The Cell in Its Environment

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The Cell in Its Environment
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Key Concepts

• How do most small molecules cross the cell
  membrane?
• Why is osmosis important to cells?
• What is the difference between passive transport
  and active transport?

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Key Terms

• Selectively permeable
• Diffusion
• Osmosis
• Passive transport
• Active transport

• Some substances can pass through the membrane
  while others cannot.
• Molecules move from an area of higher
  concentration to an area of lower concentration.
• The diffusion of water molecules through a
  selectively permeable membrane.
• The movement of dissolved materials through a
  cell membrane without using cellular energy.
• The movement of materials through a cell membrane
  using cellular energy.

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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.
• Oxygen
• Carbon Dioxide
• Water
• Food molecules
• Waste products

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Diffusion
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What is Diffusion?

• The process by which molecules move from an area
  of higher concentration to an area of lower
  concentration.
• The main method by which small molecules move
  across the cell membrane.

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When Does Diffusion Stop?

• When equilibrium is reached!

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Animation of Diffusion

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_diffusion_wor
  ks.html
• How does diffusion play a role in the following
  situations?
• smelling cookies baking in your oven
• making a pitcher of lemonade
• adding chemicals to a pool
• Can you think of any other examples of diffusion?

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Osmosis
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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.

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How is Osmosis Related to Diffusion?

• Molecules tend to move from an area of higher
  concentration to an area of lower concentration.
• 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.

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Effects of Osmosis on Cells
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Animation of Osmosis

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_osmosis_works
  .html
• Osmosis has a number of life-preserving
  functions.
• assists plants in receiving water
• helps in the preservation of fruit and meat
• used in kidney dialysis
• Osmosis can be reversed to
• remove salt and other
• impurities from water.

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Passive Active Transport
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What is Passive Transport?

• The movement of materials through a cell membrane
  without using cellular energy.
• Diffusion and osmosis are examples of passive
  transport.

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Animation of Facilitated Diffusion

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_facilitated_d
  iffusion_works.html

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What is Active Transport?

• The movement of materials through a cell membrane
  using the cells energy.
• The movement of a substance in the opposite
  direction than they naturally move by diffusion.
• Minerals
• Some sugars
• Most amino acids

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Methods of Active Transport

• Transport Proteins
• pick up molecules
• Examples of substances that are carried . . .
• Calcium
• Potassium
• Sodium

• Engulfing
• Cell membrane surrounds and engulfs, or encloses,
  a particle.
• A vacuole is formed around the engulfed particle.
• Energy is required by the cell to perform this
  function.

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Animation of Active Transport

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_the_sodium_po
  tassium_pump_works.html

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Transport is like Riding a Bike?

• Passive Transport

• Active Transport

• Riding a bike down a hill . . .

• Pedaling a bike up a hill . . .

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Why Are Cells Small?

• Cells become less efficient as they grow.
• The smaller they are, the easier it is for them
  to do their jobs.
• The smaller they are, the easier it is for
  substances to be moved in and out.

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Cells . . .

• . . . More than meets the eye!!