Transport in plants

Transport in plants

1. xylem

   • xylem vessels move water from the roots of a plant to their leaves
   • water is absorbed through root hair cells
   • water is transported through the xylem vessels, up the stem, to the leaves
   • water evaporates from the leaves
     • transpiration
   • xylem vessels consist on dead cells. They have a thick, strengthened cellulose wall with a hollow lumen

2. Phloem

   • phloem consists of columns of living cells
   • phloem vessels are involved in translocation.
     • (translocation is the transport of dissolved material within a plant)
   • the movement of food substances from the stems to growing tissues and storage tissues
   • phloem transports food from the leaves to the rest of the plant.

3. Adaptations

   • A healthy plant must balance its water loss from the leaves with its uptake of water through the roots. Transpiration provides plants with water for:
     • Cooling
     • Photosynthesis
     • Support
     • Movement of minerals
   • root hair cells = larger surface area to take up water by osmosis
   • not enough water = flaccid + wilting
   • the structure of the leaf is adapted to reduce excessive water loss:
     • They have a waxy cuticle
     • only a small amount of stomata on the upper surface
     • guard cells around the stomata
   • when it's really bright and there's lots of water then the plant changes:
     • chloroplasts make sugars at a higher rate
     • waters enters the guard cells from other cells via osmosis
     • the guard cells become turgid
     • the stomatal opening gets bigger

4. transpiration

   • water moves against gravity in xylem cells
   • water on the surface of spongy and palisade cells evaporates and diffuses out of the leaf
     • more water is drawn up through the continuous tube (xylem); producing a flow of water + dissolved minerals from roots to leaves
   • when water is scarce or the roots are damaged, the transpiration rate slows down
     • plants then wilt
   • factors that affect transpiration:
     • light intensity
       • transpiration increases when it is bright
       • the stomata open wider to allow more carbon dioxide in for photosynthesis
     • humidity
       • transpiration is slower when it is humid
       • the water concentration is already high outside so water won't diffuse out
     • wind
       • transpiration is faster when it is windy
       • water vapour is moved quickly by air movement, speeding up diffusion
     • temperature
       • transpiration in faster when it is hot