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1. According to paragraph 1, what is essential to the work of life?
2. In paragraph 1, the author makes the point that
3. Paragraph 1 supports which of the following statements?
4. The author mentions a flagellum in paragraph in order to
5. The word propelled in paragraph 2 is closest in meaning to
6. All of the following are given as examples of mechanical work EXCEPT
7. What is the main purpose of paragraph 3?
8. Which sentence below best expresses the essential information in the highlighted sentence in paragraph 3? Incorrect choices change the meaning in important ways or leave out essential information.
9. The word turnover in paragraph 3 is closest in meaning to
10. By stating in paragraph 4 that substances are of spontaneous movement, the author implies that
11. What can be inferred about concentration work from paragraph 4?
12. Look at the four squares, A , B , C and D , which indicate where the following sentence could be added to the passage. Where would the sentence best fit?
The result is not just a change in concentration but also the establishment of an electrical potential across the membrane.
Concentration work is the transport of substances across a membrane or boundary when the substances are pumped against the direction of spontaneous movement. The purpose of concentration work is either to accumulate substances within a cell or to remove by–products of cellular activity that are not needed or might be toxic if allowed to remain. A The transport of substances enables the cell to maintain internal concentrations of small molecules that differ from concentrations in the environment. B For example, compared to its surroundings, an animal cell has a much higher concentration of potassium molecules and a much lower concentration of sodium molecules. The cell’s plasma membrane helps maintain these differences by pumping sodium out of the cell and potassium into the cell. C A specialized case of concentration work is electrical work, which involves the movement of ions across a membrane against an electrical gradient. D Every membrane has some electrical potential that is generated through concentration. Electrical work is important in the mechanism whereby impulses are conducted in nerve and muscle cells.
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Cells use energy to generate the specific changes that define the different kinds of work they do.