Chap 8

• The xylem and phloem are both transport vessels that help move substances around the plant
• Memory aid for xylem and phloem

  Phloem starts with the sound "fur" which carries food, while xylem transports water
• Xylem function

  Transports water and mineral ions from the roots to the stem and leaves, provides structural support to the plant
• Vascular bundles components

  • Xylem
  • Phloem
• Phloem function


  Transports food (sucrose and amino acids) made by the plant from photosynthesizing leaves to non-photosynthesizing regions in the roots and stem
• Water from the soil is needed by the stem and leaves
• Structure of xylem vessels

  • No cell contents, cells are joined end to end with no cross walls, walls are thickened with lignin to strengthen and support the vessels
• Position of xylem and phloem in cross section of a leaf

  • Xylem is the upper pink area, Phloem is the lower green area
• Position of xylem and phloem in sections of roots

  • Xylem is on the inside (pink area in the shape of an X), Phloem is on the outside (surrounding green area)
• The nutrients that leaves make during photosynthesis are needed by other regions of the plant like stems and roots
• Vascular bundles are found throughout the root, stem, and leaves
• Position of xylem and phloem in sections of stems

  • Xylem is the inner pink areas, Phloem is the outer green part of the oval shapes
• Plants have a transport system to carry nutrients within them
• Conclusion of part one of topic 8 Transporting Plants
• Adaptations of root hair cells


  • Greatly increased surface area for increased uptake of water and mineral ions
  • Increased rate of absorption of Water by osmosis
  • Increased rate of absorption of mineral ions by active transport
• Real image of the cross section of a stem


  • Shown on the right
• Investigating the pathway of water through above-ground parts of a plant

  1. Place celery into beakers of water with food dyes

  2. Leave in sunlight for a few hours

  3. Cut cross sections of the celery stalks and observe color changes
• Root hair cells

  Specialized cells found in roots of plants adapted to absorb water and minerals from the soil
• Pathway of water through the root, stem, and leaf

  1. Water enters root hair cells from the soil through osmosis

  2. Water passes into the root cortex cells

  3. Water travels into the xylem

  4. Water travels up the stem to the leaves

  5. Water enters the mesophyll cells
• Water uptake in plants

  1. Plants absorb water through their roots

  2. Water first enters the root hair cells from the soil through osmosis

  3. Water passes into the root cortex cells

  4. Water travels into the xylem where it travels up the stem to the leaves

  5. Water enters the mesophyll cells
• Color changes in the leaves show that water is being taken up by the plant
• Speaker: 'Thank you for watching and please don't forget to subscribe to IGCSE study buddy for more biology revision videos'
• Cohesion


  Forces of attraction between water molecules that hold them together
• Setting up a potometer

  Underwater to avoid air bubbles in the xylem, joints sealed airtight, single air bubble introduced into capillary tubing, water added to push air bubble back to zero on the scale, timer started and distance the air bubble travels recorded
• Factors affecting transpiration rate

  • Temperature
  • Wind speed
  • Humidity
• Increased wind speed

  Increases the rate of transpiration
• Water does not travel through xylem vessels by osmosis
• The experiment can be repeated with different environmental conditions to test factors affecting transpiration rate
• Increased temperature

  Increases the rate of transpiration
• Transpiration pull


  Draws up a column of water molecules up the xylem as water evaporates at the leaf and diffuses out of the stomata
• Transpiration is the loss of water vapor from leaves
• A potometer may be used to measure transpiration rate
• Water movement in plants

  Water from the soil travels through the roots to the xylem and up to the leaves to replace the lost water. Water evaporates from the surfaces of the mesophyll cells into the air spaces and diffuses out of the leaves through the stomata as water vapor
• Increased humidity


  Decreases the rate of transpiration
• Sources in translocation

  Parts of plants that release sucrose or amino acids
• During spring, when the plant is still growing, storage organs like roots are the source, and growing areas of the plant are the sinks
• Increased temperature and wind speed

  Increases the transpiration rate
• Sinks in translocation

  Parts of plants that use or store sucrose or amino acids
• In the first picture, there is sufficient water in the soil to replace the water lost by transpiration. In the next diagram, the plant has wilted because more water has evaporated from the leaves and there's not enough water in the soil
• Some parts of a plant may act as a source and a sink at different times