osmosis, active transport and diffusion

• What is diffusion?

  Movement from high to low concentration
• How do molecules move during diffusion?

  They move down the concentration gradient
• Does diffusion require energy input?

  No, it is a passive process
• What type of membrane allows diffusion to occur?

  Semi-permeable membrane
• Can glucose diffuse through a semi-permeable membrane?

  No, glucose cannot diffuse through
• What is osmosis?

  Diffusion of water across a membrane
• What happens to water when there is a higher concentration of glucose outside a cell?

  Water moves out of the cell
• What is the effect of water moving out of a cell?

  It results in a decrease in mass
• What factors can increase the rate of diffusion and osmosis?

  Higher concentration difference, temperature, surface area
• What is the practical procedure for investigating osmosis using potatoes?

  1. Cut equal size cylinders from potato
  2. Weigh them and place in sugar solutions
  3. After a day, remove and damp off excess water
  4. Re-weigh and calculate percentage change in mass:

  • $\frac{\text{final mass} - \text{initial mass}}{\text{initial mass}} \times 100$

  1. Plot percentages against sugar concentration
  2. Draw a line of best fit
• What does it mean if the mass of the potato is lighter after osmosis?

  There is a negative change in mass
• What does the point where the line crosses the x-axis represent in the osmosis experiment?

  Concentration with no change in mass
• What is active transport?

  Movement against a concentration gradient using energy
• How do carrier proteins function in active transport?

  They use energy to move substances
• What is the role of energy in active transport?

  Energy is required to move substances
• What is diffusion?

  The spreading out of particles
• What does the term "net movement" in diffusion mean?

  Overall movement from high to low concentration
• What are three molecules that move in and out of cells by diffusion?

  • Oxygen
  • Carbon dioxide
  • Urea
• Why do cells need oxygen?

  For respiration carried out by mitochondria
• How does the concentration of oxygen outside the cell compare to inside?

  Higher concentration outside than inside
• What happens to oxygen molecules during diffusion?

  They move into the cell from outside
• What is produced as a waste gas during respiration?

  Carbon dioxide
• How does the concentration of carbon dioxide inside the cell compare to outside?

  Higher concentration inside than outside
• How does carbon dioxide move out of the cell?

  By diffusion from high to low concentration
• What is urea and how does it move out of cells?

  A waste product that diffuses into blood plasma
• What are the three main factors that affect the rate of diffusion?

  Concentration difference, temperature, surface area
• What is the concentration gradient?

  The difference in concentration across a membrane
• How does a greater concentration gradient affect diffusion?

  It increases the rate of diffusion
• How does temperature affect the rate of diffusion?

  Higher temperature increases the rate of diffusion
• Why does higher temperature increase diffusion rate?

  Particles have more kinetic energy and move faster
• How does surface area of the membrane affect diffusion?

  Larger surface area increases the rate of diffusion
• What is the relationship between cell membrane surface area and diffusion rate?

  Greater surface area leads to greater diffusion rate
• Where can you find questions on diffusion for practice?

  • In the vision workbook
  • Available via a link in the video
• What should you be able to describe by the end of the video?

  Diffusion and factors affecting its rate