Question

amoeba sisters | video recap
name:
amoeba sisters video recap: diffusion

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.
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?
4. does simple diffusion require an input of energy?
5. is simple diffusion passive or active transport?
6. sometimes, a substance can only travel across a cell membrane via facilitated diffusion. what is facilitated diffusion?
7. does facilitated diffusion require an input of energy?
8. is facilitated diffusion passive or active transport?

Explanation:

1. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. In the image, molecules move from the "High Concentration" side to the "Low Concentration" side. This is because there is a higher probability of molecules moving away from the crowded (high - concentration) area to the less - crowded (low - concentration) area.
2. When diffusion reaches equilibrium, the molecules do not stop moving. At equilibrium, the rate of molecules moving from one side to the other is the same in both directions. So, there is no net movement (the net movement is zero), but individual molecules are still in motion due to their kinetic energy.
3. Cell membrane characteristics that can affect the diffusion rate include membrane thickness (thicker membranes slow down diffusion as molecules have to travel a longer distance) and the presence of transport proteins (for facilitated diffusion, but also in simple diffusion, the lipid composition and fluidity of the membrane can play a role. For example, a more fluid membrane may allow some small non - polar molecules to diffuse more easily).
4. Simple diffusion does not require an input of energy. It is driven by the concentration gradient of the molecules. Molecules move down their concentration gradient (from high to low concentration) due to their own kinetic energy.
5. Simple diffusion is a passive transport. Passive transport does not require energy input (such as ATP) and relies on the natural movement of molecules down their concentration gradient.
6. Facilitated diffusion is the process by which molecules that cannot easily pass through the lipid bilayer of the cell membrane (such as polar or large molecules) are transported across the membrane with the help of transport proteins (either channel proteins or carrier proteins). The molecules still move down their concentration gradient.
7. Facilitated diffusion does not require an input of energy. The transport proteins help the molecules move down their concentration gradient, and the energy for this movement comes from the concentration gradient itself (the potential energy difference).
8. Facilitated diffusion is a passive transport. Just like simple diffusion, it does not use energy (such as ATP) and is based on the movement of molecules down their concentration gradient with the aid of transport proteins.

Answer:

1. Molecules move from high to low concentration as shown in the image (from the side with more molecules (high concentration) to the side with fewer molecules (low concentration)) because of the concentration gradient.
2. No. Molecules are still moving, but the rate of movement in both directions is equal (net movement = 0).
3. Membrane thickness and lipid composition (affecting fluidity).
4. No.
5. Passive transport.
6. Movement of molecules across the membrane with the help of transport proteins (down their concentration gradient).
7. No.
8. Passive transport.