USABO 2025
ANSWER ALL QUESTIONS IN THIS SECTION
QUESTION 1
Select ALL statements that are true concerning the Photosynthesis Reaction Center
(Photosystem II)?
A. The Photosynthesis Reaction Center contains chlorophyll and sometimes Fe-
heme groups.
B. It is a globular protein found in the cytoplasm where it acts as an antenna
protein.
C. It oxidizes carbon dioxide and produces H2O.
D. It transfers high-energy electrons to an acceptor nearby in the thylakoid
membrane.
E. The Photosynthesis Reaction Center is usually a heterotetramer, but may be a
heterotrimer in some species of cyanobacteria. - ANSWERS-A. The
Photosynthesis Reaction Center contains chlorophyll and sometimes Fe-heme
groups.
D. It transfers high-energy electrons to an acceptor nearby in the thylakoid
membrane.
E. The Photosynthesis Reaction Center is usually a heterotetramer, but may be a
heterotrimer in some species of cyanobacteria.
END OF
PAGE 1
, USABO 2025
QUESTION 2
Blood entering the kidney is filtered by the Bowman's capsule. In what order does
the filtrate pass through the following structures of the nephron?
(1) Ascending limb of the Loop of Henle
(2) Distal convoluted tubule
(3) Descending limb of the Loop of Henle
(4) Proximal convoluted tubule
(5) Collecting duct
A. 1, 3, 4, 2, 5
B. 2, 1, 3, 4
C. 2, 3, 1, 4, 5
D. 4, 1, 3, 5
E. 4, 3, 1, 2, 5 - ANSWERS-E. 4, 3, 1, 2, 5
QUESTION 3
Select ALL of the following that are accurate statements concerning ecosystems?
A. Energy flow tends to be from the sun, to producers, then consumers, and finally
back to the sun.
END OF
PAGE 2
, USABO 2025
B. Energy flow from trophic level to trophic level is 90% efficient.
C. Energy may only flow from the biotic to the abiotic portions of ecosystems.
D. Heterotrophs supply 10% of the energy needed by autotrophs.
E. Some energy lost during transfers from trophic level to trophic level is in the
form of heat. - ANSWERS-E. Some energy lost during transfers from trophic level
to trophic level is in the form of heat.
QUESTION 4
Select ALL of the structure/function relationships in the CNS that are not accurate?
A. Cerebellum: Control of motor functions
B. Cerebrum (limbic system): Long term memory
C. Hypothalamus: Circadium rhythms
D. Medulla oblongata: Breathing
E. Spinal cord: Short term memory of motor functions - ANSWERS-E. Spinal
cord: Short term memory of motor functions
END OF
PAGE 3
ANSWER ALL QUESTIONS IN THIS SECTION
QUESTION 1
Select ALL statements that are true concerning the Photosynthesis Reaction Center
(Photosystem II)?
A. The Photosynthesis Reaction Center contains chlorophyll and sometimes Fe-
heme groups.
B. It is a globular protein found in the cytoplasm where it acts as an antenna
protein.
C. It oxidizes carbon dioxide and produces H2O.
D. It transfers high-energy electrons to an acceptor nearby in the thylakoid
membrane.
E. The Photosynthesis Reaction Center is usually a heterotetramer, but may be a
heterotrimer in some species of cyanobacteria. - ANSWERS-A. The
Photosynthesis Reaction Center contains chlorophyll and sometimes Fe-heme
groups.
D. It transfers high-energy electrons to an acceptor nearby in the thylakoid
membrane.
E. The Photosynthesis Reaction Center is usually a heterotetramer, but may be a
heterotrimer in some species of cyanobacteria.
END OF
PAGE 1
, USABO 2025
QUESTION 2
Blood entering the kidney is filtered by the Bowman's capsule. In what order does
the filtrate pass through the following structures of the nephron?
(1) Ascending limb of the Loop of Henle
(2) Distal convoluted tubule
(3) Descending limb of the Loop of Henle
(4) Proximal convoluted tubule
(5) Collecting duct
A. 1, 3, 4, 2, 5
B. 2, 1, 3, 4
C. 2, 3, 1, 4, 5
D. 4, 1, 3, 5
E. 4, 3, 1, 2, 5 - ANSWERS-E. 4, 3, 1, 2, 5
QUESTION 3
Select ALL of the following that are accurate statements concerning ecosystems?
A. Energy flow tends to be from the sun, to producers, then consumers, and finally
back to the sun.
END OF
PAGE 2
, USABO 2025
B. Energy flow from trophic level to trophic level is 90% efficient.
C. Energy may only flow from the biotic to the abiotic portions of ecosystems.
D. Heterotrophs supply 10% of the energy needed by autotrophs.
E. Some energy lost during transfers from trophic level to trophic level is in the
form of heat. - ANSWERS-E. Some energy lost during transfers from trophic level
to trophic level is in the form of heat.
QUESTION 4
Select ALL of the structure/function relationships in the CNS that are not accurate?
A. Cerebellum: Control of motor functions
B. Cerebrum (limbic system): Long term memory
C. Hypothalamus: Circadium rhythms
D. Medulla oblongata: Breathing
E. Spinal cord: Short term memory of motor functions - ANSWERS-E. Spinal
cord: Short term memory of motor functions
END OF
PAGE 3
