Transport in Plants

Transport in Plants

• In small organisms, osmosis, active transport, diffusion, endocytosis, and exocytosis are sufficient to provide nutrients and gases, but in larger organisms, cells may be too far apart for these processes to be adequate.
• Plants have developed two separate vascular systems: the xylem and the phloem.

Transpiration

• 90% of water taken in by roots is given off into the air as water vapor.
• The remaining 1% is used for:
  • Photosynthesis
  • Hydrolysis of water molecules
  • Maintaining turgidity of cells
  • Transport medium
  • Cell elongation/increase in size
• The main reason for water loss is photosynthesis, which requires stomata to be open, leading to water vapor loss.

Factors Affecting Transpiration Rate

• Temperature: higher temperature increases transpiration rate due to faster molecular movement.
• Humidity: lower humidity increases transpiration rate due to a steeper water potential gradient.
• Surface area of the leaf: larger surface area increases transpiration rate.
• Draught/wind: increased wind speed increases transpiration rate by increasing water potential gradient.
• Light: stomata opens in light, leading to water loss.
• Number of stomata: more stomata increase transpiration rate.
• Cuticle: thicker cuticle decreases transpiration rate by preventing evaporation.
• Sunken stomata/stomata in pits: trapped moist air in pits increases humidity and slows down transpiration.

Xerophytes and Adaptations

• Xerophytes live in deserts or windy habitats with rapid evaporation.
• Adaptations include:
  • Leaves reduced to spines with minimum surface area for transpiration.
  • Reduced number of stomata to reduce transpiration rate.
  • Rolled leaves, leaf hairs, and stomata sunk in pits to trap moist air and slow down transpiration.
  • Waxy leaf cuticle impermeable to water.
  • Reversed stomatal rhythm: stomata open at night and close at midday.
  • Thick waxy cuticle reduces water loss and reflects heat.
  • Pale colored leaves reflect solar radiation and do not heat up.
  • Few stomata reduce water lost by transpiration.
• Examples of xerophytes include Marram grass and cactus, with adaptations such as rolled leaves, sunken stomata, fine hairs, and thick waxy cuticle.

Learn about the vascular systems of plants, including xylem and phloem, and how they facilitate nutrient and gas transport. Discover the limitations of osmosis, active transport, diffusion, endocytosis, and exocytosis in larger organisms.