3.1.3 Transport in Plants Flashcards
why do plants require a transport system?
To ensure met metabolic demands especially as they have to defy gravity to bring substances up the stem
Relate the structure of xylem to its function (mature xylem)
Long continuous columns made of dead tissue
has lignified walls
also has parenchyma which have tannin that tastes bitter in order to protect it
relate the structure of phloem to its function
sieve tube elements transport sugars the plant
companion cells which provide ATP for active transport
Plasmodesmata allow for a flow of substances in and out of the phloem
Has thick walls and sclerids for support
describe the structure and function of the vascular bundle in the roots
consists of xylem and phloem
xylem in an x shape and phloem around it
this gives it strength
describe the structure of the vascular bundle in the stem
the xylem and phloem are around the outside perimeter of the cell separated by cambia tissue
They are close to meristematic tissue to provide tissue for new xylem or phloem when required
What is the root hair cell structure
Large surface area
Thin cell wall and membrane
cytoplasm and vascular sap have lots of sugar carries lots of sugar/minerals so in a state of constant low water potential
what is the apoplast pathway?
When water goes through the cell wall and intercellular spaces after osmosis
what is the symplast pathway?
water moves through the cytoplasm of cells and the plasmodesmata after osmosis
what is the vacuole pathway?
water moves through the symplast And the vacuole
Role of casparian strip
Blocks water from reaching the xylem through the apoplast pathway
This forces all water to travel through the cytoplasm where the cell membrane can stop toxic mineral ions from entering
what is root pressure?
when cells in the endothermis use active transport to fill the xylem with mineral ions
this lowers the water potential and forces water to rush into the xylem
Define transpiration
The evaporation of water from the leaves in a plant through the stomata
Factors that affect the rate of transpiration
Increased temperature
Increased light intensity
Increased humidity decreases concentration gradient
why is water important to the plants?
Exerts Tergal pressure which helps for plant structure
Evaporation helps to cool down the plant
A solvent for minerals and ions
How can we prove root pressure is caused by the active pumping of ions?
Cyanide- stops respiration from occuring so no ATP for active transport which will not cause water to move into the xylem due to low water potential
What is the sequence of events for transpiration?
- Airflow around the plant makes the air less humid
- so now there is a gradient between in and outside the leaf
- As water vapour evaporates the leaf’s water potential is lowered so water will be drawn in from the xylem by osmosis
How do stomata open?
K+ ions enter guard cells through active transport
Which lowers water potential so water rushes in
and makes the guard cells round allowing it to open
How does water climb up through the xylem?
Through cohesion forces - the H2o molecules have hydrogen bonds to the carbohydrates of the walls of the xylem
OR
adhesive forces the H20 have hydrogen bonds to each other
How can we measure transpiration rate?
through a potometer
we can calculate distance moved by air bubble/time taken to move the distance
how is water potential a mechanism of movement for plants?
water potential = the tendency an area has for water to move into it , wants to move from high water potential to low
why is the measurements from a potometer not 100% accurate
assumes some of the water uptake is through transpiration but the rest is that some of the water is used to maintain turgor pressure.
explain why transpiration in plants cannot be avoided
stomata open for gas exchange due to photosynthesis so the transpiration cannot be avoided
explain in sequence how you should set up a potometer for valid results.
Select a healthy shoot
seal the shoot to the top with Vaseline for no air bubbles
make sure the shoot is completely underwater
seal the leaves and allow the plant to acclimatise before adding the air bubble
record the distance travelled and the amount of time taken
repeat and evaluate a mean
what are adaptations of xerophytes?
small/rolled leaves
thick waxy cuticle
stomata often closed
hair to trap moisture
How do sunken stomata help xerophytes?
Creates a moist microclimate which allows for a less steep water potential
What are adaptations of marram grass?
Rolled leaves make it resistant to dry conditions
thick waxy cuticle
dense spongy mesophyll- prevents water loss via evaporation
stomata on the inside of leaf
what is a succulent?
stores water in it parenchyma tissue (e.g cacti)
Explain how transpiration results in the movement of water up a plant stem
Loss of water from mesophyll
the adhesive and cohesive forces allow it to go up the stem due to hydrogen bonding
through the apoplast or symplast pathway
