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THE CELL IN ITS ENVIRONMENT
POWER POINT NOTES
Key Terms
• Some substances can pass through the membrane while others cannot.
• In diffusion, molecules move from an area of high concentration to an area of low concentration.
• The diffusion of water molecules through a selectively permeable membrane is osmosis.
• The movement of dissolved materials through a cell membrane without using cellular energy is
passive transport.
• The movement of materials through a cell membrane using energy is called active transport.
Introduction
• Cells have structures that protect their contents from the world outside.
• All cells are surrounded by a cell membrane that separates the cell from the outside environment.
• The cell membrane is selectively permeable, which lets some things enter and leave the cell.
• Name 3 substances that enter and exit a cell through either passive or active transport.
oxygen, carbon dioxide, water, sugar, salt, potassium, waste materials, food particles
What is Diffusion?
• The process by which molecules move from an area of high concentration to an area of low
concentration.
• The main method by which small molecules move across the cell membrane.
What is Osmosis?
• The diffusion of water molecules through a selectively permeable membrane.
• Many cellular processes depend on osmosis because cells cannot function properly
without adequate water.
How is Osmosis related to Diffusion?
• Water molecules move by diffusion from an area where they are highly concentrated through the
cell membrane to an area where they are less concentrated.
Effects of Osmosis on Cells
• Cells placed in distilled water will swell and can possibly burst.
• Cells placed in a concentrated salt solution will shrink and shrivel.
What is Passive Transport?
• The movement of materials through a cell membrane without using energy.
• Diffusion and osmosis are examples of passive transport.
What is Active Transport?
• The movement of materials through a cell membrane using the cell’s energy.
• Give two reasons why active transport may occur instead of passive transport (diffusion/osmosis).

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substance are too large to fit naturally through the cell membrane
substances are going against the concentration gradient
Methods Active Transport
• List 3 ways a cell uses active transport to move molecules/substances between the cell and its
environment.

transport proteins
 “pick up”
 engulfing
“Transport” is like Riding a Bike?


Passive Transport is like riding a bike down a hill.
Active transport is like riding a bike up a hill.
Why are Cells Small?
• The smaller they are the easier it is for them to do their job.