1. Please Do Now: 1) Define transpiration 2) What excites the electrons (and starts them along the electron transport chain) during the light dependent reactions?

2. Agenda Do Now Guard Cell notes Video Work on photosynthesis study sheet

3. Remember Plants lose water via transpiration This is bad because plants need water for a lot of things It mostly happens via stomata, little tiny holes in the leaf Leaves need stomata to let CO2 in and oxygen out during photosynthesis Water escapes whenever they are open

4. How do plants minimize their water loss through the stomata? The stomata in plants are surrounded by guard cells There are always 2, and they are capable of opening and closing the stomata It is like opening and closing a door: when closed there is no CO2 coming in, but no water escaping

5. How do guard cells open and close the stomata? The guard cells are crescent shaped with thick inner walls and thin outer walls They are basically like balloons that inflate and deflate to open/close the stomata

6. How do guard cells inflate/deflate? When the plants want the stomata to be open, they inflate the guard cells by pumping potassium ions (K+) into the cells Osmosis then draws water into the cells and inflates them to their full crescent shape

7. 7 Regulation of the guard cells Guard cells flaccid Stoma closed K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K + ions have the same concentration in guard cells and epidermal cells (the surrounding cells) Light activates K + pumps which actively transport K + from the epidermal cells into the guard cells

8. 8 Regulation of guard cells K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Increased concentration of K + in guard cells Lowers the concentration of water in the guard cells Water moves in by osmosis, down osmotic gradient H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O

9. 9 Stoma open Guard cells turgid K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Increased concentration of K + in guard cells Lowers the  in the guard cells Water moves in by osmosis, down  gradient H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O

10. Summary (fill in the blank on your own) Guard cells are important for maintaining the balance between ____________________ and _________________________

11. Summary (fill in the blank on your own) Guard cells are important for maintaining the balance between gas exchange and water loss