Chapter 2
Cell Processes and Energy
Section 2
Respiration
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.