Chapter 2Cell Processes and Energy

Section 2Respiration

Storing and Releasing Energy

• Our cells store and release energy similar to how a bank account stores our money until we make a withdrawal.

• We get the energy we need from the food we eat and when our bodies need energy we break down the food to release energy.

Respiration

• After you eat, your body converts carbs into glucose. The process of withdrawing energy from glucose is called respiration.

• During respiration, cells break down simple food molecules such as glucose and release the energy they contain.

Respiration

• The term respiration is also used to describe our breathing process.

• Due to this similarity, we often refer to the withdrawal of energy from glucose as cellular respiration.

• The other form of respiration brings oxygen into our bodies, which most cells need in order to perform cellular respiration.

The Respiration Equation

Does this formula look familiar? Where have we seen something that looks a lot like this?

It is the exact opposite of photosynthesis!

The Two Stages of Respiration• Stage #1– Glucose molecules are broken down in the cell’s

cytoplasm.– No oxygen required– Only a little bit of energy is released

• Stage #2– Tiny glucose molecules from stage #1 are broken down

even smaller in the mitochondria– Oxygen is required– A great amount of energy is released (HINT: this is why the

mitochondria are the “powerhouses” of the cell)– You also produce a little bit of CO2 and H2O, which you

release when you breathe out.

Respiration

Photosynthesis vs. Respiration

Fermentation

• Some organisms obtain energy from food without using oxygen.

• These organisms obtain their energy through fermentation, an energy-releasing process that does not require oxygen.

• The amount of energy from each sugar molecule is much lower than in respiration.

Alcoholic Fermentation

• When fermentation occurs in yeast and other single-celled organisms, alcohol is one of the products made when these organisms break down sugar, along with CO2 and energy.

• Bakers and brewers use the CO2 produced by yeast to make bread rise and put bubbles in drinks.

Lactic-Acid Fermentation

• This type occurs in your body.• When the cells in your muscles use up the

oxygen faster than you can replace it, fermentation occurs.

• One product of this fermentation is lactic acid, which feels like a painful burning sensation in your muscles when it builds up, leaving you weak and sore.