Download - © 2012 John Wiley & Sons, Inc. All rights reserved. Overview of Chapter 3 Energy & Ecosystems – Photosynthesis and Cellular Respiration Flow of Energy

© 2012 John Wiley & Sons, Inc. All rights reserved.

Overview of Chapter 3

• Energy & Ecosystems– Photosynthesis and Cellular Respiration

• Flow of Energy Through Ecosystems– Producers, Consumers & Decomposers– Ecological Pyramid– Ecosystem Productivity


Energy• The ability or capacity to do work

– Chemical, – Thermal, – Mechanical, – Nuclear, Electrical, and – Radiant/Solar BASIS OF MOST ECOSYSTEMS

• Stored energy = potential energy• Energy of motion = kinetic energy


Energy Rules (laws of thermodynamics)

– Energy cannot be created or destroyed; it can be changed/converted from one form to another

• 1st law of thermodynamics• Producers capture energy of sun• Consumers must eat other living things (or their waste)

– When energy is converted form one form to another, some of it is degraded to heat

• Second Law of Thermodynamics• Energy is lost as it passes from one trophic level to next


Trophic level• Based on main source of nutrition/energy

– Producers (fix energy from sun)– Primary consumers (herbivores)– Secondary consumers (predators or detrivores/decomposers)– Tertiary consumers (predators or detrivores/decomposers)– Quartinary consumers (predators or detrivores/decomposers)


Ecosystem Productivity• Gross Primary Productivity (GPP)

– Total amount of energy plants capture by photosynthesis• Net Primary Productivity (NPP)

– Energy captured by photosynthesis minus energy “spent” during cellular respiration

• GPP (photosyn) – cellular respiration = NPP– Plant growth per unit area per time– Only NPP is available as food to higher trophic levels


Variation in NPP by Ecosystem


Ecosystem Productivity• Aquatic Ecosystems:

• Nutrients--#1• Nitrogen & phosphorus

• Limited by light penetration--#2

• Terrestrial ecosystems• Temperature and water availability -- #1• Nutrients -- #2

• Nitrogen & phosphorus


Energy Flow Through Ecosystems


Food Chains


Food Web


Pyramid of Energy• Amount of energy at each trophic level

– (and how much is transferred to the next level)

Most energy is lost between trophic levels Limits number

of levels


Average 10% efficiency(ranges from 5-20%)


Number of tropic levels is limited by amount of energy available in ecosystem (i.e., productivity)


Pyramid of Biomass• The amount of living material (biomass) at each

level 90% reduction in

biomass between trophic levels Why?


Pyramid of Numbers

• Number of individuals at each trophic level Fewer organisms

occupy each successive level

Does not indicate: biomass of organisms

at each level amount of energy

transferred between levels


Controls on trophic levels

• Bottom up:– Trophic levels are limited by nutrient availability and

biomass of next lower level– Nutrientproducers1 consumers (herbivores) 2 consumers (predators)…

• Top Down (trophic cascade)– Consumption by higher levels limits next lower level– Predation herbivores producers


Bioaccumulation• The buildup of a persistent toxic substance in an

organism’s body, often in fatty tissues – Synthetic chemical do not metabolize well– They remain in the body for extended periods of time

• DDT• Lead• Mercury• PBDE (flame retardants)

• Dioxins• PCB• Phthalates• BPA


Biomagnification• The increased

concentration of toxic chemicals in the tissues of organisms that are at higher levels in food webs

• Diagram (right) is example of biomagnification of DDT

• LD50of 113 mg/kg in rats


Effect of DDT on Bald Eagles

Download - © 2012 John Wiley & Sons, Inc. All rights reserved. Overview of Chapter 3 Energy & Ecosystems – Photosynthesis and Cellular Respiration Flow of Energy

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