plant transport Flashcards
2.53 what do phloem vessels do?
transport food materials (mainly sucrose & amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
—> this means that movement can be in any direction around the plant
differences between xylem & phloem?
phloem:
- cells are living cells and not hollow
- substances move from cell to cell through pores in the end walls of each cell
2.54 information about the xylem?
- roots, stem and leaves form plant organ system for transport of substances around the plant
- plants also possess 2 specialist transport vessels called xylem and phloem
- xylem and phloem arranged throughout the root, stem and leaves in groups called vascular bundles
2.54 structure and function of the xylem
- xylem vessels transport water and minerals from roots to stem and leaves
key structural features:
- composed of dead cells which form hollow tubes
- xylem cells strengthened by lignin - so adapted for transport of water in transpiration stream
what are root hair cells for?
they’re adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport) into the roots
how are root hair cells adapted?
- they’re single celled extensions of epidermis cells in the root
- grow between soil particles and absorb water & minerals from soil
- increase surface area to volume ratio significantly —> this increases the rate of the absorption of mineral ions by active transport
- high proportion of dissolved minerals and sugars in cytoplasm (of root hair cell) give it low water potential (less watery) —> water moves into root hair cell by osmosis
what’s the stuff from the diagram of the xylem that i can’t put on here say??
- no cell contents just a continuous column of water
- original cell wall between cells has broken down
- walls thickened with lignin
what are the organelles in root hair cells?
- ribosomes
- mitochondria
- nucleus
- cytoplasm
- cell membrane
- cell wall
- root hair
- vacuole
2.55B what’s the route of water through the plant?
the structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport
- water moves, by osmosis, into root hair cells, through root cortex & into the xylem vessels:
- once the water gets into the xylem, it’s carried up to leaves where it enters mesophyll cells in leaves
so pathway is:
root hair cell —> root cortex cells —> xylem —> leaf mesophyll cells
2.56B transpiration definition
the loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)
(the evaporation of water from the surface of a plant)
how does transpiration work?
- loss of water occurs through evaporation of water at surfaces of spongy mesophyll cells followed by diffusion of water vapour through the stomata
- the many interconnecting air spaces between the mesophyll cells and the stomata creates a large surface area
- this means evaporation can happen rapidly when stomata are open
the effect of transpiration
- water moves through xylem vessels in a continuous transpiration stream from roots to leaves via the stem to replace the water that’s been lost due to transpiration
- due to cohesion, water in xylem creates a continuous unbroken column (each individual molecule ‘pulls’ on the one below it)
- transpiration produces tension or ‘pulls’ on water in xylem vessels
- if rate of transpiration from leaves increases, water molecules pulled up the xylem vessels quicker
the function of transpiration
- transporting mineral ions
- providing water to keep cells turgid in order to support structure of plant
- providing water to leaf cells for photosynthesis
- keeping leaves cool, the conversion of water (liquid) into water vapour (gas) as it leaves the cells & enters airspace requires heat energy. use of heat to convert water into water vapour helps cool plant down
2.57B factors that affect rate of transpiration
air movement/wind speed, humidity, light intensity, temperature
2.57B how does air movement effect the rate of transpiration?
more transpiration:
- good airflow removes water vapour from air surrounding leaf
- sets up concentration gradient between leaf and air
- increasing water loss
2.57B how does humidity effect rate of transpiration?
less transpiration:
- humidity is measure of moisture (water vapour) in air
- when air saturated with water vapour concentration gradient is weaker
- so less water is lost
2.57B how does light intensity effect the rate of transpiration?
more transpiration:
- guard cells responsive to light intensity
- when it’s high they’re turgid & stomata open allowing water to be lost
2.57B how does temperature effect rate of transpiration?
more transpiration:
- at higher temperatures, particles have more kinetic energy
- so transpiration occurs at faster rate as water molecules evaporate from mesophyll and diffuse away faster than at lower temperatures
what are the 2 types of potometer
- mass potometer measures change in mass of a plant as a measure of amount of water that’s evaporated from leaves & stem
- bubble potometer measures uptake of water by a stem as a measure of the amount of water that’s being lost by evaporation, consequently pulling water up through stem to replace it
2.58B what apparatus do you need to investigate the effect of environmental conditions on transpiration?
apparatus:
- potometer (mass or bubble)
- timer
- lamp
- ruler
- plant
2.58B what’s the method for investigating the effect of environmental conditions on transpiration (bubble potometer)?
- cut a shoot underwater —> to prevent air entering xylem and place in tube
- set up apparatus and make sure it’s airtight, use vaseline to seal gaps
- dry leaves of shoot (wet leaves affect results)
- remove capillary tube from beaker of water to allow single air bubble to form & place tube back into water
- set up lamp 10cm from leaf
- allow plant to adapt to new environment for 5 mins
- record starting location of air bubble
- leave for 30 mins
- record end location of air bubble
- change light intensity
- reset bubble by opening tap below reservoir
- repeat experiment
- calculate rate of transpiration —> further bubble travels in same time period, greater the rate of transpiration
2.58B what’s the equation for rate of transpiration?
rate of transpiration = distance moved by air bubble (m) / time (min)
