chapter 9- transport in plants Flashcards
what is a dicotyledonous plant
a plant that forms 2 seed leaves
what is a monocotyledonous plant
a plant which forms 1 seed leaf
Why do plants require specialised transport systems?
(4 things)
To ensure nutrients reach all tissues.
To allow diffusion across large distances
To overcome the low surface area to volume ratio
To meet the high metabolic demand
what is a vascular bundle/vascular tissue made up of
xylem and phloem
How are the vascular tissues arranged in the stem and the root of dicotyledonous plants?
in a circle around the edge of the stem
he vascular tissues are arranged in a bundle in the centre of the root.
what are stomata
The stomata are pores, usually found in the lower epidermis of a leaf, through which gases such as oxygen and carbon dioxide diffuse.
describe what happens during the day and night in terms of stomata, photosynthesis and respiration
day: stomata are open, P and R occur
night: stomata closed, only R occurs
what are some characteristics of xylem
no end walls
transports h2o and dissolved mineral ions
transports just up
contains dead cells (lignin)
passive process
what is the structure of the xylem (3)
dead
hollow
elongated tube
2 main functions of the xylem tissue
to transport water and minerals from the roots to the rest of the plant
to provide strength
the xylem contains cells joined end to end with no end wall, how does this feature contrbute to effection transport of water
it forms one continuous/unbroken tube which is essential for the movement of water by cohesion tension
Describe the cohesion-tension theory of water transport in the xylem. (3 things)
First, the loss of water by transpiration decreases the water potential in mesophyll cells.
This pulls water up the xylem, which puts it under tension.
Inside the column, water molecules adhere to the walls, and they’re stuck together by hydrogen bonds.
xylem contains dead cells, how does this contribute to the effective transport of water
cells do not use ATP to move the water, the movement of water would be slowed by the cell surface membrane and cytoplasm of a living cell
xylem has thick walls containing…
lignin
how does lignin in the thick walls of xylem contribute to effective transport of water
it helps strengthen the xylem and prevent collapse
characteristics of phloem
transports up and down
transports sucrose and AA by translocation
sieve and companion cells
active process
what is the name of the main transport vessels in the phloem
sieve tube elements
what is the structure of phloem sieve tube elements
many cells joined end to end to form a hollow tube separated by sieve plates
what cells are linked to the sieve tube elements and provide support with metabolic activity y
phloem companion cells
products of photosynthesis transported in the phloem such as sucrose and amino acids are called
assimilates
what materials do plants need to exchange and transport
carbon dioxide
oxygen
water
organic nutrients eg sucrose
inorganic ions (N, P, K)
as well as the transport of substances the vascular bundle has
structural support purposes
adaptations that a leaf might have to conserve water
THICK waxy cuticle
few stomata
sunken stomata
hairs
leaf curled
dense spongy mesophyll
closure of stomata during the day
small SA
how are the vascular tissues arranged in the roots of dicotyledonous plants
in a central bundle
how are the vascular tissues arranged in the leaves of dicotyledonous plants
in a midrib with many branching veins
transport tissues are arranged together in the stems leaves and toots of dicotyledonous plants in
vascular bundles
how are the vascular tissues arranged in the stem of dicotyledonous plants
in separate bundles in a ring around the edge of a stem
what are plasmodesmata
small channels/pores connecting the cytoplasm of adjacent plant cells
if a cell has been plasmolysed what does this mean and what conditions usually forces this to occur
the cell membrane and shrunk away from the cell wall, happens in low external water potential, when water moved out of the cell
if the water potential inside the cell is low will water move in or out of the cell
in
low intracellular water potenial means the salt concentration is
high
high intracellular water potential means that the salt concentration is
low
are root hair cells visible to the naked eye
yes they are 200-250micometres in size
how is water and minerals contained in soil
in small air spaces in the soil
comment on the concentration of solutes in soil and plant and what causes osmosis of water into the plant
osmosis occurs because there is a higher concentration of solutes in the plant than inside the soil
what are the three water movement pathways
symplast
vacuolar
apoplast
what is the purpose of water movement pathways
they enable the plant to get the water in as fast as possible
which water movement pathways is the slowest
vacuolar
which water movement pathways is the fastest
apoplast
what is the symplast water movement pathway
water moves through the living spaces of the cell - cytoplasm, it uses plasmodesmata to move across adjacent cells
water uses plasmodesmata to move across adjacent cells through the cytoplasm
what is the vacuolar water movement pathway
same as symplast but the water moves through the cell vacuoles as well.
its the SLOWEST
what is the apoplast water movement pathway
water moves through the cell wall and the intracellular spaces. cohesive and tension forces act on the cell walls and pull that water up the plant.
water moves through the cellulose fibres in the cell walls of connecting cells
what is the casparian strip
impermeable layer of suberin therefore all water in the apoplast pathway is forced into the symplast pathway
what is transpiration
Transpiration is the evaporation of water through stomata down a water potential gradient.
