3.1.3 transport in plants NOT ON MOCK Flashcards
why do plants require a transport system
To ensure all cells receive a strong supply of the nutrients they require. Especially important as a plant must be able to transport substances up their stem against gravity
mclaird: Many parts of a plan of either internal or underground, because there is no photosynthesis, a transport system is needed. Also some plants are relatively big so have a small surface area to volume ratio and they are also relatively metabolically active
Relate the structure of xylem to its function
mclaird: The xylem makes up part of the vascular bundle. It moves the water and soluble mineral irons in transpiration. Walls are impregnated with lignin which strengthens the cells and what makes it waterproof. The border pits allow water to move sideways within the xylem and these are created when there are incomplete rings of lignin
Relate the structure of phloem to its function
sieve tube elements transports sugars around the plant. companion cells designed for active transport of sugars into tubes. Plasmodesmata to allow flow of substances between cytoplasm of different cells
describe the structure and function of the vascular system in the roots
consists of xylem and phloem. Xylem arranged in an X shape to provide resistance against force and surrounded by endodermis, water supply
mclaird: Around the vascular bundle is a layer of cells called endodermis. Just inside the endodermis is a layer of meristem cells which are cells are able to divide called the pericycle
Describe the structure and function of the vascular system in the stem
The vascular bundles are found near the outer edge of the stem. The xylem is found towards the inside of each vascular bundle and the phloem towards the outside. In between is a layer of cambium which are meristems that divide to produce new xylem and phloem. In trees the vascular bundle forms a continuous ring
Describe the structure and function of the vascular system in the leaves
consists of xylem and phloem, forms the mid-rib and veins. Involved in transport and support
Within each vein, the xylem is located on top of the phloem
Define transpiration
Transpiration is the loss of water from a plant by evaporation and most of it occurs via the leaves and via the stomata
Name factors that affect the rate of transpiration
increased light increases transpiration
increased temperature increases transpiration
increased humidity decreases transpiration
increased air movement increases transpiration
Waxy cuticle prevents transpiration
How can leaf structure affect transpiration
Leaf surface area, thickness of epidermis and cuticle, stomatal frequency, size and position and stomatal density
How can we measure transpiration rate
potometer. Plant cutting is placed in a Watertight tube that contains an air bubble. Rate of transpiration is calculated by measuring the movement of the air bubble over time
What precautions much you take when using a potometer
all apparatus needs to be underwater to ensure no air bubbles and you have to cut the stem diagonally underwater for larger surface area
Joints sealed with Vaseline to prevent water loss
The leaves need to be dried and plant needs to be healthy and a climatisation period to be given
what is the limitations of a potometer
Measures water uptake, Cutting plant shoot may damage plants and plant has no roots so no resistance to water being pulled up
Define water potential as a mechanism of movement in plants
Water potential: the tendency of water to move by osmosis, from high water potential to low. This is the basis by which water moved to the area is it is needed within plants
What are the problems with transpiration
It is hard to distinguish between water vapour and water evaporated from the leaf. It is an estimate as water can be used by the plant for photosynthesis so not all of it evaporates out
What does transpiration provide plants with water for
The water is required for photosynthesis, it transports mineral ions from the soil into the plant and maintains turgidity. It keeps a plant cool on a hot day and provide support for stems and leaves through turgour pressure
Explain what is meant by the apoplastic pathway
A method of osmosis through the root hair cells, where water moves through the cell walls and intercellular spaces. This pathway can only be used until water reaches the casparian strip
explain what is meant by the symplastic pathway
a method of osmosis through the root hair cells, where water moves through the cytoplasm via plasmodesmata. To begin this pathway, water must be actively transported into cells
explain what is meant by vacuolar pathway
This is where water is not confined to just the cytoplasm but goes through the vacuole too
Explain what is meant by casparian strip
prevents harmful substances entering the xylem. The endodermis is home to the casparian strip . The Kasparian strip is an impermeable layer of suberin (waxy material) . As a result of water in the apoplast pathway is forced into symplast pathway
Describe the steps of the movement of water into the xylem into root hair cells
- water is found in air spaces in the soil (minerals and h2o)
- minerals are absorbed into the root hair cells by active transport
- this lowers the water potential and water moves into the root hair cells by osmosis
- water then moves across the cortex down the water potential gradient
- it travels through the cells via the 3 pathways
- when water reaches the endodermis, the apoplast pathway is blocked by the casparian strip so water is diverted into the symplast pathway.
