Resource Acquisition and Transport in Vascular Plants Flashcards
why didn’t ancestor plants need a vascular system?
- Algal plant ancestors had no need for complex vascular systems: life in ocean provided buoyancy and ample water
- Earliest forms of plants (bryophytes), lacking vascular systems, require intimate contact with water → moist environments
What were the affects of vascular tissue forming in plants?
- The evolution of conducting tissues in vascular plants changed everything
» Allowed true tissue differentiation
» Roots absorb water and minerals from the soil and distrib- ute them to the rest of the plant via the vascular tissue
» Shoot system harvests the sun’s energy and atmospheric CO2 for photosynthesis
What was the result of an increase in non-vascular plants
- ## As non-vascular plants increased in numbers, competition for light, water and nutrients also increased
What adaptions in non-vascular plants where favored due to the competition for resources?
- Favoured taller plants and leaves with larger surface area
» But larger surface = more evaporation, greater need for water
» And taller plant require stronger anchorage - That, in turn, favoured
» Production of multicellular, branching root
» Production of more efficient leaves, covering wider surface area
» More efficient long distance transport system between roots to leaves
What is the first step of transport of water and nutrients in plants?
- Roots absorbe water and dissolved minerals from the soil
What is the 2nd step of transport of water and nutrients in plants?
- Water and minerals are transported upward from roots to shoots as xylem sap.
What is the 3rd step of transport of water and nutrients in plants?
- Transpiration, the loss of water from leaves (mostly through stomata). Creates a force within leaves that pulls xylem sap upwards.
What is the 4th step of transport of water and nutrients in plants?
- Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.
What is the 5th step of transport of water and nutrients in plants?
- Sugars are produced by photosynthesis in the leaves.
What is the 6th step of transport of water and nutrients in plants?
- Sugars are transported as phloem sap to roots and other parts of the plant
What is the 7th step of transport of water and nutrients in plants?
- Roots exchange gases with the air spaces of soil taking in O2 and discharging CO2.
- In cellular respiration, O2 supports the breakdown of sugars.
Draw a diagram of the overview of transport in non-vascular plants.
Google Doc:
https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing
What are the two types of transport in plants?
- Short distance: cell–to cell transport at tissue level
- Long distance: transport of sap in xylem and phloem in the vascular system at ‘whole’ plant level
In short distance transport, what are the three routes for transporting materials between plant cells
- Apoplastic: external to the cell membrane
- Symplastic: via the cytosol of the cell (requires entry into 1 cell, then can move via plasmodesmata)
- Transmembrane: between cells across the cell membrane (repeated crossing)
What is short distance travel of substances controlled by?
- Short-distance movement of substances into and out of cell is controlled by
» Selective cell membrane permeability
» Both active and passive transport
What powers membrane transport in plants?
- H+ important to power membrane transport (≈ Na+ in animal cell)
» Membrane potential established through pumping H+ by proton pumps
» Energy of H+ gradients used to co-transport other solutes by active transport (eg, sucrose)
How does short distance transport of water occur and what is it measured in?
- Absorption or loss occurs by osmosis (diffusion of free water across channels in plasma membrane called aquaporins)
- Likelihood of water to move into or out of a cell by osmosis is measured by the water potential (Ψ)
» Expressed in pressure units of megapascal (MPa)
What is water potential?
- Ψ is the sum of the solute potential (ΨS) and the pressure potential (ΨP): Ψ = ΨS + ΨP
» ΨS is proportional to solute concentration
• Always a negative number; more concentrated = more negative
» ΨP is the physical pressure (push/pull) of solution
What is Turgor pressure?
- A measure of ΨP in plant cells: turgor pressure and turgidity
- Turgor pressure: pressure put on cell wall by protoplast (living part of the cell, ie, everything within cell membrane) from swelling caused by water
What are the measured of Turgidity?
» Turgid: when a cell has taken up the maximum amount of water and the cell wall exerts pressure back on the protoplast
» Flaccid: equilibrium between water uptake and water loss
» Plasmolysed: when a cell has lost so much water its plasma membrane is no longer connected to cell wall
What does it mean when a plant is turgid?
- A walled cell with a greater solute concentration than its surroundings (hyperosmostic) is turgid (ie, very firm)
» In a non-woody tissue push against each other → stiffening of tissues
What does it mean when a plant is wilting?
- If the cell becomes iso- or hypo-osmotic in relation to its surroundings, then it becomes flaccid → turgor loss → wilting: leaves and stems droop as a result of cells losing water
Where and how does water and nutrients enter the roots?
- Water and dissolved minerals enter root at root hair
» Apoplastic route: passive diffusion into hydrophilic cell wall
» Symplastic route: active uptake into cells
Before reaching the vascular cylinder, where does the nutrients and water have to pass through and why?
- Before reaching vascular cylinder, the nutrients and water pass through the endoderm
» The Casparian strip prevents passage via cell wall (apoplastic)
» This Forces it to pass through cell membrane at least once before reaching the vascular system → keeps many toxic substances out
