CELLULAR RESPIRATION

Cellular Respiration is the process of using oxygen to break down glucose in order to release energy and form molecules of ATP.

• Takes place in almost all organisms (including plants).
• Cellular respiration takes place in the mitochondria.

C₆H₁₂O₆ + 6O₂ à 6CO₂ + 6H₂O + ATP (energy)

Glucose + oxygen à carbon dioxide + water + energy

The breakdown of glucose is the opposite of photosynthesis.

Steps in the breakdown of glucose with oxygen:

1. Glycolysis
2. Respiration

1. Kreb’s Cycle
2. Electron Transport

1. Glycolysis – Release of a small amount of energy by breaking down glucose into ATP, pyruvic acid ( a 3-Carbon molecule) and NADH

• Glycolysis occurs in the cytoplasm of cells by using enzymes.
• Glycolysis is a fast process, gives quick energy, and uses no O₂.

Summary of Glycolysis:

Reactants: glucose

Products: 2ATP, pyruvic acid, 2 NADH

1. Kreb’s Cycle – Term used for the first set of reactions in respiration. Pyruvic acid is broken down producing carbon dioxide, NADH, ATP and FADH.

• Kreb’s cycle takes place in the mitochondria.
• NADH and FADH are electron carriers.

Steps of Kreb’s Cycle:

1. Pyruvic acid enters the mitochondria
2. Citric acid is formed à carbon dioxide is given off
3. Electrons are released to make NADH
4. Citric acid broken down à carbon dioxide given off
5. More electrons are released to form ATP, FADH₂ and NADH
6. Cycle starts over again with remaining carbon compounds

Summary of Kreb’s Cycle:

Reactants: pyruvic acid

Products: carbon dioxide, NADH, ATP, FADH₂

1. Electron Transport Chain – Second set of reactions in respiration.

• Electrons (in carrier molecules) from the Kreb’s Cycle are used
• Electrons are passed in order to generate large amounts of ATP from ADP
• Electron transport chain occurs in the mitochondria

Steps of Electron Transport Chain:

1. NADH and FADH₂ enter the reaction
2. Electrons are passed (released from NADH and FADH₂)
3. H+ (removed from NADH and FADH₂) move across membrane to outside by way of ATP Synthase. This generates ATP.
4. H and O combine to form water (H₂O) which is given off

Summary of Electron Transport Chain:

Reactants: NADH and FADH₂

Products: ATP and water

Summary of CELLULAR RESPIRATION: The process of releasing energy from glucose.

Reactants in: Oxygen and Glucose

Products out: Carbon Dioxide, Water, and 36 ATP

Cellular respiration is Aerobic (uses oxygen).

Very efficient, consumes oxygen to breakdown glucose.

Most energy is released by cellular respiration.

This process is 38% efficient. What happens to the remaining 62% of energy found in glucose?

What happens if oxygen is not available?

Can we still get energy from the cell?

ANAEROBIC FERMENTATION

Anaerobic fermentation is the breakdown of glucose in the absence of oxygen.

• Not very efficient, does not provide much energy (2 ATP)
• Bacteria, yeast, and some plants and animals use fermentation

2 Types of Fermentation:

1. Lactic Acid Fermentation

• Lactic acid is toxic and kills cells
• Lactic acid build up is the burn you feel when you exercise
• Lactic acid fermentation causes an oxygen debt. In order to get rid of lactic acid and carbon dioxide after exercise, you breathe harder.

1. Alcohol Fermentation

• Carbon dioxide and alcohol are the wastes produced by alcoholic fermentation
• Alcohol fumes give rising bread and cake it’s smell
• Carbon dioxide produces the bubbles in beer
• They make beer in sealed tanks to prevent oxygen from stopping the fermentation process
• Wine and vinegar are also produced this way using bacteria instead of yeast
• Yeast uses up sugar quickly during fermentation in the absence of oxygen

Other fermentation products:

Bread, yogurt, cheese, pickles.