Question

a lot of oxygen on the outside of the cell, but less on the inside of the cell, oxygen will work its way through the cell membrane until there are equal amounts of oxygen on both sides of the cell membrane. when there are equal amounts of a molecule on both sides of the cell membrane the concentration of that molecule is said to have reached equilibrium. when a molecule cannot simply diffuse through the cell membrane, a protein channel may be used. no energy is expended. it is called facilitated diffusion. in other words, the protein “helps” the molecule through. an example of this is osmosis when water uses a protein channel to travel through the cell membrane. water, being a polar molecule, cannot simply squeeze through the cell membrane because the hydrophobic tails of the phospholipids prevent it from doing so. so instead they have to use a special protein channel called an aquaporin to get through. osmosis uses no energy, so it is a form of passive transport. active transport sometimes, certain molecules need to move from an area of low concentration to high concentration, which requires the cell to use energy to do so. cellular transport that uses energy is called active transport. this is the opposite of diffusion, and these molecules are said to flow against their concentration gradient. molecular transport active transport cannot occur without the assistance of a carrier protein. much like facilitated diffusion, a protein in the membrane carries the molecule across the membrane, except they use energy to pump the molecules from a low concentration to a high concentration. these proteins are often called protein pumps because they use energy to pump the molecules across the membrane. there are many cells in your body that use pumps to move molecules. for example, your nerve cells (neurons) would not send messages to your brain unless you had protein pumps moving molecules by active transport. bulk transport - exocytosis & endocytosis some molecules or particles are just too large to pass through the cell membrane or to move through a carrier protein. so cells use more active processes to move macromolecules or large particles across the plasma membrane. there are two types of vesicle transport, endocytosis and exocytosis. both processes are active transport processes, requiring energy. exocytosis is when molecules exit the cell with the help of a vesicle. this is easy to remember because they both have “ex” in them. endocytosis is when molecules enter the cell with the help of a vesicle that forms around the material, then pinches off within the cell. again, easy to remember because they both start with “in”. after reading, please watch the video “membrane transport” by mcgraw hill media, then answer the following questions: 5. please compare and contrast passive transport and active transport. 6. describe what is taking place during diffusion. is this a form of passive or active transport. explain your reasoning. 7. describe what osmosis is. is this a form of passive or active transport. explain your reasoning. 8. what are the similarities and differences between diffusion and facilitated diffusion? 9. describe three ways that cells perform active transport.

Explanation:

The text discusses cellular transport mechanisms such as passive transport (diffusion, facilitated diffusion, osmosis) and active transport. Passive transport moves molecules from high - to low - concentration without energy, while active transport moves molecules against the concentration gradient using energy. Diffusion is the movement of molecules from high to low concentration and is a form of passive transport as it doesn't require energy. Osmosis is the diffusion of water across a semi - permeable membrane and is also passive. Facilitated diffusion uses protein channels for transport but still doesn't require energy like simple diffusion. Active transport can occur via protein pumps.

1. Comparison of passive and active transport: Passive transport moves molecules down the concentration gradient (from high to low) and does not require energy input from the cell. Examples include diffusion, facilitated diffusion, and osmosis. Active transport moves molecules against the concentration gradient (from low to high) and requires the cell to expend energy, usually in the form of ATP. It often uses protein pumps.
2. Diffusion: During diffusion, molecules move from an area of high concentration to an area of low concentration until equilibrium is reached. This is a form of passive transport because it does not require the cell to use energy. The driving force is the concentration gradient.
3. Osmosis: Osmosis is the diffusion of water across a selectively permeable membrane. It is a form of passive transport as it does not require energy input from the cell. Water moves from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration).
4. Similarities and differences between diffusion and facilitated diffusion: Similarities: Both are forms of passive transport, so they do not require energy input from the cell and move molecules down the concentration gradient. Differences: Simple diffusion is for small, non - polar molecules that can pass directly through the lipid bilayer of the cell membrane. Facilitated diffusion uses protein channels or carriers to transport larger, polar, or charged molecules that cannot pass through the lipid bilayer easily.
5. Three ways cells perform active transport:

• Protein pumps: These are integral membrane proteins that use energy (usually ATP) to move molecules against their concentration gradient. For example, the sodium - potassium pump in nerve cells.
• Endocytosis: The cell membrane invaginates to form a vesicle that engulfs extracellular material and brings it into the cell. This is an active process as it requires energy to reshape the membrane.
• Exocytosis: Vesicles inside the cell fuse with the cell membrane and release their contents outside the cell. This also requires energy for membrane fusion and vesicle movement.

Answer:

1. Passive transport moves molecules down the concentration gradient without energy; active transport moves molecules against the concentration gradient with energy.
2. Molecules move from high to low concentration during diffusion. It is passive as no energy is used.
3. Osmosis is water diffusion across a membrane. It is passive as no energy is used.
4. Similarities: Passive, move down concentration gradient. Differences: Simple diffusion for small non - polar; facilitated diffusion for larger/polar/charged via proteins.
5. Protein pumps, endocytosis, exocytosis.