Notes 3-4

1
Notes 3-4

• The Cell in Its Environment

2
Cell Membrane

• Provides protection for the cell
• Chooses what comes in and out of cell
• It is selectively permeable, which means it lets
  some substances pass through the membrane, and
  other substances cannot

3
Cell Membrane

• Here is the cell membrane magnified
• Remember it surrounds the entire cell
• Notice it is made up of lipids, proteins, and
  carbs (3 of the organic molecules from section
  3-3)

4
Passive Vs. Active Transport

• Passive Transport

• Active Transport

• Movement of materials through cell membrane
  WITHOUT energy
• Materials move from a high concentration of the
  material to a lower concentration of material
• Its like rolling down a hill (no energy is needed)

• Movement of materials through cell membrane WITH
  energy
• Materials move from a low concentration of the
  material to a higher concentration of material
• Its like trying to roll up a hill (imagine how
  hard that would be and how much of your energy it
  would take)

5
Passive and Active Transport

• Passive and active transport are two processes by
  which materials pass through the cell membrane.
  Active transport requires the cell to use its own
  energy, while passive transport does not.
• When looking at the images, pay attention to what
  is meant by low concentration of materials versus
  high concentration of materials.

6
Diffusion

• Molecules move across cell membrane without
  energy (passive transport)
• Move from high concentration to low concentration
• Molecules continue to pass through membrane until
  there are equal amounts of molecules inside the
  cell as outside the cell
• Remember, Molecules can only diffuse through the
  membrane if the membrane is permeable to it (if
  the membrane chooses to let it in!)

7
Diffusion

• In diffusion, molecules move from an area of
  higher concentration to an area of lower
  concentration.

8
Osmosis

• Special example of diffusion- Osmosis is the
  diffusion of WATER!
• Passive transport, no energy required
• Water will move from a high concentration of
  water to an area of low concentration of water
  until amount of water is equal inside and outside
  the cell
• If too much water moves out of cell, the cell
  will shrivel (not good)
• If too much water moves into cell, cell will
  burst (not good)
• Cell needs to maintain a balance to function
  properly

9
Osmosis
Notice how the different concentrations of water
choose whether water moves into or out of cell
10
A selectively permeable membrane separates the 2
sides of the solution. The arrow shows that water
is moving towards the right side. WHY?
Water is moving from an area where water is high
to an area where water is low, and the membrane
is permeable to water.
Why are the sugar molecules not moving across the
membrane?
The membrane must not be permeable to sugar
(otherwise the sugar would be moving to the left
side, from high to low concentrations of sugar)
11
Transport Proteins

• There are proteins embedded in the cell membrane
  that pick up materials and bring them into cell
  or carry them out of cell
• Active transport, so requires energy
• Brings materials from low concentration to high
  concentration
• Each protein recognizes and carries a specific
  molecule such as calcium, potassium, or sodium.

12
Transport Proteins

• This proton pump is a transport protein.
• ATP is the energy its using.
• Notice its pumping Hydrogen Ions out of the cell
  (from low concentration to high concentration)

Why does this process require energy (ATP)?
Because it is using active transport (it is
transporting materials from low to high
concentration).
13
Engulfing

• Cell extends its cytoplasm and cell membrane,
  surrounds molecule, and engulfs it (encloses it)
• A vacuole is formed around molecule in this
  process
• Process known as endocytosis (meaning inside
  cell)
• A form of active transport, requires energy

14
Cell Size

• Cells must be small in order to function properly
• If cells were too big, it would take too long for
  molecules to pass from one side of the cell to
  the other
• Also, if cells were too big, it would take too
  long for wastes to be removed

15
Lets Review

• Passive transport requires energy- True or False?

• Does diffusion require energy?

No, because it is an example of passive transport.
False! Active transport does! Think of it like
this you need energy to be active!
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Lets Review

• What are some examples of active transport?

• Osmosis is the diffusion of _________?

WATER
Engulfing (or endocytosis) and transport proteins