Cell Boundaries

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Cell Boundaries

• MIAMI BEACH SENIOR HIGH
• MRS DIAZ

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I. Cell (Plasma) Membrane

• The cell membrane is composed of lipids (because
  they can separate substances.)

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Cell Membrane (contd)

• The membrane is made of many phospholipids which
  have two parts hydrophilic (water loving) heads
  and hydrophobic (water fearing) tails. The heads
  are made of Glycerol (alcohol) and a phosphate
  group and the tails are chains of fatty acids.

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Phospholipids

• Phospholipids can move side to side and allow
  water and other non-polar molecules to pass into
  and out of the cell. This is known as simple
  diffusion because it does not require any energy
  and the water or molecules are moving with/down
  the concentration gradient. (high to low
  concentration)

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Cell Membrane (contd)

• Notice also that the membrane is made of two
  layers of lipids, thus we call it a phospholipid
  bilayer.

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Cell Membrane (contd)

• Also found in the cell membrane are certain
  proteins, which play an important part in the
  cell by
• 1) Coordinating cell-to-cell behaviors.
• 2) Adjusting the cells metabolism rates.
• 3) Initiating growth division times.

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Cell Membrane (contd)
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Cholesterol
Another type of lipid in the cell membrane is
cholesterol which makes the membrane stronger. .
Embedded in the phospholipid bilayer are
glycoproteins that aid in identification and in
cell recognition.
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Proteins
Proteins called integral proteins go all the way
through the bilayer, while peripheral proteins
only stay on one side. Integral proteins are also
called a protein channel. Large molecules like
lipids or carbohydrates use protein channels to
move across membranes.
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Carbohydrates
Some of the membrane proteins called
glycoproteins have carbohydrate chains attached
to help cells recognize each other and certain
molecules. Carbohydrate chains attached directly
to phospholipids are called glycolipids
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4 Functions of the cell membrane

1. Cell to Cell recognition
2. Regulates what enters the cell
3. Cell signaling
4. Separates the cell from the environment

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Passive Transport Chapter 4 Section 1

• Passive transport (no energy required) can occur
  in 4 different ways
• i) Simple Diffusion
• ii) Osmosis
• Passive Transport (contd)
• During passive transport substances always move
  from high concentration to low concentration
  (this is known as a concentration gradient).
• After passive transport when the concentration of
  molecules is the same we say equilibrium exists.

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i) Diffusion

• Diffusion is the movement of molecules down a
  concentration gradient, from high to low
  concentrations.

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ii) Osmosis

• Osmosis is the diffusion of water across a
  semipermeable (cell) membrane.
• Water will move down the concentration gradient

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b) Types of Solutions

• 1. Hypertonic solution with a higher
  concentration of dissolved particles than its
  surroundings.
• 2. Hypotonic solution with a lower concentration
  of dissolved particles than its surroundings.
• 3. Isotonic solution with an equal concentration
  of dissolved particles to its surroundings.

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c) Water Balance in a Cell

• 1. Cells placed in a hypertonic environment (salt
  water) will plasmolysis. SHRINK!

2. Cells placed in a hypotonic environment (fresh
water) will cytolysis. BURST!
Cells placed in a isotonic environment will be
balanced
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Water Movement Problemsexplain what will happen
in each example


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Active Transport (contd)

• Active transport is the movement of molecules up
  (against) the concentration gradient, from low to
  high.
• This type of transport requires energy in the
  form of ATP.

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b) Phagocytosis

• Process where a vacuole is formed around solid
  particles before they are taken into the cell.

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2) Exocytosis

• Process by which large molecules are passed out
  of the cell without going through the membrane.

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Levels of Organization

• Atoms
• Molecules
• Cells
• Tissues
• Organs
• Organ Systems
• Organism

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Final Thought

• Knowledge is not simply another commodity. On
  the contrary. Knowledge is never used up. It
  increases by diffusion and grows by dispersion.
  --Daniel J. Boorstin