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Movement of water through the dicotyledonous root

This diagram shows the movement of water through the root

  • Water is found in the spaces between the soil particles. Water enters through the cell wall and cell membrane of the root hair cell by osmosis. Water fillsthe vacuole of the root hair cell.
  • Water can now move across the parenchyma cells of the cortex in two ways:
  • Most of the water passes along the cell walls of the parenchyma cells by diffusion. Movement of water and solutes between the intercellular spaceswithout crossing the plasma membrane is known as apoplastic movement.
  • Some of the water passes from the vacuole of one parenchyma cell to the vacuole of the next cell by osmosis. Movement of water and solutes through the cells isknown as symplastic movement.
  • The water must pass through the endodermis to enter the xylem.
  • Once water is in the xylem of the root, it will pass up the xylem of the stem.

Transpiration and movement of water: http://www.phschool.com/science/biology_place/l abbench /lab9/xylem.html

This website shows a diagram of how water moves up through the plant.

http://www.neok12.com/Plants.htm

This video shows plant transport and provides some interactive quiz games.

Investigation: water uptake by roots

Aim : To measure the uptake of water by roots

Apparatus

  • Plastic 2 litre Coke bottle
  • water
  • soil
  • scissors
  • measuring scale
  • tree or plant cuttings
  • ruler

Method

  1. Remove the label from the Coke bottle. Cut the top of the bottle off 20cm from the bottom of the bottle. Poke holes in the bottom of the bottle for drainage.Hold the plant cutting in the container while you fill the container with soil. Leave one or two leaf buds about 5cm above the soil.
  2. Weigh the container to get the total weight of the bottle, soil and plant.
  3. Water the plant with enough water so that it starts to run out of the bottom of the bottle through the holes.
  4. Weigh the container again after the water has stopped running out and subtract the total weight in step 2 from the weight in step 4 to get the weight of thewater. 1 litre of water is equal to 1 kilogram of water, therefore you can work out exactly how much water is in the container.
  5. Set the containers by the window where they will receive enough sunlight. Wait for the leaves to start growing (1-3 weeks).
  6. After the leaves are growing, weigh the containers every 1-3 days for 3 weeks. Subtract the new weight from the weight calculated in step 4. The new number isthe amount of water that the plant is using. Water the plant as necessary (when the soil becomes dry), but remember to reweigh the container when you add morewater so that you can still tell how much water the plant is taking up.
  7. Draw a graph of the amount of water the plant is using. The X-axis should show the number of days since the beginning of the experiment and the Y-axis shouldshow the amount of water that the plant has used.

Question on investigation – Surely as the plant grows it forms new leaves etc which have mass? How do we subtract the mass of the new leaves to prevent

this making the mass of the entire container inaccurate in terms of how much mass is

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Source:  OpenStax, Siyavula: life sciences grade 10. OpenStax CNX. Apr 11, 2012 Download for free at http://cnx.org/content/col11410/1.3
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