transport in plants Flashcards
why do plants need a transport system
need to transport substances to other parts of the plant, get rid of waste products, high metabolic rate, multicellular, small SA;V ratio
what does xylem tissue transport
water and mineral ions
what does phloem tissue transport
sugars (sucrose)
where are the xylem and phloem found in the root
at the centre, to provide support
where are the xylem and phloem found in the stem
near outside to prevent stem bending
where are xylem and phloem found in the leaf
make up a network of veins
what are the adaptations of xylem vessels
no end walls between cells to allow water to pass through easily, cells are dead, cell walls thickened with lignin to add support, small pits in walls have no lignin which allows other cells to be supplied with water
how do sieve tube elements act as an adaptation for phloem tissue
living cells, ‘sieve’ parts are end walls with lots of holes to allow solutes to pass through, no nucleus and are joined by cytoplasm of adjacent cell
how do companion cells act as an adaptation for phloem tissue
one companion cell for every sieve tube element as they carry out living functions for both themselves and sieve elements, e.g provide energy for active transport of solutes
how does water enter a plant
water enters root hair cell
passes through the root cortex, including the endodermis to reach the xylem, via osmosis
describe how water moves through the symplast pathway
goes through the living parts of cells (the cytoplasm)
cytoplasm of neighbouring cells connect through plasmodesmata
describe how water moves through the apoplast pathway
moves through dead parts of the cell (cell walls)
when water gets to the endodermis cells in the root, water os blocked by a waxy strip in the cells walls called the Casparian strip and water has to take the symplast pathway
what is the movement of water from roots to leaves called
the transpiration stream
how does cohesion and tension help water move up plants
water evaporates from leaves (transpiration)
this creates a tension which pulls more water into the leaf
cohesion allows more water molecules to be pulled into the leaf
why does transpiration happen
result of gas exchange
plant opens its stomata to let in CO2 so that it can produce glucose
this also lets water out, as it travels down the water potential gradient
what factors affect transpiration rate and how do they affect it
light intensity- more light= faster transpiration as stomata open when its light
temperature- higher temp= faster rate as molecules have more kinetic energy and increases w.p gradient
humidity-lower humidity= faster rate as water po. gradient is increased
wind- higher wind= faster rate as water molecules are moved so w.p gradient increases
what are xerophytes
plants adapted to live in dry climates
how are cacti adapted
have a thick waxy layer to reduce water loss by transpiration
have spines instead of leaves to reduce surface area for water loss
close their stomata at hot times of th day when transpiration rates are at their highest
how is marram grass adapted
sunken pits so sheltered from the wind which traps moist air so lowers w.p gradient
layer of hairs to trap moist air around stomata
roll leaves to protect from wind and trap moist air
thick waxy layer
what are hydrophytes
plants that live in aquatic habitats
what are some adaptations sof hydrophytes
air spaces to help plants float and act as oxygen storage for respiration
stomata present on upper surface to maximise as exchange
have flexible leaves and stems to prevent damage from water currents
what is translocation
the movement of dissolved substances to where they’re needed in a plant
dissolved substances are often known as what
assimilates
what is a ‘source’
where a substance is made
what is a ‘sink’
where the substance is used up
explain the mass flow hypothesis
active transport is used to load the solutes into the sieve tubes of the phloem at the source
this lowers the water potential inside sieve tubes so water enters tubes via osmosis from the xylem and companion cells
this creates high pressure inside sieve tubes at source end
at sink end solutes move in via diffusion as they are usually at higher conc. in phloem than surrounding tissue at sink
remove of solutes increases water potential inside sieve tubes so water leaves via osmosis
this lowers pressure in sieve cells
the result is a pressure gradient from source end to sink
this gradient pushes solutes along sieve tubes towards the sink where they are used
the higher the conc. of sucrose at the source the higher the rate of translocation
where is active loading used
at the source to move substances into the sieve cell from surrounding tissue and from companion cells into the sieve tubes against the conc. gradient
how is sucrose moved
active transport and co transport proteins
how is sucrose moved through active loading
H+ ions are used to move sucrose against the conc. gradient
in the companion cell active transport is used to actively transport hydrogen ions out of the cell and into surrounding tissue cells, which creates a conc. gradient
an H+ ion binds to a co-transport protein in the companion cell membrane and re enters the cell and at the same time a sucrose molecule bind to the H+ ion (against conc. gradient)
sucrose molecules are then transported out of the companion cells and into the sieve tube elements in the same process
