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
Describe the Transmembrane route?
- Membrane transport between cells and across the membranes of vacuoles within cells
- Plant has greatest control of water route in this
Describe water stress responses?
-To limit water loss
Dormancy
Loss of leaves
Reduce number of stomata
Have stomata in pits on leaf surface
-Flooding conditions deplete available oxygen so may form
Aerenchyma: loose parenchymal tissue with large air spaces
or if in salt water may produce pneumatophores: long spongy air filled roots that emerge above mud
Describe CAM plants?
- Stomata open at night
- Store CO2 as malate
ex. cactus
How do animals maintain osmosis?
- Be able to take water from environment
- be able to secrete excess water into environment
- exchange solutes to maintain homeostasis
What is tonicity?
-Measure of a solutions ability to change the volume of a cell by osmosis
-Solutions may be:
Hypertonic: more solute, less water, take water from surroundings (low water potential)
Hypotonic: less solute, more water, lose water to surroundings
Isotonic: equal water exchange with surroundings
*Water always moves from hypotonic to hypertonic
How to regulate osmosis?
- Osmoconformers: organisms that are in osmotic equilibrium with their environment
- Osmoregulators: maintain constant blood osmolarity different than their environment (hyper/hypotonic)
What are nitrogenous wastes?
- Produced when amino acids and nucleic acids are broken down
- Bony fish and immature amphibian eliminate ammonia by diffusion via gills
- Chondrichthyes, adult amphibians, and mammals convert ammonia into urea which is dissolved in water
- Birds, reptiles, and insects convert ammonia into the water insoluble uric acid
Describe vacuoles?
- Single celled protists use contractile vacuoles
- Pump out excess water to ensure cell doesn’t burst
- Nitrogenous waste excreted through membrane
What are protonephridia?
- Network of tubes which branch into bulblike flame cells
- Flame cells remove solutes and excess water from the body
What is nephridia?
- Earthworms use nephridia
- One on each segment
- Series of convoluted tubules that remove excess water and solutes from the blood and produce urine
- Urine excreted through a pore
What are malpighian tubules?
- Insects
- Extensions of the digestive tract
- Water and potassium moved into tubules by active transport
- Creates osmotic gradient that draws water into the tubules by osmosis
How do cartilaginous fish excrete waste?
- Isotonic in seawater
- Nitrogenous wastes are urea
- Urea is reabsorbed and pooled in blood
- Solute concentration in blood is equal to that of sea water
