Cellular Respiration and Photosynthesis:
Flow of energy through our system
Name ______________________________________________ period _________________
You are sitting at your desk, next to the window, reading this page. Sunlight is shining through the
window and falling on your desk. Next to your homework is your afternoon snack, a partially eaten apple.
Is there a connection among you, the sunlight, and the apple? There most certainly is.
It is a connection that lies at the very center of the theme of life—the flow and
transfer of energy through a system.
You eat the apple, getting both the matter and the energy you need to build your body and to stay alive.
The apple tree that produced the fruit represents one group of living organisms, the group called
autotrophs, a word that means, “self feeding.”
Unlike humans, the apple tree does not eat. It makes its own food, taking the substances carbon dioxide
and water and changing them into energy rich compounds such as sugars and starches. Humans are
representatives of the other group, organisms that cannot make their own food. Because organisms such
as ourselves and all other animals must get energy from other organisms, we belong to the group called
heterotrophs, meaning, “other feeding.”
FOOD: MATTER AND ENERGY
The apple is food. It contains energy rich compounds—atoms held together as molecules by chemical
bonds that are rich in stored energy (remember that energy is held in bonds between atoms). How do
organisms use these molecules for energy?
After we eat the apple, our cells are ready to use that stored chemical energy. How does this happen?
We know that the release of energy cannot occur all at once. For example, if you hold a lighted match to a
marshmallow, the carbohydrates in the marshmallow will burst into flames. Energy is being released, and
quickly, too. This quick energy release is not what happens inside our cells. Instead, the release of
energy occurs in a series of controlled small steps. The energy stored in glucose is eventually
converted to a usable form, the energy currency of all cells, ATP. This process is known as cellular
respiration.
Note: DO NOT be confused between cellular respiration (the breakdown of large energy rich
molecules) and respiration (breathing). The two are connected, (as we shall see later) but they are
NOT THE SAME!!
1. Define autotroph:
2. Define heterotroph:
3. Write the chemical equation for glucose:
Go to my homepage (go to Lynnwood High School, click on “Staff”, click on Michaela Peterson). On the
very first page you will find a collection of links you will use to answer the questions below. Please follow
the directions carefully; we will go over much of this tomorrow.
WHAT IS CELLULAR RESPIRATION?
Go to the Khan Academy link. (http://www.khanacademy.org/video/introduction-to-cellularrespiration?playlist=Biology) You will watch only the first 4 minutes and 30 seconds.of this video (you
may watch the rest in the comfort of your own home if you are interested.) Answer the questions below
as you watch.
1. Why does this professor think that cellular respiration is the “single most important biochemical
reaction?” (A biochemical reaction is any chemical reaction done by living organisms).
2. Write the chemical reaction for cellular respiration. Write it in words under the chemical equation.
For example, under “O2” you should write “oxygen”. (He uses the term “moles”, don’t worry about
this, but pay attention to the numbers of molecules in the equation.)
3. What molecule does he say is the “energy currency” of the cell?
4. What are some of the life functions that ATP is used for? (He says it quickly, you might have to go
back or think of your own.)
Do plants need to do these life functions as well?
ATP AS ENERGY “CURRENCY”
All organisms need energy to do life’s work (reproduce, think, move, grow, etc.) However, some
forms of energy are more usable than others. Glucose, as a molecule, contains a great deal of energy in
the bonds. However, it cannot be directly used by a cell. It must be broken down into smaller more
usable units first. One metaphor that is often used is that of a $100 bill. If you walk into a convenience
store to buy gum, but you only have a $100 bill, it is unlikely that the cashier will accept it. However, you
can use a $1 bill very easily. Glucose is similar to the $100 bill. ATP is like a $1 bill. See if you can come
up with another metaphor for ATP, write it in your journal. Extra credit for good ones!
WHERE DOES CELLULAR RESPIRATION TAKE PLACE?
The name of the organelle (cell part) where cellular respiration takes place is called the
_____________________________. Go to the next link
(http://sciences.aum.edu/bi/bi4523/student/cardwell/wheredoes.html). Draw a picture of this
organelle below. Label the parts as shown on the page.
PRACTICE! Write the chemical equation in words and chemical language below (just like you did before).
WHAT KINDS OF CELLS DO CELLULAR RESPIRATION?
In reality, any cell that is alive does cellular respiration. Write down all the kinds of cells you can think of
that are alive (animal? Bacteria? What else?). Now look it up on the Internet, what other kinds of cells do
cellular respiration? (Don’t spend more than 3 minutes on this task.)
CELLULAR RESPIRATION AS A COMBUSTION REACTION
Cellular respiration is often compared to combustion reactions. Combustion reactions are what happens
when fossil fuels are burned, as with a car that has a gasoline engine or when a candle is burned.
Below is the chemical equation for the combustion of octane (found in gasoline).
2 C8H18 + 25 O2  18 H2O + 16 CO2 + energy (and heat)
What are the inputs for the combustion reaction?
What are the outputs for the combustion reaction?
How is the combustion reaction like cellular respiration? (hint: think of what goes in and comes out as
waste products)
How might combustion and cellular respiration be different? (Why don’t you burn up when you do
cellular respiration?)
APPLY WHAT YOU KNOW
Answer these questions as well as you can. Please don’t copy anyone else, but feel free to discuss out
loud.
1. What are the inputs for cellular respiration?
2. What are the outputs (waste products) for cellular respiration?
3. Mitochondria are where celulluar respiration takes place in all cells.
a. Would you expect to see mitochondria in plant cells? Why?
b. In humans, one type of cell has more mitochondria than all others. What type of cell do you
think this is?
c. When humans are cold, they might jump up and down or even shiver (did you do this during
the last snowstorm?) Shivering is when muscles “fire” very quickly on their own. How does
this help someone who feels cold?
d. I’ve said that cellular respiration (what cells do to break down energy) is not to be confused
with respiration (breathing in oxygen and breathing out carbon dioxide). However, using your
new knowledge of cellular respiration, why do you think we breathe?