3.4.2.1: Xylem & transpiration Flashcards
what do xylem transport
water and mineral ions
what are packing cells
cells that fill up space
what does organic mean
carbon based
what are andeosperms
flowering plants
describe the structure of xylem tissue
xylem vessel, lignified wall of xylem vessel, fibre, tracheid, parenchyma cell
which of these have a nucleus in xylem tissue: tracheids, fibre, xylem vessel, parenchyma cell
parenchyma cell and so tracheids, xylem vessels and fibre are dead
What is the main feature of lignin in xylem tissue
they are impermeable to anything and kill anything in the cell
what advantages does lignin give to xylem and why
lignin lines the xylem vessel elements, killing anything in the cell (tracheids, xylem vessels, fibres), and so the cell is hollow for water to move through.
Lignin also gives strength by preventing the xylem vessel elements from collapsing when water is moving through, as lignin is impermeable to water
is there lignification in the vessel element
yes
is there lignification in the tracheid
yes
is there lignification in the fibre
yes
is there lignification in the parenchyma
no, cellulose
are vessel elements living
no
are tracheids living
no
are fibre living
no
are parenchyma living
yes
describe the structure of the vessel elements in xylem tissue
stacked end to end, end walls disintegrate to form hollow tubes
describe the structure of a tracheid in xylem tissue
stacked end to end, slanted end walls
what is the function of the vessel element in xylem tissue
transport of water and mineral ions
what is the function of the tracheid in xylem tissue
transport of water and mineral ions
what is the function of the fibre in xylem tissue
provide mechanical support for tissue
what is the function of the parenchyma in xylem tissue
packing cell between vessel elements
what is meant by the term transpiration
evaporation of water vapour
how does lignin appear on xylem tissue and what does it allow the xylem tissue to do
lignin is in rings which allows the cells to stretch and grow longer
Describe very simply the direction that water vapour diffuses/evaporates in a leaf, in relation to the mesophyll cells, air spaces and the stomata
water vapour diffuses out of stomata (down water potential gradient). This water is replaced by water vapour that evaporates out of the mesophyll cells into air spaces
how much of the uptake of water is used and is transpired, and also, what is the role of each
1% is used for photosynthesis and maintaining turgor
99% is transpired for a cooling effect and to bring in mineral ions through roots
what is the transpiration stream and where is it in a plant
the transpiration stream is a single continuous column of water from the roots to the leaves
How does the transpiration stream in a plant work
transport of water up xylem into leaf, evaporation into water vapour and diffusion out of stomata, pull of water out of the leaf causes tension on water
what does the vascular bundle consist of
phloem, cambium, xylem
where are the vascular bundles positioned in a stem
around the periphery of the stem
why are the vascular bundles positioned around the periphery of the stem
wind imposes bending strain on the stem, and so the vascular bundles provide strength and structure by being around the periphery of the stem
where are the vascular bundles positioned in a root
straight down the middle
why are the vascular bundles positioned straight down the middle of a root
gravity imposes strain on the root and so the vascular bundles provide strength and structure by being straight down the middle of the root
Describe the structure of a stem and state what the parenchyma cells are
epidermis, cortex - parenchyma cell, vascular bundle (phloem, cambium, xylem), pith - parenchyma cells
describe the structure of a root and state what the parenchyma cells are
exodermis, epidermis, cortex - parenchyma cell, vascular bundle (phloem, cambium, xylem), pericycle, endodermis
by what process does water move up the stem
cohesion-tension theory
state the property of the xylem vessels that ensures water can be drawn up them more than 10m
xylem vessels are very narrow causing the water to form a single continuous line
what is the meaning of cohesion in terms of the cohesion-tension theory of the movement of water through the xylem and what does it result in
water molecules tend to attract to each other due to their hydrogen bonding which results in a continuous column of water
what is the meaning of tension in terms of the cohesion-tension theory of the movement of water through the xylem
transpiration of water out of the leaf creates a force that pulls the column of water up, stretching it and so it is under tension
describe and explain the property of water molecules that enables them to exhibit cohesion
they are polar molecules, hydrogen atoms have a partial positive charge and the oxygen atom has a partial negative charge, the opposite partial charges are attracted to each other and so causing attractions between water molecules which is called cohesion
explain two advantages of transpiration for the plant
1 - transports mineral ions around the plant
2 - Evaporation of the water from the leaves has a cooling effect which can reduce possibility of leaves overheating and enzymes being denatured
explain one disadvantage of transpiration for the plant
causes water loss which is necessary for the plant to function
Is the uptake of mineral ions by plant roots passive or active?
explain why
active transport as there is a much greater ion concentration in the root than in the soil, so uptake is against the concentration gradient.
Also, when respiratory inhibitors are added to the roots, uptake rate is reduced
Describe how root hair cells are adapted for efficient uptake of ions
large SA:Vol
lots of mitochondria (and so lots of ATP for active transport)
lots of carrier proteins (Active transport)
thin cell wall
Describe the structure of a root hair cell
nucleus, vacuole, cytoplasm, cell wall
how is a potometer set up?
entire thing should be set up underwater, should cut the leafy shoot and attach it underwater, BUT leaves need to stay dry - so water doesn’t block any stomata pores in leaf), cover any joints with vaseline to make them airtight
what measurements need to be taken when using a potometer to calculate the rate of water uptake
distance that the air bubble travels in mm, time it takes to travel that distance in s, diameter of capillary tube in mm
how would you calculate the rate of water uptake by using a potometer
speed of air bubble movement x cross sectional area of capillary tube = rate of water uptake
what 4 factors affect transpiration rate
light intensity, temperature, humidity, air movement
how does an increase in light intensity affect the rate of transpiration and explain why
increases the rate of transpiration, because:
1 - stimulates stomatal opening for gas exchange for photosynthesis
2 - increased number of open stomata increases SA for diffusion of water vapour
how does an increase in temperature affect the rate of transpiration and explain why
increases the rate of transpiration, because:
1 - increased evaporation out of mesophyll cells
2 - air spaces in leaf become saturated with water vapour
3 - increased diffusion gradient to outside of leaf
how does an increase in humidity affect the rate of transpiration and explain why
decreases the rate of transpiration, because:
1 - increased number of water molecules in air surrounding stomatal openings
2 - reduced diffusion gradient to outside of leaf
how does an increase in air movement affect the rate of transpiration and explain why
increases the rate of transpiration, because:
1 - saturated air moves away from leaf surface
2 - increases diffusion gradient to outside of leaf
