Vascular Transport Flashcards
what are the advantages to life on land
An advantage because:
- less light limitation
- more plentiful oxygen and CO2
what are challenges to life on land
A challenge because:
- Gravity has to be overcome, early plants only had cellulose not lignin
- Water is less plentiful: must maintain moisture
- Water/nutrients are at different locations than gases
- Dispersal of gametes and offspring
- Different Stressors like UV light, temperature fluctuations
how are plants adapted to maintain moisture
- Maintain Moisture:
- Water transport systems: transport from soil to leaves
- Cuticle/stomata: avoid / regulate water loss
- Pollen grains/seeds: resistant to dessication
how have plants adapted to reproduction and dispersal on land
- Reproduction and dispersal:
- Animal pollination / fruits
- More targeted pollen / seeds dispersal
how have plants adapted to Obtain resources from two locations on land
- Obtain resources from two locations
- Larger leaves to increase photosynthesis
- Larger plants
- Shoot and root systems
- transport systems: Xylem and Phloem
how have plants adapted to Support their plant body against gravity on land
- Support plant body against gravity
- Support of plant body: thicker cell walls and lignin
how have plants adapted to Protect against abiotic and biotic stresses on land
- Protect against abiotic and biotic stresses
- Secondary metabolites
which came first, increased photosynthetic surfaces, or increased water transport infrastructure
Increase photosynthetic surfaces?
or Increased water transport infrastructure?
It seems that increased water transport infrastructure did. This is based on small plants from the devonian (400mya) that had no true leaf structures, but had xylem and a simple type of. It was found in New Brunswick.
what was Psilophyton
Psilophyton: extinct vascular plant (420-360mya) had no leaves, grew to 0.5m tall. Had lignified xylem tissue, upwards growth not to increase photosynthetic area.
For the first 100 million years, no organisms could decompose lignin, lead to carboniferous coal.
what do Xylem and Phloem do
Xylem transport: uptake of water and minerals by root, transported upward through xylem driven by respiration.
Phloem transport: Photosynthetic produces sugars which are transported downwards so roots can perform respiration. Gas exchange occurs all over.
why aren’t mosses tall
Mosses lack vascular tissue and lignin and so can’t grow as tall as trees.
what happens to gases in a plant body
Gas exchange occurs all over the surface of a plant, and doesn’t get transported far.
where does secondary growth occur
Secondary growth begins with the formation of a ring/tube shaped lateral meristem called a cambium. It is between the primary phloem and xylem.
what happens to meristomaic cells in secondary growth from lateral meristem
The meristomatic cells divide throughout the life of the plant and either push cells inwards (which become xylem type cells , secondary xylem) or push outwards (which become secondary phloem).
what is wood
A vascular cambium cell adds xylem more often than phloem in secondary growth. Secondary Xylem = wood
How does secondary growth account for added perimeter
Since the cells on the perimeter of the stem can’t divide it would begin to split open as the radius increases. But another lateral meristem forms called the cork cambium which makes more dermal cells to account for the increasing perimeter, make up the outer layer of a stem or root (cork cells).
what is Periderm, Phelloderm, and bark
Cork Cambium: secondary dermal tissue (cork) add cork cels to outside and phelloderm inside. Cork cells = Periderm, Periderm + Phelloderm = Bark
how is everything organized in the stem of edicts
Vascular bundles in eudicots are organized in a ring. Primary Phloem outside, Primary Xylem inside, with the vascular cambium in between.
why do tree rings happen
When there is seasonal changes in secondary xylem production, tree rings form for every year of growth.
At the end of the fall the tree goes dormant, stopping growth. More vascular bundles early in year, less later.
what is dendrochronology
Dendrochronology = Looking at tree rings from different years. Looking at thickness, or other factors to correlated to climate, atmosphere, etc.
what are Annual vs Perennial Plants
Annual plant = Herbaceous plant - mostly composed of a primary body (derived from embryo)
Perennial plants = shrubs and trees - composed of primary and secondary tissues.
how do primary and secondary growth help transport
Primary and secondary growth helps to transport water in tall trees.
Leaves evaporate water → helps to pull up xylem sap
Secondary xylem (wood) → stabilizes stem, forms new xylem every year.
what are the three transport routes in plants
Water and nutrients in the plant body move via three pathways with different properties
- Apoplastic
- Symplastic
- Transmembrane
Apoplastic route: Inside cell walls - easy
Symplastic rout: in cytosol, through plasmodesmata -easy
Transmembrane: crossing lipid bilayer more than once, in and out of cell - harder
What are some examples of transmembrane transport of solutes in plants
Active transport: proton pump creates membrane potential pH gradient
Co-transport of ions/nitrates with protons (e.g. mineral uptake into roots)
Co-transport of neutral solutes with protons (e.g. sucrose in phloem)
Passive transport: ion channels (don’t depend on protons, may be gated)
what happens to water in regards to plasma membranes
Plasma membrane is made of fats (lipids)
- Although water-repellant, they are not water impermeable
- Aquaporins: bidirectional channel proteins that allow only water molecules to pass in a single file at a rate of 3 billion per second (faster than diffusion through membranes)
Free water will move into cells with a high solute [] due to osmosis
what is water potential
Potential energy of water under given conditions. Compared to pure water under reference conditions.
→ Direction of water flow is driven by water potential (Ψ)
- Measured in MPa
- Free water moves from regions of higher water potential to regions of lower water potential
- Ψ = Ψs + Ψp
how do solutes and pressure affect water pressure
Solutes have a negative affect on Ψ by binding water molecules
Positive pressure has a positive effect on Ψ by pushing water
Negative pressure has a negative effect on Ψ by pulling water
what is solute potential
The Solute potential Ψs = osmotic potential of a solution, is directly proportional to its molarity
- Ψs is always negative. Solutes in plants cells: ions and sugar
what is pressure potential
Pressure potential Ψp is the physical pressure on a solution
ex: Turgor pressure = positive pressure, xylem sap is under negative pressure
what is water pressure in living plant cell, pure water, and 0.1M sugar solution
Definition: pure water Ψ = 0
Osmotic pressure of 0.1M sugar solution: -0.2MPa
Pressure of living plant cell: 0.5-1MPa (70-120 Psi)
how much water do trees use
Trees use 500-2,000L of H2O daily if not limited
Western red cedar used 800L / day for example
how is water taken up in roots
In the endodermis is a ring of cells that act as a barrier. The Casparian strip runs through their cell walls and blocks transport, forcing everything to go through the cells. So water must pass through the symplastic rout. Once in the xylem it is only apoplastic.
how much water is lost from evaporation in trees
Water evaporates at the leafs surface. One maize plant losses 60L per season, passes through stoma.
how is water pulled up xylem
A different in water potential pulls water up through the plant’s xylem until it leaves via transpiration or is used by the plant.
Cohesion by h-bonds keeps water together. Adhesion by h-bonds cause water to stick to cell walls
Molecules pull each other along according to the cohesion-adhesion theory.
what happens if hydrogen bonds break in xylem
If the hydrogen bonds break - cavitation occurs, air get in the xylem and it stops working. Most transport is in young xylem.
how is water loss regulated in plants
Transpiration: Water loss by aerial organs
Cuticle prevents water loss at surface → 95% of H2O is lost through stomata, regulated by stomata density and pore opening/closing.
how are guard cells opened and closed
K+ ions are pumped into cells, H2O floods in and guard cells ballon to open stomata.
Potassium ions are pumped out of cells, H2O floods out and guard cells shrink to close stomata.
