transport in plants Flashcards
what adaptations of plants increase SA:V?
some plants have a branching body type
leaves are flat and thin
roots have root hair
what is mass flow
the bulk movements of materials
How is mass flow helpful to cells?
help to bring substances quickly from one exchange site to another
maintain the diffusion gradients sites between cells and their fluid surroundings
ensure cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
what is the function of the xylem?
because the vascular tissue carries dissolved minerals and water up the plant
structural support
food storage
function of phloem tissue?
transport organic compounds, particularly sucrose, from source to the sinks
what 4 tissues make up xylem?
tracheids( narrow tapered cells with pits)
vessel elements (large w/ thickened cell walls and no end plates when mature)
xylem parenchyma (can store water)
schlerenchyma cells (fibres & sclereids)
describe the structure of a xylem
- lignified cell walls
- no end plates
- no protoplasm
- pits in wall
- small diameter of vessels
draw a diagram for xylem and vessel in roots
check google
draw a diagram for xylem and vessel in leaf
check google
draw a diagram for xylem and vessel in stems
check google
describe the structure of a sieve tube element in the phloem
- sieve plates with sieve pores
- cellulose cell wall
- no nucleus, vacuole or ribosomes in mature cells (some ER & mitochondria are present)
- thin cytoplasm
describe the structure of a companion cell
- nucleus and other organelles present
- transport proteins in plasma membrane
- large numbers of mitochondria
- plasmodesmata (channels in the cell wall)
what is a transpiration stream?
refers to the movement of water from the roots to the leaves
what is transpiration?
the loss of water vapour from a plant to its environment by evaporation and diffusion
why is transpiration useful?
- provides a way to cool down plant via evaporative cooling
- helpful in uptake of mineral ions
- turgor pressure of the cells provides support to leaves and
stem of non woody plants
describe the process of transpiration (2 steps)
- evaporation of water molecules from the surface of mesophyll cells to air space (H2O(l) -> H2O(g))
- diffusion of water vapour out of stomata when there is a concentration gradient
how does humidity affect the rate of transpiration
humidity -> water content in air so the water potential gradient is created
how does air movement affect rate of transpiration
air movement -> maintaining conc. gradient to replace saturated/ humid air
how does temperature affect rate of transpiration
temperature -> temp ↑ leads to thermal energy ↑ so kinetic energy ↑ so evaporation is higher
how does light intensity affect rate of transpiration
light intensity -> signals guard cells to open and close stomata so the SA of transpiration ↑
what factors affect the rate of transpiration
light intensity, temperature, air movement and humidity
what two pathways that move water along the cortex?
apoplastic pathway and symplastic pathway
what does the apoplastic pathway do?
through cell wall by diffusion. can occur from cell wall to cell wall directly or through intracellular spaces
what is the casparian strip made of and purpose?
it is made of suberin and is a thick, waterproof and a waxy band. stops the apoplastic pathway
what is the symplastic pathway?
when water is transported through osmosis in the cytoplasm and plasmodesmata of the cells
what is the cohesion-tension theory?
cohesion is the idea of attraction between H2O molecules and adhesion is the idea of the attraction to the xylem vessel. when water moves through xylem due to these properties of H2O
what is the role of the stomata?
the guard cells open when turgid and close when they lose water. helps the process of transpiration
describe the process of water movement through a lead (5 steps)
1) water vapour diffuses from air spaces through stoma by transpiration lowering the water potential
2) water evaporates from a mesophyll cell wall into the air spaces, creating a transpiration pull
3)water moves out through the apoplastic pathway to symplastic pathway
4)water leaves xylem vessel through a non lignified area (pit)
5) water moves up the xylem vessel (transpiration stream)
what is translocation?
the transport of assimilates via the phloem from sources to sinks which requires the input of metabolic activity
list some examples of sources for assimilates
-> green leaves and green stem
-> storage organs (e.g.tubers and tap roots)
-> food stores in seeds
