Cellular Respiration
Cells need energy to function, that is, to grow, to
digest food, to get rid of waste, etc. Cells or organisms
that are autotrophs get their energy by making their own
food using the energy from the sun in the process of
photosynthesis. They don’t use all the food they make
right away, but store it in their bodies. Cells or
organisms that cannot make their own food
(heterotrophs) for fuel have to eat autotrophs and get
the energy that is stored in their bodies. Once the
molecules that have the energy are in their bodies, they
need to break down the chemical bonds of those molecules to release the energy in them.
The main molecule that contains this energy is glucose. The process of breaking down
molecules to get energy from glucose (a type of sugar) and other carbohydrates is called cellular
respiration, or just respiration for short. Because living things need a continuous supply of
energy, the cells of all living things carry out respiration continuously. This is why organisms must
eat food on a regular basis to make sure the molecules are in their bodies for when they need the
energy. For example, if all of a sudden you had to run real fast, your body will break down the
sugars that are stored in your cells to give you that energy to run. If you don’t have enough, you
won’t be going too far.
The raw materials needed for respiration
to take place are glucose (C6H12O6 ) and
oxygen. Respiration takes place in 2 stages.
The first stage takes place in the
cytoplasm of the organism's cells. There,
glucose molecules are broken down into
smaller molecules in a process called
glycolysis. Oxygen is not involved (anaerobic)
in this stage of respiration, and only a small
amount of energy is released.
The second stage of respiration takes place in an organelle called the mitochondria. There,
the small molecules are broken down into even smaller molecules. These chemical reactions
require oxygen (aerobic), and a great deal of energy is released as ATP (adenosine
triphosphate). Two other products of respiration are carbon dioxide and water.
Photosynthesis and respiration can be thought of as
opposite processes. Together, these two processes
form a cycle that keeps the levels of oxygen and carbon
dioxide fairly constant in the atmosphere. This occurs
when plants produce O2 as a product of photosynthesis
which is used by organisms. Organisms in turn produce
CO2 which is used by plants and other producers.
Photosynthesis and respiration are the two most
important endothermic and exothermic chemical
reactions on the planet. They give us food to eat for
energy and air to breathe. In these processes you can
see how energy is converted from light energy to
chemical energy. It will then be transformed to
mechanical and heat energy. Energy just gets
“recycled” because of the law of conservation of energy
that says, Energy can neither be created nor destroyed. It is just transformed from one kind to
another
Look carefully at the chemical equations and observe how the reactants in one equation become the
products of the other equation and vice versa.
Respiration
C6H12O6 + 6 O2  6 CO2
Photosynthesis Energy In 6 CO2 + H2O  C6H12O6
+ H2 O
Energy out
+ 6 O2
Some cells obtain their energy through ferment
energy releasing process that does not require oxyge
However, the amount of energy released from each s
molecule during fermentation is much lower than the
released in respiration. You’ve seen fermentation wh
put in bread. The product, CO2, causes the bread to r
also may have experienced it in your body when you
ran out of oxygen from running as fast as you could f
as you could. One product of this type of fermentatio
known as lactic acid. When lactic acid builds up, you
feel weak and sore. Just breathe in some oxygen and
will go
back to respiration in the mitochondria again.
Name: ____________________________
Cellular Respiration
Date: ______ Class: _____ Seat # ______
1. Why do organisms need energy? Give examples. _____________________________________________
______________________________________________________________________________________
2. What is an autotroph? ___________________________________________________________________.
3. Do autotrophs use all the food they make in photosynthesis? ____________________________________
4. Where is the energy in the molecules produced in photosynthesis? ________________________________
5. What is the main molecule in which the energy is stored? __________________
6. What are organisms that are not able to make their own food for energy called? _______________________.
7. What is respiration? _______________________________________________________________________
8. True or False? Respiration that takes place inside of cells is the same as breathing air in and out of the lungs.
9. Use the table below to list the raw materials and products of respiration.
Respiration
Raw Materials
Products
Match the events in respiration with the stages in which they occur.The items in the second column may be
used more than once.
Event in Respiration
Stage Of Process
______10. Takes place in the mitochondria
a. first stage
______11. Takes place in the cytoplasm
b. second stage
______12. Oxygen is involved.
c. both first and second stages
______13. Energy is released.
______14.Glucose molecules are broken down.
15. What is the name used to describe the energy released in cellular respiration? _____________ ______________
16. What is the organelle in which cellular respiration takes place? __________________________________
17. Describes the relationship between photosynthesis and respiration.
_________________________________________________________________________________________
__________________________________________________________________________________________
18. What does the law of conservation of energy say? ___________________________________________________
_________________________________________________________________________________________________
19. Give an example of how energy changes forms. _______________________________________________________
20. What is fermentation? _________________________________________________________________
21. True or False? Fermentation releases more energy than respiration.
22. What will happen if you run out of oxygen from running real fast and long?
______________________________________________________________________________
23. What is in the bubbles in bread that makes it rise? ____________________________________