Transport in Plants Flashcards
What is the vascular bundle in roots?
- vascular bundle in centre
- xylem in an ‘X’ shape in the center
- phloem surrounding xylem
What is the vascular bundle in stems?
- vascular bundles around the outside of stem
- xylem towards the inner part
- phloem on the outer part
What is the vascular bundle in leaves?
- vascular bundles form midrib and veins
- xylem is found on the upper side of bundles
- phloem is found on the lower side of bundles
What are the structural features of xylem vessels?
made of elongated dead cells that are thickened with lignin, joined end-to-end to form tubes
What are the functional features of xylem vessels?
the transportation of water and soluble minerals up the plant, to give structural support
What are the structural features of phloem sieve tubes?
made of elongated living cells called sieve tube elements, join to form tubes, companion cells
What are the functional features of phloem vessels?
the transportation of organic compounds made by photosynthesis in the leaves to other parts of the plant
What is transpiration?
the loss of water vapour from a plant to its environment by diffusion down a water potential gradient, takes place mostly through stomata in the leaves
What are the factors that affect the rate of transpiration?
humidity, wind and temperature change, light intensity, dry conditions
How does transpiration relate to gas exchange?
CO2 for photosynthesis also diffuses through stomata
How can rate of transpiration be measured?
with a potometer
What are the adaptations of xerophytes?
- hinge cells shrink allowing leaves to roll
- thick, waterproof cuticle made of cutin
- no stomata on lower epidermis
- hairs on leaf
- spines or thorns
- sunken stomata
- trichomes
- swollen, succulent stems
How does water move from soil into the roots?
behind root cap, some epidermis cells are drawn out into long hairs which reach between soil particles to absorb water, which moves by osmosis down a water potential gradient into cells
What is the symplast pathway?
the movement of water across the cortex of the root by moving into the cytoplasm or vacuole of a cell by osmosis and into adjacent cells through plasmodesmata
What is the apoplast pathway?
the movement of water across the cortex of the root by soaking from cell to cell through the cellulose fibres of the cell wall
What is the casparian strip?
a thick, waxy band of suberin in the cell walls of endodermal cells, which are impenetrable to water and so close the apoplastic pathway
How does water move through the xylem?
the hydrostatic pressure at the top of the xylem becomes lower than at the bottom of the xylem, so water moves upwards by mass flow
What is translocation?
the transport of assimilates (soluble organic substances) within a plant
What is active loading?
the loading of a high concentration of sucrose into sieve elements from a source, creating a pressure difference for mass flow
What is a hydrostatic pressure gradient?
hydrostatic pressure is the pressure exerted by a liquid, it is the same a water pressure, creating a gradient
What are sinks and sources?
a source is a place where sucrose is loaded into sieve elements, like leaves, and a sink is a place where sucrose is unloaded, like roots
What is parenchyma?
- thin-walled, packing tissue, air spaces
- cortex in roots, pith and cortex in stems, mesophyll with chloroplast in leaves
- metabolically active, gas exchange, water transported through cells
What is collenchyma?
- modified parenchyma, extra cellulose at corners of cells for strength
- midrib in leaves
What is the endodermis?
- one cell thick
- surrounds vascular tissue in stems and roots
What is the mesophyll?
- specialised parenchyma in leaves, contain chlorophyll
- palisade is column shaped, near upper surface of leaf for more sunlight, contain more chlorophyll
- spongy is spongy, air spaces between cells
What is the pericycle?
- a layer of cells inside the endodermis and next to the vascular tissue
- one cell thick in roots, new roots grow from it, sclerenchyma in stems
What is vascular tissue?
- xylem and phloem
- centre of roots, vascular bundles in stems with sclerenchyma fibre caps
What are the features of xylem vessel elements?
lignin in walls, empty lumen inside, non-lignified cell wall areas where there was once plasmodesmata called pits, end walls break down
What are the features of phloem sieve tube elements?
little cytoplasm, no nucleus, no ribosomes, sieve plates
What are the features of companion cells?
at least one next to each sieve tube element, large number of mitochondria and ribosomes, numerous plasmodesmata between companion cell and sieve tube element
How does water move from xylem to leaves?
water is drawn into the leaf through pits in xylem vessel walls, it moves through the leaf through the apoplastic or symplastic pathway
What is the epidermis?
- continuous layer of cells, one cell thick, outside of plant
- covered with waxy cuticle in stems and leaves, has stomata in leaves, root hair extensions in roots
- protection from drying out, gas exchange, more surface area
What is cohesion?
the attraction of water molecules due to hydrogen bonding
What is adhesion?
the attraction of water molecules to the cellulose and lignin in the walls of the xylem vessel
What is root pressure?
the increase of pressure at the bottom of the xylem vessel by active pumping of solutes into the xylem, lowering water potential and causing water to be drawn into the xylem, increasing water pressure
What is callose?
a carbohydrate which seals a sieve plate if a sieve tube is cut, to prevent contents from escaping
How does water move from root hair to xylem?
by crossing the cortex of the root through the symplastic or apoplastic pathway down a water potential gradient into the xylem in the centre of the root
What are passage cells?
endodermal cells which keep their symplastic pathways open as other cells become completely suberised
