membrane & diffusion notes

KEY CONCEPT The cell membrane is a barrier KEY CONCEPT The cell membrane is a barrier that separates a cell from the external that separates a cell from the external environment.environment.

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane has two major functions.The cell membrane has two major functions.

cell membrane

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane has two major functions.The cell membrane has two major functions.

o forms a boundary between inside and outside of the cell

cell membrane outside cell

inside cell

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane has two major functions.The cell membrane has two major functions.

– forms a boundary between inside and outside of the cell– controls passage of materials

cell membrane outside cell

inside cell

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.

cell membrane

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane is made of a phospholipid The cell membrane is made of a phospholipid

bilayer.bilayer.

cell membrane

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane is made of a phospholipid bilayer.The cell membrane is made of a phospholipid bilayer.

• There are other molecules embedded in the membraneThere are other molecules embedded in the membrane..

protein

cholesterol

proteincarbohydratechain

protein channel

cell membrane

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane is made of a phospholipid bilayer.The cell membrane is made of a phospholipid bilayer.• There are other molecules embedded in the membrane.There are other molecules embedded in the membrane.• The The fluid mosaic model fluid mosaic model describes the membrane.describes the membrane.

protein

cholesterol

proteincarbohydratechain

protein channel

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane is selectively permeable.The cell membrane is selectively permeable.

Some molecules can cross the membrane while others cannot.

Cell membranes are composed of two Cell membranes are composed of two phospholipid layers.phospholipid layers.• The cell membrane is selectively permeable.The cell membrane is selectively permeable.

Some molecules can cross the membrane while others cannot.

KEY CONCEPT Materials move across membranes because of concentration differences.

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

Concentration Gradient: when there is a difference in concentration between two areas

Passive transport does not require energy input from a cell.

• Molecules can move across the cell membrane through passive transport.

• There are two types of passive transport.

• osmosis

• diffusion

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• Molecules diffuse down a concentration gradient.

• How would you define DIFFUSION?!

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• Osmosis is the diffusion of water molecules across a semipermeable membrane.

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• There are three types of solutions.

• isotonic

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

• hypotonic

• hypertonic

Some molecules can only diffuse through transport proteins.

• Some molecules cannot easily diffuse across the cell membrane.

• Facilitated diffusion is diffusion through transport proteins.

3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis