8. Which of the following statements is CORRECT about diffusion? a. it is very r

Question

8. Which of the following statements is CORRECT about diffusion? a. it is very rapid over long distances b. it requires an expenditure of energy by the cell. c. it is a passive process it occurs when molecules move from a region of lower concentration to one of higher concentration. it requires integral proteins in the cell membrane. e. 39. Carrier molecules in the cell membrane are required for a. b. c. d. e. diffusion osmosis facilitated diffusion only active transport only both facilitated diffusion and active transport 40. A cell with an internal concentration of 0.02 molar glucose is placed in a test tube containing 0.02 molar glucose solution. Which of the following terms describes the internal concentration of the cell relative to its environment.? a. isotonic b. hypertonic c. hypotonic d. flaccid e. none of the above 41. One of the functions of cholestero in animal cell membranes is to facilitate transport of ions b. a. store energy c. maintain membrane fluidity d. speed diffusion e. all of the above. 42. White blood cells engulf bacteria through what process? a. exocytosis b. phagocytosis c. pinocytosis d. osmosis e. all of the above.

Explanation / Answer

38. c. it is a passive process

Diffusion does not require any carrier molecules. The process also does not require expenditure of any energy, hence it is not an active process, rather it is a passive process.

39. e. both facilitated diffusion and active transport

Carrier molecules are transmembrane proteins which allow the transport of molecules across the membrane. Facilitated diffusion is a passive process but it requires the presence of appropriate carrier proteins. Similarly, active transport makes use of energy to transport molecules against the concentration gradient across the membrane, with the help of carrier molecules.

40. a. isotonic

The concentration of glucose is same (0.02 molar) in both inside and outside of the cell, so the osmotic pressure is same in both side of the membrane. Thus the cell is placed in an isotonic (same osmotic pressure) environment.

41. c. maintain membrane fluidity

Cholesterol is a very important component of animal cell membranes. At higher temperatures, it maintains the rigidity of the membrane, thus preventing membrane disruption. At lower temperatures, it prevents tight packaging of phospholipids and thus enhancing the membrane fluidity. Thus, it is very important for the structure and functioning of plasma membrane.

42. b. phagocytosis

Phagocytosis allows the white blood cells to engulf solid particles including bacteria. These bacterial cells are then degraded inside the white blood cells.

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