Plant

• Transpiration is the loss of water vapour from the stomata by evaporation. It is affected by light intensity (increases, more stomata open), temperature (increases, more kinetic energy), humidity (decreases, decreases water potential outside the leaf), and wind (increases, moves humid air).
• Cohesion tension theory: water moves up the plant to replace water lost by transpiration against gravity, cohesion between water molecules (dipolar so forms hydrogen bonds), adhesion (water sticks to xylem walls, a more narrow xylem has an increased impact of the effect of capillarity), increased root pressure (water moves into root by osmosis so increased positive pressure, pushing water up the xylem).
• Potometer

  1 - sample of underwater plant (prevents air bubbles in xylem)

  2 - fill potometer with water

  3 - seal and use petroleum jelly to ensure it is air tight

  4 - one air bubble introduced and record distance travelled

  5 - calculate volume of water up taken by plant and divide by time taken to find rate.
• Phloem is made from companion cells (provide ATP for active transport) and sieve tube elements (living cells with no nucleus/few organelles and perforated end walls).
• Translocation Pt 1

  1 - Photosynthesis creates organic substances

  2 - Increased concentration of sucrose at the source, sucrose diffuses down the concentration gradient into companion cells via facilitated diffusion

  3 - Active transport or hydrogen ions occurs from companion cell into space within cell walls creating concentration gradient, hydrogen ions move down concentration gradient via carrier proteins into sieve tube elements

  4 - co-transport of sucrose with hydrogen ions via protein co-transporters to transport sucrose into sieve tube element.
• Translocation Pt 2

  5 - Increased sucrose into sieve tube elements decreases water potential so water enters from surrounding xylem vessels via osmosis so hydrostatic pressure increases and liquid is forced towards the sink cell

  6 - Sucrose used in respiration at sink or stored as insoluble starch, more sucrose is actively transported into the sink cell so water potential decreases so water moves from sieve tube element to sink cell or xylem decreasing hydrostatic pressure.