84 ❯ STEP 4. Review the Knowledge You Need to Score High
Rapid Review
The following terms should be thoroughly familiar to you:
Photosynthesis:process by which plants use the energy from light to generate sugar.- Occurs in chloroplasts
- Light reactions (thylakoid)
- Calvin cycle (stroma)
Autotroph:self-nourishing organism that is also known as a producer(plants).
Heterotroph:organisms that must consume other organisms to obtain energy—consumers
(humans).
Transpiration:loss of water via evaporation through the stomata (natural process).
Photophosphorylation:process by which ATP is made during light reactions.
Photolysis:process by which water is split into hydrogen ions and oxygen atoms (light
reactions).
Stomata:structure through which CO 2 enters a plant, and water vapor and oxygen leave a plant.
Pigment:molecule that absorbs light of a particular wavelength (chlorophyll, carotenoid,
phycobilins).
- D—Sugar is a product not of the light-
dependent reactions of photosynthesis but of the
Calvin cycle (the dark reactions). The outputs of
the light-dependent reactions are ATP, NADPH,
and O 2. - C—C 4 plants fix carbon more efficiently than do
C 3 plants. Please see the explanation for question
5 for a more detailed explanation of this answer. - A—The stomata is the structure through which
the CO 2 enters a plant and the oxygen produced
in the light-dependent reactions leaves the plant. - B—The source of the oxygen produced during
photosynthesis is the water that is split by the
process of photolysis during the light-dependent
reactions of photosynthesis. In this reaction, two
hydrogen ions and an oxygen atom are formed
from the water. The oxygen atom immediately
finds and pairs up with another oxygen atom to
form the oxygen product of the light-dependent
reactions. - C—This is a trick question. We reversed the two
compounds (NADPH and ATP) in this one.
More ATP than NADPH is used in the Calvin
cycle. It is for this reason that cyclic photophos-
phorylation exists—to produce ATP to make up
for this disparity. - A—The carbon of CO 2 is used to produce the
sugar created during the Calvin cycle. - C—The light-dependent reactions occur in the
thylakoid membrane of the chloroplast.
Remember, the thylakoid system resembles the
various stacks of poker chips located within the
stroma of the chloroplast. The light-independent
reactions occur in the stroma of the chloroplast.