USABO Cheat Sheet 2026

The 30 highest-yield USABO facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. A student is writing a report on the fruit fly. According to the formal rules of binomial nomenclature, which of the following is formatted INCORRECTLY? → Written in the report as: *Drosophila Melanogaster*
2. Which two products are generated by non-cyclic photophosphorylation (the Z-scheme) in photosynthesis? → ATP and NADPH
3. A scientist is studying a facultative anaerobe. Under which condition would the most ATP be produced per molecule of glucose? → In the presence of oxygen.
4. Rubisco is described as having 'dual catalytic specificity.' Which statement correctly describes this property? → It can catalyze both carboxylation and oxygenation of RuBP
5. In non-cyclic photophosphorylation, which molecule serves as the ultimate electron donor? → Water (H2O)
6. Which of the following structures in the eye is responsible for controlling the amount of light entering the eye and is composed of smooth muscle fibers? → Iris
7. Which of the following are most responsible for carrying and transporting triacylglycerols in the body? → Chylomicrons and VLDL
8. In C4 plants, which cell type performs initial CO2 fixation, and which enzyme catalyzes this reaction? → Mesophyll cells; PEP carboxylase
9. What is the primary CO2 acceptor molecule in the Calvin cycle that is carboxylated by Rubisco? → Ribulose-1,5-bisphosphate (RuBP)
10. What is the primary objective of immunology and disease in USA Biology Olympiad? → To ensure competence and proficiency in core immunology and disease concepts
11. The P680 designation for the Photosystem II reaction center chlorophyll refers to what property? → It absorbs light most efficiently at a wavelength of 680 nm
12. Which approach is most effective for mastering immunology and disease in USA Biology Olympiad? → Combining theoretical study with practical application and regular review
13. In USA Biology Olympiad, what role does continuing education play in immunology and disease? → To keep professionals current with evolving standards, technologies, and best practices
14. What triggers the conversion of the inactive phytochrome form (Pr) to the active form (Pfr)? → Red light at 660 nm
15. During the complete oxidation of one molecule of glucose, how many molecules of CO2 are produced in the mitochondrial matrix? → 6
16. In a phylogenetic tree, a group of organisms that includes the most recent common ancestor and all of its descendants is referred to as: → Monophyletic
17. The Casparian strip is a critical component of the root endodermis. What is its primary function? → To force water and solutes to pass through the plasma membrane of endodermal cells.
18. Photorespiration reduces photosynthetic efficiency primarily because it: → Releases previously fixed CO2 via the glycolate pathway
19. What is a best practice in USA Biology Olympiad immunology and disease? → A method or technique recognized as superior based on evidence and expert consensus
20. Which of the following molecules acts as an allosteric inhibitor of phosphofructokinase-1 (PFK-1), a key regulatory enzyme in glycolysis? → Citrate
21. Which of the following describes a key characteristic of a K-selected species compared to an r-selected species? → Extensive parental care and few offspring
22. What is the primary role of abscisic acid (ABA) in plant responses to water deficit? → Triggering stomatal closure by inducing K+ efflux from guard cells
23. Which two amino acids are the least likely to occur in the middle of an alpha-helical protein structure? → Glycine and proline
24. In the process of chemiosmosis, the energy used to synthesize ATP is directly derived from: → The flow of protons down their electrochemical gradient through ATP synthase.
25. What is the direct product of the carbon reduction step (Stage 2) of the Calvin cycle, produced using both ATP and NADPH? → Glyceraldehyde-3-phosphate (G3P)
26. Which plant hormone primarily promotes cell elongation by activating plasma membrane H+-ATPases to loosen cell walls via expansins? → Auxin (IAA)
27. In CAM (Crassulacean Acid Metabolism) plants, when do stomata typically open, and why? → At night, to fix CO2 into organic acids while minimizing water loss
28. Which scientist(s) is incorrectly matched with his/her/their discoveries? → Frederick Griffith – discovery of transformation through bacteriophages.
29. Which metabolic pathway is common to both aerobic cellular respiration and fermentation? → Glycolysis
30. Which process likely explains why exons of the tissue plasminogen activator (TPA) are also found in other proteins? → Exon shuffling