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Question

Difficulty: MediumCell Structure and Function

In order to maintain homeostasis, a living cell must strictly regulate the exchange of water, nutrients, and waste products across its outer boundary. Which cellular structure forms a selectively permeable phospholipid barrier that controls the entry and exit of substances?

  1. A
    Cell wall
  2. Plasma membraneAnswer
  3. C
    Cytoskeleton
  4. D
    Endoplasmic reticulum

Answer

The plasma membrane forms the selectively permeable phospholipid barrier regulating cellular transport.
The plasma membrane (cell membrane) is composed of a phospholipid bilayer with hydrophilic heads facing the aqueous environment and hydrophobic tails forming an interior barrier. Embedded transport proteins, channels, and receptor proteins enable the membrane to maintain homeostasis through selective permeability.

Step-by-Step Solution

1
Analyze the functional requirement described in the question stem
The question asks for the outer boundary structure responsible for selective permeability and transport control.
Identifying the target biological role clarifies which cellular structure performs this function.
2
Evaluate the composition and function of candidate cellular structures
The plasma membrane is composed of a phospholipid bilayer with embedded transport proteins that selectively allows certain molecules to pass while blocking others.
Matching structural composition (phospholipid bilayer) and functional role (selective permeability) pinpoints the correct organelle.
3
Distinguish between boundary support and selective transport regulation
While structures like the cell wall provide rigid outer structure in specific organisms, the plasma membrane is universally responsible for regulated transport and homeostasis across all cells.
Eliminates distractors that provide physical structure or internal synthesis rather than outer selective barrier control.

Key Concept

Cell membrane structure and selective transport
Estimated Time:1m 0s
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Topics

Cell Structure and Function

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