Which of the following might result in an organism experiencing free-running, endogenous rhythms? Select all that apply. Group of answer choices Putting the organism in an environment with cotant conditions (e.g., no variation in light or temperature) Severing the retinohypothalamic tract (RHT) Lesioning the suprachiasmatic nucleus of the hypothalamus (SCN) Knocking out the gene for melanopsin \
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These are biological rhythms that occur in the absence of external cues, such as light or temperature changes, and are regulated by internal biological clocks. Show more…
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Case Study-Physiology of Behavior Many mammals, if kept in constant darkness and a constant temperature, with food and water available at all times, still demonstrate daily cycles of activities such as sleeping, eating, drinking and just about anything that can be measured. The persistence of these patterns suggests the presence of an internal clock. These patterns are not exactly 24 hours long and therefore are known as circadian rhythms. In mammals, the master circadian "clock" consists of two clusters of neurons in the brain called the suprachiasmatic nuclei (SCN). If the SCN is destroyed, the animal becomes arrhythmic, they are just as likely to eat, drink, sleep or wake at any time of the day. Researcher Martin Ralph and his team used artificial selection to produce two strains of hamster: one with a short circadian period and one with a long circadian period. Adult hamsters from each line had their SCNs destroyed. After several weeks, the scientists transplanted SCN tissue from fetal hamsters into the brains of adult hamsters whose own SCNs had been destroyed. The treatments and results are in the table below. Treatment Recipient | No Treatment | SCN Destroyed | SCN destroyed, Short-period transplant | SCN destroyed, Long-period transplant Short-period adult | Short-period | Arrhythmic | Not done | Long-period Long-period adult | Long-period | Arrhythmic | Short-period | Not done 1. Explain why destroying the SCN makes the adult hamster arrhythmic. Answer- 2. What result would you expect if SCN tissue from a long-period hamster were transplanted into a long-period adult whose own SCN was destroyed? Answer- 3. What do the results of the transplantation experiments tell you about where in the body the circadian rhythm phenotype (long versus short) is expressed? Answer- 4. What would you suggest is the proximate cause of the hamster's circadian rhythms? 5. What are the possible ultimate causes of a circadian rhythm? Answer-
Madhur L.
Hypothesize what would happen if circadian rhythms disappeared.
Circadian rhythms are theorized to be influenced by two primary factors. Compare and contrast the endogenous clock hypothesis and the environmental stimulus hypothesis. Explain the mechanism(s) in an organism of your choice.
Keemin L.
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