GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Cellular Respiration and Photosynthesis
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #183 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
You are studying three different reduction-oxidation couples in the electron transport chain. Their energies are as follows:
"A" +.02 V
"B" - .31 V
"C" - .41 V
What correctly describes the flow of electrons through these redox couples?
A, B, C
B, C, A
C, B, A
A, C, B
C, A, B
C, B, A
Electrons flow throughout the electron transport chain via redox reactions. They flow from the most negative voltage to the most positive voltage within the chain. Thus the correct flow would be from C (most negative) to B (Less negative) to A (most positive).
Example Question #1 : Help With Light Reactions
Which molecule transfers electrons from photosystem II to photosystem I?
Ferredoxin
Cytochrome c
Plastocyanin
NADP+
Plastocyanin
Photosystems I and II are each capable of conducting electrons, with photosystem II handing off electrons to photosystem I. This is accomplished by the electron carrier molecule plastocyanin.
Example Question #2 : Help With Light Reactions
Which product is made in photosystem I?
NADH
Glucose
ATP
NADPH
NADPH
Photosystems I and II are responsible for the light-dependent reactions of photosynthesis. These two photosystems work in tandem to create ATP and NADPH products. ATP is created in photosystem II, while NADPH is created in photosystem I.
Example Question #3 : Help With Light Reactions
What fuels ATP synthase to make ATP from ADP + Pi in the light reaction of photosynthesis?
Light excites photosystem II to split water into hydrogen and oxygen. Oxygen accumulates in the thylakoid space. Oxygen then moves down its concentration gradient from the thylakoid space to the stroma by passing through ATP synthase, fueling the synthesis of ATP
Light excites photosystem I to generate electrons that pass through the thylakoid membrane to excite ATP synthase to generate ATP
Light excites photosystem II to split water into hydrogen and oxygen. Hydrogen ions accumulate in the thylakoid space. Hydrogen moves down its concentration gradient from the thylakoid space to the stroma by passing through ATP synthase, fueling the synthesis of ATP
The mechanism by which ATP synthase is fueled is not entirely known
NADPH is formed from NADP+ reductase in the thylakoid membrane. NADPH can then donate hydrogen to ATP synthase to fuel the synthesis of ATP
Light excites photosystem II to split water into hydrogen and oxygen. Hydrogen ions accumulate in the thylakoid space. Hydrogen moves down its concentration gradient from the thylakoid space to the stroma by passing through ATP synthase, fueling the synthesis of ATP
Excitation of photosystem II splits water in the thylakoid space into hydrogen and oxygen. The hydrogen then passes through ATP synthase to move down its concentration gradient and into the stroma. Excitation of photosystem I passes electrons to NADP+ reductase to convert NADP+ to NADPH. Regeneration of NADPH is necessary for the Calvin cycle.
Example Question #45 : Cellular Metabolism
During the photosynthetic light reactions, which of the following molecules acts as the electron acceptor?
Electrons excited in photosystem I are accepted by 
Example Question #1 : Help With The Calvin Cycle
What molecule is remade in the Calvin cycle so that carbon dioxide can attach when entering?
Glucose-6-phosphate
1,3-bisphosphoglycerate
Ribulose-1,5-bisphosphate
Glyceraldehyde-3-phosphate
Ribulose-1,5-bisphosphate
In order to keep the Calvin cycle going, the 5-carbon molecule that carbon dioxide attaches to in the first step must be remade at the end of the cycle. This molecule is called ribulose-1,5-bisphosphate, or RuBP.
Example Question #2 : Help With The Calvin Cycle
Which of the following is an advantage of C4 photosynthesis compared to C3 photosynthesis?
C3 plants fix carbon dioxide through rubisco; however, oxygen competes for rubisco binding, reducing the ability for C3 plants to fix carbon. C4 plants use phosphoenolpyruvate (PEP) carboxylase instead of rubisco, which binds carbon dioxide specifically.
C3 plants are more suitable than C4 plants for growth in arid climates because they keep their stroma closed longer than C4 plants.
The calvin cycle in C4 plants does not require NADPH; therefore, the light reactions are more efficient because they do not have to regenerate NADPH from NADP+
C3 plants physically separate carbon fixation and the Calvin cycle, whereas C4 plants execute both processes in the chloroplast stroma.
C3 plants have fewer photosystems than C4 plants; as a result, C4 plants are able to utlize a broader spectra of light in the light reactions of photosynthesis.
C3 plants fix carbon dioxide through rubisco; however, oxygen competes for rubisco binding, reducing the ability for C3 plants to fix carbon. C4 plants use phosphoenolpyruvate (PEP) carboxylase instead of rubisco, which binds carbon dioxide specifically.
C3 plants use rubisco to fix carbon dioxide; however, oxygen also competes for binding. C4 plants have evolved to use PEP carboxylase, which only binds carbon dioxide, eliminating competition with oxygen. Furthermore, C4 plants separate carbon fixation and the Calvin cycle by location, but C3 plants do not. The light reactions of C3 and C4 plants are very similar, but C4 plants are more suited for arid climates due to their ability to close their stroma for longer periods of time to prevent water loss.
Example Question #2 : Help With The Calvin Cycle
Plants that utilize only the Calvin cycle to __________ carbon dioxide are known as __________ plants.
oxidize . . . C3
phosphorylate . . . C3
oxidize . . . C2
fix . . . C3
fix . . . C2
fix . . . C3
The purpose of the Calvin cycle is the fixation of carbon dioxide, which essentially turns inorganic carbon dioxide into an organic compound that can be used for energy production. C3 plants only use the Calvin cycle, whereas C4 plants can use a number of processes to fix carbon, including the use of phosphoenolpyruvate carboxylase (PEP carboxylase).
All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
