bi 101 food webs and ecosystems - home | lbcc

1/30/2014

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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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• 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


(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


- 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


- 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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Trophic levels within an ecosystem


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


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).

bi 101 food webs and ecosystems - home | lbcc

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