4.2.3.2 plant organ system

• What do the roots, stem and leaves form?

  a plant organ system for transport of substances around the plant
• What are stomata?

  Openings all over the leaf surface
• what do the guard cells do?

  control the opening and closing and also the size of the stomata
• what happens when the stomata open?

  plants lose water vapour
• what is transpiration?

  water vapour evaporates from the cells lining the air spaces and then passes out of the leaf through the stomata by diffusion
• what happens as water evaporates from the surface of the leaves?

  more water is pulled up through the xylem to take its place
• what is the transpiration stream?

  the constant movement of water molecules through the xylem from the roots to the leaves
• what is the transpiration stream driven by and what does this mean?

  driven by evaporation of water - anything that affects the rate of evaporation will also affect transpiration
• What are the things that affect evaporation, therefore transpiration?

  changing temperature, humidity, air movement and light intensity
• How are root hair cells adapted?

  For the efficient uptake of water by osmosis and mineral ions by active transport
• what does xylem tissue do?

  transports water and mineral ions from the roots to the stems and leaves
• what is the xylem composed of and how are they adapted?

  hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream
• what is the role of stomata and guard cells?

  to control gas exchange and water loss
• what does phloem tissue do?

  transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage
• what is translocation?

  the movement of food molecules through phloem tissue
• what is phloem composed of?

  tubes of elongated cells
• what can move from one phloem cell to the next and how?

  cell sap - through pores in the end walls