This lesson introduces the plasma membrane’s selective permeability and the basic process of diffusion. These ideas explain how materials can move into and out of cells without the cell using energy.
A plasma membrane is selectively permeable, or semipermeable: it allows some substances to pass while limiting or preventing others. This selectivity helps a cell obtain needed materials, retain essential substances, and keep harmful materials out. Without it, the cell could not maintain the conditions needed to survive.
All flashcards
What is selective permeability?
A membrane property that allows some substances to cross while restricting others.
What is a concentration gradient?
A difference in the concentration of a substance between regions.
Why can lipid-soluble molecules cross the plasma membrane relatively easily?
They pass through the membrane’s hydrophobic core more readily than charged or polar substances.
What is facilitated diffusion?
Passive movement of substances down their concentration gradients with help from membrane proteins.
What is turgor pressure?
Pressure from cell contents against the cell wall that helps stiffen plant cells.
Quiz questions
What distinguishes a channel protein from a carrier protein in facilitated diffusion?Answer: A channel forms a passage through the membrane for particular substances.
How does facilitated diffusion move a substance across a membrane?Answer: Through a membrane protein, down its concentration gradient, without ATP expenditure.
Across a semipermeable membrane, which way does water move by osmosis?Answer: From the side with more free water toward the side with less free water.
What may happen to an animal cell placed in a hypotonic solution?Answer: Water enters, causing the cell to swell and possibly lyse.
How does turgor pressure help support nonwoody plants?Answer: Water pressure pushes cell contents against the walls, stiffening the cells.
Based on Concepts of Biology by Samantha Fowler, Rebecca Roush, James Wise (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.