Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

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Study for the Biology STAAR Test. Improve your skills with flashcards and multiple choice questions, each question is accompanied by hints and explanations. Prepare for success!

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What characterizes the plasma membrane's structure?

  1. Rigid and impermeable

  2. Fluid and semi-permeable

  3. Solid and permeable only to ions

  4. Hollow and impermeable

The correct answer is: Fluid and semi-permeable

The plasma membrane is characterized by its fluid and semi-permeable structure, which is fundamental to its function in living cells. This fluidity is primarily due to the phospholipid bilayer, where the phospholipids can move laterally within the layer, allowing for flexibility and the ability to adapt to changing conditions. The semi-permeable nature of the plasma membrane means that it selectively allows certain substances to pass through while restricting others, thereby maintaining homeostasis within the cell. This selective permeability is critical for various cellular processes, including the transport of nutrients, waste products, and signaling molecules. The presence of embedded proteins and cholesterol further contributes to this property, with proteins facilitating the transport of materials and cholesterol helping to maintain membrane stability and fluidity. Overall, the fluid and semi-permeable characteristics of the plasma membrane enable it to perform essential functions in cell communication, nutrient exchange, and protection against harmful substances.

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