Chapter 47
Ecosystems: A Summary
AP Biology
Spring 2011

Ecosystem is the sum of the organisms
residing there and the environment
Nature of Ecosystems
Primary producer: plant that serves as
an autotroph by harnessing sun’s energy
 Consumer: animal or heterotroph that
derives energy from consuming plants or
other animals

Nature of Ecosystems
Detrivore: animal that consumes debris
and small bits of organic matter
 Decomposer: eats wastes and remains
of plants and animals

Nature of Ecosystems
Minerals: increase
and decrease in
natural cycles
 The organisms of an
ecosystem develop
trophic levels

◦ Food chain represents
passage of energy from
one trophic level to the
next
Nature of Ecosystems
Tropic Levels

A food web is a complex interaction
among species of the ecosystem
◦ In a grazing food chain, the energy goes
from producers to consumers
◦ In a detrital food chain, energy goes from
producers to detrivores to decomposers

An alteration in one species of a food web
may affect many different organisms
The Nature of Food Webs
Food Web

Primary production: rate at which
plants harness the sun’s energy
◦ Depends on availability of water and nutrients
◦ Is higher on land than water
Energy Flow Through Ecosystem

Biomass pyramid: used as a tool to
represent dry weight of the organisms at
each trophic level
◦ Plants or producers make up the base of the
pyramid
◦ Consumers make up the upper portion of the
pyramid with the largest carnivores at the very
top
Energy Flow
Through Ecosystem

Energy pyramid: shoes how energy is
lost when transferred to each trophic level
◦ Energy transfer in watery ecosystems is usually
more efficient than those on land
Energy Flow Through Ecosystem

The effects of dangerous chemicals can
become intensified as they move up the
food chain
◦ An insecticide called DDT resulted in the
deaths of birds and other animals
 Book “Silent Spring” by Rachel Carson, brought
this problem to public’s attention
◦ Mercury from various industries enters the
water supply and becomes intensified in fish
Biological Megnification

Biogeochemical Cycles: nutrients move
through environmental stores and living
organisms
◦ Elements enter living portion of cycle by
becoming incorporated into plants
◦ Ex. Water, carbon, nitrogen, phosphorous
cycles
Biogeochemical Cycles

Water cycle: begins when water
evaporates from bodies of water and
transpiration occurs in plants
◦ Water condenses in clouds and rains down
◦ Water collects in watersheds, aquifers and in
groundwater

Future water supply may be ocean
through utilization of a desalinization
process to remove salts
Water Cycle
Water Cycle

Carbon cycle: most contained in earth’s
crust
◦ Carbon in ocean is originally formed from shells
of small organisms
◦ Crust lifts up eventually and becomes part of
land mass
Carbon Cycle
Diffusion takes place between carbon in
atmosphere and that in ocean
 There is a loop-like current which delivers
carbon dioxide to ocean reservoir
 Carbon changes from between carbon
dioxide and bicarbonate

Carbon Cycle

Man adversely affects carbon cycle by
releasing more carbon into air
contributing to global warming
Carbon Cycle
Main gases that contribute to greenhouse
effect are: carbon dioxide, water,
nitrous oxide, methane, and
chlorofluorocarbons
 Suns heat is absorbed by earth’s surface
 Some of heat is reflected back into
atmosphere, but atmospheric gases send
some heat back to earth

Greenhouse Gases and Climate
Change

Greenhouse effect: heat builds up in
lower atmosphere, the air temperature
near Earth’s surface rises
◦ Natural necessary phenomenon to maintain
reasonable temperatures on earth
◦ Increase in greenhouse gases is creating
abnormal global warming
◦ Global warming is causing warmer ocean
temperature which result in melting glaciers
and more severe storms
Greenhouse Gases and Climate
Change

Nitrogen exists in atmosphere as N2 which
is not in a usable form for plants
◦ Some natural processes such as lightening and
volcanoes can convert the nitrogen to a usable
form
Nitrogen Cycle

The bacteria Rhizobium that exists in
nodules on legumes also converts the
nitrogen to a usable form
◦ Nitrogen changes from N2 to NH3 which then
converts to NH4+ and NO3-, which are able to
be used by plants
Nitrogen Cycle

Manmade interference helps to denitrify
the ecosystem
◦ The leaching of water through the soil and the
absence of crop rotation help to deplete the
soil of nitrogen

When fertilizers run off into water
sources, it causes algae blooms which are
disadvantageous to animal species
Nitrogen Cycle
Nitrogen Cycle

Phosphorous cycles between land and
ocean
◦ Phosphates are necessary for major cellular
components like nucleic acids, plasma
membranes and ATP
Phosphorous Cycle
Plants get phosphorous from the water
and soil
 Animals get it from consuming plants or
other animals

◦ Phosphorous levels are quite often a limiting
factor for plant growth
◦ Lock of phosphorous in soil can be due to
absence of crop rotation
Phosphorous Cycle

An excess of phosphorous can result from
water that runs off from fertilized fields
◦ Excessive amounts of phosphorous in watery
environment can cause eutrophication
◦ Algae bloom occurs that harms plant and
animal species
◦ Difficult to reverse
Phosphorous Cycle