Chapter 7.3Cell Transport

Warm-Up

What do you know so far about the cell membrane?

What do you want to know about the cell membrane?

Cell Membrane Structure & Function• Phospholipid Bi-layer (hydrophilic heads, hydrophobic tails)

– Fluid-Mosaic Model– Proteins & cholesterol embedded within the phospholipid bi-layer– Selectively Permeable – controls was enters and exits the cell

Fluid-Mosaic Model• Channel Proteins:– Allow molecules, such as

water, to pass through the cell membrane

• Recognition/ID Protein:– Has carbohydrate chains attached

that are used as ID markers– Allow cells to communicate with

eachother and identify foreign invaders (other blood type, virus)

• Protein Pump:– Use ATP (energy) to pump

substance across the membrane

Fluid-Mosaic Model

• Cholesterol:– Lipid that controls the

fluidity of the cell membrane

Cell membrane transport

• There are 2 types of cell membrane transport:

– Passive Transport• Things flow fromHigh to low

– Active Transport• Things flow from Low to high

Another perspective on passive and active transport

Passive Transport

• Diffusion– The movement of particles from areas of high

concentration to low concentration – http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html – http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html

Equilibrium

• When is equilibrium reached when discussing cell membrane transport?– When the concentrations of particles are the same

on both sides

Facilitated Diffusion

• Particles flow from high concentration to low concentration but this time they need the help of proteins to get through the cell membrane.

Facilitated diffusion

Passive transport

• Osmosis– The diffusion of water across a selectively permeable membrane– Important in maintaining cell homeostasis– Water flows to side of membrane where the water concentration

is lower until equilibrium is reached

Osmosis

• Osmosis is controlled by the amount of solutes on either side of a membrane

Osmosis – Types of Solutions

• When dealing with osmosis, water can either move into the cell or out of it.

• The solute can not move to equal out the solution so the water has to.

• We describe the solutions that cells are in as either hypotonic, isotonic, or hypertonic.

What are the concentrations?

90%

40%

Isotonic Solution

• Isotonic solution – Concentration of solute is the same in the cell and the area around the cell.

• Give me an example of an isotonic solution that some of you use everyday

Isotonic solution

Hypotonic Solution

• Hypotonic Solution – Concentration of solute is lower in the solution than in the cell.

• Where is water going to move in order to reach equilibrium (Equal concentrations)?– Inside the cell

Hypotonic solutions

• Since water moves into the cell the cell can explode

•http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

• So, Hypotonic solution, low concentration of solute, cell can explode

Plant and animal cells in a hypotonic solution

Hypertonic Solution

• Hypertonic solution – concentration of solute is higher in the solution than in the cell.

• Where is water going to move in order to reach equilibrium (Equal concentrations)?– Outside the cell

Hypertonic solutions

• Since water moves out of the cell the cell will shrink

•http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

• So, Hypertonic solution, high concentration of solute, cell will shrink

Plant and animals cells in a Hypertonic Solution

Osmosis

• http://www2.nl.edu/jste/osmosis.htm

• http://www.coolschool.ca/lor/BI12/unit4/U04L06/rbc.html

Active Transport

• Molecules move from low concentration to high concentration– Requires energy….why?

Active Transport

• Molecular Transport –– Protein Pumps• Small molecules and ions carried across the cell

membrane by proteins in the membrane that act like pumps

• Bulk Transport– Endocytosis – in!– Exocytosis – out!

Other membrane transport activities that require energy

• Endocytosis– Engulfing of large particles or liquids from outside the

cell

2 types of Endocytosis

• Phagocytosis– Engulfing of large particles from outside the cell

• Pinocytosis– Engulfing of liquids from outside the cell

Other membrane transport activities that require energy

• Exocytosis– Release of large particles or liquids from inside the

cell

Inside the cell

Outside the cell