4.A: Cell Structure and Function (Exercises)
- Page ID
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Passive Transport
The most direct forms of membrane transport are passive. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement. In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion. A physical space in which there is a different concentration of a single substance is said to have a concentration gradient.
Multiple Choice
Water moves via osmosis _________.
A. throughout the cytoplasm
B. from an area with a high concentration of other solutes to a lower one
C. from an area with a low concentration of solutes to an area with a higher one
D. from an area with a low concentration of water to one of higher concentration
- Answer
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C
The principal force driving movement in diffusion is __________.
A. temperature
B. particle size
C. concentration gradient
D. membrane surface area
- Answer
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C
Free Response
Why does osmosis occur?
- Answer
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Water moves through a semipermeable membrane in osmosis because there is a concentration gradient across the membrane of solute and solvent. The solute cannot effectively move to balance the concentration on both sides of the membrane, so water moves to achieve this balance.
Active Transport
Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient, that is, if the concentration of the substance inside the cell must be greater than its concentration in the extracellular fluid, the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight material, such as ions, through the membrane.
Multiple Choice
Active transport must function continuously because __________.
A. plasma membranes wear out
B. cells must be in constant motion
C. facilitated transport opposes active transport
D. diffusion is constantly moving the solutes in the other direction
- Answer
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D
Free Response
Where does the cell get energy for active transport processes?
- Answer
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The cell harvests energy from ATP produced by its own metabolism to power active transport processes, such as pumps.
Energy and Metabolism
Cells perform the functions of life through various chemical reactions. A cell’s metabolism refers to the combination of chemical reactions that take place within it. Catabolic reactions break down complex chemicals into simpler ones and are associated with energy release. Anabolic processes build complex molecules out of simpler ones and require energy. In studying energy, the term system refers to the matter and environment involved in energy transfers.
Review Questions
Which of the following is not an example of an energy transformation?
A. Heating up dinner in a microwave
B. Solar panels at work
C. Formation of static electricity
D. None of the above - Answer
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D
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Which of the following is not true about enzymes?
A. They are consumed by the reactions they catalyze.
B. They are usually made of amino acids.
C. They lower the activation energy of chemical reactions.
D. Each one is specific to the particular substrate(s) to which it binds. - Answer
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A
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Free Response
Does physical exercise to increase muscle mass involve anabolic and/or catabolic processes? Give evidence for your answer.
- Answer
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Physical exercise involves both anabolic and catabolic processes. Body cells break down sugars to provide ATP to do the work necessary for exercise, such as muscle contractions. This is catabolism. Muscle cells also must repair muscle tissue damaged by exercise by building new muscle. This is anabolism.
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Explain in your own terms the difference between a spontaneous reaction and one that occurs instantaneously, and what causes this difference.
- Answer
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A spontaneous reaction is one that has a negative ∆G and thus releases energy. However, a spontaneous reaction need not occur quickly or suddenly like an instantaneous reaction. It may occur over long periods of time due to a large energy of activation, which prevents the reaction from occurring quickly.
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With regard to enzymes, why are vitamins and minerals necessary for good health? Give examples.
- Answer
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Most vitamins and minerals act as cofactors and coenzymes for enzyme action. Many enzymes require the binding of certain cofactors or coenzymes to be able to catalyze their reactions. Since enzymes catalyze many important reactions, it is critical to obtain sufficient vitamins and minerals from diet and supplements. Vitamin C (ascorbic acid) is a coenzyme necessary for the action of enzymes that build collagen.