structure of xylem and phloem Flashcards
what are the structural similarities between xylem and phloem
both tube shaped
hollow
What 2 types of cells are xylem made up of
1.vessel elements
2. Tracheids
Similarities between vessel elements and tracheids
- Hollow cells
- lignified cells
Differences between vessel elements and tracheids
vessel elements are much larger than tracheids
vessel elements join from end to end to allow water to flow vertically, whereas tracheids have tapered ends which make water flow horizantally
why are vessel cells and tracheids hollow
to allow water and minerals to flow
what direction does water flow in xylem
what direction does water flow in phloem
xylem: water flows vertically
phloem: water flows horizontally and vert
why does water flow horizantally in the tracheids
tracheids have tapered ends
what are sink cells
fruit and root cells
what regulates transpiration
guard cells
how does water flow in phloem cells
The Sieve plates allow water to flow vertically, whilst the pores between the sieve cells allow water to flow horizontally.
Companion cells function
egulates the movement of nutrients to allow itself and the sieve cells to survive
Key characteristics of phloem:
Hollow cells
Tube like structure
Sieve plates for vertical transport of water
Pits between the sieve cells for horizontal transport of water
Companion cells
Transpiration
passive net movement of water through the xylem and evaporation through the stomata
how much water is used in phtoyhensis and what happens to the water that is not used in photosytehnsis
Only 1% of the water from the xylem is used for photosynthesis
the rest of the water evaporates into the stomata because there is a higher concentration of water vapour inside than outside the leaf
Function of the stomata
gas and exchange and is the stie where carbon dixodie enters the cell
ALL FUNCTIONS OF TRANSPIRATION:
Assists photosynthesis
Helps plants regulate heat and water balance
Distributes nutrients throughout the plant
Prevents wilting and cell damage
Why does evaporation cause water to move up the xylem
Water evaporates through the stomata causing the air pressure in the leaf to be lower than in the roots. This low pressure causes a force to draw water up the xylem.
Why does more water get drawed up the xylem than expected?
Water sticks together(cohesion)
Function of capillary action: How is it caused?
Capillary actions help water flow in the xylem
caused by the adhesion of water molecules to the surface of the xylem.
the 2 mechanisms of transpiration/ways water moves up the xylem
evaporation in the stomata and capillary action
TRANSLOCATION:
Is the movement of nutrients created in the leaves to other areas of the plant
How is the translocation of glucose happen
1.Glucose is produced during photosynthesis as it moves into the companion cells and sieve cells of the phloem.
2.As glucose moves into the sieve cells, the water also follows into the sieve cells, creating a higher turgor pressure
- The turgor pressure causes the liquid in the phloem to move across the plant, therefore glucose is actively transported from source cells into sink cells(root and fruit cells)
4.Once glucose is unloaded into the sink cells, the concentration in the phloem is reduced and water will diffuse back into the xylem.
5.Other solutes, such as amino acids or important minerals, travel through the phloem in a similar manner to glucose
Factors affecting transpiration rate
Water loss as leads to high solute concentrations and a reduction in turgidity, which in turn can damage the plant or cause it to wilt
Environmental conditions that affect transpiration rates
temperature – at higher temperatures, more water evaporates from the leaves
* water availability – when water availability is high the roots absorb more water.
what gases are exchanged in the stomata
oxygne & carbon dioxde
what happens when the stomato closes
, gases cannot freely leave or enter a leaf, thereby reducing the rate of photosynthesis, transpiration, and water loss.
whathappesn when the stomato opens
-water vapour can freely leave the leaf as part of transpiration
-CO2 can freely enter the leaf as an input of photosynthesis
-O2 can exit the leaf after it is produced during photosynthesis.
To increase the rate of transpiration, plants:
actively pump potassium ions into guard cells as this will increase the concentration of solutes. Then water will diffuse into the guard cells via osmosis. This causes the vacuoles to increase in size, and each guard cell becomes turgid. Turgid guard cells are shaped like beans, which leaves the stomata open.
To reduce the rate of transpiration, plants:
actively pump potassium ions out of guard cells as this will cause water to diffuse out of the vacuoles. This causes guard cells to becomes flaccid, closing the stomata
In order for guard cells to open the stomata
active transport must pump potassium ions against the concentration gradient.
If there is not enough active transport in the stomata,
, guard cells will lose their turgidity, hence stomata pores will be closed.
what are the 4 main forces that cause water to move up The xylem and how
osmosis
adhesion-
TrANSPIRATION-
cohension
adhesion
tendency of water and other surfaces to stick together
cohension
the bonding of water molecules
how does the stomata close
the guard cells become flaccid
how does capillary aciton cause water to move up the xylem
s it is caused by the adhesion of water molecules to the surface of the xylem. In small enough tubes, this force of adhesion is large enough to pull the water up the xylem.
how does osmosis cause water to move up the xylem
water moves up the xylem underpressure caused by osmosis as the roots require active transport because there is a high concentration of ions inside the root than outside the root
Why is the rate of transpiration high on a windy day?
wher eis majority of the plant
ground tisuse
chracteriistcs of xylem
dead
hollow
lignified
pits between vessle elments for vertical transport of water
why does the stomata need to open
gas exchange
how does transpiration cause water to move up the xylem
the negative pressure produced in the leaf pulls water up the xylem
how does adhesion cause water to move up the xylem
water is attracted to the sides of the walls of the xylem
why does cohension cause water to move up the xylem
water is polar therefore water molecuels bond to other water moleucels
the amount of water lost in plants depends on
humdiity and wind
Water loss via transpiration increases under the following conditions
Higher temperatures
Stronger winds
Low humidity
Large number of open stomata
Water loss via transpiration decreases under
Lower temperatures
Weak or no winds
High humidity
Few open stomata
Glucose moves from the leaf cells to the phloem by
facilcaited diffusion
Why does the cytoplasmic pathway contain active transport? 3 marks
The nutrients, minerals and water in the soil will diffuse from an area of high concentration into an area of low concentration of the plants through the cytoplasmic pathway.
cytoplasmic pathay requires active tranpsort so that substnaces can be transported against the concentration against from the soil even when the cocnentration in the soil is low and the concentration in the cytoplasm is high
Why does the cytoplasmic pathway contain active transport? 1 or 2 marks
the cytoplasmic pathway contains active transport in order to transport more nutrients, minerals and water from the soil into the cytoplasm even against the concentration gradient depending on the requirements of the plants
Does cohesion help in the process of transpiration or translocation and how?
Cohesion is the tendency of the water molecules to stick together and therefore it helps with transpiration as it allows the water to move up the xylem
