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Description
Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
almost 7 years ago
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| Question | Answer |
| What is positive pressure? | Pushing contents forwards by pressure from behind |
| What is negative pressure? | Drawing contents in by vacuum or loss |
| What are the challenges of +? (4) | Providing sufficient force Allowing for stress-points (elasticity) Avoiding blockages Gravity |
| What are the solutions for +? (4) | Bulk flow Physical properties of vessels Pumps Closed systems |
| What are the challenges of -? (4) | Providing sufficient suction Not allowing embolisms Countering elasticity - avoiding collapse Gravity |
| What are the solutions for -? | Negative bulk flow Physical properties of vessels - capillary action Closed systems Solid walls for vessels- no elasticity Valves |
| Describe the circulatory system in plants | Water and minerals enter roots from soil Water is transported to aerial parts of the plant Leaves exchange CO2 and O2 through photosynthesis/respiration Photosynthesis produces sugars which need to be transported to metabolising cells Roots and other parts exchange O2 and CO2 via respiration |
| What are the challenges of plant transport? | No pumps: must use physics alone Need to transport H2O and sugars in two separate directions How to load the transport system How to regulate content loading and flow rate Height - how to defy gravity In addition to bulk flow of metabolites, the transport system must also provide physical support |
| What solutions can the plant do to overcome this? (7) | Diffusion osmosis + pressure capillary action thermodynamics chemistry of water - pressure |
| Hypertonic: | Hypertonic Plasmolysed Ψcell>Ψs |
| Isotonic: | Flaccid Ψcell=Ψs |
| Hypotonic | Turgid Ψcell<Ψs |
| What are the 2 transport systems in plants? | Xylem and Phloem |
| What is the structure of the xylem? | Perforated plates Vessel member Tracheids Fibre |
| What do the xylem transport? | Water and dissolved nutrients from roots to shoots |
| What is the structure of phloem? | Companion cell Schlerenchyma cell Sieve element Sieve areas Sieve plate fibre |
| What do the phloem transport? | Sugars from photosynthesising organs to the rest of the plant |
| What do both transport systems transport? | Hormones |
| What are the tracheary elements | Tracheids and vessel elements pits - perforation plate/perforated end wall |
| How do these cells arise? | Develop from parenchyma cells which undergo elongation |
| Describe this process of elongation | Specific sites of 2' thickening Bands of cellulose form Bands are strengthened with lignin |
| What happens when elongation stops? | Elongation stops 2' cell wall continues to thicken Area of 1' wall left without 2' thickening (pits) Cell dies leaving hollow tube Pits enable water to flow between tubes |
| Compare water movement through vascular bundles | Tracheids: H2O moves only Through pits:slow Vessel elements: H2O moves through end-wall Perforations and pits:Fast |
| What movement of materials occurs in xylem? | Bulk FLow |
| How and what sort of pressure is generated? | Negative pressure: Continuous column of water Transpiration of water from leaf creates negative pressure Very high pressures are generated |
| Why is lignin essential for this type of pressure? | if no strengthening via lignin the cell wall would collapse in on itself under suction |
| Describe transpiration | H2O vapour diffuses from the moist airspace to outside down a water potential gradient Through stomata to allow gas exchange As H2O diffuses out, water around the cells become concave, increasing the tension of that water film |
| What sort of pressure is generated? | A (-) pressure that pulls on the water column (via cohesive forces) |
| What is transpiration cohesion-adhesion? | Transpiration in leaves provides the pull Cohesion of H2O molecules as a result of Hydrogen bonding transmits this pull along the entire length of the xylem to the roots |
| How does this adhesion assist in water flow? | Adhesion of H2O to xylem walls helps to counteract the gravimetric forces on the water column |
| Describe phloem | Between sieve elements are sieve plates These sieve elements are still alive Companion cells connected to sieve elements via plasmodesmata |
| What is the function of the companion cell? | Regulates cells via plasmodesmata Many mitochondria Provides crucial metabolites to STE (e.g. proteins/ATP). |
| Describe the sieve tube member | Alive No nucleus Few organelles Clear to allow fast flow through cell |
| Describe bulk flow in the phloem | Sucrose actively transported into companion cells as the source No plasmodesmata between companion and leaf cell, prevents sucrose from travelling back to source Psi decreases in companion cell as solutes are added Water taken into companion cell via osmosis Increases pressure potential at source end of phloem Forces sap down sieve-tube elements to sink (+) pressure Sucrose removed from companion cell to the sink, water follows too as it follows its water potential gradient |
| Diargram for monocot root architecture | Monocot root Epidermis Endodermis Cortex Pericycle Phloem Xylem (vessel elements) Stele |
| Diagram for dicot root architecture | Epidermis Endodermis Cortex Pericycle Phloem Xylem Stele |
| How is traffic of molecules regulated in plant transport? | Specific transport proteins in the plasma membrane and tonoplast regulate traffic of molecules between the three compartments |
| What is the apoplast route? | Through cell wall between the fibres and intracellular space |
| What is symplast route? | Through cytoplasm, linked fby plasmodesmata |
| What is the transmembrane route? | Through cell walls and intercellular spaces |
| Which is the fastest and slowest route? | Symplast is slow Aploplastic route is fast |
| How is apoplast transport blocked? | Apoplast transport across endodermis is blocked by waxy casparian strip (suberin) |
| Why is this important? | Allows control over what enters the xylem Forces water into the symplast as it has to cross the cell membrane |
| How is gravity defied? | Use positive root pressure Guttation Occurs overnight when rate of transpiration is slow Driven by AT of mineral nutrient ions into root + Root pressure limited to pushing sap just a few meters Many plants can't generate + root pressure |
| How does capillary action work? | Can only raise liquid a few centimeteres up a tube Many tall trees have more tracheids than vessels, smaller diameter, thinner more capillary action than vessels |
| Negative pressure | main driving force for sap transport Suction doesn't work past 10 M in tube elements Higher you get greater effect gravity has on the H2O column |
| What does gravity limit? | Gravity limits height of trees, can't drive H2O any higher |
| Why is control over transpiration necessary? | Maintains balance between need to preserve water and to regulate gas exchange Control regulated by stomata |
| How do stomata open? | Cell turgid/stoma open uneven thickening, middle thicker Radially orientated cellulose microfibrils, resists stretching so cell increases in length rather than width Guard cells attached at their tips so expansion causes buckling K+ enters cell, cell psi lowers water enters cell- cell becomes turgid |
| How is water transported? | Rapid transport of K+ across plasma membrane and tonoplast causes turgor change in guard cells |
| How do stomata close? | K+ leaves cell, increase in cell psi, water leaves cell becomes flaccid |
| Describe directional changes to phloem flow as organs develop | Only leaves that are photosynthesising are sources, generate + pressure translocation to sugar requiring sinks |
| Why aren't photosynthesising young leaves sources? | Young leaves don't make enough sugar to sustain growth so sinks |
| Draw basic dicot stem morphology | Vascular bundle fascicle cambium(stem cell region) pith epidermis cortex VB in monocots are more scattered wood=xylem growth |
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