Cell Energetic
Respiration is a process used by plants and animals to create energy for the cells in the body to use. In respiration, glucose
in the cells is broken down into smaller units of energy called ATP. The ATP acts as a battery that can plug into the cell
and provide it with energy. There are two types of respiration, depending on whether or not oxygen is available for the
cell to use. Aerobic respiration is the process used to make ATP when oxygen is present. Anaerobic respiration is used
when oxygen is absent or is in short supply.
1. What is respiration
2. What is the ultimate source of energy that is broken down in respiration?
3. What is created when glucose is broken down?
4. What is the function of ATP in cells?
5. What are the two types of respiration?
6. What determines which type of respiration is used by the cell?
Before talking about respiration, we have to understand ATP. ATP (adenosine triphosphate) is made of three phosphate
molecules attached to a molecule of adenosine. The energy in ATP is stored in the bonds holding the phosphate together.
Imagine yourself and a friend are holding hands and pulling away from each other. A lot of energy is being used to
maintain that grip. What will happen if you let go of your friend’s hand? The energy will be released and used to send you
both sprawling across the room in opposite directions. The same thing is true of the phosphates in ATP– energy is being
used to keep them together. If a phosphate is removed from ATP, the energy in the bond is released and is used by the cell
to do work. When the phosphate is removed, the cell now has a new molecule (ADP – adenosine diphosphate), plus one
free phosphate (the one that was removed) and energy.
7. Where is the energy is ATP stored?
8. What must happen for the energy is ATP to be released?
9. What can the cell do with this energy released by ATP?
So, in a nutshell, plants contribute glucose to the cell, which the cell uses for energy. Because glucose is so big, the cell
breaks it down into smaller bundles of energy, called ATP, to prevent waste. ATP is made of adenosine attached to three
phosphate molecules. The energy in ATP is stored in the bonds holding phosphates together. When a phosphate is
removed, the bond energy is released for the cell to use. The ATP is converted to ADP, phosphate and energy.
In order to make ATP, the cell must break down glucose molecules. There are two ways that the cell does this – aerobic
and anaerobic respiration. Aerobic refers to oxygen. If oxygen is present, the cell uses aerobic respiration to make ATP
from glucose. Another name for aerobic respiration is cellular respiration because it happens in the cell. Cellular
respiration is very efficient – each glucose can be broken down into 38 ATP molecules for the cell to use. Cellular
respiration also creates two waste products – CO2 and H2O. The CO2 is what we breath into the air when we exhale. Plants
use this CO2 during photosynthesis.
10. What process does the cell use to break down glucose when oxygen is available?
11. What source of molecular energy is made by this breakdown of energy?
12. What two waste products are created by aerobic respiration?
13. What is the other name for aerobic respiration?
14. How much ATP is made from each glucose broken down in cellular respiration?
The reactants for cellular respiration (what is used) are oxygen and glucose. The products (what is made) are CO2, H2O,
and ATP. The formula for respiration is below:
Glucose (C6H12O6) + Oxygen (O2)
CO2 + H2O + ATP energy
Notice that the products of cellular respiration are the reactants of photosynthesis. This means that cellular respiration
provides plants with the ingredients they need to make glucose. Also notice that the reactants of cellular respiration are the
products of photosynthesis. This means that photosynthesis provides cells with what they need to create ATP energy.
Without photosynthesis, we couldn’t make energy and we would die. Without animals, plants would not have what they
need to make food, and they would die. Both processes rely on the other to work.
Glucose (C6H12O6) + Oxygen (O2)
CO2 + H2O + sunlight energy
CO2 + H2O + ATP energy (respiration)
Glucose (C6H12O6) + Oxygen (O2) (photosynthesis)
15. What are the reactants of cellular respiration?
16. What are the products of cellular respiration?
17. Why are cell respiration and photosynthesis dependant on each other?
Sometimes oxygen is not available or is in short supply, but the cell still needs to make ATP for necessary processes. In
this case, the cell switches from aerobic to anaerobic respiration to make the ATP. Another name for anaerobic respiration
is fermentation. Fermentation is used by yeasts, bacteria, and by muscles that are being overworked. The advantage of
anaerobic respiration is that is doesn’t require oxygen to run. The disadvantage is that it is inefficient, and only 2 ATP are
made from each glucose molecule. The rest of the glucose goes into waste byproducts that hold much untapped energy.
18. What process does the cell use to make ATP when oxygen is not available?
19. What is another name for anaerobic respiration?
20. What is the disadvantage of using fermentation instead of cellular respiration?
21. What types of cells use fermentation?
There are two types of fermentation. The first type, alcoholic fermentation, is used to make beer, wine, and bread. In
alcoholic fermentation, glucose is converted into 2 ATP, ethyl alcohol, and CO2. The ethyl alcohol is what gives beer and
wine their alcoholic content. The CO2 gives beer its foam.
22. What are the two byproducts (waste products) of alcoholic fermentation?
23. What food products are made by this process?
The second type of fermentation is called lactic acid fermentation. This process is used by your muscles to create ATP
energy when they are running out of oxygen during very strenuous exercise. The byproduct (waste) created in this process
is lactic acid. Lactic acid accumulates in your muscles and makes them sore and tired. This is why muscles ache after a
hard workout. Lactic acid fermentation is also used by yeast to create such products as sour cream, sauerkraut, and yogurt.
The lactic acid is what gives these products their sour taste.
24. What is the second type of fermentation that is used by muscles during heavy exercise?
25. What food products are created from lactic acid fermentation?
26. What is the byproduct (waste) of this process?
27. How many ATP are generated?