BIOLOGY
Class Notes
9-2
Aim: Energy Transfer
(A) Producers
 Sunlight is the main energy source for life on
Earth
 Some types of organisms use energy that is
stored inorganic compounds
 Autotrophs: organisms that take energy from the
sun and convert it to food—producers
 Producers can either use energy from the sun or
from chemicals
o Photosynthesis: autotrophs use light
energy to power chemical reactions that
convert carbon dioxide and water to
carbohydrates—gives off oxygen
 Land—plants
 Water—algae
(B) Consumers
 Acquire energy from other organisms
 Heterotrophs
o Herbivores—eat only plants
o Carnivores—eat only animals
o Omnivores—eat both
o Decomposers—break down organic matter
(C) Feeding Relationships
 Energy flows through an ecosystem in one
direction from producers to consumers
o Food chains: series of steps in which
energy is transferred from one organism to
another
o Food webs: more complex—links all the
food chains in an ecosystem together
o Each step—trophic level
o Food webs are more complex and more
accurate than food chains
(D) Ecological Pyramids
 Shows the relative amounts of energy or matter
within each trophic level
o Energy: only part of the energy that has
been stored gets passed on to the next
trophic level—most of the energy is used
by the organisms for life processes—only
10% of the energy is passed on
o Biomass: the total amount of living tissue
in a given trophic level—represents the
amount of potential food available for each
trophic levels
The further along the food chain you go, the less food (and hence energy) remains
available.
The above energy pyramid shows many trees & shrubs providing food and energy to giraffes.
Note that as we go up, there are fewer giraffes than trees & shrubs and even fewer lions than
giraffes. In other words, a large mass of living things at the base is required to support a few at
the top.