1. Energy & Living Systems
Agricultural Biology

2. Almost all energy in living systems comes from the sun
Plants, algae, and certain bacteria absorb sunlight
Photosynthesis:
The process of converting light energy (from the sun) to chemical energy (sugar)

3. Autotrophs vs. Heterotrophs
Organisms that use energy from sunlight
Most are photosynthetic
Heterotrophs:
Organisms that get their energy from food (rather than directly from sunlight)
Humans and other animals
Get energy from cellular respiration

4. Discussion
With the person sitting next to you, come up with 3 examples of autotrophs and 3 examples of heterotrophs. Following this, discuss why you think it is important that heterotrophs and autotrophs exist together in environments.

5. Cellular Respiration A metabolic process similar to burning fuel
This process releases much of the energy in food to make ATP
ATP: the main energy source of cells

6. How do we get energy from eating food?
1) Food is eaten.
2) Digestion begins.
3) Chemical energy is released gradually by enzyme-assisted reactions.
4) Some energy is released as heat.
5) The remaining energy is stored in ATP molecules.
6) ATP delivers energy within the cell (to power chemical reactions).

7. Energy Flow in an Ecosystem