- water and mineral ions are diverted into the symplast pathway. this insures all the mineral ions are in the cytoplasm
- plasma membrane transporters actively pump mineral ions from the cortex into the medulla and xylem
- Water then passes/moves via osmosis down the water potential gradient into the xylem and medulla and it can’t come out once it is gone
If the water potential inside the cell is low will the water move in or out by osmosis
in
Describe root pressure
Water is pushed up the xylem by hydrostatic pressure. Mineral ions are pumped into the xylem vessels in the route by the endodermal cells which lowers the water potential in the xylem. Water moves in from the surrounding cells by osmosis which raises the hydrostatic pressure so pushes water up the xylem
describe capillarity
Water rises up narrow tubes due to the adhesive forces between the water molecules and the wall of the tube
Explain the cohesion tension theory
water molecules form hydrogen bonds with each other, causing them to stick together (cohesion) . The surface tension of the water also create this sticking affect, therefore as water is lost through transpiration, more can be drawn up by the stem from the roots
What would happen if the roots were deprived of oxygen
The pumping of the ions would stop as it requires ATP produced in aerobic respiration. Oxygen required for aerobic respiration
Give to limitations of root pressure hypothesis
The pressure measured is not enough to get water to the top of the trees
Relies on the use of the plants energy atp for active transport
give adaptations of xerophytes That allow them to live in dry conditions
small/rolled leaves
densely packed mesophyll
thick waxy cuticle
stomata often closed
Hairs to trap moist air
Give adaptations of hydrophyte that allow them to live in wet conditions
thin or absent waxy cuticle,
stomata often open,
wide, flat leaves,
airspaces for buoyancy
Summarise the mechanism of translocation
sucrose produced in leaves loaded into sieve tubes via active transport and requires energy
lowers water potential, causing water to move in from xylem
Assimilates move along the city tube towards areas of lower hydrostatic pressure(sink) . Sucrose defuses into surrounding cells where it is needed
Define source in terms of translocation
any exporting region that produces photosynthetic above and beyond that of its own needs eg mature leaves
Define sink in terms of translocation
Any non photosynthetic organ or an organ that does not produce enough photosynthate To meet its own needs e.g. storage organs or roots
What is the mass flow model in terms of translocation
The flow moves from the source to the sink.
Source: sugars are actively loaded into the sieve element-companion so complex. Called phloem loading
sink: sugars are un loaded into the sink cells, called phloem unloading
In source tissue, active phloem loading leads to a buildup of sugars. Causes a steep drop in water potential, so water enters sieve elements from xylem via osmosis and this phloem turgour pressure increases
in sink tissue, phloem unloading leads to lower sugar concentration. Less solids so water potential increases and water leaves phloem And enters sink sieve elements and xylem. This phloem turgour pressure decreases
How did the solutes move in translocation
The solution is moving in the same elements buy bulk flow. No membranes are crossed from one save tube to another and solutes are moving at the same rate as the water. Water movement is driven by pressure gradient and not water potential gradient. The water enters and exits the phloem by osmosis and the sucrose is loaded in and unloaded out of the phloem using energy
describe phloem loading from the source cells
sucrose movement into the phloem is via two simultaneous methods.
Via apoplastic pathway from the cell wall through the cell membrane into the companion cell. It requires active transport against its chemical potential gradient. Involves a sucrose H+ co transporter
via symplast pathway. through open pores called plasmodesmata, A passive process which happens when there is enough solution gradient
Describe how to measure volume and transpiration rate
measuring the volume of water taken up by the shoot involves calculating the volume of a cylinder e.g. the length of capillary tube. The volume of a cylinder is given by the formula V = pie r squared X height
R is the radius of the capillary tube and H is the length of capillary tube.
rate of transpiration = Volume divided by time taken
ppq:The following statements refer to the movement of water from the cortex of the route into the xylem. Which of the following statements are true
most of the water moves across the root cortex by the apoplast pathway
at the endodermis water has to enter the symplast pathway
casparian Strips in the endodermis contain the chemical lignin
1 and 2 are true
ppq: which mechanism is used at each point
into root cells across root via symplast pathway up the stem in the xylem across leaf via apoplast pathway out of leaf via stomata
into root cells OSMOSIS
across root via symplast pathway OSMOSIS
up the stem in the xylem MASS FLOW
across leaf via apoplast pathway MASS FLOW
out of leaf via stomata DIFFUSION
ppq:Define the process of adhesion
Attraction of water molecules to the impermeable walls of xylem tissue
ppq: Describe how the student could ensure that a valid comparison could be made between the two leafy shoots
The student could look at both of the leaf surface area and ensure they are both the same sizes
also compare the transpiration rate per unit area
ppq: The cohesion tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves, use this theory to explain how water moves from the roots to the leaves
Evaporation at the top of the xylem, which creates the tension in xylem. Water molecules stick together to form a chain and the chain is pulled up by tension
ppq: Soluble mineral ions are present in soil, explain why water molecules can form hydrogen bonds with nitrate ions
Water molecules are polar so that hydrogen bonds conform between the partially positive hydrogen atoms in the water and an oxygen atom of nitrate
ppq: Name the pours through which most water vapour is lost from a leaf
stomata
ppq:Describe how the guard cells around in the leaf pores are adapted to their role
They have an unevenly thick cell wall so able to change shape
ppq: Name one other part (not stomata) from which water may be lost
Epidermis/cuticle
ppq: Complete the following passage
when water is lost from the cells of the leaf it reduces the ___ in those cells. as a result, water enters the cells by ___. this process occurs across the plasma membrane which is ___. if all the water lost from the leaf cells is not replaced, they lose ____ And the leaf may wilt
when water is lost from the cells of the leaf it reduces the WATER POTENTIAL in those cells.
