Describe how a penis becomes erect during sexual intercourse
What will be an ideal response?
For males, intercourse requires an erection. The penis consists mostly of long cylinders of spongy tissue. When a male is not sexually aroused, his penis is limp, because the arteries that transport blood to its spongy tissue remain constricted. When he becomes aroused, increased activity of sympathetic nerves causes smooth muscle in the walls of these arteries to relax so that the arteries dilate. The resulting inflow of blood expands the spongy tissue and compresses veins that carry blood out of the penis.This pressure enlarges and stiffens the penis so it can be inserted into a female's vagina.
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Enhancers are the binding sites for the
A. promoters of DNA synthesis. B. suppressor factors. C. co-activation factors. D. mediator factors. E. specific transcription factors.
Lakes with elevated dissolved nutrients and low water clarity are called
A. lotic. B. oligotrophic. C. eutrophic. D. pelagic. E. photic.
Pelagic organisms live:
a. in the water column. b. on the sediment. c. in the sediment. d. in hydrothermal vents. e. close to shore.
Which of the following statements in TRUE?
A. Euchromatin, found in interphase cells, is readily visible and easily viewed. B. Many active genes are found in euchromatin, because proteins involved in transcription can easily access these regions of DNA. C. A region of DNA is either heterochromatin or euchromatin, it cannot go back and forth between the two forms. D. When DNA is being replicated, the chromosomes are composed chiefly of heterochromatin. E. All of the answers are correct.