1. 4.2 Energy Flow
Understanding:
Most ecosystems rely on a supply of energy from sunlight
Light energy is converted to chemical energy in carbon compounds by photosynthesis
Chemical energy in carbon compounds flows through food chains by means of feeding
Energy released by respiration is used in living organisms and converted to heat
Living organisms cannot convert heat to other forms of energy
Heat is lost from ecosystems
Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels
Skills:
- Quantitative representations of energy flow using pyramids of energy
Nature of science:
Use theories to explain natural phenomena: the concept of energy flow explains the limited length of food chains.

2. Tertiary consumer, Producer, Secondary consumer, Primary consumer, Herbivore, Carnivore, Predator, Prey
Trophic levels?

3. Most food chains start with green plants.
They provide the source of energy for every organism above them in the food chain.
So where do they get their energy from?
Understanding:
Most ecosystems rely on a supply of energy from sunlight

4. Radiation from the Sun (light energy)
Used for photosynthesis, to make new biomass.
Biomass is the dry mass of living material in an animal or plant.
Understanding:
Most ecosystems rely on a supply of energy from sunlight

5. Who uses the sun? Autotrophs Producers for food webs
Heterotrophs are indirectly dependent on the sun
Understanding:
Most ecosystems rely on a supply of energy from sunlight

6. Energy Conversions Plants create carbon compounds from light.
Light energy converted to chemical energy in photosynthesis
Heterotrophs consume the chemical energy from the plants – creates a flow of energy through food chains
Understanding:
Light energy is converted to chemical energy in carbon compounds by photosynthesis
Chemical energy in carbon compounds flows through food chains by means of feeding

7. Energy Flow Cells produce ATP from respiration
Not all chemical energy from food chain used in respiration to create ATP
Chemical energy is converted to other types of energy
Understanding:
Energy released by respiration is used in living organisms and converted to heat

8. Main Energy Conversions
Organisms can perform energy conversions:
Light energy to chemical energy in photosynthesis
Chemical energy to kinetic energy in muscle contraction
Chemical energy to electrical energy in nerve cells
Chemical energy to heat energy in adipose tissues
Where is energy lost along the way?
Understanding:
Energy released by respiration is used in living organisms and converted to heat

9. The amount of available energy decreases from one stage to the next.
Energy Loss
Energy is transferred along food chains from one stage to the next.
Not all can be absorbed by organisms at the next one.
The amount of available energy decreases from one stage to the next.
MOST: Energy lost from heat production in respiration
Not all parts of the organism consumed
Faeces/waste
Most food chains are short. There are rarely more than four stages, because 80-90% of energy is lost at each stage so cannot be passed on to the next trophic level.
Understanding:
Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels

11. Energy Loss
Able to measure how much energy is added per year to a trophic level by measuring biomass
Compare different trophic levels in food chains
See how much energy is lost at each level
Understanding:
Living organisms cannot convert heat to other forms of energy
Nature of science:
Use theories to explain natural phenomena: the concept of energy flow explains the limited length of food chains.

12. Pyramids Numbers Energy
What is it?
Example diagram with explanation
What is it?
Example diagram with explanation

13. Shows the number of individuals at each trophic level
Numbers
Shows the number of individuals at each trophic level
Horizontal bars arranged around a central axis

14. Numbers
Can look like a pyramid

15. Numbers
Sometimes it doesn’t

16. Pyramids of Energy
Represent amount of energy converted to new biomass by each trophic level in a community.
Skills:
- Quantitative representations of energy flow using pyramids of energy

17. Pyramids of Energy Bar chart with a bar for each trophic level.
Amount of energy per unit area per year.
Units: Kilojoules per metre squared per year (KJm-2yr-1)
Length of each bar proportional to amount of energy it shows
Skills:
- Quantitative representations of energy flow using pyramids of energy

19. Pyramids of Energy
Construct the following pyramid of energy on graph paper:
Make sure it is to scale and write you scale on!
Producers: 10,000 KJm-2yr-1
First consumers: 1000 KJm-2yr-1
Second consumers: 100 KJm-2yr-1
Third consumers: 10 KJm-2yr-1
If you finish – make up some numbers and give to a partner to make the pyramid
Skills:
- Quantitative representations of energy flow using pyramids of energy

20. Exam Questions: 3 Marks
Explain the shape of the pyramids of energy that are constructed by ecologists to represent energy flow in an ecosystem.

21. Exam Questions: 3 Marks
Explain the shape of the pyramids of energy that are constructed by ecologists to represent energy flow in an ecosystem.
energy flows up from one trophic level to the next (in a community);
energy is lost at each stage by waste products/feces/not all the organism is consumed;
most energy is lost through respiration/heat;
each level on the pyramid is about 10%–20% of the size of the one below it / 80%– 90% energy lost between levels;
labelled diagram of pyramid of energy (indicating trophic levels);