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Cell Membranes and Transport

Homeostasis

� Homeostasis is the balance cells must

maintain with their surrounding environment.

� Cells maintain homeostasis by controlling what enters and exits the

cell.

The Cell Membrane

� Made of a bilayer of phospholipids

� Phospholipids have a hydrophobic tail (water

fearing) and hydrophilic head (water loving).

� Proteins are embedded in the membrane to

help move materials in-and-out of the cell.

The membrane is called a

fluid-mosaic – why?

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3

Figure 7-12 The Structure of the Cell Membrane

The Cell Membrane The Cell Membrane

� Cell membranes are SELECTIVELY

PERMEABLE – what does this mean?

Ex. The strainer lets water

pass through, yet keeps the pasta in. It is selectively

permeable.

The cell membrane has some control over what can cross it, so that only

certain molecules either enter or leave the cell.

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Passive Transport

• Movement of molecules across the cell membrane that DOES NOT USE ENERGY.

• Materials move from an area of HIGH CONCENTRATION to an area of LOW CONCENTRATION.

Summary for page 1

� You have 2 minutes to write your

summary.

� Ex. Homeostasis is the balance cells must

maintain with their surrounding environment.

� The cell membrane is made up of a

phospholipid bilayer and carrier proteins that helps control what enters and leaves the cell.

� The membrane is also selectively permeable and uses passive transport to move materials from a high concentration to an area of low

concentration.

Diffusion

� Diffusion – Movement of molecules through the cell membrane

• A type of PASSIVE TRANSPORT because it DOES NOT USE ENERGY.

Diffusion Checkpoint

� What direction will the molecules move?

Diffusion Checkpoint Pt. 2

� When is equilibrium reached?

� EQUILIBRIUM is reached when

concentrations are equal on both sides of the cell membrane.

� Lets act it out!!!!!

Osmosis

� Osmosis – diffusion of WATER molecules through the cell membrane (passive

transport)

• Water always diffuses from an area of LOW SOLUTE CONCENTRATION to an area of HIGH SOLUTE CONCENTRATION.

• OR ���� High Water Concentration to Low Water Concentration

� Solute is…..??

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Osmosis Osmosis

� Hypotonic solution –

solute concentration

is lower on the outside of the cell

than inside the cell.

• Water moves INTO the cell

� Hypo= low, below normal

Osmosis

� Hypertonic solution –solute concentration

is higher on the outside of the cell

than inside the cell.

• Water moves out of the cell

� Hyper= excessive; more

Summary for page 2

� You have 2 minutes to write your

summary.� Ex. Diffusion is the movement of molecules through the cell

membrane. It is a type of passive transport. Equilibrium is

reached when concentrations are equal on both sides of the cell membrane.

� Osmosis is the diffusion of WATER molecules through the cell

membrane. It travels from an area of high concentration to an

area of low concentration.

� Hypotonic solution is when solute concentration is lower on the

outside of the cell than inside the cell.

� Hypertonic solution is when solute concentration is higher on the outside of the cell than inside the cell.

Osmosis

� Isotonic solution –solute concentration

is equal on both sides of the cell membrane.

• Water diffuses in-and-out equally

� Iso= equal or the same

Osmosis and Plant Cells

� Plant cells require a hypotonic environment so water moves into the cell and the cell swells• Swelling of the cell builds up turgor pressure

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Osmosis and Plant Cells

� Plant cells in hypertonic environments lose water and the cell shrivels up. • Shriveling of the cell is called plasmolysis.

Osmosis Checkpoint

� What would happen to animal cells in

hypotonic and hypertonic environments?

Osmosis Summary for page 3

� You have 2 minutes to write your

summary.� Ex. Isotonic solution is when solute concentration is

equal on both sides of the cell membrane.

� Plant cells require a hypotonic environment so water moves into the cell and the cell swells(turgor pressure ).

� Plant cells in hypertonic environments lose water and the cell shrivels up (plasmolysis).

Osmosis

� For example, marine fish:

Facilitated Diffusion

� Facilitated diffusion - moves molecules in-and-out of the cell using a carrier protein (passive transport)

� Why would molecules need help from a carrier protein?• Too big

• Can not dissolve in the phospholipid bilayer.

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Active Transport

� Active transport - movement of molecules across the cell membrane that requires

energy.

� Can move materials from an area of LOW

CONCENTRATION to an area of HIGH CONCENTRATION. (Opposite of diffusion)

Active Transport

� Why does your body need to use active

transport?

� Na+/K+ pumps for neuron function

� Video

� Remember to take notes!!

Endocytosis

� Large molecules can be engulfed by

cells in a process called

ENDOCYTOSIS. (Active transport)

� Pinocytosis - process of engulfing a

liquid. (“Cell drinking”).

� Phagocytosis - process of engulfing a solid. (“Cell eating”).

Endocytosis

Summary for page 4 & 5

� You have 2 minutes to write your

summary.� Facilitated diffusion - moves molecules in-and-out of

the cell using a carrier protein (passive transport).

� Active transport is the movement of molecules across the cell membrane that requires energy.

� Large molecules can be engulfed by cells in a process called endocytosis. Pinocytosis is process of engulfing a liquid. Phagocytosis is process of engulfing a solid.