Transport in plants part 2 Flashcards
How does water leave the leaf
water evapourates from the cell lining the cavity immediately above the guard cells this lower the water potential of the cells causing the water to enter them via osmosis from neighbouring cells, the water is drawn from the xylem into the leafs
water may also reach these cells via the apoplast pathway from the xylem
Why do terrestrial plants have a lack of assess o water
not near pond
stomata open for gas exchange for photosynthesis therefore water is lost when the stomata is open
What must terrestrial plants be adapted to do
replace the water is lost
reduce the loss of water
How can the water loss be reduced
stomata close at night
waxy cuticle on the lead reduces water loss due to the evapouration through the epidermis
stomata found on under surface of the leaves not the top surface this reduces evapouration due to non-direct heating from the sun
deciduous plants lose leaves in winter when ground is frozen and temperature to low for photosynthesis
What is marriam grass
plant that lives on sand dunes
What problems does marriam grass face
water drains away quickly, sand is salty and leaves are exposed to windy conditions
What is an xerophyte
a plant adapted to living in arid conditions
How is marriam grass adapted
leaf rolled longitudinally so air is trapped inside this means air is humid which reduces water loss
thick waxy cuticle to reduce water loss by evapouration (outer side of lead rolled)
stomata on inner side of rolled lead so they are protected by enclosed air space
stomata are in pits in the lower epidermis which is folded and covered by hairs this reduces air movement and loss of water vapour
spongy mesophyll is very dense with few air spaces so less surface area for evapouration of water
What are cacti
they are succulents these store water in their stem which becomes fleshy and swollen
How are cacti adapted
stem is often ribbed or fluted so it can expand when water is available
spines instead of leaves this reduces surface area of the leaves therefore less water is lost by transpiration
stem is green for photosynthesis roots are widespread in order to take advantage of any rain that does fall
What are the other xerophytic features
close the stomata when water vapour is low reduce water loss and the need to take up water
low water potential in their lead reduce water loss as water potential gradient reduced due to high salt concentration and air spaces reduced
very long tap roots that reach water deep underground
What is a hydrophyte
plants that live in water
What problems do hydrophytes have
getting oxygen to submereged leaves
keep afloat
need to have leaves in sunlight for photosynthesis
What are the adaptions of hydrophytes have
large air spaces in the leaf to keep the leaf afloat so it can absorb sunlight
stomata on upper epidermis so they are exposed to air for gas exchange
leaf stem has large spaces to help with buoyancy but allows oxygen to diffuse into roots for aerobic respiration
How do hydrophytes transpire
water will not evapourate into water or air that has a very high humidity so if water cannot leave then the transpiration stream stops and mineral ions cannot go up the leaves these release water droplets which evaporate from the lead surface
Where does translocation occur
it occurs in the phloem
What does it transport
assimilates these are substances made from the plant which are usually absorbed from the environment
Describe a source
this is the part of the plant that loads assimilates into the sieve tube elements
Describe a sink
This is the part of the plant that removes assimilates from the sieve tubes
What are the main assimilaties
amino acids and sugars
Describe active loading
sucrose is loaded into the sieve tube by an active process this involves energy from the ATP in companion cells
- hydrogen ions go out of the companion cells by using the energy and by active transport
- there is a high concentration of hydrogen ions outside the cells then in the cells this creates a concentration gradient
- the hydrogen ions diffuse back into the companion cells through special cotransporter proteins but proteins only allow the movement of hydrogen ions into the cell if they are accompanied by sucrose molecules this is known as cotransport or secondary active transport as it results from the active transport of hydrogen ions out of the cell and moves sucrose against its concentration gradient into the cell
- as the concentration of sucrose in the companion cell increases it can diffuse through the plasmodesmata into the sieve tube due the creation of a concentration gradient
Describe the movement of sucrose
sucrose along with a solution of amino acids and other assimilates moves by mass flow in the sieve tube, the solution is called sap and it can flow up or down
- the flow is caused by a difference in hydrostatic pressure between the two ends of the tube producing a pressure gradient
- water enters the tube at the source thus increasing pressure and leaves the tube at the sink reducing the pressure therefore the gradient is created and the sap flows from the source to the sink
Describe how sucrose moves in the source
sucrose entering the sieve element makes the water potential inside the sieve tube more negative
water moves into the sieve tube element by osmosis from the surrounding tissues this increases the hydrostatic pressure in the sieve tube at the source
Name places which could be a source
roots or leaves depending on the time of year
What is a sink
anywhere that removes sucrose from sieve tube elements
What is sucrose used for
growth or respiration in a meristem or converted for storage in a root
Describe the movement of sucrose in the sink
when sucrose is being used it can diffuse out of sieve tube by plasmodesmata or active transport
the removal of the sucrose from sap makes the water potential less negative and the water moves out of the sieve tube into surrounding cells
this reduces the hydrostatic pressure in the sink
Describe the movement along the phloem
water enters the sieve tubes at the source
this increases the hydrostatic pressure therefore a pressure gradient is formed and sap flows from a high pressure to low pressure by mass flow
- either direction depending on where the sucrose is needed
