Plant Organ Systems

• phloem tubes transport food:

  • made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through
  • transport food substances (mainly dissolves sugars) made in the laves to the rest of the plant for immediate use
  • transport goes in both directions
  • process is called translocation
• xylem tubes take water up

  • they are made of dead cell joined end to end with no walls in between and a hold down the middle
  • strengthened with a material called lignin
  • they carry water and mineral ions from the roots to the stem and the leaves
  • the movement of water from the roots, through the xylem, and out through the leaves is called the transpiration stream
• transpiration is the loss of water from a plant
• transpiration is caused by the evaporation and diffusion of water from a plant's surface
• the evaporation caused by transpiration causes a slight shortage of water in leaves, and so more water is drawn up from the rest of the plant to replace it
• the roots, stem, and leaves form a plant organ system for transport of substances around the plant.
• Guard cells are adapted to open and close stomata.

  • they have a kidney she which opens and closes the stomata
  • when the plant has lots of water the guard cells fill with it to go plump and turgid
  • this makes the stomata open so gases can be exchanged for photosynthesis
  • when the plant is short if water, the guard cells lose water and become flaccid
  • this makes the stomata close and helps to stop too much water vapour escaping
  • Thin outer walls and thickened inner walls make the opening and closing work
  • they're sensitive to light so close at night to save water
• You usually find more stomata on the undersides of leaves than the top because the lower surface is shaded and cooler so less water us lost through the stomata than if it was on the upper surface
• Root hair cells are adapted for the efficient uptake of water by osmosis, and minerals by active transport
• Xylem tissue transports water and mineral ions from the roots to the stem and leaves. it is composed if hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream
• the role of stomate and guard cells are to control gas exchange and water loss
• Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. the movement of food molecules is called translocation
• phloem is composed of tubes of elongates cells. cell sap can move from one phloem cell to the next through pores in the end walls