Transport In Plants Flashcards
Why do plants need a transport systems
High metabolic rate
Have a small SA:V ratio
Large diffusion distance
Rate of diffusion too small
Multicellular
Function of guard cells
They bend to open & close stomata + control gas exchange
How are guard cells adapted
Many chloroplasts & mitochondria to provide ATP
Cells able to change shape
Transport proteins in CSM
Wall thicker on one side
Action of guard cells
Mineral ions actively transported into the cell
Decreased water potential & increased w.p. gradient
Water enters the cell via osmosis -> cell = turgid & stomata opens
Vascular system in leafs, stem & root
Features of the xylem
- dead cells
- lignified walls
- empty lumen
- bordered pits
Function of the xylem
Transport water & dissolved minerals
- up the plant
- from roots to leaves & other upper parts of plant
What’s good about each of the xylem components
Features of the phloem
- sieve tube elements
- peforations
- companion cells
- parenchyma cells
Function of phloem
Transport assimilates
Such as amino acids & sucrose from source to sink (up & down)
How is the sieve tube element adapted for its function
No nucleus & little cytoplasm
Allows for mass sap flow
As it is arranged end to end to form continuous sieve tubes
What are sieve plates
Separate sieve tube elements and these also filter out organelles between sieve tube elements
What do perforations in sieve plates do
These allow the mass flow of sap between sieve elements
What do parenchyma cells do
They’re packing cells which fill spaces between sieve tubes
What do plasmosdesmata do
These are gaps in the cell wall between companion cells, & sieve tube elements
Differences between Xylem & phloem
Similarities between xylem & phloem
How are stems dissected for observation
What is transpiration
The loss of water vapour from the aerial parts of a plant (especially from the stomata) as a consequence of gas exchange
Why is transpiration important
- maintains cell turgidity
- coding of plant by water evaporating out of stomata
- supplies water for growth, cell elongation & photosynthesis
- the stream transports mineral ions up the plant
Why is transpiration unavoidable
Stomata has to be open
To allow for gas exchange
Gas exchange required for photosynthesis & so water vapour leaves the lead
Why is transpiration diffusion not osmosis
As it doesn’t occur over a partially permeable membrane
Environmental factors to increase transpiration
Measuring transpiration using a Potometer
Safety measures using a Potometer
- use healthy shoot
- cut stem at a slant underwater
- dry leaves
- use petroleum jelly to ensure seal between shoot & potometer is airtight (so no leaks in apparatus)
Why do we use these safety measures in a Potometer
Movement of water into plants -> how does H2O enters via roots
- Root hair cells actively take up mineral ions
- Reduces the water potential of the root hair cells
- Water moves by osmosis, down w.p. gradient into root hair cells
- Through aquaporins
How is root pressure generated
-> active transport by endodermis of mineral ions into xylem & medulla
-> lowers w.p.
-> water enters medulla & xylem of roots by osmosis
-> this increases hydrostatic pressure of roots
How does water move up the stem
Root pressure = high pressure @ bottom of plant
Evaporation / water loss @ top = low pressure @ top of plant
-> pressure gradient created therefore tension in the xylem
Cohesion between H2O molecules = they stick together, forming continuous therefore, water is then pulled up by mass flow down the pressure gradient
What’s another way water can move up the stem
Capillary action
- water molecules attracted to side of narrow xylem vessel by adhesion therefore, H2O is pulled up the side of a xylem vessel
What are the 3 pathways from the root hair to the xylem
Vacuolar
Symplastic
Apoplast
Vacuolar pathway
Passes through vacuoles & cytoplasm of cells by osmosis
What is the symplastic pathway
Passes through the cytoplasm of cells using plasmosdesmata by osmosis
What is the apoplastic pathway
Passes through gaps in the cell wall via mass flow:
At endodermis, blocked by Casparian strip & water + dissolved minerals forced to enter symplastic pathway
-> casparian strip is impermeable to wax / waterproof
How is H2O loss from the top of the plant replaced
1, apoplastic/symplastic/vacuolar pathway
2, down water potential gradient,
3, by water from xylem
Endodermal cells -> xylem (h2o movement)
Endodermal cells actively transport mineral ions from cortex into medulla & xylem therefore reducing their w.p.
Water moves into medulla & xylem by osmosis down w.p. gradient
H2O -> out of leaf
Xylem water - > via osmosis / apoplastic pathway - > spongy mesophyll
Evaporates out of the cell walls into spaces in leaves
Diffuses out of open stomata down water potential gradient
H2O can be lost via stomata / the epidermis
What is translocation
The movement of assimilates up & down the plant
How are assimilates actively loaded into the phloem at the source
Where does sap move
From source to sink
Movement of sap at source versus at sink
How can the roots act as a source & a sink
Converts starch into sugars, which are loaded into phloem
Stores sugars into starch, which requires sugars to be unloaded from the phloem
Why are sugars transported as sucrose
Because it’s metabolically inactive
Soluble
Doesn’t get used up by respiration during transport
Mass flow attempts to explain how solutes more from source to sink. What’s some evidence for and against it
What is meant by the term transpiration stream
The movement of water from roots to leaves
