HOMEOSTASIS and the PLASMA MEMBRANE

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HOMEOSTASIS and the PLASMA MEMBRANE

• Chapter 7-3

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Maintaining a Balance

• All organisms are subject to changes in their
  environment temperature, pressure, gas levels,
  sunlight, chemicals, etc.

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• Cells must be able to control what enters and
  what leaves while at the same time maintaining
  concentrations of water, salts, glucose, etc. as
  they eliminate wastes and other
  unnecessary materials.

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STRUCTURE of the PLASMA MEMBRANE

• The plasma membrane which is selectively
  permeable is responsible for this regulation.

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Plasma Membrane

• 2 layers of phospholipids (phosphate heads with
  lipid tails)

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• hydrophobic tails facing away from the watery
  environments
• hydrophilic heads facing watery environments

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• The lipid layer is periodically embedded with two
  kinds of proteins
• integral proteins
• peripheral proteins

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Integral Proteins

• Proteins that span the width of the cell membrane
  from surface to surface act as channels to help
  ferry non-lipid soluble materials into the cell
  (glucose, amino acids, large molecules, etc.)

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Peripheral Proteins

• Proteins that are on one surface of the membrane
  only
• act as markers (flags) or as docking sites for
  other chemicals such as
  hormones and enzymes.

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Fluid-Mosaic Model

• Because the lipids are not bound together, they
  can move side-to-side in a fluid fashion.

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peripheral protein
integral protein
peripheral protein
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Cellular Transport
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• Molecules are constantly in motion and are always
  colliding with each other.

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Movement of Materials Through a Cell Membrane

• Passive Transport
• Active Transport

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• PASSIVE TRANSPORT
• Does NOT require energy from the cell - from HIGH
  to LOW concentration

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Active Transport

• A process that requires energy that enables
  material to move across the cell membrane AGAINST
  a concentration gradient

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Passive TransportDiffusion

• Diffusion Simulation

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• The process by which molecules of a substance
  move from areas of high concentration to areas of
  low concentration.

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• Diffusion Gizmo ExploreLearning

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Osmosis

• Diffusion of water molecules through a
  selectively permeable membrane.

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OSMOSIS The diffusion of water molecules.
Diffusion across a membrane (osmosis)
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Effects of Osmosis on Cells

• Isotonic concentration of solutes is the SAME
  inside and outside cell membrane

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Effects of Osmosis on Cells

• Hypertonic solution has HIGHER solute
  concentration than the cell

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Effects of Osmosis on Cells

• Hypotonic solution has a LOWER solute
  concentration than the cell

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• Hypertonic, Hypotonic, Isotonic

• Passive Transport

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Facilitated diffusion

• Movement of specific molecules through a cell
  membrane through protein channels

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• ACTIVE TRANSPORT
• Requires ENERGY by the cell. From LOW to HIGH
  concentration

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• Individual molecules are carried through the
  membranes via proteins in the cell membrane.

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• Active transport

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Endocytosis (Type 1)

• the process of taking the material INTO the cell
  by infoldings of the cell membrane.

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Two Types

• Phagocytosis engulfing of large particles into
  the cell.

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Two Types

• Pinocytosis cell takes in fluid from the
  surrounding environment

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• Types of Endocytosis with sound

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Exocytosis (Type 2)

• Molecules are taken up by the cell forming
  pockets along the membranes to REMOVE molecules
  from the cell.

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Exocytosis
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Quiz
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If you start with A, do you end up with B or C?
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• 1. Define diffusion.
• 2. Define osmosis.
• 3. Define active transport.
• 4. What is endocytosis and exocytosis?