Transport Plants

• Root hair cell structure and function

  Absorb water and mineral ions from the soil

  
• Osmosis


  Water moves into the root hair cell by osmosis
• Water uptake by root hair cells

  Water moves from high water potential in the soil to low water potential in the root hair cell through the partially permeable cell membrane by osmosis

  
• Root hair cells

  • The cytoplasm and cell sap is a more concentrated solution (low water potential)
  • The soil contains water in more dilute solution (high water potential)

  
• Water movement from root hair cells to xylem


  Once inside the root hair cell, the water must travel to the xylem

  
• Water movement up the xylem

  1. Water moves up the xylem due to pressure gradient created by transpiration

  2. Cohesion of water molecules
• Cohesion


  Water molecules 'stick together' due to hydrogen bonds
• Transpiration


  Loss of water from plant leaves by evaporation at the surfaces of the mesophyll cells, followed by loss of water vapour through the stomata

  
• Transpiration is what makes water move up the xylem vessels
• Transpiration rate

  Affects the rate of water uptake
• Measuring transpiration

  Use a potometer to measure the volume of water absorbed by a plant over time

  
• Factors affecting transpiration rate

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
  • Water supply
  • Leaf surface area
  • Leaf shape
• Effect of temperature on transpiration rate

  As temperature increases, the rate of transpiration increases
• Effect of humidity on transpiration rate

  As humidity increases, transpiration decreases
• Effect of wind speed on transpiration rate

  As wind speed increases, the rate of transpiration increases
• Effect of light intensity on transpiration rate

  As light intensity increases, the rate of transpiration increases
• Effect of leaf surface area on transpiration rate

  The greater the surface area of the leaf, the more transpiration can occur
• If the rate that water is lost by transpiration > rate that water is taken up from the soil, then the plant will wilt
• Transport system in living organisms

  A system that allows exchange of substances, such as food molecules and waste products, between the organism and its environment
• Every living organism needs to exchange substances, such as food molecules and waste products, between itself and its environment
• Transport processes used by living organisms for exchange

  • Diffusion
  • Osmosis
  • Active transport
• These transport processes occur across the cell membrane of cells
• Diffusion


  Definition to be provided
• Size of a cell

  Affects the rate of diffusion
• Unicellular organisms


  • Have a large surface area compared to their volume
  • Do not need to have specialist exchange surfaces or transport systems because the distance between the cell membrane and the centre of the organism is very small
  • Diffusion, osmosis and active transport through the cell membrane occur at a sufficient rate to meet the organisms needs
• Multicellular organisms


  • Have smaller surface area compared to their volume
  • Distance between surface of organism to its centre is larger
  • As diffusion, osmosis and active transport cannot occur at a sufficient rate to meet the needs of the organism, larger organisms usually have exchange surfaces and transport systems
• Exchange surfaces in animals

  • Lungs and alveoli for gas exchange
  • Small intestine and villi for absorption of nutrients
• Exchange surfaces in plants

  • Root hair cells for absorbing mineral ions and water
  • Leaf for gas exchange
• Transport systems in animals

  • Blood vessels and heart transport substances around the body
• Transport systems in plants

  • Xylem transports water and mineral ions from roots to the plant
  • Phloem transports sugars (sucrose) and amino acids around the plant

  
• Phloem

  Transports sucrose and amino acids between the leaves and other parts of the plant

  
• Xylem


  Transports water and mineral ions from the roots to other parts of the plant
• Why plants need transport systems

  • Plants need carbon dioxide, sunlight and water for photosynthesis
  • Plants have a branching shape which gives them a large surface area in relation to their volume

  
• Leaf adaptations for obtaining sunlight and carbon dioxide

  • Broad, flat and thin
  • Large surface area
  • Carbon dioxide diffuses through the stomata and airspaces (spongy mesophyll)
  • Water is absorbed in the roots and transported to the leaf in xylem

  
• Plant transport systems


  1. Xylem transports water and mineral ions

  2. Phloem transports sucrose and amino acids

  
• Xylem


  • Made up of many hollow, dead cells joined end-to-end
  • The end walls of the cells have broken down, forming a long, continuous tube
  • Xylem vessels travel from the root to stem to leaves
  • Xylem vessels contain no cytoplasm or nuclei
  • The cell wall contains cellulose and lignin
• Lignin


  Hard, strong material in the cell wall of xylem that helps plants stand upright
• Wood


  Mostly composed of lignified xylem vessels

  
• Functions of Xylem


  • Transport water
  • Support the plant
• Phloem


  • Made up of many cells joined end-to-end
  • The end walls have not completely broken down, but instead have many holes in them - forming sieve plates
  • Phloem transports sucrose and amino acids around the plant