plant transport Flashcards
describe the apoplast pathway
- water moves into the walls of epidermal cells
- spaces separate cellulose fibres in the cell wall which moves water through
describe the symplast pathway
- continual pathway across the root cortex
- water moves through cytoplasm via plasmodesmata
how are root hair cells adapted for the uptake of water and mineral ions
- large surface area
- thousands of root hair cells provide large total surface area
- cell wall permeable to water
- thin cell walls
- large numbers of mitochondria
- large numbers of protein carriers
outline the features/importance of the epidermis
- outer layer of root
- epidermal cells have root hairs to increase surface area
outline the features/importance of the xylem
- dead cells contain rings of lignin to form waterproof vessels
- water and dissolved minerals transported
- pits in vessels allow water to move
- water moves us tracheids which have tapered ends
- fibres provide structural support
- packing cells around vessels and tracheids are parenchyma
outline the features/importance of the phloem
- living tissue
- transports sucrose around the plant
outline the features/importance of the endodermis
- surround the pericycle
- layer of cells containing waterproof casparian strip
outline the features/importance of the vascular bundle
- contains xylem, phloem and cambium cells
- roots restrict pull stresses
- stems provide flexible support but resist bending
outline the processes of the cohesion-tension theory
- water evaporates from surface of epidermal cells
- water diffuses from sub-stomatal chamber into atmosphere
- water evaporates from cell walls into sub-stomatal chamber
- water moves through leaf tissue via pathways
- water leaves xylem and moves into apoplast due to cohesion
- water drawn up xylem by tension
- water enters xylem
- casparian band prevents water movement via apoplast pathway
- water uptake into root hair cells
outline the processes of investigating transpiration rate
- cut shoot underwater to stop air entering xylem vessels
- cut shoot at a slant to increase surface area
- remove capillary tube and wait for air bubble to form
- shut screw clip
- remove potometer from underwater and use vaseline to ensure air tight joints around shoot
- dry leaves because excess water slows transpiration rate
- allow time for shoot to acclimatise
- record position of air bubble on scale
- start timing and calculate distance moved
explain how an increase in temperature effects the rate of transpiration
- increases rate of transpiration
- increases kinetic energy which causes an increased rate of evaporation from mesophyll cells
explain the effect of increasing humidity on the rate of transpiration
- decreases rate of transpiration
- lowers water potential gradient between air spaces in the leaf and the outside
explain the effect of increasing air movement on the rate of transpiration
- increases rate of transpiration
- wind removes water vapour which increases water potential gradient
explain the effect of increasing light intensity on the rate of transpiration
- increases the rate of transpiration
- more open stomate
- increases rate of photosynthesis so more water is needed
explain how mass flow of materials between the source and the sink would be brought about
- sucrose loaded into sieve tube by diffusion which lowers water potential
- water enters sieve tube down a water potential gradient
- hydrostatic pressure in sieve tube increases
- sucrose is unloaded at sink which increases water potential in sieve tube
- water moves out of sieve tube which reduces hydrostatic pressure
- pressure gradient means sucrose moves from source to sink
what is meant by translocation
process in which substances are moved from the site of production (source) to the place they are needed (sink)
give two problems with the mass flow hypothesis
- suggests flow is in one direction when it is actually bidirectional
- cytoplasmic streaming can be observed
describe the process of the ringing experiment
- ring of bark is scraped away which also removes some phloem
- sugar tries to be transported down the stem but stopped by the ring
- bulge of sugar forms above the ring
- suggests sugar moves down the stem in the phloem
explain how aphids can be used to test for translocation
- stylets in the mouth are used to penetrate phloem tubes
- if anaesthetised with carbon dioxide and the stylet cut off so it remains in the phloem, pure phloem sap can be collected for analysis
outline the structure/function of sieve tubes in the phloem
- formed form sieve tube elements (parenchyma cells) - stacked on top of each other
- cells walls a perforated where they join and form sieve plates - allow flow through and cytoplasmic strands to link cells
- living cells however lack most organelles for easier flow
outline the structure/function of companion cells in the phloem
- found next to each sieve element
- very dense cytoplasm containing many mitochondria and ribosomes and are very metabolically active
- connected to sieve element via plasmodesmata
describe how root pressure is achieved
- at endodermis ions are actively taken up to by-pass the casparian strip which allows active uptake of ions
- lowers water potential in xylem causing water to be drawn through endodermis
- this pulling produces a positive hydrostatic pressure inside the xylem, forcing water upwards
outline and explain the process of autoradiography as an experiment fro translocation
- 14CO2 placed into bag surrounding a leaf
- source and sink leaves are placed on photographic film for 24 hours
- when film is developed, presence of radioactivity shows up only
- it is concluded that sucrose is transported both up and down the stem
how does radioactive carbon reach growing areas of the plant
- plant uses the radioactive carbon for photosynthesis which incorporates it into glucose
- glucose is converted into sucrose with the radioactive carbon
- the sucrose is transported through the phloem to the growing buds by translocation
describe how respiratory inhibitors can be used to provide evidence for the phloem being the tissue used for translocation
- eg. cyanide
- reduces translocation of organic solutes when applied to the phloem but not the xylem
explain how nitrogen enters the plant
- enters as nitrate ions
- diffuse into apoplast stream
- enter symplast pathway by active transport against the concentration gradient
- flow via the plasmodesmata into the cytoplasmic stream
explain how the columns of water in the xylem are held up
- cohesive forces between water molecules
- adhesive forces between water molecules and the hydrophilic lining of the xylem
what is meant by transpiration
the loss of water through the leaves of a plant
