EXAM 3 083answers - BIO 152 EXAM 3 083 Name The endocrine...

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BIO 152 EXAM 3 083 Name The endocrine system is not on your final exam. It was on this exam from 2008. But it’s a good idea not to forget everything you know about the endocrine system. 1. (9 points) Discuss and contrast possible advantages and disadvantages of hermaphroditism that involves cross-fertilization (two individuals fertilize each other’s eggs) with hermaphroditism that involves self-fertilization (one individual fertilizes its own eggs). When two individuals fertilize each other it is sexual reproduction and the offspring will not be identical to either parent. This makes it unlikely that any offspring will inherit recessive lethal genes in both sets of chromosomes. Self-fertilization is asexual and all the offspring will be identical to the parent. Mutation in the second copy of an already mutated gene can often be very deleterious to the offspring and all its offspring as well. 2. (9 points) Describe how a sound, a touch, and an odor are transduced into changes in the pattern of action potentials. How does the brain know which sense is which when the action potentials finally reach the brain? Sound pressure waves move through the fluid of the cochlea and cause the basilar membrane to move. Movement of that membrane pushes the hair cells up into the tectorial membrane, bending the ‘hairs’ (stereocilia). Bent hairs cause a depolarization of the hair cell membrane and that stimulates release of a neurotransmitter from the hair cell. The neurostransmitter binds to receptors at the tips of auditory nerve axons, causes influx of sodium ions, depolarization of the axon membrane, and generation of an action potential. The AP travels to the auditory center of the cerebral cortex where the neurons that receive it generate a perception of sound. When sensory nerve endings specialized for touch sensation are pressed, PM proteins change shape and open ion channels. The depolarization of the axon tip membrane generates an AP and the AP travels to the cerebral cortex to an area different from the auditory center. Odorant molecules bind to receptors in the membranes of chemoreceptor cells in the olfactory epithelium. Binding causes signal transduction, depolarization, and release of a signal onto the tips of olfactory nerve axons inside the olfactory bulb of the CNS. APs are generated in these axon tips and carried back to olfactory centers in the brain. The brain know which is which because a particular sensory neuron’s signals are sent to discrete locations in the brain.
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