transport in plants

• what is phloem made up of?

  • sieve tubes elements
  • companion cells
• what are sieve tube elements?

  • living cells
  • contains no nucleus
  • contain few organelles
• what are companion cells?

  • provide ATP required for active transport of organic substances
• What is the xylem made of?

  • made of dead and hollow cells
  • do not contain any organelles or end walls
  • stack onto each other to make a continuous hollow column = good for transporting water + mineral ions
  • strengthened with waterproof chemical lignin
• how is water transported into the plant?

  • water absorbed into plants through the root hair cells by osmosis
  • root hair cells = maximised osmosis
• transport of water in the xylem?

  • water from the roots travels to the xylem through symplast pathway or apoplast pathway
• what is the symplast pathway?

  • through the cytoplasm of a cell
  • water moves cell to cell towards the xylem by osmosis through gaps in each cell wall plasmodesmata
• what is the apoplast pathway?

  • through the cell wall water travels
  • moves through the cell walls due to cohesive force of water
  • the water molecules stick together form a continuous stream of water to xylem
  • faster way to transport water due to no resistance
• what are xerophytes?

  • plants with the adaptations reduce water loss = found in places with reduced water e.g. desert
• feature of xerophytes?

  • curled leaves to trap moisture to increase local humidity
  • hairs to trap moisture to increase local humidity
  • sunken stomata to trap moisture to increase humidity
  • thicker cuticle to reduce evaporation
• what are hydrophytes?

  • plants that live in or on the water so require adaptions to survive in an excess of water
• feature of hydrophytes?

  • include short roots
  • very thin no waxy cuticles
  • stomata being permanently open and on the top surface of the leaf
  • ensure no additional water is retained in the plant = efficient water loss
  • ensures enough light is absorbed for photosynthesis = being large + wide + on the surface of the water
• what is transpiration?

  • The loss of the water vapour from the stomata by evaporation
  • the rate of transpiration is effected by 4 conditions
• how does light intensity affect transpiration?

  • Positive correlation
  • more light causes more stomata to open = large surface area for evaporation
• how does temperature affect the transpiration?

  • positive correlation
  • more heat means more kinetic energy
  • faster moving molecules and therefore more evaporation
• how does humidity affect the transpiration?

  • negative correlation
  • more water vapour in the air will make potential more positive outside of the leaf
  • reduces the water potential gradient
• how does wind affect the transpiration?

  • positive correlation
  • more wind will blow away humid air containing water vapour
  • maintaining the water potential gradient
• how does water move up the xylem?

  • water moves up a plant from the the roots against gravity
  • cohesion
  • capillarity - adhesion
  • root pressure
• what is cohesion?

  • water dipolar molecules (slight negative oxygen and slight positive hydrogens)
  • this enables hydrogen bonds to form between the hydrogen and oxygen of different water molecules
  • this creates cohesion between water molecules they stick together
  • therefore water travels up in a continuous water column
• what is adhesion?

  • when water sticks to other molecules
  • water adheres to the xylem walls
• what is root pressure?

  • water moves into the roots by osmosis increases the volume of liquid
  • pressure inside the root increases
  • this means positive pressure
• cohesion + adhesion + root pressure = cohesion-tension theory
• 1. water vapour evaporates out of stomata on leaves. This loss in water volume creates a lower pressure?
  2. water is lost by transpiration = more water is pulled up the xylem to replace it
  3. hydrogen bonds = cohesive creates column of water
  4. water molecules adheres to walls of the xylem
  5. xylem it creates tension
• mass transport in plants

  carbon dioxide + water = glucose + oxygen

  transports organic substances to all cell in plant

  all cells need sugar to respire
• how does translocation work in simple forms?

  source to sink
• what is a source cell?

  photosynthesising leaf cell

  • sucrose lowers water potential
  • water enters through osmosis
• what is the sink cell?

  respiring cell

  • uses up the sucrose = more positive water potential
  • water leaves the sink cell by osmosis
• source to sink explanation

  • higher hydrostatic pressure = solution is forced towards sink cell
  • high concentration of sucrose diffuses down the concentration gradient (facilitated diffusion)
  • H+ ions move via active transport to spaces in the cell wall
  • creates conc gradient
  • co transport sucrose with H+ ions
• movement of sucrose in phloem sieve tube element

  • increase sucrose in sieve tube lowers water potential
  • water enters sieve tubes via osmosis from xylem
• Translocation 3

  • sucrose used in respiration at sink and stored as insoluble starch
  • sucrose actively transported = water potential to decrease
  • osmosis of water from sieve tube into sink
  • decrease the volume of water = hydrostatic pressure decrease
  • soluble organic substances move due to pressure different