2.1 Energy Flow in Ecosystems
• Biomass is the total mass of all living things in a
given area. (measured in g/m2 or kg/m2)
• Organisms interact with the ecosystem by:
1. Obtaining food from the ecosystem
2. Contributing energy to the ecosystem
Energy Flow in Ecosystems
– Plants are called producers because they make
CO2 + H2O + sunlight C6H12O6 + O2
– Consumers get their energy by feeding on
producers or other consumers.
- Decomposers break-down wastes &
dead organisms, through the process of
Energy Flow & Energy Loss in Ecosystems
• Methods to represent energy moving through ecosystems.
– Food chains: show the flow of energy in an ecosystem.
– Food webs: represent interconnected food chains.
They model the feeding relationships in an ecosystem
– Food pyramids: show the changes in available energy
from one trophic level to another in a food chain.
They’re also called ecological pyramids
• Each step is a trophic level
Terrestrial & aquatic food
– Producers chains
= 1st trophic level
– Primary consumers
= 2nd trophic level
– Secondary consumers
= 3rd trophic level
– Tertiary consumers
= 4th trophic level
• Consumers in a food chain can be classified as:
1. Detrivores (decomposers) - obtain energy & nutrients
from dead organisms & waste matter.
they have their own, separate food chains & they
feed on every trophic level.
Eg. small insects, earthworms, bacteria beetle is a
& fungi detrivore.
2. Herbivores - primary consumers
eat plants (producers) only
Ex. Horse eating hay
3. Carnivores - secondary or tertiary consumers
Secondary consumers eat non-producers (herbivores)
• Eg. Frog eating a grasshopper
Tertiary consumers eat secondary
• also called top predators, top
carnivores or top consumers
• Eg. Lions eating humans
4. Omnivores - consumers that eat both
• plants & animals
• Eg. include humans and bears
• Most organisms are part of
many food chains.
– Arrows in a food web
represent the flow of energy
– Following the arrows leads
to the top carnivore(s).
This food web represents a terrestrial
ecosystem that could be found in
• Energy enters at the first tropic level (producers), where
there is a large amount of biomass & therefore a lot of
• It takes large quantities of organisms in one tropic level to
meet the energy needs of the next trophic level.
• 80% - 90% of energy taken in by consumers is used in
chemical reactions in the body, or is lost as heat energy.
The amount of life an ecosystem can sustain is based on
the bottom level of the ecological pyramid, where
producers capture energy from the sun.
• Lower trophic levels have much larger populations than
• This shows the importance of maintaining large, biodiverse
populations at the lowest levels of the food pyramid.
Take the Section 2.1 Quiz