Water, Cells, Membranes and Cellular Transport

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Water, Cells, Membranes and Cellular Transport
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HOMEOSTASIS

• survival depends on the ability to maintain
  proper conditions
• maintaining balance is called homeostasis

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The Cell Membrane

• selective permeability- the cell membrane allows
  some materials to enter/exit
• Fluid Mosaic Model- a collage of many different
  proteins and other molecules embedded in a fluid
  lipid bilayer

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The Fluid Mosaic Model
http//home.earthlink.net/shalpine/anim/Life/memb
.htm
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Diffusion

• diffusion- movement of particles from an area of
  higher concentration to an area of lower
  concentration
• the cell membrane does not limit the diffusion of
  water

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Example of Diffusion
http//osmosisproject.tripod.com/diffusion.html
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Osmosis

• osmosis- the diffusion of water across a
  selectively permeable membrane
• concentration gradient- natural movement from
  high to low concentration
• the concentration gradient controls osmosis
• water will flow to the side of the membrane where
  water concentration is lower

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Osmosis Prefixes

• iso- the same
• hypo- less
• hyper- more
• You have 3 types of solutions isotonic,
  hypotonic, and hypertonic

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Osmotic Solutions

• isotonic- same amount of water inside and outside
  the cell
• water enters and exits at the same rate
• hypotonic- less water inside the cell
• water enters the cell
• hypertonic- more water inside the cell
• so water exits the cell

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http//www.tvdsb.on.ca/westmin/science/sbi3a1/Cell
s/Osmosis.htm
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Now you know why its wrong to put salt on slugs.
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Passive Transport

• Any type of transport that does NOT require
  energy (ATP)
• movement is with the concentration gradient
• i.e.- diffusion of water, facilitated diffusion

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Passive Transport cont.

• facilitated diffusion- passive transport of
  materials across the membrane using transport
  proteins
• transport proteins facilitate (assist) molecules
  across the membrane
• movement is with the conc. grad.

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Active Transport

• moves materials against a concentration gradient
• counteracts the force of diffusion
• requires energy from the cell
• transport proteins are involved

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Transporting Large Particles

• endocytosis- a cell surrounds and takes in
  material from its environment
• the material does not pass directly through the
  membrane
• exocytosis- reverse of endocytosis
• materials are expelled from the cell

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Endo- and Exocytosis
http//www.northland.cc.mn.us/biology/Biology1111/
animations/transport1.html