USABO semi-final part A&B Questions and Answers 100% Correct.

USABO semi-final part A&B Questions and Answers 100% Correct. 1) The recent SARS virus is a: a) Lentivirus b) Coronavirus c) Egtved virus d) Baculovirus e) Retrovirus 2) Which of the following cell organelles is typically identified by its sedimentation coefficient? a) Golgi apparatus b) Mitochondria c) Nucleus d) Nucleolus e) Ribosome 3) Timber companies plant trees right after clear-cutting. Which of the following ecological and/or evolutionary processes would, in principle, take too long for timber companies to wait for, if nature just took its course? a) Competitive exclusion b) Coevolution c) Decomposition d) Mutualism e) Succession 4) Bird migration is probably initiated by the effect of: a) Changes in light intensity on wing muscles b) Changes in duration of darkness on endocrine glands c) The availability of food d) The direction of the prevailing winds e) The increased temperature of the springtime sun 5) Calico cats are always female and have multiple patches of differently colored fur. This phenomenon is caused by: a) Epistasis b) Incomplete penetrance c) Presence of codominant alleles d) Random X-chromosome inactivation e) Somatic hypermutation 6) Which of these statements about plant hormones is correct? a) Auxins, such as IAA, are only found in very young or just germinating plants b) Auxins and cytokinins act synergistically to promote lateral growth at the apical meristem c) Cytokinins do not occur naturally in plants d) Ethylene is a gas that plays a role in senescence e) Gibberellins, such as GA3, play a predominant role in the generation of statoliths 7) In general, parasites tend to a) become more virulent as they live within the host b) become deactivated as they live within the host c) be only mildly pathogenic USABO semi-final part A&B Questions and Answers 100% Correct. USABO Semifinal Exam – Part A 2 d) completely destroy the host e) require large amounts of oxygen USABO Semifinal Exam – Part A 3 8) The main function of the sinus glands of lobsters is: a) sensory b) excretory c) reproductive d) endocrine e) balance 9) Of the following parts of the vertebrate nephron, which consists of capillaries? a) Bowman's capsule b) Distal tubule c) Loop of Henle d) Collecting tubule e) Glomerulus 10) The Gram stain is one of the major tools used in the classification of bacteria. Which of the following statements is NOT true regarding the Gram stain? a) A gram-negative bacterium has peptidoglycan in its cell wall b) A gram-negative bacterium has an inner lipid bilayer and an outer lipid bilayer c) A gram-positive bacterium has peptidoglycan in its cell wall d) A gram-positive bacterium has a periplasmic layer e) None of the above 11) The carbon atom is one of the most important atoms in organic molecules. The carbon atom has all of the following properties EXCEPT: a) C has a valence of four electrons b) C-C covalent bond is very stable; much more energy is required to break a C-C bond than to break an ionic bond c) C can only form single or double bonds d) C that has four different functional groups is called an asymmetric carbon e) C can bond functional groups, which include hydroxyl, carbonyl, carboxyl, amino, sulfhydryl and phosphate 12) Carnivory in some plants appears to have evolved to compensate for soil that is relatively deficient in: a) Potassium b) Calcium c) Manganese d) Nitrogen e) Molybdenum 13) When the base composition of DNA from bacterium Mycobacterium tuberculosis was determined, 18% of the bases were found to be adenine. What is the G + C content? a) 18% b) 32% c) 36% d) 64% e) 72% USABO Semifinal Exam – Part A 4 14) In order for a poinsettia plant to flower again, you would have to subject it to which of the following special treatments: a) Place it in a brown paper bag b) Place it where the lights remain off at night c) Give it a cold treatment, keeping it refrigerated d) Give it plenty of light, so that it can photosynthesize e) Provide plenty of water and essential elements 15) Which of the following bonds/interactions involved in folding a protein into its proper 3D shape is INCORRECTLY matched with its description? a) Hydrogen bond: a bond formed by the attraction of a hydrogen atom to an electronegative atom b) Hydrophobic effect: the attraction between a hydrophobic molecule and a hydrophilic molecule c) Electrostatic interaction (ionic bond): the bond between a positively charged ion and a negatively charged ion d) Van der Waals force: an attractive force that occurs due to resonating dipole moment when atoms or groups of atoms are very close together e) All of the above are correctly matched with their description 16) Which organism could have aposematic coloration? a) A tree snake b) A barnacle c) A hawkmouth larva d) A poison-arrow frog e) A zebra 17) During agarose gel electrophoresis, DNA molecules move from the to the . a) cathode … anode b) left … right c) anode … cathode d) right … left e) none of the above 18) What provides the best evidence for the independent origin of microphylls and megaphylls? a) Microphylls have a single unbranched vein, while megaphylls have a branching vascular system b) Microphylls are small, while megaphylls are larger c) Both are vascularized d) Both appear as lateral appendages of the stem e) Both are photosynthetic organs 19) If the nucleoli in a eukaryotic cell were destroyed, the cellular activity that would be most affected is: a) The formation of the nuclear lamina b) The appearance of the middle lamella c) The activity of the nuclear membrane d) The synthesis of ribosomes e) The storage of RNA .