transpiration and translocation

• phloem tubes transport...


  food
• phloem tube structure


  made of columns of elongated living cells with small pores in the end walls (called sieve walls) to allow cell sap to flow through
• phloem tubes function


  transports food/cell sap (mainly dissolved sugars) made in the leaves to the rest of the plant - this transport (translocation) goes in both ways
• xylem tubes transport...


  water and minerals ions
• translocation is...


  the movement of cell sap through the plant's transport vessels
• xylem tubes function


  takes water and mineral ions up the stem to the leaves from the roots (this goes only one way) - the movement of water out of the leaves is called transpiration steam
• xylem tube structure


  made up of dead cells joined end to end with no end walls between them and hole down middle - they are strengthened with a material called lignin, supporting the stem
• translocation goes...


  both (up and down the plant)
• transpiration is...


  the loss of water from a plant caused by evaporation and diffusion of water from a leaf's surface which results in more

  water being drawn up from the roots
• transpiration goes...


  one way (up the plant)
• transpiration stream


  the movement of water through a plant from the roots until it is lost by evaporation from the leaves, causing more water to enter through the roots
• what cell absorbs water and mineral ions from the roots?

  root hair cells
• root hair cell structure

  elongated 'hair-like' structure this gives them a large surface area to maximise rate of absorption and has lots of mitochondria to provide energy for active transport
• root hair cell function

  absorbs water and mineral ions from the soil by osmosis with active transport
• factors affecting transpiration


  light intensity, temperature, air flow, humidity
• higher light intensity results in...

  higher rate of transpiration

  - this is because stomata open in lighter conditions, allowing water to pass through
• warmer temperature results in...

  higher rate of transpiration

  - this is because the water particles have more energy to evaporate out of the stomata
• faster air flow results in...

  higher rate of transpiration

  - this is because the water particles can be swept away off the leaf's surface more easily
• higher humidity results in...

  lower rate of transpiration

  - this is because there is a lower concentration gradient between the leaf's surface and the air - diffusion happens quickest with a high concentration gradient
• a potometer can be used to...

  observe the rate of transpiration
• potometer


  a device used for measuring the rate of water uptake of a plant due to photosynthesis and transpiration
• guard cells are adapted to...

  open and close stomata
• how does the shape of guard cells enable it to function?

  it's kidney-like shape enables it to surround the stomata and open/close it
• what happens when the plant has lots of water?

  the guard cells fill with it and go plump and turgid- this makes the stomata open so gases can be exchanged for photosynthesis.
• what happens when the plant is short of water?

  the guard cells lose water and become flaccid, making the stomata close- this helps stop too much water vapour escaping
• how do the walls of guard cells help them?


  thin outer walls and thickened inner walls make the opening and closing work
• where are the most stomata found on a leaf?


  underside of the leaf, because the lower surface is shaded and cooler - so less water is lost through the stomata than if they were on the upper surface
• guard cells are adapted for ... within a leaf

  gas exchange and controlling water loss