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