Biology- Water Relations (exam 1)

Path of water through plant

- Cross cell wall and cytoplasms and get into root hair, can go into cortex - Root hairs- increase surface area to take up more water - Cell walls- cellulose= hydrophilic

Control of solutes in cell: ys

- Uptake of ions regulated by composition of plasma membrane Transport proteins - Passive - Active - Couples Membrane are selective

Water potential

- Uptake of water by a plant cell is limited (by the volume of cell wall enclose) (can't really stretch) - Volume enclosed by cell wall - Full cytoplasms exerts pressure against wall- will prevent no more uptake of water - Turgor pressure- prevents wilting, pressure against wall

Apoplast vs symplast

-Apoplast: outside plasma membrane -Symplast: inside cells -Connected by plasmodesmata

Water in xylem

All water that enters xylem must cross a membrane at least twice (filtered) - Into endodermis (or before that) - Out of endodermis Membranes select which ions can enter a cell Can use active transport (ATP) to pump in water Distributes throughout

Movement of water in xylem

Long distance transport - Bulk flow (later) Osmosis - Movement of water across a semi permeable membrane Animal cell bursts - No cell wall Plant cell swells - Cell wall - Doesn't burst

Water realtions

Movement of sap - Xylem - Phloem Opening/closing of stomata - Regulate size for photosynthesis and to conserve water

Water potential: y

Pure water at one atmosphere pressure: y=0 Add solutes - y is negative Water moves to location with lowest Y Equation: - Y=Yp (pressure) + Ys (solutes) - Ys will be 0 or lower

Water uptake by roots: 2 paths

Symplastic movement - Continuous - Epidermis ---> cortex ---> endodermis ---> xylem (apoplectic in xylem) Apoplectic movement - Ends at endodermis - Other water has to pass a membrane Endodermal cells are waterproofed - Casparian strip (lignin and wax) - Blocks apoplectic water movement