Bioe 20B-W6D1-Nov 5-ANNOTATED SLIDES PDF

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are on your own: Scavenger Hunt Tuesday, 11/5/24 2. Due Sunday: HW 6, Quiz 6, Mid-Course Check In 3. Midterm 2 is on November 21st (Development to Photosynthesis) Week 6, Day 1 Water and Sugar Transport...

REMINDERS ANNOUNCEMENTS 1. Discussion sections this week are on your own: Scavenger Hunt Tuesday, 11/5/24 2. Due Sunday: HW 6, Quiz 6, Mid-Course Check In 3. Midterm 2 is on November 21st (Development to Photosynthesis) Week 6, Day 1 Water and Sugar Transport TODAY’S AGENDA (8-9:35AM) Water potential How does water move through plants Transpiration-cohesion tension theory 5 min-break How do guard cells work? How are sugars transported? Kahoot! Water and Sugar Transport  Learning Goals for Today 1 Water potential 2 How does water move through plants? 3 Transpiration-Cohesion-Tension Theory 4 How do guard cells work? 5 How are sugars transported? Water Potential Water potential (Ψ) – describes the tendency of water to move Water will move where water potential is most negative “psi” Ψ can either be 0 or negative Water potential = solute potential + pressure potential Salts, sugars, ions Measured in MPa Ψ = Ψs + Ψp Ψ = -0.2 + 0.2 Ψ = -0.2 + 0 When no contact Ψ = 0 MPa Ψ = -0.2 MPa à Ψp is 0 Turgid when no more Flaccid when no pressure water can enter cell exerted between cell membrane and cell wall Water Potential Reminders: Water potential of a salt solution is more negative than pure water What is the water potential of pure water? Ψ = 0 MPa Water Potential Calculate the water potential (Ψ) of this plant given: Solute potential (Ψs) is -0.2 Pressure potential (Ψp) = 0.1 Ψ = -0.2 + 0.1 Ψ = -0.1 MPa Will water leave or move into the plant? Water will move into the plant Water Potential What is turgor pressure? Pressure of the cell wall pushing back on the water within cell membrane of plant cell; force exerted outward on the cell wall by water inside the cell What is plasmolysis? There is no contact between the cell membrane and cell wall because there’s so Ψ = Ψs + Ψp little water. Why can we switch between the words potential and pressure? Potential describes why water moves and we are measuring pressure to determine that (MPa).  Learning Goals for Today 1 Water potential 2 How does water move through plants? 3 Transpiration-Cohesion-Tension Theory 4 How do guard cells work? 5 How are sugars transported? What is the difference Life in the fast lane = Apoplast; What is the Casparian strip prevents water from entering the between apoplastic and Slow lane = Symplast function of the xylem via apoplast; acts symplastic transport? Casparian strip? as a filter for water by forcing it to pass via symplast Symplastic Water/nutrients pass through cell membrane + plasmodesmata Water/nutrients can switch between symplastic and Apoplastic apoplastic transport Water/nutrients pass What plant structure are through cell wall we in here? ROOTS!  Learning Goals for Today 1 Water potential 2 How does water move through plants? 3 Transpiration-Cohesion-Tension Theory 4 How do guard cells work? 5 How are sugars transported? Water Potential Remember that water potential will move where it is most negative!! Water potential is helpful for predicting the movement of water Water potential varies within the plant and environment Transpiration Cohesion Tension How does water move up a plant? Active or passive? Pushed or pulled? 1) TRANSPIRATION: Water will evaporate out of leaves due to outside air having a more negative water potential than inside leaves 2) COHESION: Water will stick together and adhere to the cell wall due to polar properties and hydrogen bonding 3) TENSION: When water moves out of leaves it creates negative pressure, pulling on other water molecules to move with it What is the driving force? Transpiration à Air has a very negative water potential (not much H2O) You measure the water potential (Ψ) of the soil in a pot and find it is close to 0. What can you say about when the pot was likely watered? A. The pot has not been watered for a while B. The pot was recently watered What do you predict the water potential (Ψ) of dry air is? A. Close to 0 What about air on a foggy day? B. Very negative Water potential (Ψ) will be less negative C. Very positive or close to 0 What is the water potential at the roots? In the stem? At the top of the plant? 0 Water potential (Mpa) - Roots Stem Top Height from ground (meters)  Data from Burgess et al., 2006 1) Where on the tree is water potential the most negative (e.g. the strongest)? Top of the tree 2) What time of day is water potential the most negative (e.g. strongest) at all heights on the tree? Midday 3) What do you think might be driving the temporal (time) pattern? Intensity of transpiration cohesion tension How does H2O moveCasparian in plants? Strip The most important mechanism for moving water through a plant is: A. It is pushed up B. It is pulled up  5-min Break! Attendance Time Scan the QR code or go to https://tinyurl.com/W6D1waterpotential to answer the following question: Q: What is the difference between apoplastic and symplastic transport? (This will be used for taking attendance today.)  Learning Goals for Today 1 Water potential 2 How does water move through plants? 3 Transpiration-Cohesion-Tension Theory 4 How do guard cells work? 5 How are sugars transported? How do guard cells work? Casparian Strip Stomata are made Guard cells open & close in response up of 2 guard cells to changes in turgor pressure Less water Flaccid guard cells present = more negative water = closed potential More water Turgid guard cells present = less = open negative water potential What causes rapid changes in Blue light! turgor pressure?  How do guard cells work?Casparian Strip Remember that water will What causes rapid changes in move where water turgor pressure? (Process uses ATP!) potential is most negative! 1) H+ pumped out Blue light triggers this! 2) K+ rushes in due to the difference in charge 3) Symport couples H+ diffusion into cell with other negative anions What happens to water potential in the guard cell? This makes water potential more negative!  Learning Goals for Today 1 Water potential 2 How does water move through plants? 3 Transpiration-Cohesion-Tension Theory 4 How do guard cells work? 5 How are sugars transported?  “Pressure flow model” How does translocation work? Describe the process of sugar transport including the role that water potential plays in the process. Recall that xylem and phloem are in close proximity to each other in vascular bundles 1) A source cell (leaf) moves sugar into Remember that water will phloem which makes the water potential move where water potential is most negative! more negative there 2) Water from the xylem will move into the phloem 3) When sugar gets deposited into a sink cell (fruit) water potential in the phloem will get less negative, making water leave to xylem where it is more negative  Girdling a branch: Fruits get bigger and sweeter Sugar (inner bark is phloem) Girdling a trunk: Roots starve and tree dies  Kahoot Review: Water and Sugar Transport