Photosynthesis and Cell respiration review key
Chapters 8 & 9
NAME
1.
What are the 3 parts of the ATP molecule?
Adenine, ribose and 3 phosphate groups
2.
When is energy released from ATP? Where?
When a phosphate group is removed, the chemical bond energy is released. This occurs in the mitochondria
of all eukaryotic cells
3.
What happens to the ATP molecule itself when a phosphate group is removed?
The ATP molecule becomes an ADP molecule, because it now has 2 phosphates attached instead of 3. It is
recycled when energy becomes available to add the 3rd phosphate group to the ADP, so it becomes ATP again.
4.
Write the chemical equations for both cellular respiration and photosynthesis. Be able to describe in
words what is going on chemically in each of them. Be able to explain how the organisms that perform these
processes are interdependent.
C6H12O6 + 6 O2  6 CO2 + 6 H20 + ENERGY (ATP)
The above equation is for cellular respiration. It shows how 1 glucose molecule, in the presence of an
adequate oxygen supply, yields carbon dioxide, water vapor and energy that can be used for cell activities,
such as growth, reproduction, homeostasis, movement, etc. Cell respiration produces more energy (in the
form of ATP) than other forms of energy conversion, such as fermentation, but it requires oxygen as the
equation illustrates.
SUNLIGHT
6 CO2 + 6 H20
 C6H12O6 + 6 O2
The above reaction if for photosynthesis. It shows how plants use specialized organelles (chloroplasts) to use
the sun’s energy, carbon dioxide and water to create glucose molecules, which are used for energy during cell
respiration.
All eukaryotic cells need to perform cell respiration to access the energy stored in ATP. The body only stores a
small amount of ATP, so it needs to be recycled using energy from the food that is eaten (by heterotrophs) or
stored (by autotrophs). Plants need the carbon dioxide in the atmosphere to perform photosynthesis, and
carbon dioxide just happens to be a by-product of cell respiration. What is a “waste” gas to the heterotroph is
necessary to the autotroph. Heterotrophs also eat the autotrophs to replenish the ATP, so neither would
survive without the other. If plants ran out of carbon dioxide, they would not be able to perform
photosynthesis.
**NOTE The answer to number 4 covers almost every single one of the objectives related to photosynthesis and
cell respiration required in the curriculum (there are actually quite a few, but many of them are redundant
5.
For each of the following, identify whether the organism is a heterotroph or and autotroph by placing an
H or an A beside it. Use your best penmanship skills!
__H___mushroom
___H__Amoeba
__H___leopard
__A___sunflower
___A__maple
___H__deer
___A__alga
___A__wheat
6.
What are the light-absorbing molecules in plants that gather energy called? What is the primary one
called?
Pigments. Chlorophyll.
7.
Why do most plants appear green?
The chlorophyll reflects the green wavelength of the visible light spectrum back at our eyes, so we see green.
The rest of the visible light wavelengths are absorbed.
8.
Identify 3 major factors that affect the rate of photosynthesis.
Sunlight—high light intensity increases the rate of photosynthesis, but it does eventually level off at a
maximum rate
Water—is one of the reactants, so it is a necessity; tissues can also be damaged if they become too dry
Temperature—the enzymes responsible for photosynthesis function best between 0 and 35 degrees Celcius.
The lower the temperature, the slower the rate of photosynthesis
9.
Desert plants are subjected to extremes of the factors mentioned in number 8. How do plants that live
in extreme environments meet the challenge of photosynthesis?
Two groups of specialized plants have evolved to survive harsh conditions: C4 and CAM plants.
C4 plants (such as corn, sugar cane and sorghum—crop plants) have a special biochemical pathway that
allows them to capture even very low levels of carbon dioxide
CAM plants (pineapple trees, desert cacti) close their leaves during the day when it is hot, and open them at
night when it is cool to allow carbon dioxide to enter
10.
What are the 3 stages of cell respiration, in their correct order? Where is the most energy gained?
Glycolysis—Krebs cycle—electron transport chain. Glycolysis provides a total of 4 ATP molecules, but since 2
are needed to get things started, we say it provides 2 because it has to “pay back” the ones used. Oxygen is
not needed for glycolysis to occur. The Krebs cycle provides 2 ATP molecules, but requires oxygen to proceed.
Lastly, the electron transport chain produces 32 ATP molecules, and HERE IS THE ANSWER TO THE QUESTION
“WHY DO WE BREATHE?” Oxygen is needed in the final step of the electron transport chain, so if none is
present, we lose out on the 32 ATPs from there, and the 2 from the Krebs cycle. We could not survive on the
little energy produced by glycolysis!
11.
Besides glycolysis, how can energy be converted without oxygen?
Energy can be produced by either alcoholic fermentation or lactic acid fermentation, depending on the
organism. Both pathways begin with glycolysis, and occur if there is no oxygen present for the Krebs cycle.
Alcohol fermentation—yeast, some bacteria—is a different chemical reaction that results in alcohol and
carbon dioxide. This is useful in commercial enterprises, as both products can be made and sold. Carbon
dioxide causes breads to rise, alcohol creates beverages that people seem to enjoy
Lactic acid fermentation—other bacteria, humans—produces a substance called lactic acid which allows us to
have cheese, yogurt, etc. When this happens in humans (when we run out of oxygen, after exercise, etc), it is
the lactic acid buildup in our muscles that causes us to be sore. In the first 90 seconds or so of exercise, we
have depleted the amount of ATP generated by cell respiration and then begin lactic acid fermentation. If we
continue exercise (marathons, etc.), we will actually have to start burning fats to obtain the energy needed to
recycle our ATP. This is why aerobic exercise is good for weight control.
12.
What is “oxygen” debt?
Oxygen debt is the oxygen needed by the body to get rid of the lactic acid that builds up in the muscles after
vigorous exercise.