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A bacterial strain develops a mechanism that destroys most DNA arriving from other species. What is a likely effect on acquisition of antibiotic resistance through horizontal gene transfer? A. It becomes less frequent because incoming resistance genes are less…
Which combination could contribute to the rise during the first six minutes and the fall during the final six minutes? A. Early adrenaline release; later brainstem autonomic signals slowing the heart B. Early disappearance of all blood flow to the lungs; later…
At 2.5 s the pressure shown drives air out of the lungs. Which muscle activity would support forced expiration? A. Contraction of the diaphragm and external intercostals B. Relaxation of every respiratory muscle while thoracic volume increases C. Contraction…
What is a role of fibrin in forming a blood clot? A. It converts all platelets into red blood cells B. It forms an insoluble network retaining cells and platelets C. It dissolves the injured vessel wall D. It acts as a hormone that raises blood glucose
An alveolar cell contains abundant organelles associated with secretion. Which identification is most consistent with this observation? A. An erythrocyte B. A type I pneumocyte with no secretory activity C. A type II pneumocyte producing surfactant D. A neuron…
What is a function of the structure labelled X? A. It increases conduction speed along the axon B. It is the site where every neurotransmitter is released C. It contains the nucleus for the entire neuron D. It reverses the direction of every action potential
Which interaction exemplifies negative feedback in regulation of the ovarian cycle? A. Oestradiol enhances all gonadotropin secretion at every concentration and stage B. FSH permanently prevents every follicle from growing C. All progesterone is produced only…
A blood-feeding organism secretes a molecule that blocks thrombin activity. Which step is directly inhibited? A. Formation of fibrin from fibrinogen B. Formation of all erythrocytes in bone marrow C. Synthesis of haemoglobin from fibrin D. Production of…
Which row identifies X, the short newly synthesized segment Y and the end Z? A. X: 3′; Y: continuous leading strand; Z: 5′ B. X: 5′; Y: Okazaki fragment; Z: 3′ C. X: 5′; Y: RNA chromosome; Z: 5′ D. X: 3′; Y: Okazaki fragment; Z: 5′
What happens during splicing of a typical eukaryotic pre-mRNA? A. The RNA is converted into a double-stranded chromosome B. Exons are removed and all introns become codons C. Retained exons are joined after intron removal D. DNA primers are permanently…