Energy – The
Importance
of Light
REVIEW
Producers are the most important part of a
food chain because without them the next
trophic levels would have nothing to eat
Since producers synthesize their own food
using light from the sun, sunlight is the
initial energy source for almost all
communities
Energy Flow
• Energy is transferred from one organism to the next
when carbs, lipids, and proteins are digested
• Consumers use the energy they obtain for cellular
respiration and the byproduct of heat is lost to the
environment
Energy Flow
• No organisms can utilize 100% of the energy from
the food they eat, instead they use 10-20% and they
lose about 80-90%
Why is the energy flow so inefficient?
• Not all parts of organism is eaten as a food source
• Not all food swallowed can be digested and
absorbed
• Some organisms die before being eaten
• Byproduct of cell respiration is heat loss
– The more you move the more food required
– Birds and mammals need to eat more to maintain body
temperature
Pyramids of Energy
• Pyramid of energy – a graphical representation of
the amount of energy that flows from one trophic
level to the next in a community
• Pyramids of energy must always take this shape
because energy is transferred inefficiently
The units used are
kilojoules per square
meter per year
kJ m-2 yr-1
Energy & Nutrients
• Sunlight fuels food chains and heat energy is lost
through food chains via cellular
respiration….therefore, energy enters as light and
exits as heat but as long as the sun shines,
ecosystems can use up and lose energy this way
• BUT…Nutrients (organic molecules) on Earth must
be recycled!
How is this possible?
How are Nutrients Recycled?
• An effective way of “unlocking” organic molecules
that have been stored away in organisms cells is
DECAY
• Decomposers break down dead organisms:
– Saprotrophs (bacteria and fungi) recycle nutrients by
breaking down organic molecules
– Decomposers play a major role in soil formation