Objectives for Ch 36 1.Describe how proton pumps function in transport of materi
ID: 204284 • Letter: O
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Objectives for Ch 36 1.Describe how proton pumps function in transport of materials across plant membranes, using the terms proton gradient, membrane potential, cotransport. 2. Explain how solutes and pressure affect water potential 3. Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have higher, lower, or the same solute concentration 4. Explain how aquaporins affect the rate of water transport across membranes 5.Describe the routes for water transport in plants 6. Describe the potential and limits of root pressure to move xylem sap 7. Define the term transpiration. 8 Explain how transpirational pull moves xylem sap up from the root tips to the leaves. 9.Describe the role of guard cells in photosynthesis-transpiration 10. Explain how and when stomata open and close 11. What is considered a sugar source or a sugar sink? 12. Describe the process of sugar loading and unloading using the concept of pressure flow Remember: water potential is a measure of the potential energy of water relative to the potential energy of pure, free water that is not bound to solutes or surfaces. The potential energy of water refers to water's ability to perform work as it moves to a state of lower free energyExplanation / Answer
1. Proton pump moves hydrogen ions out of the cell by using ATP. This creates a proton gradient with higher hydrogen ion concentration. This pump helps to produce a voltage called as membrane potential. Plants use the energy stored in membrane potential for transport of solutes across the membrane. The examples of such mechanisms are cotransport, chemiosmosis, countertransport, etc. The proton pump is used to synthesize ATP in chemiosmosis.
2. When solutes are added to a solution, the water potential gets lowered because solutes allow the water molecules to bind together. This way water molecules surrounding the solute have less freedom to move due to intermolecular interactions. Therefore, high solute concentration means relatively low water potential.
Plant cells have a cell wall which limits the expansion of cells. Pressure potential is the physical pressure on a solution. Thus, on increasing the pressure on a solution, the water potential also increases. This causes the cell membrane to press against the cell wall. This pressure is called as turgor pressure.
3. Water has the tendency to move in the direction of lower water potential. Therefore, when a plant cell is placed in a lower solute concentration, water will move out of the cell, this results in the shrinkage of cells due to osmosis. Cells become flaccid in this condition.
When a plant cell is placed in a higher solute concentration, water will enter into the cell, this results in the swelling of cell and cells become turgid.
When a plant cell is placed in the same solute concentration, this means that the amount of solute inside the cell and outside the cell will be equal.
4. The plasma membranes of the plant have specific transport proteins known as aquaporins. These proteins help in the movement of water by increasing the rate of flow. The diffusion of water occurs down to the water potential gradient.
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