how does wind affect the rate of transpiration
increase in wind=increase in rot
more water evaporates from spongy mesophyll cells and diffuses out of the stomata.
creating a lower water potential inside the mesophyll cells
water is pulled up xylem=tension=cohesion=forms water column
decrease in water vapour and increase in the water potential gradient
what is a hydrophyte
plants adapted to grow partly under water or in wet habitats
List three adaptations of hydrophytes to survive in wet habitats.
no waxy cuticle
increased number of stomata
wide flat leaves to capture light
which is an adaptation of a hydrophyte
a) a thick waxy cuticle
b) many stomata on the upper surfaces of the leaves
b
what increases the rate of transpiration
increase in temp
increase in wind
decrease in humidity
how does an increase in temperature increase rate of transpiration
increases the KE and so increases evaporation
how does an increase in light increase rate of transpiraiton
increases the open stomata
what is a xerophyte
plants that have adapted to survive in habitats where water supply is limited
List 4 adaptations shown by the leaves of xerophytes which help reduce water loss.
Thick waxy cuticle
Stomata in sunken pits
Leaves which are curled
Leaves covered in hairs
what does a potometer measure the rate of
A potometer directly measures the rate of water uptake. This is proportional to the rate of transpiration.
what are the limitations of using a potometer to measure transpiration?
It assumes that all of the plant’s water will be transpired
The plant’s roots are removed, This means the calculated rate doesn’t account for the rate of water uptake in the roots.
first step of translocation: a carrier protein (not a co-transport protein) moves … ………… this creates a
H+ ions from the cytoplasm of the companion cell to the cell wall, using active transport.
This creates a concentration gradient, and the H+ ions are returned to the cytoplasm via a co-transport protein, which also transports sucrose.
3rd step of translocation, what happens after H+ and sucrose are back inside the companion cell and what does this cause
sucrose diffuses into the sieve tube element (this transport is not active).
This causes the water potential in the sieve tube element to decrease (adding solutes decreases the water potential).
5th step of translocation, what happens after a wpg is created in the sieve tube element, and what does this cause
Water moves from the xylem into the sieve tube element by osmosis
This causes the hydrostatic pressure in the sieve tube element to increase.
what happens at the sink cell in translocation
At the sink cell, sucrose moving out of the sieve tube element decreases the hydrostatic pressure here.
As a result, the sucrose solution moves down the hydrostatic pressure gradient (since the sucrose solution is a fluid, it exerts hydrostatic pressure).
Finally, sucrose moves into the sink cell.
what is the source cell and sink cell in translocation
source: leaf cell
sink: root cell
near the source cells sucrose is loaded into the sieve tube element which does what do the wp and hydrostatic pressure
which decreases the water potential (Adding solutes like sucrose will decrease the water potential)
and increases the hydrostatic pressure (Hydrostatic pressure is increased as water moves in from the adjacent xylem, down the water potential gradient by osmosis.)
in between source cells and sink cells the sucrose solution moves up/down a what..
down the hydrostatic pressure gradient.
The sucrose solution exerts a hydrostatic pressure gradient to drive mass flow
“Sieve tube elements of the phloem are connected by sieve plates” does this support or undermine the mass flow hypothesis, and why
undermine
sieve plates, although they have holes, hinder mass flow more than if there were no sieve plates at all: the phloem should have maximum space to make translocation as efficient as possible.
Therefore, the presence of sieve plates does not support the mass flow hypothesis.
Additionally, the idea that sieve plates may stop the phloem bursting under pressure has not been confirmed experimentally.
“The sap found in mature leaves of a celery has a higher sucrose concentration than sap found in its stalk.” does this support or undermine the mass flow hypothesis, and why
supports
In this example, the mature leaves are the source and the stalk is the sink. A high concentration of sucrose near the source and a lower concentration of sucrose near the sink would suggest that the sieve tube elements in these locations have different water potentials. Therefore, water will move into the sieve tube element near the source cells by osmosis and out of the sieve tube element near the sink cells.
This supports the idea that water moves by osmosis during translocation, and therefore supports the mass flow hypothesis.
“A part of a potato plant was observed under a microscope. It was found that the companion cells had a lot of mitochondria.” does this support or undermine the mass flow hypothesis, and why
supports
Mitochondria are responsible for generating ATP. The fact that companion cells have a lot of mitochondria suggests that ATP is needed. ATP is required as part of the mass flow hypothesis. The presence of many mitochondria therefore supports the mass flow hypothesis.
“It was observed that, in sap, salts travel at a different speed to amino acids” does this support or undermine the mass flow hypothesis, and why
undermines
If all substances are transported under pressure, they would all be expected to travel at the same speed through the phloem. Therefore, since salts and amino acids travel at different speeds, this undermines the mass flow hypothesis.
