water Passive transport moves solute from high to low concentration b) In active transport how do solutes move along their concentration gradient?

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1 Membrane Transport Model 1: Active versus Passive Transport Body fluids are solutions of water and dissolved solutes (ions, glucose, amino acids, etc.). The plasma membrane is a selectively permeable barrier that allows passage of some molecules but prevents the passage of many life essential molecules. The passage of these solutes through the semipermeable plasma membrane is essential for life. Active transport and passive transport are the two transport mechanisms responsible for moving of substances across the cell membranes. oxygen Solute water glucose ions Phospholipid membrane channel protein carrier protein transport protein Simple Diffusion Facilitated Diffusion Passive Transport Active Transport Questions 1. On the model: for each transport process label which side of the membrane has a high solute concentration (amount) and which side has low solute concentration. 2. Examine the model for how solutes move in regards to their concentration gradient, (i.e. high to low, low to high). Several groups will answer down for both passive and active, as the arrow is moving down. These groups need to be directed to look at concentration differences. a) In passive transport how do solutes move along their concentration gradient? Passive transport moves solute from high to low concentration b) In active transport how do solutes move along their concentration gradient? Active transport moves solute from low to high concentration

2 3. Movement of molecules is often stated as moving up or down the concentration gradient. Fill-in the blanks: Passive transport move solutes down its concentration gradient, and active transport move solutes up its concentration gradient. 4. Cells use energy in the form of ATP to do work. Which transport process(es) will use ATP? Explain why. Active transport requires ATP to transport solutes across the cell membrane, as it needs energy to move molecules up it s gradient. Moving a ball-up a hill (i.e. active transport) would require us to push the ball (utilize energy), while a ball will roll down hill (passive) on its own without assistance. The transport processes get there name from whether they require energy or happen passively on own. 5. Diffusion is the random movement of molecules until equilibrium is reached. a) Examine model one. What type of transport: active or passive is diffusion? Explain why. diffusion is a type of passive transport, because solutes are moving from an area of high concentration to low concentration (down gradient). b) Examine the model. List the two types of diffusion. simple diffusion, facilitated diffusion c) Which process(es) involve transport directly through the phospholipid membrane? through membrane = simple diffusion Which process(es) require protein channel/carrier for transport? with protein carrier = facilitated diffusion d) Solutes being transported by simple diffusion are impermeable/permeable (circle one) to the plasma membrane. Solutes being transported by facilitated diffusion are impermeable/permeable (circle one) to the plasma membrane. simple = permeable; facilitated = impermeable 6. Rate of diffusion through a membrane is influenced by several factors. Predict which condition will allow diffusion to occur faster: Size of molecules - smaller of larger? larger size Temperature of molecules - cooler or warmer? warmer temperature Membrane surface area less or more? more surface area Membrane permeability less or more? more permeable

3 Steepness of concentration gradient less different or more different? more different concentration gradient 7. Water is a polar molecule that needs to constantly move in and out of the cell at rapid speed to maintain equilibrium. What transport process will water use to pass through the plasma membrane (be specific)? Explain why. Membrane is impermeable to polar molecules, so water will mainly use facilitated diffusion to transport across the membrane. Aquaporin is the channel for water transport. Since water is small molecule, some water can go directly through the membrane by simple diffusion. Though much faster with aquaporin. 8. The Na-K pump actively transports potassium into the cell and sodium out of the cell across the plasma membrane. Draw a cell showing the Na and K distribution. Na is actively transported out of the cell, thus moving from low (inside) to high (outside) concentration. Vice versa for K. Na K Na K 9. A cell uses valuable energy to run active transport. Why does a cell need active transport? In your explanation provide two example of when active transport would be used in the body. Active transport is used to store and conserve our nutrients (i.e. storage of glucose in liver, reabsorption of ions/nutrients in kidney tubule). Also used to maintain membrane polarity

4 Model 2 Osmosis Osmosis is the process by which water moves into and out of cells through a semipermeable cell membrane to maintain equilibrium of solutes on both sides. It is a solute balance that causes water to move across the cell membrane. The saying goes: Water follows salt (solute). Semipermeable Membrane Net H 2 O Diffusion Questions for Model On model 2: Label the water and solute molecules. Solute = big blobs; Water = three-overlaying circles 11. Based on the model: a) How does water move in regards to its own concentration gradient. Water moves down (high to low) its gradient b) How does water move in regards to the solute concentration gradient. Water moves from area of low solute to high solute concentration. 12. What causes osmosis, an imbalance in water concentration or solute concentration? Imbalance in solute, water follows salt. (this is stated in background paragraph). 13. What type of transport process is osmosis? Does it require energy to move water? Write a grammatically correct sentence to explain why. Osmosis is a type of diffusion (facilitated diffusion). Osmosis does not require energy, as water is moving down its concentration gradient.

5 14. The solutions in the two arms of this U-tube are separated by a membrane that is impermeable to glucose. The left arm contains 6 M glucose and the right arm contains 14 M glucose. Predict the solution volume and glucose concentration in each arm at the end of equilibrium. 15. In another scenario, the solutions in the two arms of this U-tube are separated by a membrane that is permeable to sucrose. The left arm contains 2 M sucrose and the right arm contains 12 M sucrose. Predict the solution volume and sucrose concentration in each arm at the end of equilibrium.

6 Model 3 Tonicity Hypotonic Isotonic Hypertonic Solute RBC 16. Based on Model 3, how does the impermeable solute concentration in the solution (fluid surrounding the cell) compare to the inside of the cell. Hypotonic = less Isotonic = same Hypertonic = more 17. Based on your knowledge of osmosis (refer to model 2), for each tonicity solution predict the net water movement. Hypotonic = into cell Isotonic = no net water movement Hypertonic = out of cell 18. Tonicity is the ability of a solution to change the shape/tone of a cell by altering internal water volume. Based on your answer above, predict the change in shape of the RBC after it has reached equilibrium with the solution. Draw a representative final RBC final for each solution. Images should cells with these sizes: Hypotonic = cell will swells (larger), isotonic = cell stays same shape, hypertonic = cell shrinks (crenate). 19. Use model 3 and question responses to answer this question. Is tonicity due to solution containing a permeable or impermeable solute? Justify your answer. Tonicity is due to impermeable solutes. Stated in question 16, plus they can see in #15 a permeable solute did not alter tube volume.

7 20. Normal blood glucose concentration produces body osmolarity of about 300 mosm/l. An elderly woman with diabetes has an elevated blood glucose concentration that raises her blood osmolarity to 400 mosm/l. In this diabetic patient, predict the water movement, if any, of the extracellular fluids and the shape of her red blood cells. In diabetic patient water will move out of the RBC. The cells normally live in an isotonic state, the normal blood glucose of 300 mosm/l gives indication of the intracellular amount of glucose. Normal Diabetic 300 mosm 300 mosm 300 mosm 400 mosm 21. A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water with a ph of 7.0, equal to the volume of blood lost, is transferred directly into one of his veins. What will be the most probable result to the person s red blood cells from this transfusion? Explain Why? The red blood cells will burst because distilled water is a hypotonic solution. Note: some students will think this is an isotonic solution because the ph is neutral 22. Recap: fill-in the below summary table. Transport Mechanism Gradient Direction Protein Carrier? ATP needed? Examples of Molecules Simple Diffusion high to low No No Oxygen Facilitated Diffusion high to low Yes No Na, Glucose Osmosis high to low Yes No Water Active Transport low to high Yes Yes Na, Glucose