Amoeba Sisters Answer Key Amoeba Sisters Video Recap: Diffusion ANSWER KEY 1. In diffusion, the net movement of a substance travels down its concentration gradient. Explain using the image below. 2. When diffusion has reached equilibrium, we say that the net movement of the molecules is zero. Does this mean these molecules below would stop moving? Explain using the image below. By moving down its concentration gradient, the particles have a net movement from the area of high concentration (represented on left of image) to a low concentration (represented on right of image). Since it is the net movement, this is the overall movement. No, the particles would continue to move. However, the net movement (which is the overall movement) would be zero. This means that the particles shown below would be moving and can cross over to the other side, but the overall (net) movement is zero. There is no longer a concentration gradient to travel down as equilibrium has been reached. 3. Simple diffusion can occur through a cell membrane! According to the video, what are some cell membrane characteristics that can affect the diffusion rate? The surface area and thickness of the cell membrane are two characteristics mentioned in the video. (A larger surface area and thinner cell membrane can allow for a faster diffusion rate than a smaller surface area and thicker cell membrane). 6. Sometimes, a substance can only travel across a cell membrane via facilitated diffusion. What is facilitated diffusion? 4. Does simple diffusion require an input of energy? 7. Does facilitated diffusion require an input of energy? ______________No______________________________ ______________No______________________________ 5. Is simple diffusion passive or active transport? 8. Is facilitated diffusion passive or active transport? ____________Passive____________________________ ____________Passive____________________________ Facilitated diffusion is a type of diffusion where a substance travels through a protein in order to travel across the cell membrane. Amoeba Sisters Answer Key Amoeba Sisters Video Recap: Diffusion ANSWER KEY Diffusion is a critical process required for oxygen to leave the alveoli of the lungs to enter the blood and for carbon dioxide (a waste gas) to leave the blood and enter the alveoli. 9. Knowing what you know about how a substance travels in diffusion, in order for oxygen to leave the alveoli and enter the blood, there would be a [ HIGHER or LOWER ] concentration of oxygen in the alveoli compared to the blood. 10. Knowing what you know about how a substance travels in diffusion, in order for carbon dioxide to leave the blood and enter the alveoli, there would be a [ HIGHER or LOWER ] concentration of carbon dioxide in the alveoli compared to the blood. 11. Explain your reasoning for questions #9 and #10. The gases travel by diffusion, and therefore they have a net movement from a high concentration to a low concentration. Therefore, the gases in this scenario will have a net movement to the area of lower concentration. In #9, the oxygen must leave the alveoli and enter the blood. The oxygen concentration is therefore higher in the alveoli (which is circled “higher”) and lower in the blood. In #10, the carbon dioxide must leave the blood and enter the alveoli. The carbon dioxide concentration is therefore higher in the blood and lower in the alveoli (which is circled “lower”). There are many factors that can affect the rate of diffusion! The following are only a few examples from the video that can affect the rate of diffusion. Briefly explain how each factor listed below could affect the rate of diffusion. Distance 12. The video mentions that the greater the distance that needs to be traveled, the slower the diffusion rate. Temperature Characteristics of Substance Increasing Difference of Concentration 13. 14. 15. The video mentions that a higher temperature would mean there is more movement of the molecules so the diffusion rate is increased. The video mentions that a substance with a greater mass will generally have a lower diffusion rate than a substance with a lower mass. (The video additionally mentions that smaller, nonpolar substances will more easily travel across a cell membrane if a cell membrane is involved.) The video mentions that increasing the concentration of a substance in a given area (as shown in image on left side) can increase the rate of diffusion.
