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Capítulo 1
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1. The specific answer would depend on the question asked. Advantages of working with a cell culture include the ability to study a single cell type, ease of obtaining large numbers of cells, ability to minimize number of unknown variables by using carefully controlled in vitro conditions. The advantage of using a whole organism is that information obtained is more meaningful in understanding the role of the process in the overall activity of the organism. For example, one might want to study glucose transport across the plasma membrane of cultured liver cells in response to insulin, but the results would not tell you much about the role of this process in maintaining proper blood glucose levels.

2. They greatly increase the surface area/volume ratio of the cell, allowing much greater exchange between the cell and the lumen of the intestine. Would be unable to absorb sufficient nutrients from the lumen to survive.

3. Cancer cells grow in a much less controlled manner than normal cells, which is why they continue to proliferate in the body. Cancer cells tend to have fewer requirements for growth and are therefore more readily cultured in diverse media than normal cells. Culturing such cells was a logical first step in the development of culture conditions.

4. Cancer cells grow in a much less controlled manner than normal cells, which is why they continue to proliferate in the body. Cancer cells tend to have fewer requirements for growth and are therefore more readily cultured in diverse media than normal cells. Culturing such cells was a logical first step in the development of culture conditions.

5. These receptors mark specific cells as targets for particular hormones. Without such receptors, cells would not be able to bind a specific hormone and thus would not be able to respond to it. If all cells had the same receptors, hormones would not be able to selectively activate specific target cells. All cells would become potential targets.

6. That viruses contain genetic material; that they are capable of producing more of themselves, albeit only inside a host cell; that they contain complex biological macromolecules; that they evolve. These are all important criteria of living organisms.

7. Activities in cells are not directed by agents with a conscious, purposeful goal. Activities that occur in a cell must be directed and regulated by mechanisms operating within the system.

8. The nuclear envelope that separates the nucleus and cytoplasm in a eukaryotic cell provides the basis for regulating the movement of substances between the two compartments. The DNA of a bacterial cell is presumably much more accessible to cytoplasmic substances than that of a eukaryotic cell.

9. Such as, the capture and uptake of other organisms, the sensing of conditions in the external environment and making the appropriate responses, the ability for locomotion. Most activities of this cell are shared by a muscle or nerve cell.

10. A highly flattened cell because it will have a much greater surface area/volume ratio.

11. You could examine the filtrate under the electron microscope and determine whether the infectious agent was cellular, i.e., bacterial, or noncellular, i.e., viral. You could try to culture the infective agent. If it was a bacterium, you should be able to culture the agent in the absence of host cells, but not so if it were a virus. You could determine the size of the genome (i.e., the RNA or DNA that constituted its genetic material). If it was cellular, it would be expected to have a much larger genome than if it was viral.

12. Mitochondria would have been acquired somewhere along the line connecting the branch to Archaea and the line leading to the diplomonads. Chloroplasts would have been acquired along the short line leading to plants (which in this tree also includes green algae).







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