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QuestionBiology

Select the feature that best describes cell membranes: A. They are selectively permeable. B. They are impermeable. C. They allow all substances to pass through. D. They are rigid and inflexible.
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Answer

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Step 1:
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Step 2:
: Understand the key characteristics of cell membranes

Cell membranes are complex biological structures that play a crucial role in controlling what enters and exits a cell. To determine the best description, we need to consider the membrane's fundamental properties.

Step 3:
: Analyze the membrane's structure

Cell membranes are composed of a phospholipid bilayer with embedded proteins. This unique structure allows for controlled movement of substances across the membrane.

Step 4:
: Evaluate the given options

A. Selectively permeable B. Impermeable C. Allow all substances to pass through D. Rigid and inflexible

Step 5:
: Reasoning

- Option B (impermeable) is incorrect because membranes do allow some substances to pass through. - Option C is incorrect because not all substances can freely pass through the membrane. - Option D is incorrect because cell membranes are actually flexible and dynamic.

Step 6:
: Understand selective permeability

Selective permeability means the membrane can: - Allow some molecules to pass through - Block other molecules - Control the movement of substances based on size, charge, and other properties

Final Answer

They are selectively permeable. The cell membrane's ability to selectively control what enters and exits the cell is a critical function that maintains cellular homeostasis and protects the cell's internal environment.