Bacterial cells found in your tap water (low nutrients) will rely heavily on __________ to obtain nutrients.

Question

BlackTom AI · Accepted Answer

Active transport uses energy to move nutrients into the cell against a concentration gradient, so it is the mechanism relied upon when environmental nutrient concentrations are very low.

1) Relevant concepts and definitions
- Simple diffusion: passive movement of molecules down their concentration gradient through the membrane lipids. No energy or proteins required.
- Facilitated diffusion: passive movement down a gradient through membrane transport proteins (channels or carriers). Also no energy input.
- Active transport: movement of solutes against their electrochemical or concentration gradient using energy (ATP hydrolysis or the proton motive force) and specific transporters (e.g., ABC transporters, symporters, antiporters).
- Endocytosis: uptake of large particles or volumes by membrane invagination; typical of eukaryotic cells, not prokaryotic bacteria.

2) Step-by-step reasoning
- In tap water the external concentration of many nutrients is extremely low compared with the bacterial cytoplasm.
- If a bacterium tried to rely on simple diffusion or facilitated diffusion, transport would only occur down a gradient; with lower outside concentration there will be no net inward flux (and diffusion could even cause net loss).
- To accumulate nutrients to physiologically useful intracellular levels, bacteria must move solutes from low (outside) to higher (inside) concentrations. That requires energy input.
- Bacteria therefore use active transport systems (ATP-driven ABC transporters or proton/sodium-motive force–driven symporters/antiporters) to concentrate nutrients.

3) Intermediate conceptual steps (no numeric calculation)
- External [nutrient] << Internal [nutrient] → passive flux unfavorable.
- Energy + specific transporter → net inward transport possible.

4) Why the correct answer is correct
Active transport is the only listed mechanism that provides the energy-dependent, uphill movement required to import scarce nutrients from dilute environments such as tap water.

5) Why other options are incorrect
- Simple diffusion: passive and cannot concentrate nutrients when external levels are low.
- Facilitated diffusion: still passive; carriers only allow movement down a gradient, so cannot import against a low external concentration.
- Endocytosis: a eukaryotic mechanism; bacteria generally lack the membrane machinery for endocytosis and use transport proteins instead.

6) Conclusion
Therefore, active transport is the appropriate mechanism for bacteria in low-nutrient tap water, confirming the provided answer: active transport.

Bacterial cells found in your tap water (low nutrients) will rely heavily on __________ to obtain nutrients. 单项选择题

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