Energy & Living Systems
Agricultural BiologyMrs. Sperling
• 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)
Autotrophs vs. Heterotrophs
• Autotrophs: 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
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
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).
Energy Flow in an Ecosystem