Membrane Structure and Function Answer Key

Membrane Structure and Function How do substances move in and out of cells? Why? Advertisements for sports drinks, such as Gatorade®, PowerAde®, and Vitaminwater™, etc. seem to be everywhere. All of these drinks are supposed to help your body recover and replenish lost electrolytes, fluids, and vitamins after exercise. But how do the essential molecules contained in these drinks get into your cells quickly to help you recover after exercise? Model 1 – Simple Diffusion 1. How many different types of molecules are shown in Model 1? There are two different types of molecules shown in Model 1. 2 Count and record the number of triangles and circles found on each side of the membrane. Triangles on the left -14 Triangles on the right -0 Circles on the left -12 Circles on the right - 13 3. Which shape is larger? The triangle is larger. 4. Describe the direction of the movement of the molecules in Model 1? The molecules are going in random directions in Model 1. 5. Which molecules are able to pass through the semipermeable membrane? Justify your answer. Circles are able to pass through the semipermeable membrane. This is because they are small and both sides almost have an equal distributed amount of circles. 6. If you left this “system” for an extended period of time and then viewed it again, would you expect to find any changes in the concentrations of the molecules on either side of the membrane? Justify your answer. You would not expect to find any changes in the concentration of the molecules on either side of the membrane. The triangles will only stay on the left side because they are too big to pass through the membrane. Circles will be on both sides equally due to their small size and sporadic movement. Model 2 – The Selectively Permeable Cell Membrane 7. What two major types of biological molecules compose the majority of the cell membrane in Model 2? The two major types of biological molecules that are composed of the majority of the cell membrane in Model 2 are phospholipids and proteins. 8. How many different protein molecules are found in Model 2? There are four different protein molecules in Model 2. 9. What is the difference between the position of the surface proteins and the membrane-spanning proteins? The surface proteins do not span the cell membrane, while membrane spanning proteins do. 10. When a carbohydrate chain is attached to a protein, what is the structure called? When a carbohydrate chain is attached to a protein, the structure is called a glycoprotein. 11. When a carbohydrate is attached to a phospholipid, what is the structure called? When a carbohydrate is attached to a phospholipid, the structure is called a glycolipid. 12. What types of molecules are shown moving across the membrane? The type of molecules that are shown moving across the membrane are smaller polar and nonpolar molecules. 13. Where exactly in the membrane do these molecules pass through? The molecules pass through between the phospholipids. 14. How does the concentration of the small molecules inside the cell compare to that outside the cell? There are more small molecules outside than the cell inside, so the concentration is higher outside compared to the inside. 15. Because particles move randomly, molecules tend to move across the membrane in both directions. Does the model indicate that the molecules are moving in equal amounts in both directions? Justify your answer using complete sentences. The model does not indicate that the molecules are moving in equal amounts in both directions, because more molecules are moving into the cell compared to moving out of the cell. This is represented with the arrows. Read This! When there is a difference in concentration of a particular particle on either side of a membrane, a concentration gradient exists. Particles move along the concentration gradient from high to low concentration until a state of equilibrium is reached. At that point, there is no more net movement in one direction, although the particles continue to move randomly across the membrane, often called dynamic equilibrium. The net movement of particles along the concentration gradient is called diffusion. 16. Look back at Models 1 and 2. Which particles are moving by diffusion across the membranes shown? The particles that are moving by diffusion across the membranes shown, are the dots in Model 1 and small polar and nonpolar molecules. 17. Using all the information from the previous models and questions. Write the correct response to correctly fill in each blank. a. Diffusion is the net movement of molecules from an area of (low/high) concentration to an area of (low/high) concentration. First blank -high Second blank -low b. The molecules will continue to move along this (semi-permeable membrane/ concentration gradient) until they reach (diffusion/equilibrium). First blank -concentration gradient Second blank -equilibrium c. Once equilibrium is reached, molecules will continue to move across a membrane (randomly/in one direction). Randomly Model 3 – Facilitated Diffusion 18. Which part of the cell membrane is shown in more detail in Model 3? The part of the cell membrane that is shown in more detail in Model 3 are the membrane spanning proteins. 19. What is the gap between the proteins called? The gap of the proteins called is the gated channel. 20. What type of molecules attach to the protein? The type of molecules attached to the protein are the glucose. 