Transpiration occurs mainly through the leaves. Image credit

Transpiration occurs mainly through the leaves. Image credit

ZIMSEC O Level Combined Science Notes: Investigating water loss in plants

Aim: To determine how plants loose their water

Materials: plants or branches from plants, weighing balance, containers, water, oil/Vaseline.

investigating water loss in plants


  1. Select three small, leafy branches from a plant. Make sure the branches are roughly the same size.
  2. Cut the branches and put the stems in water immediately
  3. Half fill three containers with water.
  4. Place one stem with all its leaves into a container labeled A
  5. Place another branch with all the leaves removed in a container labeled B
  6. Place a third branch in with the stem covered in vaseline/oil into a container labeled C
  7. Place a thin film of oil over the surface of the water in each container.
  8. Weigh each container and record the masses in a table
  9. Weigh the containers at regular intervals over the course of a few days
  10. Calculate the percentage loss in weight for each branches


  • The branch in container A losses the most water followed by the plant in container labeled C.
  • There is hardly any change in the mass of container B
  • This is because water is lost via the leaves through the process of transpiration
  • The plants in A and B have all their leaves so they loose the most water
  • This is because 95% of the water that enters into plants is lost through the leaves via the process of transpiration
  • Very little water is lost through the stems because there is hardly any difference between the water lost by plants A and C
  • The oil layer minimises water loss through the process of evaporation


  • Most water is lost through the leaves
  • This is called transpiration
  • Very little water is lost through the stems

To access more topics go to the Combined Science Notes page.

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