Chemical Energy & Food

• Food molecules contain chemical energy

• released when chemical bonds are broken

• Calorie = amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius

• 1000 calories = 1 kilocalorie, or Calorie

• Cells use many molecules for food

• Ex. fats, proteins, and carbohydrates

• energy stored in each of molecule varies

• because chemical structures and energy-storing bonds differ

• Break down food molecules gradually

• use energy stored in chemical bonds to produce compounds

such as ATP that power activities of the cell.

Overview of Cellular Respiration

• If oxygen is available

• organisms get energy from food using cellular

respiration.

• In symbols:

6 O2 + C6H12O6 � 6 CO2 + 6 H2O + Energy

• In words:

Oxygen + Glucose � Carbon dioxide + Water + Energy

• Cell must release chemical energy in food

molecules slowly or lose most of it in the form of

heat and light.

Stages of Cellular Respiration

• 3 main stages of cellular respiration:

1. Glycolysis

• produces only a small amount of energy

• Most of glucose’s energy (90%) still locked in chemical bonds of pyruvic acid at end of glycolysis

2. Krebs cycle

• a little more energy is generated from pyruvic acid

3. Electron transport chain

• produces bulk of energy in cellular respiration by using oxygen, a powerful electron acceptor

Oxygen and Energy

• Pathways of cellular

respiration that require

oxygen are called aerobic.

• The Krebs cycle

• Electron transport chain

• Both processes take place

inside the mitochondria.

Oxygen and Energy

• Gylcolysis is an anaerobic process.

• does not:

• directly require oxygen

• rely on an oxygen-requiring process to run

• Still considered part of

cellular respiration.

• Takes place in the cytoplasm

of a cell.