Cellular Respiration: Energy for Life

Learning Objectives

State the purpose of cellular respiration.

Write the overall chemical equation for aerobic respiration.

Identify the reactants and products of the reaction.

Explain the role of the mitochondria as the 'powerhouse' of the cell.

Distinguish between aerobic and anaerobic respiration.

Powering the Cell

All living things need a constant supply of energy to carry out life processes, from moving and growing to thinking and repairing. This energy comes from the food we eat. But how does a cell turn a molecule of sugar into usable energy? The answer is cellular respiration.

Cellular respiration is the process that releases energy from glucose (a sugar) in the presence of oxygen. It's the reason we need to breathe and eat.

The Equation for Respiration

Cellular respiration is the opposite of photosynthesis. It's a chemical reaction that breaks down glucose to release energy. The overall equation is:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (Energy)

Let's break that down:

Reactants (Ingredients):

C₆H₁₂O₆: One molecule of Glucose. This is the sugar from the food we eat.

6O₂: Six molecules of Oxygen. This is the gas we breathe in.

Products (What's Made):

6CO₂: Six molecules of Carbon Dioxide. This is the gas we breathe out.

6H₂O: Six molecules of Water.

ATP (Adenosine Triphosphate): This is the most important product! ATP is the main energy-carrying molecule used by cells. It's like the rechargeable battery that powers all the work inside the cell. The process of respiration produces about 36-38 ATP molecules from one molecule of glucose.

The 'Powerhouse': The Mitochondrion

In eukaryotic cells (like ours), cellular respiration takes place in a special organelle called the mitochondrion (plural: mitochondria). This is why the mitochondrion is nicknamed the 'powerhouse of the cell'. It's the site where food energy is converted into ATP, the usable energy currency of the cell.

Aerobic vs. Anaerobic Respiration

The process described above is aerobic respiration because it requires oxygen ('aerobic' means 'with air'). This is the most efficient way to get energy from glucose.

But what happens if there's no oxygen available? Cells can still get a small amount of energy through anaerobic respiration. This process, also called fermentation, breaks down glucose without using oxygen.

It happens entirely in the cytoplasm of the cell.

It produces much less ATP (only 2 molecules per glucose).

In human muscle cells, anaerobic respiration produces lactic acid. This is what can cause your muscles to feel sore during intense exercise when you can't get oxygen to them fast enough.

In yeast, anaerobic respiration produces alcohol and carbon dioxide. This is the process used to make bread rise and to brew beer.

Key Terms

**Cellular Respiration: The process by which cells break down glucose and other food molecules in the presence of oxygen to release energy in the form of ATP.
**ATP (Adenosine Triphosphate): The main energy-carrying molecule used to power all cellular activities.
**Mitochondrion: An organelle found in large numbers in most eukaryotic cells, in which the processes of respiration and energy production occur. Often called the 'powerhouse of the cell'.
**Aerobic: A process that requires the presence of oxygen.
**Anaerobic: A process that does not require oxygen.
**Fermentation: An anaerobic process in which energy can be released from glucose even though oxygen is not available.