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1/30/2014
1
BI 101 Food webs and Ecosystems
Learning objectives
• Name the inputs and outputs of photosynthesis, and how this relates to respiration.
• Understand the importance of light wavelengths in photosynthesis.
• Describe the flow of energy through the ecosystem, and understand how this affects the biomass of tropic levels
• Understand the cycling of nutrients such as carbon and water
• Recognize how impacts to the nutrient cycles affect the whole community
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Biosphere
Ecosystem
Community
Population
Organism
What is an ecosystem?
√
√
Levels of study in Ecology
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• A set of universal laws governing all energy changes in the universe
• The First Law of Thermodynamics
– Total amount of energy in the universe remains constant
– Energy cannot be created nor destroyed
• However, it can change forms
– During each conversion, some energy is lost into the environment as heat energy
The Laws of Thermodynamics
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5
• The Second Law of Thermodynamics
– Disorder in closed systems is continuously increasing
• Entropy is a
measure of
the disorder
of a system
• Simply put, the
Second Law
states:
“entropy increases”
Figure 5.3 Entropy in action
Disorder happens "spontaneously"
Organization requires energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(both): © Keith Eng, 2008
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Overview of photosynthesis
Cross-section of leaf
Cuticle
Epidermis
Mesophyll
Vascular
bundle
Bundle
sheath
Stoma
Vacuole Nucleus
Cell wall Chloroplasts
Inner membrane
Outer membrane
Granum
Stroma
Chloroplast
Thylakoid Mesophyll cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Right): © Roger Brooks/Beateworks/Corbis RF
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Plant Anatomy: Vegetative Organs
Leaves:
Roots:
Stem:
Form = Function
Photosynthesis
Gas exchange
Light absorption
Anchorage
Storage
Transport
Absorption
Support
Transport
Storage
leaf blade
leaf vein
stem
Leaf Vein
(one vascular
bundle) cuticle
Upper
Epidermis
Lower
Epidermis
Palisade
Mesophyll
Spongy
Mesophyll
50m
xylem
phloem
cuticle-coated cell
of lower epidermis
one stoma (opening
across epidermia)
Oxygen and water vapor diffuse out of leaf at stomata.
Carbon dioxide in outside air enters leaf at stomata.
Water, dissolved mineral ions from roots and stems move into leaf vein (blue arrow)
Photosynthetic
products (pink
arrow) enter
vein, will be
transported
throughout
plant body
Fig. 29-14, p.501
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Making Energy - Photosynthesis
• Chloroplasts contain the pigment chlorophyll.
• Chlorophyll a & b
Photosynthesis: The Components What are the inputs?
What are the outputs?
? ?
?
? ?
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Photosynthesis: The Components
6CO2 + 6H2O + Light energy C6H12O6 + 6O2
What are the inputs?
- light
- water
- carbon dioxide
What are the outputs?
- glucose
- oxygen
Light is a wave of energy: colors are different wavelengths
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Photosynthesis: Input - Light
Intensity
The color you see
Energy (wavelength)
absorbed
Photosynthesis: Light Absorption
Plants are green because…
• Reflect green light.
• Absorb red, blue
and purple light.
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Photosynthesis: Light Absorption
Plant pigments absorb light….
Absorb red, blue
and purple light Reflect green light
Autumnal Changes in Leaf Color
Chloroplasts of mature leaves contain several groups of pigments:
Chlorophylls - Green Carotenoids - Yellows In fall, chlorophylls break down first and other colors are revealed!
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Discussion Question
What would happen if a leaf lacked carotenoids?
a. The leaf would absorb all energy levels
b. The leaf would turn yellow/orange during the fall
c. The leaf would not absorb Carbon dioxide
d. Photosynthesis would not be as efficient
e. The leaf would require oxygen
Photosynthesis: The Components
6CO2 + 6H2O + Light energy C6H12O6 + 6O2
What are the inputs?
- light
- water
- carbon dioxide
What are the outputs?
