Plant transport

• Why do plants require a transport system?

  To ensure all cells receive a strong supply of the nutrients they require and transport substances up their stem.
• Relate the structure of xylem to its function

  Long continuous columns made of dead tissue allowing transportation of water. Contain pits allowing water to move sideways between vessels. thickened with a tough substance providing structural support.
• Xylem

  Two main functions - the transport of water and mineral ions and support. The flow of materials in the xylem is up from the roots to the shoots and leaves. Made of dead cells. Hollow structures.
• Relate the structure of phloem to its function

  Sieve tube elements transport sugars around the plant. Companion cells designed for active transport of sugars into tubes. Plasmodesmata allow flow of substances between cytoplasm of different cells.
• Phloem

  Unlignified, in the areas between the cells the walls become perforated to form sieve plates which let phloem contents flow through.
• Vascular tissue

  Xylem arranged in an X shape to provide resistance against force. Surrounded by endodermis, a water supply.
• Vascular system in the stem

  Xylem on the inside of the bundle to provide support and flexibility, phloem on the outside. Layer of meristem cells that produce new xylem and phloem tissue when required.
• Transpiration

  The evaporation of water from the leaves of a plant. A consequence of gaseous exchange when the plant opens the stomata to exchange O2 and CO2
• Factors that affect the rate of transpiration

  Increased light increases transpiration, increased temperature increases transpiration, increased humidity decreases transpiration, increased air movement increases transpiration, waxy cuticle prevents transpiration
• Measuring transpiration rate

  Potometer. Plant cutting is placed in a water-filled tube that contains an air bubble. Rate of transpiration is measured by the movement of the air bubble over time.
• Water potential

  The tendency of water to move by osmosis from high water potential to low. Pure distilled water has the highest water potential of 0.
• Apoplastic pathway

  A method of osmosis through the root hair cells, where water moves through the cell walls and intercellular spaces. The casparian strip stops this pathway.
• Symplastic pathway

  A method of osmosis through the root hair cells where water moves through the cytoplasm via plasmodesmata. Water must be actively transported into cells to begin this pathway
• Cohesion-tension theory

  Water molecules form hydrogen bonds with each other (cohesion). The surface tension of the water creates adhesion. Allows water to be drawn up the stem from the roots
• Adaptations of xerophytes

  Small rolled leaves, densely packed mesophyll, thick waxy cuticle, stomata often closed, hairs to trap moist air.
• Adaptations of Hydrophytes

  Thin or absent waxy cuticle, stomata often open, wide flat leaves. air spaces for buoyancy
• Translocation

  Sucrose produced in leaves are loaded into sieve tube elements via active transport. This lowers water potential causing water to move in from the xylem. Assimilates move along the sieve tube towards areas of lower hydrostatic pressure and sucrose diffuses into surrounding cells where it is needed.