The brains of Alzheimer disease patients display characteristic lesions called senile plaques formed by the accumulation of a protein fragment called amyloid beta-protein. How are the plaques believed to influence the progression of the disease?
1.Amyloid beta-protein accumulates inside cells, disrupting cell structure and function.
2.The plaques are present in brains of both normal elders and AD patients and differences between these groups in their number and rate of development are insignificant.
3.The plaques cause the degeneration and death of specific neurons, particularly in the limbic system.
4.The plaques cause the random degeneration and death of neurons throughout the brain.
3
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Which of the following atoms cannot participate in biological hydrogen bonds?
A. nitrogen B. oxygen C. carbon D. both nitrogen and oxygen E. both oxygen and carbon
Humans are susceptible to scurvy because
A. they cannot synthesize amino acids. B. they do not have enough adipose tissue for vitamin A storage. C. they cannot synthesize vitamin C. D. they have a high incidence of fruit allergies. E. constant seasickness and nausea on long voyages leads to weakness and anemia.
The following statements describe how cancer is staged. Which of the statements is true?
A. Most cancers are grouped into stages 1-4; however, treatment options are only available for stages 1-3. B. Once a cancer reaches each stage, it cannot be reversed, as tumors only grow in size, even with aggressive treatments. C. Cancer is described based on the size of the tumor, if the tumor has invaded nearby tissues, if it has spread to lymph nodes, and if it has moved to other organs of the body. D. Cancer is described by ten stages, each with their own subdivisions. The lower the stage, the worse the prognosis.
The Keeling curve depicted here has an annual cycle. What is the primary cause of this cycle?
What will be an ideal response?