2.5.2 diffusion across membranes

Question 1

simple diffusion

Answer 1

movement of molecules from area of high concentration to area of low concentration
- passive process
- doesn’t involve ATP

Question 2

examples of how concentration gradient across cell membrane is maintained

Answer 2

• oxygen diffuses into cytoplasm of respiring cells into mitochondria = used for aerobic respiration
• carbon dioxide diffuses into palisade mesophyll of plant leaf & then diffuses into chloroplasts = used for photosynthesis

Question 3

factors affecting rate of simple diffusion

Answer 3

1. temperature –> increases = molecules have more kinetic energy = rate of diffusion increases
2. diffusion distance –> thicker membrane = slower rate of diffusion
3. surface area –> large SA = increased rate of diffusion
4. size of diffusing molecules –> smaller ions/molecules diffuse more rapidly
5. concentration gradient –> steeper gradient = faster rate of diffusion

Question 4

describe facilitated diffusion

Answer 4

• small molecules with polarity insoluble in lipid bilayer as can’t interact with hydrophobic tails
• diffuse through water-filled protein channels (pores)
• cholesterol molecules reduce membrane permeability to small water-soluble molecules
• glucose molecules too large for water-filled protein channels = bind to transmembrane carrier protein
• specific carrier proteins for different molecules