THE CELL MEMBRANE, DIFFUSION

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THE CELL MEMBRANE, DIFFUSIONOSMOSIS
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THE CELL MEMBRANE
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Cell Processes

• All materials exchanged between a cell and its
  environment takes place at the cells membrane.
• The cell membrane is made up of
  phospholipidsphosphate-lipids (fat)
• The cell membrane is selectively permeable
  meaning that some substances can pass through
  while other things cannot.

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Cell membrane foundation is a bilayer of
phospholipids
Phosphate head - Polar

• Whats a phospholipid?

Two fatty acid tails. These lipids are non-polar.
Detailed picture of phospholipid
Stick-figure drawing of phospholipid
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Whats a bilayer of phospholipids?

• bi means two
• a bilayer of phospholipids is a double layer of
  phospholipids

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Why are the phospholipids arranged this way?

• Most cells have watery environment on both sides
  of membrane
• Water attracts the hydrophilic (water loving)
  polar phosphate ends of the phospholipids
• Hydrophobic (water fearing) non-polar tails hide
  inside the bilayer

OUTSIDE OF CELL
INSIDE OF CELL
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• There are also proteins embedded in the
  phospholipid bilayer
• Many of the proteins have carbohydrates attached

Carbohydrate attached to protein
protein
OUTSIDE OF CELL
Cell membrane bilayer of phospholipids
proteins
INSIDE OF CELL
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Roles of proteins and carbo-hydrates in the cell
membrane

• Proteins may form
• channels or pumps to help move material across
  cell membrane
• Carbohydrates
• are like chemical ID cards, which allow cells to
  identify each other

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Cell Membranes
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• Passive Transport
• Active Transport

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DIFFUSION
Molecules move from areas of higher
concentrations to areas of lower concentrations
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What is Diffusion?

• Diffusion is the main method by which small
  molecules move across the membrane
• It is the movement of particles from an area of
  high concentration (crowded) to low concentration
  (less crowded)
• It does not require energy

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What diffusing molecules look like
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OsmosisThe diffusion of water or the movement of
water molecules from an area of high
concentration to an area of low concentration.
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Osmosis

• can affect animal cells?cells may shrivel or blow
  up (like a balloon)

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OSMOSIS
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• In this picture a red blood cell is put in a
  glass of distilled water (all water with no salt
  or sugar in it).  Because there is a higher
  concentration of water outside the cell, water
  enters the cell by OSMOSIS.  In this case too
  much water enters and the cell swells to the
  point of bursting open.  In the end pieces of
  cell membrane are left in the water.

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Isotonic
Isotonic contains the same concentration inside
outside the cell. Water diffuses into out of
cell at the same rate.
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Hypotonic contains a low concentration) The
water diffuses into the cell, causing the cell to
swell and possibly explode.
Hypotonic
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Hypertonic contains a high concentration The
water diffuses out of the cell, causing the cell
to shrivel.
Hypertonic
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Moving small particles

• Some particles are small enough to travel between
  the phospholipid molecules (H2O, and O2)
• Others are too large or are repelled by the cell
  membrane (like opposite sides of a magnet) so
  they must use a transport protein to enter of
  leave the cell

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Protein doorways

• Transport proteins may be used without using
  energy?passive transport

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Protein doorways

• Transport proteins may also use energy because
  particles are moving against the gradient or
  from low concentration to high concentration?activ
  e transport (like trying to squeeze many people
  into a telephone booth.) Active transport uses
  energy in the form of ATP (Adenosine
  Tri-phosphate)

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Moving large particles uses active transport

• Cell membrane may use endocytosis where the
  membrane surrounds a large particle and encloses
  it in a vesicle so it may be brought to the
  proper area of the cell.
• THINK endocytosis?enters cytoplasm

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• Cell membrane may use exocytosis where vesicles
  form at the ER (endoplasmic reticulum) or the
  golgi complex and surround the particles and
  carry them to the cell membrane to be removed
  from the cell.
• THINK exocytosis?exits cytoplasm

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Question? How does the cell membrane know what to
let in and what to let out?
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SELECTIVE PERMEABILITY
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SELECTIVE PERMEABILITY
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Critical thinking Questions

• Please copy down the following questions

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Create an analogy about how riding a bicycle up a
hill is similar to active transport. How is
riding a bicycle down a hill similar to passive
transport?
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Why are fresh fruits and vegetables sprinkled
with water at produce markets or at grocery
stores?
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Seawater is saltier than tap water. Explain why
drinking large amounts of seawater would be
dangerous to humans.