- glucose
- oxygen
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Guard Cells
Vascular plants: have stomata
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Discussion Question
What would happen to the rate of photosynthesis if the light levels remained the same and the carbon dioxide levels were increased.
a. Rate of photosynthesis would increase
b. Rate of photosynthesis would decrease
c. Rate of photosynthesis would remain the same
d. There is no relationship among the two
Plants and Respiration
• Photosynthesis:
6 CO2 + 6 H2O + Light Energy C6H12O6 + 6 O2
• Respiration:
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy
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Food webs
Primary producers—the autotrophs
• Auto = self + trophy = nourishment
• Organisms take nourishment directly from the environment
http://www.njscuba.net/biology/eco_water.html
Phytoplankton—ocean Terrestrial plants
http://www.100mag.com/know002.html
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Consumers—heterotrophs
• Hetero = other + trophy = nourishment
Food webs
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Detrital food web
Discussion Question
Which trophic level is incorrectly matched with its function?
a. Primary producer – autotrophic organisms
b. Primary consumer – consumes producers
c. Secondary consumer – consumes primary consumers
d. Primary producer – consumes plants
e. All of the above are correctly matched.
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29
Trophic levels within an ecosystem
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Detrivores (also known as scavengers) are special consumers that eat dead organisms
Decomposers are organism that break down organic substances, making them available to other organisms
bacteria and fungi are the principal decomposers in land ecosystems
Sun
Fungi Bacteria
Decomposers
Trophic level 1
Producer
Trophic level 2
Trophic level 3
Carnivore
Secondary consumer
Top carnivore
Trophic level 4
Tertiary consumer
Herbivore
Primary consumer
Discussion Question: The world is green
“Three hundred trout are needed to support one man for a year. The trout, in turn, must
consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons
of grass. “ -- G. Tyler Miller, Jr., American Chemist (1971)
Q: Why do we observe less predator biomass and more prey and plant biomass?
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Energy pathways in ecosystems
• All ecosystems need energy so its living members can grow and reproduce
• Source of energy = the sun
• One-way path
• Flows through various organisms, and eventually dissipates into the environment as heat
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
17% Growth
33% Cellular respiration
50% Feces
Much of the energy captured by plants is lost as energy passes through the ecosystem
How heterotrophs use (and lose) food energy
Energy Flows Through Ecosystems
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The 10% rule • About 10% of the energy is retained from one food level to
the next.
• Acquiring and digesting food takes up energy!
• Not all of the prey/plant/host can be eaten and/or digested
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Discussion Questions:
• What does it mean to ‘eat low on the food chain?’
• In terms of the energy pyramid, why do some people think it is important for us to do so?
Food Supply – Energy Pyramid Energy is used much more efficiently if humans eat plants (first tropic
level) instead of meat (second tropic level). A given area of farmland can support more people if the crops are fed directly to people rather than to
livestock that people then eat. For example if a man needs 3,000 Calories per day, then 30,000 Cal beef are needed, which in turn need 300,000 Cal of corn. This works out to be 1.5 acres of corn per day per person. If the person ate corn directly then
10 people could be supported by the same 1.5 acres of corn.
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Biogeochemical Cycles
• In contrast to the one-way flow of energy, materials (such as water, carbon and nitrogen) cycle through ecosystems.
– Water cycle
– Carbon cycle
– Nitrogen cycle
– Phosphorus cycle
Water cycle
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Burning or clear-cutting forests breaks the water cycle
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Grandma Johnson Problem
Grandma Johnson had very sentimental feelings toward Johnson Canyon, Utah, where she and her late husband had honeymooned long ago. Her feelings toward this spot were such that upon her death she requested to be buried under a creosote bush overlooking the canyon. Trace the path of a carbon atom from Grandma Johnson’s remains to where it could become part of a coyote. Your path must contain at least one plant in it. (NOTE: the coyote will not dig up Grandma Johnson and consume any of her remains).