1) Energy can neither be created or destroyed, it only changes forms. Some forms of energy are more useful than
others.
2) As energy changes form, it will always be in the direction of a less usable form. When you change glucose into
ATP, a more usable form, you’re still changing it into a less usable form because not all that energy becomes ATP,
some of it becomes heat.
Not all the energy is completely turned into
ATP – some is turned into heat. If there’s 27
pieces of pie and it needs to be divided
evenly between 7 people, 6 pieces will be
leftover. The same thing is here, it must be
divided evenly but it doesn’t convert
perfectly, and since you can’t destroy energy
it turns into the least usable form, heat.
Heat
Glucose
ATP
3) There must always be an outside source of energy to keep a closed system (example, cell) functioning. The
example Mr. Stevens gave was a bedroom – it takes energy from you to keep it clean and organized. When that
energy stops coming in, it begins to clutter, and eventually it becomes so cluttered it no longer serves its purpose
and it’s unusable. The same is with cellular reactions – they can’t take place without more energy, because they
can’t sustain themselves. Rooms don’t auto-clean.
4) Cells function on chemical energy. Chemical energy comes from breaking the chemical bonds that bond
molecules. ATP is a complex molecule used as an energy source:
Chemical
Energy
A
P
P
P
A
P
P
Adenosine Diphospahte (ADP)
Adenosine Triphospahte (ATP)
+
+
P
1 leftover Phosphate
(Pi)
Hydrolysis
5) ATP vs. Glucose – The $100 bills represent glucose and the $20 bills represent ATP. The straight breakdown of
glucose provides 690 Kcal, and the hydrolysis reaction of ATP to ADP (shown above) provides 7.3 Kcal. The
conversion of glucose to ATP yields 36 ATP, and if you do the math, that converts to 262.8 Kcal. This is a smaller
number of Kcal than the straight breakdown of glucose provides, but if a cellular reaction consumes 20 Kcal, 3
ATP are used, leaving 33 left over, while using straight glucose would leave none left over (any extra Kcal not
used in the process is converted to heat. Cells aren’t bankers, they don’t give change.) So even though you lose
Kcal when you convert glucose to ATP, it’s still a good deal because glucose is wasteful and will only give 1
reaction when the more usable ATP can yield many reactions.
6) Cellular respiration is basically the process of breaking down glucose to make ATP. The inner membrane of the
mitochondria make up the cristae, where the glucose molecules (C6H12O6) and oxygen molecules (O2) interact to
form water (H2O), carbon dioxide (CO2), and ATP.
C6H12O6 + 6O2
6H2O + 6CO2 + ATP
Glucose
(C6H12O6)
Oxygen
(O2)
Water
(H2O)
Carbon Dioxide
(CO2)
ATP
Mitochondria are in every type of eukaryotic cell because ATP is a necessary compound for its functioning and it
has no other way to get it without having mitochondria that perform cellular respiration.
7) Photosynthesis is essentially the opposite of cellular respiration, and it’s the process that comes before cellular
respiration in plants. In heterotrophs food is consumes, and that’s where the glucose comes from in them, but in
plants photosynthesis is the process that produces it. The process of photosynthesis is the process in which
chloroplasts take sunlight, water (H2O), and carbon dioxide (CO2) to produce glucose (C6H12O6) and oxygen (O2).
Notice how animals exhale carbon dioxide and inhale oxygen, and plants intake carbon dioxide and export
oxygen.
Sunlight + 6CO2 + 6H2O
C6H12O6 + 6O2
Also notice how the formulas for photosynthesis and cellular respiration are simply flipped, only with sunlight
taking the place of ATP in photosynthesis. The product of this reaction is the reactant for cellular respiration,
which plays a very large role in how the whole thing fits together.
Glucose
Carbon Dioxide
(C6H12O6)
(CO2)
Sunlight
Water
(H2O)
Oxygen
(O2)
Sunlight
Cellular
Energy
ATP
CO2 + H2O
Photosynthesis
Cellular
Respiration
C6H12O6 + O2
(Glucose + Oxygen)
A
P
P
+
P
This diagram can look quite intimidating at first, but it shows the flow of energy and the processes involved. To make
it easier to understand, start at the right and work backwards. The cellular energy comes from the hydrolysis
reaction of ATP to ADP + Pi as shown. Remember Pi is just a way of referring to the extra phosphate that’s separate
from the ADP. ADP + Pi can then be “recycled” back into ATP through a dehydration synthesis reaction powered by
glucose (another cellular respiration reaction). ATP is originally formed through cellular respiration, and all the
substances needed as the reactants for that process are provided by photosynthesis. Photosynthesis takes sunlight,
CO2, and H2O and turns it into C6H12O6 + O2, providing what’s needed to initiate the cellular respiration reaction.