Biology Chapter on Diffusion

Diffusion

• Definition: The movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient due to their random movement.
• Down a concentration gradient: Higher concentration to lower concentration.
• Against a concentration gradient: Lower concentration to higher concentration.
• Reasons for diffusion:
  • Random movement of molecules provides energy for diffusion.
  • Difference in concentration of a substance.

Factors affecting the rate of diffusion (TADS):

• Temperature: Increased temperature increases the rate of diffusion as kinetic energy of molecules increases.
• Distance of diffusion: Longer distance, longer time for diffusion.
• Air currents: Currents in the same direction as diffusion increase the rate of diffusion.
• Stirring: Increases the rate of diffusion by increasing kinetic energy of molecules.
• Size of molecules: Smaller molecules diffuse faster.
• Surface area to volume ratio: Larger surface area to volume ratio, faster diffusion rate.

Active Transport

• Definition: The movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration against a concentration gradient, using energy released during respiration.
• Uses carrier proteins: Specific proteins embedded in cell membranes that bind to and transport particles.
• Energy source: Energy released during respiration.

Factors affecting active transport:

• Number of mitochondria: More mitochondria means more energy for active transport.
• Concentration of oxygen: Higher oxygen concentration increases the rate of aerobic respiration, providing more energy for active transport.
• Number of carrier proteins in the membrane: More carrier proteins mean a greater capacity for active transport.

Diffusion

• Movement of particles from an area of high concentration to an area of low concentration. This is down a concentration gradient.
• Factors affecting diffusion:
  • Temperature: Higher temperatures increase the rate of diffusion due to increased kinetic energy of molecules.
  • Distance: Longer distances mean longer diffusion times.
  • Air currents: Currents in the same direction as diffusion increase the rate.
  • Stirring: Increases kinetic energy leading to faster rates of diffusion.
  • Size of molecules: Larger molecules diffuse slower (inversely proportional).
  • Surface area to volume ratio: Larger surface area to volume ratios lead to faster rates of diffusion (directly proportional).

Active Transport

• Movement of particles against a concentration gradient (low to high concentration).
• This process requires energy released during respiration.
• It is facilitated by carrier proteins embedded in the cell membrane.
  • Carrier proteins bind to specific molecules, ensuring specificity in transport.

Factors Affecting Active Uptake

• Number of mitochondria: More mitochondria lead to increased rates of active transport because mitochondria are responsible for aerobic respiration, which generates energy needed.
• Concentration of oxygen: Higher oxygen concentration increases the rate of aerobic respiration, providing more energy for active transport.
• Number of carrier proteins: More carrier proteins mean a higher capacity for active transport.