Module 3: Plant Transport Systems Flashcards
(42 cards)
What is transpiration?
Evaporation of water from the surface of a leaf (1),
What is the Transpiration Stream?
The transpiration stream is the flow of water moved up from the soil into the root hair cell and through the root cortex by osmosis. Then up the xylem and stem to the leaves.
Structure of Xylem:
Long tubes joined end to end. No walls- Allows for uninterrupted flow. No cytoplasm. Walls thickened with lignin to prevent collapse. Water and ions enter and leave through non-lignified pores. Annular lignin rings and lignin spirals.
Structure of Phloem:
Transports solutes. Sieve tubes joined end to end, separated by sieve plates. Companion cells on the side of sieve tubes.
Suggest how water can be lost from a cut stem when all leaves have been treated with petroleum jelly? (Petroleum covering the bottom of leaves)
Stomata are located in the stem as well as the leaves and so water loss by transpiration can still occur.
Water can evaporate from the upperside of the leaves.
4 examples of adaptions to reduce water loss in plants:
The surface covered in reflective hairs (reduce diffusion gradient of water by keeping air surrounding plant moist)
The ability to store carbon dioxide so stomata only need to open at night.
Leaves are reduced to spines to prevent damage from animals.
Small leaves - smaller surface area - reduces water loss
Sunken Stomata
At the endodermis, water has to enter _______
the symplast pathway
Most water moves across the root cortex by the ____________
apoplast pathway
What is adhesion?
The attraction of water molecules to its surroundings (e.g impermeable walls of the xylem tissue)
Translocation occurs through____ by _______
Translocation occurs through sieve elements by mass flow
Sucrose is actively loaded into the phloem at regions known as ____________
Sources
Sucrose ________ the water potential of the cell it’s in .
decreases
What are the adaptions of hydrophytes?
- No waxy cuticles
- thin leaves
- flexible stem + roots
- little to no roots ~ direct diffusion into stem
- lots of stomata
- Aerenchyma ~ made from apoptotic parenchyma -provide air spaces - low resistance transportation pathway + buoyancy
- Large leaves (on the surface of water) - maximise site of gaseous exchange.
Why do plants need transport systems?
- Metabolic demand - provide for photosynthesis for aerobic respiration and active transport
- Size - long distance for nutrients to travel - transport system allows fast transport
- Surface Area : volume ratio - can’t rely on simple diffusion.
- Water aids thermoregulation and turgidity(Structural aid)
Difference between sap and dew?
The sap is in the phloem and dew is the water lost by transpiration.
Evidence of cohesion tension theory?
Trunk diameter changes due to the rate of transpiration.
Hydrophytes
Live either partially or completely submerged in water.
Xerophytes
Live where water loss by transpiration (due to hot and dry conditions) is greater than water uptake.
What are the two methods of calculating the number of stomata?
Method 1: drop water on microscope slide - place ripped leaf - examine
Method 2: Paint a leaf’s surface with nail vanish - allow to dry -peel off a place on a dry microscope slide.
Xerophyte adaptations:
- deep horizontal roots
- waxy cuticle - waterproof to reduce loss
- sunken stomata - create local humidity - reduce conc. gradient of water out of plant.
- Hairs and spikes ^^ + prevent damage from animals
- Thick leaves - Reduce SA:Vol area
Describe active translocation:
Solutes are produced at sources and are transported into the phloem using proton pumps.
The active loading causes a higher solute concentration, which decreases the water potential. This causes water to flow into the phloem from the xylem by osmosis.
This causes the source to become an area of high pressure (because of the incompressibility of water) - this creates a pressure gradient that will move the solutes by mass flow.
Solute leaves at sink, increasing water potential, causing water to exit into the xylem.
How can translocation rate be measured?
Using aphid stylets - once aphids penetrate the phloem sever stylets - collect sap at different distances. Provide the tree with radioactive C02 to form radioactive sucrose. The time taken for the radioisotopes to reach each stylet and their distance from the source can be used to calculate the rate.
Tracheary elements:
Tracheids and vessel elements
Tracheids:
Smaller tubes with tapering end walls overlap adjacent tracheids, providing the plant with mechanical strength. Water passes between tracheids through empty lumens, pits in cell walls, and unlignified cell walls.
