Movement through Cell Membranes, Cell Specialization, Levels of Organization

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Chapter 5

• Movement through Cell Membranes, Cell
  Specialization, Levels of Organization

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Movement through Cell Membranes

• 4 ways material gets into the cell through cell
  membrane
• 1. Diffusion - substance moves from areas of
  higher concentration of molecules to areas of
  lower concentration

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1. Diffusion

• Depends on two factors
• Concentrations of the substance on either side of
  the membrane
• Permeability of the membrane to the substance
• Permeability how easily a substance can pass
  through a membrane

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• Diffusion will only occur across the cell
  membrane if there are unequal amounts on either
  side of the membrane AND the membrane is
  permeable to that particular substance
• Cell membranes are not permeable to all
  substances, only some they are selectively
  permeable

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2. Osmosis

• The diffusion of water through a selectively
  permeable membrane
• Water moves from an area of higher WATER
  concentration to an area of lower WATER
  concentration
• Osmotic pressure force exerted by osmosis that
  moves water from a more dilute solution to a more
  concentrated solution

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• The cytoplasm of cells has a lower concentration
  of water than fresh water what happens if you
  put a cell into fresh water? (more dilute) into
  salt water? (more concentrated)

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• Plants and bacteria have cell walls which can
  withstand very high osmotic pressure
• Many cells never contact fresh water ex the
  concentration of blood is roughly the same as the
  concentration of the cytoplasm, so osmotic
  pressure not much of a problem
• Other cells, like paramecium, have contractile
  vacuoles to rid themselves of the excess water
  brought in by osmosis this process uses energy
  to contract the vacuole

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3. Facilitated diffusion

• Molecules are transported through the cell
  membrane by carrier proteins (to facilitate means
  to help)
• This still only works if there is a difference in
  the concentrations of the solutions on either
  side of the membrane

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• Diffusion, osmosis, and facilitated diffusion are
  considered passive transport because no energy is
  required movement is from high concentration to
  low concentration

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4. Active transport

• Unlike diffusion, osmosis, and facilitated
  diffusion, this process requires energy and can
  move molecules against the concentration gradient
  (from lower to higher concentration) or move
  molecules with an electrical charge (ions)

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• 1. Individual molecules movement of Na, K,
  Ca into or out of cell or other particles
  against the concentration gradient

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• 2. Large amounts of materials moved by movement
  of the cell membrane
• a. endocytosis process of taking material into
  the cell by means of infolding, or vesicles, of
  the cell membrane
• i. phagocytosis eating solid particles
• ii. pinocytosis drinking fluid particles
• b. exocytosis large molecules are removed from
  the cell

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Cell Specialization

• All cells are not the same there are different
  types of cells that perform different functions
  within an organism
• Some cells are specialized to
• Move
• React to their environment
• Make certain products

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Levels of Organization

• Within a multicellular organism, there are 4
  levels of organization (smallest to largest)
• 1. Cells
• 2. Tissues group of similar cells that perform
  similar functions
• a. muscle
• b. epithelial
• c. nerve
• d. connective

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• 3. Organs group of tissues that work together
  to perform a specific function the tissue can
  be different types
• 4. Organ system group of organs working
  together to perform a certain function
• a. muscular
• b. skeletal
• c. circulatory
• d. nervous

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