Multiple Choice
Why are bacterial cells less likely than animal cells to burst in a hypotonic solution?
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6. The Membrane
Introduction to Membrane Transport
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Which of the following best describes secondary active transport?
A
The movement of one substance against its concentration gradient, coupled to the movement of another substance down its gradient.
B
The diffusion of water across a selectively permeable membrane.
C
The movement of molecules across a membrane using energy directly from ATP hydrolysis.
D
The movement of molecules across a membrane down their concentration gradient without the use of energy.
Verified step by step guidance1
Step 1: Understand the concept of secondary active transport. Secondary active transport involves the movement of one substance against its concentration gradient, which is powered by the movement of another substance down its concentration gradient. This process does not directly use ATP but relies on the energy created by the gradient of the second substance.
Step 2: Compare secondary active transport to other transport mechanisms. For example, primary active transport uses energy directly from ATP hydrolysis to move substances against their concentration gradient, while passive transport involves the movement of substances down their concentration gradient without energy input.
Step 3: Eliminate incorrect options. The diffusion of water across a selectively permeable membrane refers to osmosis, not secondary active transport. The movement of molecules using energy directly from ATP hydrolysis describes primary active transport, not secondary active transport. The movement of molecules down their concentration gradient without energy describes passive transport, not secondary active transport.
Step 4: Focus on the correct description. Secondary active transport is characterized by coupling the movement of one substance against its gradient with the movement of another substance down its gradient. This coupling is often facilitated by transport proteins such as symporters or antiporters.
Step 5: Conclude that the correct answer is: 'The movement of one substance against its concentration gradient, coupled to the movement of another substance down its gradient.' This matches the definition of secondary active transport.
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