as a result, water enters the cells by OSMOSIS.
this process occurs across the plasma membrane which is PARTIALLY PERMEABLE
if all the water lost from the leaf cells is not replaced, they lose TURGIDITY And the leaf may wilt
ppq: complete the following paragraph
At step a, charged particles are moved out of the companion cells by the process of ___. this creates a ___ Gradient between the companion cells and its surroundings. At step b, the charged particles and assimilates are co transported by ___into the companion cells. the assimilates build up in the companion cells and move by ___ into the sieve tube element at step c assimilates, such as sucrose and____ can be loaded in this way
At step a, charged particles are moved out of the companion cells by the process of ACTIVE TRANSPORT
this creates a CONCENTRATION Gradient between the companion cells and its surroundings.
At step b, the charged particles and assimilates are co transported by FACILIATED DIFFUSION into the companion cells.
the assimilates build up in the companion cells and move by DIFFUSION into the sieve tube element at step c
assimilates, such as sucrose and AMINO ACIDS can be loaded in this way
ppq: Suggest what evidence a scientist might expect to see in companion cells using an electron microscope
Many mitochondria, plasma does matter between companion cells and save tubes and many ribosomes
ppq: Distinguish between the term transpiration and the transformation stream
transpiration: loss of water vapour from parts of the plant e.g. leaves
transpiration stream: Movement of water up xylem vessels, from roots to leaves
ppq: Explain why believes not all be in the same size in an investigation may affect the results and suggest how the student could improve this this
If the surface area of the leaves is different, there will be a different number of stomata so the student should choose shoots with similar sized leaves or a least a similar size surface area
ppq: Explain why put in the potometer Underwater and then leaves getting wet will affect the results and suggest had a student could improve this
The water potential outside the leaf is too high so the student should assemble without watching the leaves or waiting until the leaves dry
ppq: Describe how the lab warming up quickly will affect the results and suggest had a student could improve the investigation
increased temperature will increase evaporation and transpiration so therefore the students should control the temperature and carry out in a room with controlled temperature
ppq: Name the sugar most commonly transported through the stem of a plant and the tissue that transports the sugar
Sucrose and phloem
ppq: Sugar molecules are actively loaded into the transport issue. Describe how active loading takes place
Hydrogen ions are pumped out of companion cells. This creates gradient and the hydrogen ions re-enter the companion cells. Sucrose moves with hydrogen ions down concentration gradient by facilitated diffusion. Sucrose diffuses into sieve tube elements through plasmodesmata
ppq: Describe how assimilates are loaded into the phloem
Active transport of hydrogen irons out of companion cells. This creates concentration gradient. Facilitated diffusion of hydrogen ions back into companion cells. Sucrose moves in with hydrogen ions by cotransport and sucrose diffuses through plasmodesmata into sieve tube element
ppq: Suggest why a bunch of flowers might survive longer if the ends of the stems are removed immediately before the flowers are placed in water
because of air in the xylem
ppq: Explain why water loss from the leaves of a plant is unavoidable
Stomata open to allow gassiest exchange for photosynthesis. Photosynthesis is essential for the plant to gain energy and some water is lost through the cuticle
ppq: State what is meant by the term is source and sink
source: site where sucrose are loaded into phloem
Sync: site was sucrose is unloaded from phloem
ppq: when the bar is removed from a tree, the phloem is also removed. If I complete ring of bark is removed, the tree trunk can be seen to swell above the cut.
Suggest two reasons why the trunk swells above the cut
Sugars cannot pass the cut, this decreases water potential and water moves into the cells. The damage triggers increased cell division to produce cells to store sugars and the cut causes infection
