AP Biology Chapter 55


The sum of all the organisms living in a given area and the abiotic factors with which they interact (varying sizes of areas)

Energy flow in ecosystems

Enters as sunlight, goes to autotrophs, dispersed among heterotrophs

Chemical cycling in ecosystems

Chemical elements cycled among biotic and abiotic parts of the ecosystem (Photosynthesis, Chemosynthesis)

How to study ecosystem processes

Alter environmental factors such as temperature or nutrients

What do cells do to energy and matter

Transform according to the law of thermodynamics

First law of thermodynamics

Energy cannot be created or destroyed but only transferred or transformed

Second law of thermodynamics

Every exchange of energy increases the entropy of the universe (Energy conversions are often inefficient)

Law of Conservation of Mass

Matter cannot be created or destroyed, only transformed

Primary producer

Trophic level that supports all others (Autotroph)

Primary consumer

Herbivore that eats the primary producers (Heterotroph)

Secondary consumer

Carnivores that eat herbivores

Tertiary consumer

Carnivores that eat other carnivores


Get nutrients from nonliving organic material (dead organisms, fallen leaves)


Nonliving organic material

Two important detrivore groups

Prokaryotes and Fungi

How do detrivores digest organic material?

Secrete enzymes and absorb

Primary production of an ecosystem

The amount o flight energy converted to chemical energy by autotrophs in the form of organic compounds

What limits the possible photosynthetic output of ecosystems

The amount of solar radiation that ultimately reaches Earth's surface

Gross Primary Production (GPP)

Total primary production in an ecosystem-- the amount of energy from light converted the chemical energy or organic molecules per unit time

Net Primary Production (NPP)

Gross primary production minus the energy used by the primary producers for their "autotrophic respiration" (Usually half of GPP on average)
(Expressed as energy per unit area per unit time)

Standing crop

The total biomass of photosynthetic autotrophs present

Net Ecosystem Production (NEP)

Measure of the total biomass accumulation during a given period of time

How to measure NEP?

Measure the net flow of CO2 or O2 entering or leaving the ecosystem

What controls primary production in aquatic ecosystems?

Light and nutrients

Limiting nutrient

The element that must be added for production to increase (Usually Nitrogen or Phosphorous--sometimes iron)


In aquatic ecosystems, Detrivores decompose dead primary producers and deplete the water of much or all of its oxygen and cause the loss of many fish species

What controls primary production in terrestrial ecosystems?

Temperature and Moisture


The total amount of water transpired by plants and evaporated from a landscape-- increases with temperature

What limits primary production in terrestrial ecosystems?

Soil nutrients (Nitrogen and Phosphorous)
Soil pH

What adaptations have plants made to help better take in nutrients

Nitrogen-fixing bacteria form a symbiosis with plant roots
Mychorrizhal phosphorous-supplying association between fungi and plants
Release enzymes to attract nutrients

Secondary Production

The amount of chemical energy in consumers' food that is converted to their own new biomass during a given period

Energy production efficiency

Percentage of energy stored in assimilated food that is not used for respiration

Net secondary production

The energy stored in biomass represented by growth and reproduction

Assimilation of primary production

Consists of total energy taken in used for growth, reproduction, and respiration (not including losses in feces)

Trophic efficiency

Percentage of production transferred from one trophic level to the next (generally only about 10% and range from 5-20%
(90% of the energy in one trophic level is typically not transferred to the next)

Pyramid of Net production

Demonstrates the loss of energy with each transfer in a food chain, trophic levels are arranged in tiers where the width of each trophic level is proportional to the net production in Joules

Biomass pyramid

Represents ecological consequences of low trophic efficiencies, each tier represents the standing crop (total dry mass of all oragnisms) in one trophic level

Turnover time

Measures a species standing crop in the duration of time it grows, reproduces, and dies
Standing crop/Production

Carbon cycle

CO2 -> Photosythesis -> Cellular respiration

Nitrogen cycle

N2 -> N fixation -> Organisms -> Denitrification

Biogeochemical cycles

Cycles that involve both biotic and abiotic components (Nutrient cycles)

What are the two general categories of biogeochemical cycles

Global and Local

The water cycle (lol)

Evaporation, Condensation, Precipitation

Phosphorous cycle

Weathering of rocks adds phosphorous to soil, some leaches into groundwater and surface water and may eventually reach the sea, producers take in phosphates, consumers eat producers, phosphate is returned to soil or water (Phosphorous never goes into the

How have ecologists worked out the details of chemical cycling?

Isotope usage
-- follow nonradioactive naturally occurring isotopes
--adding tiny amounts of traceable radioactive isotopes (C14)

What factors control the rate of decomposition

The same factors that limit primary production: temperature, moisture, nutrient availability

Hubbard Brook Deforestation Study

Showed that the amount of nutrients leaving an intact forest ecosystem is controlled mainly by the plants

Ecosystem damages

Farming, Mining, Salts from irrigation, Oil spills

What do restoration ecologists work to do?

Identify and manipulate the processes that most limit recovery of ecosystems from disturbances


Using organisms- usually prokaryotes, fungi, or plants, to detoxify polluted ecosystems

Biological Augmentation

Uses organisms to add essential materials to a degraded ecosystem

How much of visible light is converted to chemical energy by photosynthetic organisms?

Only 1%

Is net primary productivity higher in the summer or fall?

Fall because there is a need for less respiration because less photosynthesis is occurring