Cell Transport

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Chapter 4

• Cell Transport
• Passive and Active Transport

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Cell Transport

• Cell membranes help maintain homeostasis by
  controlling which substances may enter or leave
  the cells.
• Cells can transport substances across the
  membrane with or without the use of energy!
• 1. Passive Transport (no energy)
• 2. Active Transport (energy)

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• Passive Transport
• Movement across the cell membrane that does not
  require energy from the cell
• Semi-permeable Membrane (Figure 4-1)
• 3 Types of Passive Transport
• 1.
• 2.
• 3.
• Demo Food Coloring

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Vocabulary Words

• Diffusion
• Movement of a substance from an area of low
  to high
• Going down a gradient (spraying air
  fresher/food coloring)
• Concentration Gradient
• A difference in the concentration of a substance
  (high to low)

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• Equilibrium
• Condition in which the concentration of a
  substance is equal throughout a space
• Osmosis
• Diffusion of water through a selectively
  permeable membrane
• 3 Types of Water Movement
• Hypotonic Water moves into the cell (SWELLS)
• Hypertonic Water moves out of the cell
  (SHRINKS)
• Isotonic Cell stays the same size

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Direction of Water Movement Pg. 41
Solvent does the dissolving (water) Solute
what is being dissolved Osmosis Animation
Osmosis Potato Demo
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Osmosis in Potato Slices
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Proteins Help Some Substances Cross the Cell
Membrane (pages 78-80)(Diffusion Through Ion
Channels)

• Most ions and polar molecules cannot simply pass
  through the cell membrane
• Ex of ions Cl-, Na, K, and Ca2
• Able to cross the cell membrane through
• Ion Channels
• doughnut-shaped transport protein with a polar
  pore through which ions can pass
• Note Some ion channels are always open and
  others need a stimulus to open such as, an
  electrical charge, or binding of specific
  molecules to the ion channel. Very specific

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Diffusion through ion channel

• Ions are essential because (examples)
• ability of nerve cells to send electrical
  signals, muscle cells in heart could not make
  heart beat without ion movement

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• The movement of some substances is not only
  determined by concentration gradient, but also
  charge
• The inside of a cell is usually negative so
  molecules with a positive charge are attracted.
• Molecules with a negative charge inside the cell
  are more likely to go out.

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• Question Why do athletes drink sports drink
  during and after a game?
• Replacing sodium and potassium ion lost (during
  sweating)
• The diffusion of ion through ion channels is a
  form of passive transport because there is no
  energy required.

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Facilitated Diffusion

• What are carrier proteins?
• Proteins that carries a specific substance across
  a cell membrane
• Facilitated Diffusion
• passive transport using carrier proteins
• moves substances down a concentration gradient
  without using the cells energy.

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• Using Figure 4-4
• How does facilitated diffusion work?

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Follow-up Passive Transport

• 3 types of Passive Transport
• Diffusion
• Osmosis
• Facilitated Diffusion
• Passive Transport PT

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Questions to Think about

• 1. Why are green leafy vegetables sprinkled with
  water at the grocery store?
• This prevents them from wilting due to water
  loss
• 2. Why is salt sometimes used to preserve foods?
• Salt solution is hypertonic, the microorganisms
  present on the foods will shrink and die.

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• 3. Why should you not drink sea water?
• Sea water contains high concentrations of
  solutes, so drinking sea water would increase the
  of solutes outside body cells. The cells
  would lose water because of osmosis and possibly
  die.
• 4. Why do people gargle with salt water as a
  remedy for a sore throat?
• Some pain associated with a sore throat is
  caused by swelling of the throat tissues, which
  contain water. When a person gargles salt water,
  which contains a lower of water than do most
  throat tissues, water moves by osmosis from the
  throat tissues into the salt water. This
  decreases the swelling and relieves some of the
  pain!

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Section 4-2 Active Transport

• ACTIVE TRANSPORT
• The transport of a substance across the cell
  membrane against its concentration gradient, thus
  requiring ENERGY
• Low concentration to a high concentration
• ATP energy needed
• Carrier proteins in active transport act more
  like pumps.

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Active and Passive Transport
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Sodium-potassium Pump Figure 4-5

• One of the most important membrane pumps in
  animals cells.

Sodium-Potassium Pump
Pumps 3
Pumps 2
Potassium ions
Sodium ions
Out of the cell
Into the cell
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• The Na-K pump is important for 2 main reasons
• 1. Prevents sodium ions from accumulating in the
  cell--toxic to the cell.
• 2. Na-K Pump helps maintain the concentration
  gradient of sodium ions and potassium ions across
  the cell membrane.
• Animation Na/K Pump

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Vesicles Move Substances Across Membranes

• Many substances are too large to be transported
  by carrier proteins, such as polysaccharides and
  proteins, and must be transported by vesicles
• Endocytosis The movement of a substance into a
  cell by a vesicle (entering)
• ExocytosisThe movement of a substance by a
  vesicle outside of a cell (exiting)
• Pinocytosis cell drinking

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Figure 4-6
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Membrane Receptor Proteins Receive Information

• A protein that binds to a specific signal
  molecule, enabling the cell to respond to the
  signal molecule is called a Receptor Protein.
• Examples
• Muscles could not contract without receptor
  proteins and signal molecules that tell the
  muscles when to contract and relax.

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Membrane Receptor Proteins Receive Information

• A. A receptor Protein binds to a specific signal
  molecule and enables the cell to respond to a
  signal molecule
• B. Cells must communicate with each other to
  coordinate growth and metabolism and homeostasis
• C. Functions of Receptor Proteins are specialized
  to particular substances
• D. Many drugs affect the binding of signal
  molecules to receptor proteins.
• E. Other molecules, like beta-blockers, bind to
  receptor proteins and prevent the heart rate from
  increasing.
• Active Transport AT