3.2.3 - Transport across cell membranes

Which types of molecules are able to pass through the plasma membrane via simple diffusion?

• Non-polar

• Small

• Lipid-soluble

Which types of molecules aren’t able to pass through the plasma membrane via simple diffusion?

• Polar

• Large

• Lipid insoluble

What are the 5 types of transport across membranes?

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Active transport

• Co-transport

What are some adaptations for rapid transport and examples?

• Increased surface area - folds in the phospholipid bilayer for larger surface area

• Increased number of channel/carrier proteins - folds in the phospholipid bilayer for more proteins

• Many mitochondria (only in active/co-transport) - for greater hydrolysis of ATP therefore more energy

What is a passive process?

Transport down the concentration gradient - requires no energy

How does facilitated diffusion take place with a carrier protein?

Molecules will bind with the carrier protein which causes a change in shape (application = 3D tertiary structure) of the protein which enables the molecule to be released on the other side

Define osmosis

Movement of water from high water potential to low water potential across a partially permeable membrane

Is a water potential closer to -1, more or less pure than a water potential closer to 0?

Less pure closer to -1 because it has less water in it and more of other molecules dissolved in it

What does isotonic, hypotonic and hypertonic mean?

Isotonic - water potential is same in and out of cell

Hypotonic - water potential is higher outside the cell

Hypertonic - water potential is higher inside the cell

Define active transport

The movement of a substance from a low to high concentration using energy and a carrier protein

Where does the energy come from in active transport

The hydrolysis of ATP

Define the steps in co-transport

• Na+ ions are actively transported out of the epithelial cell into the blood

• This reduces Na+ concentration in the epithelial cell

• Na+ ions diffuse down the concentration gradient into the epithelial cell from ileum

• They diffuse down the concentration gradient via a co-transporter protein which transports two molecules at once

• The other molecule that gets transported is either glucose or an amino acid and this is against the concentration gradient

• The glucose/amino acid then moves into the blood via facilitated diffusion