Transport in plants

Transport in plants

xylem
1. xylem vessels move water from the roots of a plant to their leaves
2. water is absorbed through root hair cells
3. water is transported through the xylem vessels, up the stem, to the leaves
4. water evaporates from the leaves
  1. transpiration
5. xylem vessels consist on dead cells. They have a thick, strengthened cellulose wall with a hollow lumen
Phloem
1. phloem consists of columns of living cells
2. phloem vessels are involved in translocation.
  1. (translocation is the transport of dissolved material within a plant)
3. the movement of food substances from the stems to growing tissues and storage tissues
4. phloem transports food from the leaves to the rest of the plant.
Adaptations
1. 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:
  1. Cooling
  2. Photosynthesis
  3. Support
  4. Movement of minerals
2. root hair cells = larger surface area to take up water by osmosis
3. not enough water = flaccid + wilting
4. the structure of the leaf is adapted to reduce excessive water loss:
  1. They have a waxy cuticle
  2. only a small amount of stomata on the upper surface
  3. guard cells around the stomata
5. when it's really bright and there's lots of water then the plant changes:
  1. chloroplasts make sugars at a higher rate
  2. waters enters the guard cells from other cells via osmosis
  3. the guard cells become turgid
  4. the stomatal opening gets bigger
transpiration
1. water moves against gravity in xylem cells
2. water on the surface of spongy and palisade cells evaporates and diffuses out of the leaf
  1. more water is drawn up through the continuous tube (xylem); producing a flow of water + dissolved minerals from roots to leaves
3. when water is scarce or the roots are damaged, the transpiration rate slows down
  1. plants then wilt
4. factors that affect transpiration:
  1. light intensity
    1. transpiration increases when it is bright
    2. the stomata open wider to allow more carbon dioxide in for photosynthesis
  2. humidity
    1. transpiration is slower when it is humid
    2. the water concentration is already high outside so water won't diffuse out
  3. wind
    1. transpiration is faster when it is windy
    2. water vapour is moved quickly by air movement, speeding up diffusion
  4. temperature
    1. transpiration in faster when it is hot

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