12.13 - Mass transport in plants Flashcards
What is mass transport?
What theory, tissue and direction do plants have mechanisms for the transport of these:
- Water + inorganic ions
- Sucrose + Amino acids (organic solutes)
The bulk movement of substances from one area of an organism to another at the same/similar rate.
Water + inorganic ions,
theory = cohesion-tension and transpiration
tissue = xylem
direction = upwards, roots to shoots + leaves
Organic solutes
theory = mass-flow hypothesis
tissue = phloem
direction = any direction, from source to sink(s)
WATER UPTAKE FROM THE SOIL
Water enters the root hair cells within the epidermis…
What adaptations do root hair cells have?
…by osmosis.
- hair like extensions that increase their surface area to increase the uptake of water and increase the area for channel & carrier proteins
- thin cellulose cell walls so they have a short diffusion distance
1) Root hair cells actively transport ions using energy…
2) From the soil across their membranes into their cytoplasm, via…
3) This lowers the…
4) Water enters the root hair cells by…
5) Water then passes across the cells of the…
6) The xylem vessels transport…
…from the hydrolysis of ATP
…carrier proteins
…water potential of the cytoplasm (of the RHC) compared to the water potential of the soil
…osmosis, down a water potential gradient
…cortex, then across the endodermis then into the xylem vessels
…water + ions up the plant’s stems into the leaves
XYLEM TISSUE STRUCTURE = FUNCTIONS
- Dead cells that form hollow tubes with no cytoplasm or organelles =
- End walls break down so xylem forms a continuous tube w/ no end walls =
- Cell walls are strengthened with lignin =
- xylem pits =
= faster water flow / less resistance / can’t be stopped by organelles
= a continuous column of water can form due to cohesion
= this makes the xylem waterproof + rigid / provides support from tension / enables adhesion of water
= little holes that allow water to move laterally between xylem vessels / get around blocked vessels
How do plants obtain water and inorganic ions? Where does the water go next? Where does the water leave the plant?
What does transpiration involve?
What is meant by transpiration?
Where do xylem transport water from and to?
From the soil via their roots. The water passes from the roots to the stem where it is transported up the plant in xylem vessels to the leaves. Water leaves the plant through stomatal pores by diffusion.
The mass transport of water.
The loss of water from the leaf.
From the roots to the leaves.
TRANSPIRATION + COHESION-TENSION THEORY
1) Stomata open (To enable CO2 to enter leaf for photosynthesis) which causes water to diffuse in from…
2) The loss of water from the air spaces causes water…
3) This lowers the WP of the mesophyll cells, so water moves…
4) This sets up a…
5) Water from the xylem enters the leaf, causing water to be…
6) Water forms a…
7) Water molecules form weak H-bonds between them so…
8) They are also attracted to the walls of the xylem, there are forces of…
9) The pulling force is great and the column of water is under…
10) The movement of water through plant from roots -> leaves is…
1)…the air spaces at a higher WP inside the leaf to a lower WP of the air outside the leaf.
2)…to move down a WP gradient from the mesophyll cells to the air spaces
3)…by osmosis from adjacent mesophyll cells
4)…WP gradient across the leaf to the xylem vessels
5) …pulled up under tension through the xylem from the roots
6)…continuous column in the narrow xylem vessels
7)…they tend to stick together = COHESION
8)…ADHESION between the water and the xylem.
9)…tension
10)..the transpiration stream.
On a hot day, during rapid transpiration, the diameter of a tree trunk will…
…reduce slightly because of the movement of water making the xylem vessels slightly narrower as the xylem experiences negative pressures.
Root pressure exists to push water a short distance up the…
This arises from the movement of water across the…
Which has sufficient pressure to push water up the…
Only effective for a…
…xylem.
…endodermis.
…xylem
…short distance.
Explain how water enters the xylem from the endodermis in the root and is then transported to the leaves. (7)
(ROOT)
- Active transport by endodermis
- Of ions into the xylem
- lowers the WP in xylem, water enters xylem by osmosis down a WP gradient
(XYLEM TO LEAF)
- evaporation / transpiration from leaves
- creates cohesion between water molecules
- adhesion - water molecules bind to xylem
- creating a continuous column of water
Root pressure moves water through the xylem. Describe what causes root pressure. (4)
1) Active transport by endodermis
2) Ions into the xylem
3) Lowers WP in xylem
4) Water enters by osmosis
Describe how high pressure is produced in the leaves (3)
1) WP becomes lower / more negative (as sugar enters)
2) Water enters phloem by osmosis
3) Increased volume of water = increased pressure
FACTORS AFFECTING THE RATE OF TRANSPIRATION
1) LIGHT INTENSITY
High light intensity means…
2) TEMPERATURE
increased temperature means…
3) HUMIDITY
Increased humidity means…
4) WIND SPEED
Increasing the wind speed means…
5) STOMATAL DENSITY
Higher stomatal density (more stomata) means…
1) …more stomata are open, letting more CO2 in for photosynthesis
2) …increased rate of transpiration.
^ temp = ^ KE = ^ rate of diffusion and evaporation of water
3) …decreased rate of transpiration. High humidity in the air means that there is a smaller conc. gradient due to air spaces in the leaf being saturated with water vapour, and air outside the leaf also being more saturated with water vapour due to the high humidity.
4)…increased rate of transpiration. Wind over a leaf moves the water vapour away from the stomatal pores, increasing the WP gradient.
5)…higher rate of transpiration.
Name the factors that affect transpiration.
Light intensity
Temperature
Air movement / wind speed
Humidity
Stomatal Density
MEASURING THE RATE OF TRANSPIRATION
DESC > EXPLANATION
1) A leafy shoot is diagonally cut under water…
2) Care is taken to prevent getting water on the leaves as..
3) The potometer is filled completely with water to make sure there are no air bubbles to…
4) Using a rubber tube, the leafy shoot is fitted to the potometer under water.
5) The potometer is removed from under the water and all joints are sealed with waterproof jelly…
6) An air bubble is introduced into the capillary tube, as transpiration occurs, water moves through the capillary tube and the bubble of air moves with it…
7) The distance moved over a period of time is recorded and a mean is calculated of a number of repeats to…
8) The volume of water uptake over a period of time can be calculated with…
THE UNITS ARE…
1)…preventing damage to the xylem (as it ensures a continuous column of water)
2)…water could prevent the loss of water vapour through the stomata.
3+4) Prevent air entering the xylem and ensuring a continuous column of water
5)…to prevent water loss from potometer and prevent air from entering.
6)…to determine the volume of water entering the shoot you use: Lπr^2
7)…determine a reliable mean
8) RATE OF UPTAKE = Lπr^2 / time
UNITS = cm^3min^-1 or dm^3 hour^-1
Name some precautions when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot.
- Ensure joints are sealed / airtight / watertight
- cut shoot under water
- cut shoot at a slant
- dry off leaves
- ensure no air bubbles are present
- shut tap
- note where bubble is at start or move it to start position
