1. 4.2 Energy Flow

2. Understanding: Most ecosystems rely on a supply of energy from sunlight.
Usually, initial source of energy = sunlight
Autotrophs convert light energy  chemical energy (photosynthesis)
Plants
Eukaryotic algae
Blue-green bacteria
Heterotrophs use C compounds in food (plants, other heterotrophs) as source of energy
Consumers
Saprotrophs
Detritivores
Which ecosystems do NOT rely on sunlight for their initial
energy?
Deep sea vents

3. Understanding: Light energy is converted to chemical energy in C compounds by photosynthesis

4. Energy from cell respiration is lost as HEAT!

5. How plants use all that food they produce:

6. Understanding: Chemical energy in C compounds flows through food chains by means of feeding.
Food chain = linear sequence of organisms showing trophic levels and energy flow
Each organism eats the previous one
2-5 organisms per food chain
Producers always organism #1. Consumers are all the rest.
Last organism = top of the food chain!
Consumers obtain energy from C compounds in organisms they eat
What do the arrows in a food chain indicate?
Direction of energy flow

7. Understanding: Energy released by respiration is used in living organisms and converted to heat.
Energy supplied by ATP
Energy used for:
Making polymers (DNA, RNA, protein, triglycerides, starch, glycogen)
Membrane proteins for passive or active transport
Cell membranes, vesicles, membrane-bound organelles
Protein that makes up muscle fibers (actin & myosin)
All living cells produce ATP by cell respiration (plants, animals, fungi, bacteria, protists)
Cell respiration transfers chemical energy in C compounds chemical energy in ATP
Energy transformations are never 100% efficient – much is lost as HEAT!
DBQ p 216

8. Understanding: Living organisms cannot convert heat to other forms of energy.
Energy conversions organisms can do:
Light  chemical
(photosynthesis)
Chem  kinetic
(muscle contraction)
Chem  electrical
(nerve impulses)
Chem  heat
(adipose insulation)
Energy conversions organisms cannot do:
Heat  any form of energy
(Heat is still useful for organisms in that it maintains body temp, but it cannot be converted to another form of energy and eventually escapes the body and enters atmosphere.)

9. Understanding: Heat is lost from ecosystems.
Organisms create heat as waste product of cell respiration.
Birds and mammals increase rate of heat generation to maintain body temp (homeostasis).
Then heat is transferred from warm body to cooler environment until lost from ecosystem entirely.

10. Nature of Science: Use theories to explain natural phenomena: the concept of energy flow explains the limited length of food chains.
Food chains limited to 4 or 5 trophic levels.
Explanation using scientific theories?
Energy flows through food chains.
Energy is lost at each trophic level.

11. Understanding: Energy losses between trophic levels restrict the length of food chains & the biomass of higher trophic levels.
Biomass = total mass of a group of organisms
Biomass has chemical energy!
Biomass (energy) can be measured (per m2/yr) in an ecosystem
Same trend always found: energy added to biomass by each successive trophic level is less
Reason for trend: energy loss between trophic levels
Lost as heat during cell respiration
Not all of organism is entirely consumed (bones, hair, feathers, parts of plants)
Not all of food eaten is digested, absorbed and assimilated (egested thru feces)

12. Energy Pyramids
Transfer of energy between trophic levels is usually ~10 – 20%
The amount of energy remaining after 4 or 5 trophic levels is not enough to support another trophic level

13. Energy Pyramid

14. Pyramid of Biomass

15. Skill: Quantitative representations of energy flow using pyramids of energy.
Units = kJ/m2/yr or written as kJ m-2 yr-1
Should not be triangle - length of bars should be proportional to each other
DBQ p219