4. Transports across cell membranes

Question 1

Define diffusion.

Answer 1

the net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.

• passive transport
• only small non-polar molecules can diffuse across cell-surface membranes such as oxygen and carbon dioxide

Question 2

What are protein channels and describe some of their features.

Answer 2

• A channel protein is a protein that allows the transport of specific substances across a cell membrane
• water filled channels
• allows only specific water soluble ions to pass through
• channel will remain closed unless specific ion is present.

Question 3

list some features of facilitated diffusion.

Answer 3

passive process
relies on kinetic energy of diffusing molecules - molecules binds to protein, which causes it to change shape and allow the molecule to pass through
happens through transmembrane channels and carriers
occurs down a concentration gradient