18-3 Energy Transfer

EnergyWhy do organisms need energy?

Maintain HOMEOSTASIS, growth, reproduction, etc.

How does energy affect an ecosystem?Determines how many and what

kind of organisms live in an ecosystem.

Energy Flow:• The sun is the ultimate source of

energy• The PRODUCERS use this energy to

make “food” energy for themselves and for the CONSUMERS

Trophic LevelsThe organism’s position in the sequence of energy transfers.

A.K.A. Trophic Level is a group of organisms whose feeding source is the same number of steps from the Sun.

Common Trophic Levels:•First = Producers (Autotrophs)

–LARGEST

•Second = Herbivores (Heterotrophs, Consumers)

•Third and above = All other consumers (Heterotrophs, Omnivores, Carnivores, Decomposers)

–SMALLEST

• Omnivores (Humans)– Eat Plants & Animals

• Detritivores (Scavengers)– Feed On Dead Plant & Animal

Remains (buzzards)• Decomposers

– Fungi & Bacteria

ConsumersHeterotrophs eat other organisms

to obtain energy. (e.g. animals)• Herbivores

– Eat Only Plants• Carnivores

– Eat Only Other Animals

Energy Gain by Trophic Levels:• At each trophic level, the energy stored in an

organism is about 1/10 that of the level below it  (10%).

Implications on the ecosystem: Because energy diminishes at each successive

trophic level, few ecosystems can contain more than 4 or 5 trophic levels.

Organisms at higher levels (large carnivores) tend to be fewer in number than those at lower levels (producers).

Food Chain• A single pathway of feeding (and

energy transfer) relationships among organisms in an ecosystem.

Ex) Food chain

Food Web

• A diagram of the interrelated food chains in an ecosystem.

• More accurate description of the ecosystem.

Can you now answer these questions?

1.Contrast between producers and consumers.

2.Explain the important role of decomposers in an ecosystem.

3.Contrast a food chain with a food web.

4.Explain why an ecosystem usually contains only a few trophic levels.

Energy flows through an ecosystem and nutrients cycle in an ecosystem. Ecosystem Recycling (18.4)

Water Cycle Steps:  EVAPORATION from

lakes, rivers, and oceans. 

 TRANSPIRATION from plants and trees.

 CONDENSATION – Cloud Formation

PRECIPITATION – Rain, Snow, Sleet, Hail.

 RUN OFF, or RETURNED back into the Cycle.

GROUNDWATER- water in soil or in underground formations of porous rock.

The Water Cycle

The Carbon Cycle

Cellular Respiration

Photosynthesis

Combustion

Death and decomposition

Human Influences Atmospheric CO2 has risen more than

30% in the past 150 years. Burning of fossil fuels- coal, oil,

and natural gas Burning down the tropical rain

forest

The Nitrogen Cycle

Nitrogen Fixation: the process of converting atmospheric nitrogen (N2) into nitrate, its useable form.

Nitrogen-fixing bacteria: turn nitrogen gas into nitrates. Located in soil and the roots of some plants.

Ammonification: bacteria decompose dead matter and release the nitrogen they contain as ammonia

Denitrification: bacteria break down nitrates and return nitrogen to the atmosphere

Key Terms

So… How do plants and animals get nitrogen?

Phosphorous Cycle obtained by plants from water and soil, and

animals from the food they eat used to form bones, teeth, and molecules such

as DNA and RNA Source: erosion of rocks into the soil or water,

decomposition of organisms, and fertilizers