21. Explain in detail what happened that allowed the glucose molecules to pass through. The hormones attach to the binding site on channel protein causing channel to open by changing its shape, which allows the glucose to go into the cell. Read This! Some molecules, such as glucose, use gated channels as shown in Model 3; however, not all channels are gated. Some channels remain permanently open and are used to transport ions and water across the cell membrane. 22. Explain why the type of protein channel in Model 3 is called a gated channel. The protein channel in Model 3 is called a gated channel because they act as gates. When the hormone is bounded with the protein, it acts as a gate that only allows some things to go through. In this instance, it is allowing glucose to pass. 23. To facilitate means to help. Explain why this type of diffusion is called facilitated diffusion. This is called facilitated diffusion, because glucose needs help from the insulin, which allows the channel to go bigger. It is still diffusion. Because the glucose moves. 24. The “tails” of phospholipids are nonpolar; therefore, they do not readily interact with charged particles such as ions. How can this explain why facilitated diffusion is necessary for the transport of ions such as Na+ and K+ across the cell membrane? In other words, why would these ions not cross by simple diffusion? These ions would not cross due to diffusion because they are polar, so facilitated diffusion is the only way they can cross. Model 4 – Active Transport 25. Which part of the cell membrane is shown in more detail in Model 4? Look back at Model 2 if needed. The part of the cell membrane that is shown in more detail in Model 4 is the membrane spanning proteins. 26. What shape represents the substance being transported across the membrane in Model 4? The shape that represents the substance being transport across the membrane is a diamond. 27. List two binding sites found on the protein. The two binding sites found on the protein are ATP and ion binding sites. 28. In which direction is the transported substance moving—from an area of high concentration to low or from an area of low concentration to high? Support your answer. The substance is moving from a domain with low concentration to high concentration. More particles are seen in the area toward the direction the arrow is pointing. 29. Is the substance being moved along (down) a concentration gradient? Justify your answer. The direction is going from low concentration to high concentration. More particles are seen in the area toward the direction the arrow is pointing. 30. ATP is a type of molecule that can provide energy for biological processes. Explain how the energy is being used in Model 4. Energy is used to change the shape of the protein(open the channel). 31. What happens to the ATP after it binds to the protein? ATP changes to ADP after it binds to the protein. 32. The type of transport shown in Model 4 is called active transport, while diffusion and facilitated diffusion are called passive transport. Given the direction of the concentration gradient in active and passive transport examples, explain why active transport requires energy input by the cell. Active transport moves molecules up the concentration gradient. Passive transport molecules move down the confederation gradient. Moving molecules needs energy. 33. Complete the table below to show the difference between active and passive Transport. Use “yes” or “no” to fill in the table. Active Transport Passive Transport Diffusion Facilitated Diffusion Requires energy input by the cell yes no no Molecules move along (down) a concentration gradient no yes yes Moves molecules against (up) a concentration gradient yes no no Always involves channel (membrane-spanning)proteins yes no yes Molecules pass between the phospholipids no yes no Moves ions like Na+ and K+ no no yes Moves large molecules yes no yes Moves small nonpolar and polar molecules no yes no 34. Based on what you’ve learned, develop a definition for active transport. Active transport needs energy by the cell so molecules can move up the concentration gradient. It involves channel proteins that move large molecules. Extension Questions (yes, you have to do them) 35. Given the information in the graph, which type of cell transport would be best to move substances into or out of the cell quickly? The type of transport that would be best to move substances into or out of the cell quickly would be active transport. 36. Which type of transport would be the best if the cell needs to respond to a sudden concentration gradient difference? The type of transport that would be best if the cell needs to respond to a sudden concentration gradient difference, would be diffusion. The rate increases when the concentration difference increases. 37. Why would the line representing facilitated diffusion level off as the concentration gets higher, while the line representing diffusion continues to go up at a steady rate? Facilitate diffusion relies on proteins a lot. The amount of proteins there are correlated with how fast substances can be moved. Although the concentration may continue to increase, the channels will limit the rate of this facilitated diffusion. 38. Why does active transport, on the same graph, start off with such a high initial rate compared to diffusion and facilitated diffusion? Active transport only relies on a supply of energy, not on a concentration gradient.