AP Biology Exam Questions and Answers Graded A+

AP Biology Exam Questions and Answers Graded A+ Ligands A molecule that binds specifically to a receptor site of another molecule. Local Regulators A secreted molecule that influences cells near where it is secreted. Biotic Describes living factors in the environment. Abiotic Non-living things keystone species a species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. analogous structures Body parts that share a common function, but not structure vestigial structures A structure that is present in an organism but no longer serves its original purpose homologous structures Structures in different species that are similar because of common ancestry. Positive Feedback A type of regulation that responds to a change in conditions by initiating responses that will amplify the change. Takes organism away from a steady state. Negative Feedback A type of regulation that responds to a change in conditions by initiating responses that will counteract the change. Maintains a steady state. Stimulus any event or situation that evokes a response Stimuli Changes in the environment Neurotransmitters Chemicals that transmit information from one neuron to another