Osmotic Regulation Flashcards
What is osmosis?
-Movement of free water molecules through membrane from a solution of a low solute concentration to a solution of high solute concentration
Describe water potential?
- Used to predict the way which water will move
- Always moves from high to low water potential
- Total potential energy of water in the cell is the water potential (influenced by the potential caused by both solute concentration and pressure)
- When cell is placed in a solution with a different solute concentration, water moves in the direction that will eventually result in equilibrium
- Low water potential = high solute concentrations
What are aquaporins?
- Water channels that exist in vacuole and cell membranes
- Speed up osmosis
- Allow for equilibrium to be established quickly
How does water move?
- It can diffuse through cell membranes
- Ions or organic compounds rely on membrane bound transporters (active or passive)
Describe negative and positive pressure?
- Negative pressure pulls
- Positive pressure pushes
Describe how water potential regulates water movement?
- Entire plant has decreasing water potential as one moves higher
- This allows water to move up the plant against gravity
What path does water take in a plant?
- Into roots
- Up xylem
- Fills empty spaces in-between the mesophyll cells in the leaf
- Evaporates through the stoma
Describe the roots?
- Water only moves into the roots if the soils water potential is greater
- Root has more solute than fresh water
- Roots are usually turgid
- Root hairs: absorb most of plants water
- Mycorrhizae: surface area for water and mineral absorption is increased by mycorrhizae
- Casparian strip: watertight layer in between endodermis cells, water must travel through cell via symplastic route, plants can regulate fluid and ion concentration before entering the xylem
Describe water movement in the xylem?
-Water has tensile strength: water molecules cohere to one another due to h-bonds
Water molecules adhere to the walls of the xylem due to polarity
Tensile strength of water column varies inversely with its diameter
-An air bubble can break tensile strength
Describe leaves?
- Water from xylem then moves into leaves
- Leaves have lower water potential than the xylem’
- Water vapor leaves the leaf through the stoma
- Outside air has lower water potential than the leaf
Describe the rate of transpiration?
- Managed by guard cells
- Closing stomata can help control water loss
- Stomata must be open at some point to let carbon dioxide in
- Stomata close at high temps or when CO2 concentrations increase
- They open when blue light wavelengths hit which promote uptake of ions by guard cells
Describe guard cell physiology?
- Turgor in guard cells results from the active uptake of potassium, chloride, and malate
- Abscisic acid initiates a signaling pathway to close stomata in drought stress
Describe mineral absorption?
- Often active transport across endodermis (transport via xylem)
- Three transport routes: apoplastic route, symplastic route, transmembrane route
Describe the Apoplectic route?
-Movement through the cell walls and the space between cells
Describe the Symplastic route?
-Through cytoplasm connected by plasmodesmata
