Ecosystems and the
Biosphere
Energy Transfer
 All organisms need energy to carry out essential
functions – growth, movement, maintenance, repair,
and reproduction
 In ecosystems, energy flows from sun to autotrophs to
organisms that eat autotrophs to organisms that feed
on other organisms.
 Amount of energy ecosystem receives and the amount.
transferred from organism to organism have an effect
on the ecosystem’s structure.
Energy Flow
 Whenever one organism eats another, molecules are
metabolized and energy is transferred.
 Energy flows through an ecosystem from producer to
consumer
Trophic level
 Trophic level indicates the organism’s level of
nourishment, or position in the sequence of energy
transfer illustration
 First level – all producers
 Second level – herbivores
 Third level – predators of herbivores
Food Chain
 single pathway of feeding
relationship that results in
energy transfer to mouse to
snake to hawk
 Feeding relationships in
ecosystems are usually too
complex to be represented by a
single food chain.
 Many consumers eat more than
one type of food and many
organisms may feed on the
same organisms.
Food Web
 Models of complex feeding
networks within ecosystems;
series of food chains
interwoven
Energy Pyramid
 distribution of energy and
matter in an ecosystem
 Shows the distribution of
energy in a food chain
 Energy flows upwards from
producers to consumers
 Energy is lost as head
between each tier of the
pyramid; average of 10% of
energy is passed from one
level to the next level
Other Pyramids
 Biomass pyramid shows
the total mass or organisms
at each tropic level
 Less biomass at higher
tropic levels than lower
levels
 Pyramid of numbers shows
the actual number of
organisms present in each
trophic level
Water Cycle
 Crucial to life - ells are 70-90%
water
 90% of water evaporates from
terrestrial ecosystems passes
through plants in a process
called transpiration – plants
take in water through roots
and release water and take in
CO2 through the stomata in
their leaves
 In pic to right note:
evaporation, condensation
precipitation, transpiration
Carbon Cycle
 Photosynthesis and cellular
respiration form the basis of
carbon cycle
 In photosynthesis, plants
use carbon dioxide, water,
and solar energy to make
carbohydrates and produce
oxygen
 Both autrotrophs and
heterotrophs use oxygen to
break down carbohydrates
during cellular respiration
Nitrogen Cycle
The most important thing about the nitrogen cycle is that
bacteria are involved

All organisms need nitrogen to make
proteins and nucleic acids.

Nitrogen gas makes up about 78% of the
atmosphere.

Bacteria break down the corpses and
wastes of organisms and release the
nitrogen they contain as ammonia –
ammonification.

Bacteria in the soil takes the ammonia
and oxides it into nitrites – nitrification.

Nitrogen is returned to the atmosphere
through denitrification.

Plants can absorb nitrates from the soil,
but animals cannot. Animals get nitrogen
by eating plants and other organisms and
then digesting the proteins and nucleic
acids.