plant transport. ✔️ Flashcards
(26 cards)
Functions of the xylem?
- Transports water and mineral ions up the plant (transpiration pull).
- Supports the plant (lignin).
Structure of the xylem?
- Lignified cell walls - provides mechanical strength
- Non-lignified pits - allows water and mineral ions to move out.
- Dead - allows lignin to be deposited.
Function of phloem?
- Transports assimilates (sugars) up and down the plant.
- From source to sink.
Structure + properties of phloem?
- Alive - to do active transport for translocation.
- Cell walls partially broken down - individual sections called sieve tube elements.
- Companion cell - Keeps phloem alive. Involved in translocation.
- Plasmodesmata.
What is the plasmodesmata?
Gaps that link cytoplasm of adjacent cells.
E.g. companion cell and sieve tube elements.
Describe the apoplast pathway of water?
- Water moves through cell wall by tension.
- Meets casparian strip, where it is forced into cytoplasm (symplast).
Describe the symplast pathway of water?
- Through cytoplasm (diffusion) and plasmodesmata (osmosis).
What is the casparian strip?
- Embedded in cell wall of endodermal cells.
- Made of waxy (waterproof) suberin.
Function of casparian strip?
- Forces water moving in apoplast pathway to enter symplast pathway.
- Across plasma membrane.
- Filters out toxins.
- Allows minerals in water to enter plant.
How does water moves from the endodermis into the xylem?
- Ions move into xylem before water through active transport.
- Decreases water potential in xylem.
- Water moves into xylem by osmosis.
- Generates root pressure which pushes water up xylem.
- Transpiration decreases water potential in leaves.
Define transpiration?
Loss of water vapour by evaporation through stomata.
Why is transpiration good for plants?
- Cools plants down.
- Causes transpiration stream/pull.
What is the transpiration stream?
- Pull of water up the xylem from the roots to the leaves due to transpiration.
- Water evaporates from the leaves, decreasing water potential.
Why is transpiration bad for plants?
- Losing water.
- Loses turgor pressure.
- Could become flaccid of plasmolysed, causing the plant to wilt.
Define cohesion?
Hydrogen bonds between water molecules.
Define adhesion?
Hydrogen bonds between water molecules and the cell wall.
Factors that increase the rate of transpiration?
- High temperature - Increase kinetic energy. Molecules move more.
- Low humidity - Steeper water conc. gradient.
- Windy - Maintains steep water conc. gradient.
- High light intensity - More stomata will open, more carbon dioxide, more photosynthesis.
What equipment is used to estimate rate of transpiration?
Potometer.
How do you estimate the rate of transpiration?
- Distance travelled by bubble in capillary tube.
- Calculate volume of water taken up by plant.
- Only an estimate as the plant may use water for photosynthesis or to maintain turgor pressure.
How do you calculate water uptake from a potometer?
- Radius of cylinder (capillary tube) x Distance travelled by bubble.
Define translocation?
Transport of assimilates from source to sink in plants.
Why do phloem cells need to be alive?
Phloem loading requires energy, released in the form of ATP by respiration in mitochondria.
What are the two proteins called in companion cells?
- Proton (H+) pump
- Co-transporter
Explain phloem loading?
- Protons (H+) pumped out of companion cell to surrounding area by active transport. Uses ATP.
- Increases H+ concentration outside of companion cell. Generates H+ gradient.
- H+ and sucrose move back into companion cell through co-transporter proteins.
- Increased sucrose concentration inside companion cell.
- Sucrose moves through plasmodesmata into sieve tube down a concentration gradient by diffusion.
- Decreases water potential inside sieve tube.
- Water moves into sieve tube by osmosis, generating turgor pressure.
- Turgor pressure moves assimilates in the phloem (mass flow).
