Identify and define the categories of food perishability. Compare the perishability of sugar, milk, and hard cheeses (such as parmesan)
What will be an ideal response?
Answer: Foods are classified as perishable, semiperishable, and nonperishable. Perishable foods are generally fresh and have high water activity. Semiperishable foods have a lower water activity or have been preserved in some way. Nonperishable foods have a very low water activity and can be stored for long periods of time without spoilage. Milk is considered a perishable food with a high water activity and nutrient content; it must be refrigerated to avoid spoilage. Hard cheeses would be semiperishable because the added acid, salt and dehydration that occurs during cheese production. Granulated sugar has a very low water activity and is nonperishable.
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Determining the exact nucleotide sequence of a gene or gene fragment obtained from an unknown organism is based on which of the following methods?
a. Hybridization b. Sequencing c. Amplification (PCR) d. Genotypic
Explain how Vibrio cholerae causes cholera without apparent damage to the intestinal epithelium
A. This microbe causes destruction of the cellular structures underneath the intestinal epithelium-this is what induces the watery rice-stool characteristic of the illness. This leaves the overlying intestinal epithelium intact. B. This microbe directly invades the intestinal epithelial cells, but does not kill them. Instead, while multiplying inside them, it causes them to secrete large amounts of chloride ions. This induces water to follow by osmosis, resulting in the watery rice-stool characteristic of the illness. C. This microbe attaches to the surface of intestinal epithelial cells, secreting an exotoxin that causes the epithelium to secrete large amounts of chloride ions. This induces large amounts of water to follow by osmosis, resulting in the watery rice-stool characteristic of the illness. D. The inflammatory reaction to the presence of this microbe causes the watery rice-stool characteristic of the illness. Therefore, it's technically the immune response that initiates the disease, although this response is induced by the presence of the microbe on the intestinal epithelium.
Some insects
a. lack wings. b. mature without undergoing metamorphosis. c. are highly social. d. have mouth parts specialized for bloodsucking. e. fit all of these descriptions.
Which of the following would increase the rate of heat exchange between an animal and its environment?
A) feathers or fur B) vasoconstriction C) wind blowing across the body surface D) blubber or fat layer