosphre.
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Nitrogen Cycle
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Phosphorus Cycle
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Abundant phosphorus stimulates plant and algal productivity.

Major component of water pollution.
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Reduced levels of dissolved oxygen.
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Phosphorus Cycle
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Sulphur Cycle
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Sulphur is an essential component of proteins for living organisms.
Sulphur compounds determine the acidity of rainfall, surface water and soil.
Sulphur is tied up in soil as mineral rocks.
Weathering or emission from deep seafloor vent or volcanic eruption releases sulphur.
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Sulfur Cycle
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Sulfur compounds are important determinants of the acidity of water.

Particulates may also act as critical regulators of global climate.
Sulfur cycle is complicated by a large number of possible oxidation states.
Sulphur is oxidised to sulphur dioxide, sulphate or hydrogen sulphide.
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Sulhur cycle Contd.
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Human activities also releases a large quantity of sulphur, primarily through burning fossil fuels
Sulphur dioxide and sulphate causes human health problems.
When ocean water warms up, tiny organisms produces dimethylsulphide(DMS) which oxidises sulphur dioxide and then sulphate to the atmosphere.
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Sulfur Cycle
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Summary:
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Food Webs
Ecological Pyramids
Biogeochemical Cycles
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