3.1.3 transport in plants Flashcards
why do multicellular plants need transport systems
they have a small surface area to volume ratio and have a relatively high metabolic rate. exchanging substances by direct diffusion would be too slow to fit metabolic needs
what makes up a vascular bundle
xylem, phloem and sometimes a layer of cambium cells
what is the function of the xylem
transports water and mineral ions in solution and provides support to the plant
how are xylem vessels adapted for their function
they are long tube like structures formed from cells joined end to end with no end walls. the cells are dead and have no cytoplasm
walls are thickened by lignin which supports it and stops it collapsing
water and ions move in and out of the the tube through small pits where there is no lignin
what is the function of the phloem
phloem tissue transports assimilates round plants
how are phloem vessels adapted for their function
sieve tube elements are joined end to end. there is a sieve plate at the end of each cell to allow solutes to pass through.
sieve tube cells have no nucleus and few organelles and cytoplasm that is connected through sieve plates
companion cells carry out the living functions for themselves and the sieve tubes
where are vascular bundles found in stems and why
the vascular bundle is near the outside to provide support to the stem and stop it bending
where are vascular bundles found in leaves and why
the vascular bundles make up a network of veins which support the thin leaves
where are vascular bundles found in roots and why
xylem in centre surrounded by phloem to provide support to the root as it pushes through the soil
how does water enter a plant through its roots
water enters root via osmosis. the soil by roots often has a high eater potential and leaves have a lower water potential. this creates a water potential gradient which keeps water moving up the plant
how does water move through the root to the xylem in the symplast pathway
water goes through the cytoplasm. the cytoplasm of neighbouring cells join by plasmodesmata. it moves by osmosis
how does water move through the root to the xylem in the apoplast pathway
goes through the cell walls. the cell walls are absorbent so water can diffuse through them. the water can carry solutes and moves from low hydrostatic pressure to high hydrostatic pressure
what is a casparian strip
it is a waxy strip at the endodermis that blocks the apoplast pathway
what is a transpiration stream
the movement of water from rots to leaves
what causes a transpiration stream
water evaporates from leaves (transpiration) which creates tension which pulls more water into the leaf.
water molecules are cohesive so when some are pulled up others follow.
water is also adhesive so it is attracted to the xylem walls which propels it forwards
how does light effect transpiration rate
the more light there is the faster transpiration rate because the stomata open when it gets light so carbon dioxide can diffuse into the leaf for photosynthesis but water can also leave through stomata.
how does humidity effect transpiration rate
lower the humidity higher the transpiration rate. if the air around the plant is dry then water potential gradient is increased, increasing the rate
how does temperature effect transpiration rate
higher the temperature the faster the transpiration rate. warmer molecules have more energy and evaporate faster. this increases the water potential gradient making water diffuse out faster
how does wind effect transpiration rate
the windier it is the faster the transpiration rate. lots of air movement moves water molecules away from the stomata which increases the rate of transpiration
how do we set up a potometer
- cut shoot at a slant to increase surface area and under water to prevent air bubbles
- assemble under water so no air can enter
make apparatus water tight with Vaseline. - dry the leaves
- make an air bubble in capillary tube
how do we use a potometer
record the start position of the bubble, start a stopwatch and watch how far the bubble moves in a set time. this shows us transpiration rate
what is a xerophyte
plants that are adapted to live in dry climates. e.g. marram grass and cacti
what is a hydrophilic plant
a plant that is adapted to survive in water
what adaptions do xerophytes have to reduce water loss
- stomata in sunken pits sheltered from the wind to slow transpiration
-layer of hairs to trap moist air to slow transpiration - roll leaves in hot and windy conditions to trap moist air and reduce exposed stomata
- thick waxy epidermis to reduce water loss as it is waterproof
-spines to reduce surface area
-close stomata at hot times of day
what adaptions do hydrophilic plants have to survive in water
air spaces in tissues help the plants float and store oxygen
stomata only present on the top of leaves to maximise gas exchange
flexible leaves and stems to prevent damage from currents
what is translocation
translocation is the movement of dissolved substances (assimilates) it requires energy
what is a sink
has a high concentration of assimilates as its where a substance is made up
what is the mass flow hypothesis
active transport actively loads the solutes into the sieve tubes of phloem at source
this lowers water potential in the sieve tubes so water enters the tubes by osmosis from the xylem and companion cells
this creates high pressure at the source end
at the sink end solutes are removed from phloem to be used up which increases water potential so water leaves via osmosis. this lowers the pressure
the pressure gradient from the source to the sink so solutes are pushed up the phloem
what is a source
the area where assimilates are used up so there is a low concentration
how does active loading at the source work
atp used to actively transport H+ out of the cells into tissues which sets up a concentration gradient as there is more H+ outside cell
H+ binds to cotransport protein and re-enters cell and a sucrose molecule also binds so it moves into the cell using the H+ ion
same process happens to load into th sieve tubes
