plant transport Flashcards
(33 cards)
what does xylem transport and in what direction
water and mineral ions in solution
these substances move up the plants from the roots to the leaves
what does phloem transport and in what direction
mainly transports sugars
both up and down the plant
where are xylem and phloem found in roots
found in the centre to provide support for the root as it pushes through the soil
where are xylem and phloem found in the stem
near the outside to provide a sort of ‘scaffolding’ that reduces bending
where are xylem and phloem found in the leaves
make up a network of veins which supports thin leaves
adaptions of xylem vessels
- long tube-like structures
- formed by vessel elements joined end to end
- there are no end walls in these cells, making an uniterrupted tube that allows water to pass through the middle easily
- the cells ar dead, so contain no cytoplasm
- cell walls are thickened with lignin which helps supports the walls and prevents them collapsing inwards
- unlignified pits allow water and mineral ions to move out the vessels <– which is how other cells are supplied with water
how can lignin be deposited in xylem tissue
in different ways e.g. in a spiral or as distinct rings
these patterns allow flexibility and prevents the stem from breaking
adaptions of phloem tissues
pholoem tissue transports solutes, mainly sugars like surcrose around the body
formed by cells arranged in tubes
purely a transport tissue (unlike xylem)
- sieve tube elements
- cpmpanion cells
what are sieve tube elements
- living cells that form a tube for transporting sugars through the plant
- they’re joined end to end to form sieve tubes
- the sieve parts are the end walls, which have holes in them to allow solutes to pass through
- no nucleus, very thin layer of cytoplasm and few organelles
- the cytoplasm of adjacent cells is connected through holes in the sieve plates
what are companion cells
- no nucleus and other organelles in sieve tube elemts means they can’t survive on their own
- so theres a companion cell for every sieve tube element
- they carry out the living functions for both themsleves and their sieve cells
-e.g. provide the energy for active transport of solutes
how does water from the soil reach the xylem
enters through root hair cells and then passes through the root cortex, including the endodermis, to reach the xylem
- water is drawn into the roots via osmosis
explain the symplast pathway
- goes through the living parts of cells - the cytoplasm
- the cytoplasm of neighbouring cells connects through plasmodesmata (small channels in the cell walls)
- water moves through the symplastic pathway via osmosis
explain the apoplastic pathway
- goes through non living parts of the cells - the cell walls
- the walls are absorbent and water can simply diffuse through them, as well as passing through the spaces between them
- when water reaches the casparian strip, the water converts to the symplastic pathway
what is the casparian strip and why is it useful
- a waxy strip which blocks water on the apoplast path
- means the water has to go through a plasma membrane
- cell membranes are partially permeanle and are able to control whether or not substances in teh water get through.
- Ones past this barrier, the water moves into the xylem.
how does water travel through the leaves
- water leaves xylem and moves into cells mainly by apoplast pathway
- water evaporates from the cell walls into the spaces between cells in the leaf
- when the stomata (tiny spores in the surface of the leaf) open, water evaporates - it diffuses out of the leaf and into the surrounding air
how is cohesion and tension involved in water transport
- water evaporates from the leaves at the ‘top’ of the xylem
- this creates a tension which pulls more water into the leaf
- water molecules are cohesive (they stick together) so when some are pulled into the leaf, the others follow
- this means the whole column of water in the xylem, from the leaves down to the roots, moves upwards
how is adhesion involved in water transport
water molecules are attracted to the walls of the xylem vessels.
this helps water to rise up through xylem vessels
four factors effecting transpiration rate
- light intensity
- temperature
- humidity
- wind
how and why does light intensity affect transpiration rate
the lighter it is, the faster the transpiration rate
- this is because the stomata open when it gets light (the lighter it is, the wider they open).
- when its dark the stomata are usually closed so there’s little transpiration
how and why does temperature affect transpiration rate
the higher the temperature, the faster the transpiration rate
- warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
- this increases the water potential gradient between the inside and outside of the leaf <– making water diffuse out of the leaf faster
how and why does humidity affect transpiration rate
the lower the humidity, the faster the transpiration rate
- if the air around the plant is dry, the water potential gradient between the leaf and the air is increased, which increases transpiration rate
how and why does wind affect transpiration rate
the windier it is, the faster the transpiration rate
- lots of air movement blows away water molecules from around the stomata
- this increases the water potential gradient which increases the rate of transpiration
what are xerophytes
plants like cacti and marram grass
they’re adapted to live in dry climates
their adaptions prevent them losing too much water by transpiration
cacti adaptations
- thick waxy layer on the epidermis<– this reduces water loss by evaporation because the layer is waterproof
- they have spines instead of leaves <– reduces surface area for water loss
- cacti also close their stomata at the hottest times of the day when the transpiration rates are the highest
