BIO311D WK4 Discussion B Assignment

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Austin Community College District *

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Biology

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Feb 20, 2024

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BIO311D: Week 4 Discussion B Submit assignment via Canvas by 10pm Fri. 8pts available towards your final grade. You may complete the assignment by yourself if you choose not to attend discussion times. **Attendance not required –but advised** For the first 10-15 minutes of discussion, your TA will do a recap of some of the key points covered this week. After, split into your breakout rooms. Work through the assignment below. After a time, your TA will bring you back to talk over your answers before you submit. Recap of stomata function Observation: Most plants typically open their pores when (blue, 380 to 500 nm ) light is present and when CO 2 concentration is low. Pathways suggested to explain this include the following: 1. Light is absorbed (blue-light) by signal transduction receptors in guard cell membranes. 2. This blue-light signal pathway (specific kinases) triggers proton pumps to actively transport H+ ions out of guard cells 3. As a result of step 2, K+ ions tend to flow into guard cell. 4. Accumulation of K + increases turgidity - K + levels increase, the water potential of the guard cells drops, and water enters the guard cells, stomata open .
5. When guard cells lose water, the cells to become flaccid and the stomatal closes . This may occur when the plant has lost an excessive amount of water, or daily as light levels drop and the use of CO 2 in photosynthesis decreases. Q1. Think about a “genetic experiment” that would be another way of testing the hypothetical pathway for control of stomatal opening. Instead of treating your leaves experimentally, you would use a specific genetic mutant (think of the use of Arabidopsis in experiments show in class) and compare pore opening of it with the response of normal control plants (“wild-type” genotypes). a) Would pores open in the light if there was a mutation in the blue-light receptors phot1, phot2 ? [0.5pts] No pores would open. Because the signal transduction pathway that transports K+ into the cell is initiated by the blue light receptor being activated. (b) What if there was a mutation in the particular type of K + channel in this pathway so that it would not open? [1pt] Pores would not open so the stomata will remain closed. If potassium cannot get into the cell, there is no change in solute concentration. Therefore, the water does not flow into the cell. Thus, if no water flows into the guard cells, it stays flaccid. Hence, the stomata remain closed and would not open. (c) What is there was a mutant K + channel that did not close? [1pt] The pores would stay open. If potassium is coming in, water is also coming in and when that happens, the cell opens. The continuous water makes the cell turgid and potassium channels need to close to prevent continuous K+ from coming in. Q2. In an experiment to test the effect of light intensity on stomatal opening, which of the following would be the LEAST important variable to control? [1pt] a) wavelength of light b) amount of water in the soil c) osmotic concentration in the leaf d) concentration of K+ ions in cell wall fluids
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