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TRANSPIRATION

TRANSPIRATION. What is Transpiration?. An evaporation of water in the form of water vapour from the surface of the plant to the atmosphere Where does transpiration take place?. Transpiration. Transpiration mainly takes place through openings on leaves – STOMATA

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TRANSPIRATION

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  1. TRANSPIRATION

  2. What is Transpiration? • An evaporation of water in the form of water vapour from the surface of the plant to the atmosphere • Where does transpiration take place?

  3. Transpiration • Transpiration mainly takes place through openings on leaves – STOMATA • If the stomata is opened, then water vapour will be lost into the atmosphere • In some cases, transpiration also takes place through the lenticels and cuticles

  4. Transpiration • A thin film of water covers each mesophyll cell

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  6. Transpiration • A thin film of water covers each mesophyll cell • There are numerous air spaces between the mesophyll cells

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  8. Transpiration • A thin film of water covers each mesophyll cell • There are numerous air spaces between the mesophyll cells • Water evaporates from the film of water surrounding the mesophyll cells into the air spaces (and eventually diffuses out of the stomata into the atmosphere)

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  10. Transpiration 4) As water diffuses out of the cell, the water potential within the cell will decrease. Due to OSMOSIS, water from adjacent cells will be drawn into the cell to replace the water loss These adjacent cells will in turn draw water from other neighboring cells

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  12. Transpiration 5) Water is drawn from the XYLEM vessels (in the veins) into the neighboring mesophyll cells There will be a water potential difference between the xylem vessels and the mesophyll cells. As water is drawn from the xylem vessels, a suction pressure will develop and this pressure will pull water up the xylem vessels from the roots to the leaves

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  14. Transpiration • The pressure that allows water to be pulled from the roots to the leaves in the xylem vessels is called TRANSPIRATION PULL • It allows the transportation of water and minerals in plants

  15. Investigation #1:Studying the loss of water by a plant into the atmosphere

  16. polythene bag Procedure

  17. Discussions • What is the purpose of enclosing the pot and lower part of the plants with a polythene bag? Ans: The polythene bag prevents evaporation of water from the soil, and also prevents vapour released by soil microorganisms from affecting the result of the experiment

  18. Discussions 2) What do you think will happen in the two set-ups after 2 hours? Ans: Water would be found condensed on the bell jar with the leafy plant inside

  19. Discussions 3) How can you show that it is water? Ans: We can use anhydrous cobalt chloride paper to test it. It will turn the paper from blue to pink. Alternatively, we can use anhydrous copper sulphate. Water will turn it from white to blue

  20. Discussions 4) Why is it better to use forceps instead of fingers to hold cobalt chloride paper? Ans: It is to avoid moisture on our fingers from being absorbed by the cobalt chloride paper

  21. Discussions 5) How would you explain the results of this experiment? Ans: Transpiration occurs in plants through their leaves

  22. I have no trouble absorbing sunlight, but I just keep losing and losing water. Is there any way that I can prevent excessive water loss?

  23. Adaptations to Prevent Water Loss 1) Waxy layer of cuticle on the leaf’s outer surface of the epidermis

  24. Adaptations to Prevent Water Loss • A waxy layer of cuticle covers the outer surface of the epidermis • More stomata are present in the lower epidermis than the upper epidermis • Guard cells control the closing and opening of stomata

  25. Stomata • Stomata are pores in the epidermis where gaseous exchange takes place during photosynthesis (or respiration)

  26. Stoma Guard cell Epidermal cell

  27. Opened Stoma Closed Stoma

  28. Each stoma is surrounded by two guard cells which contain chloroplasts It is kidney-shaped The inner wall is thicker than the outer wall Guard cell Stoma Guard Cells

  29. How Guard Cells Control the Size of Stoma • Guard cells contain chloroplasts that carry out photosynthesis in the presence of light. Carbohydrates are formed and thus lower the water potential of the cell • Water enters the guard cells from adjacent cells by osmosis and guard cells become turgid

  30. How Guard Cells Control the Size of Stoma • The inner wall is thicker than the outer wall, so the cell stretches to the outer side and stoma is opened • At night, there is no photosynthesis. Guard cells become flaccid and so they return to the original shape and stoma is closed

  31. Distribution of Stomata in Leaves

  32. Distribution of Stomata in Leaves 1) Normal Plants - Mainly on the lower surface of plants 2) Floating plants - Mainly on the upper surface of plants - Leaves may also have air sacs to keep them afloat. These sacs can be used in gaseous exchange

  33. Distribution of Stomata in Leaves 3) Submerged Aquatic Plants - No stomata (not required since gaseous exchange can be carried out by diffusion though the leave surface) - No cuticle (the primary function of cuticle is to prevent excess water transpiration which is not present in aquatic plants)

  34. Distribution of Stomata in Leaves 4) Plants in dry and hot conditions - usually have much less stomata to reduce the amount of water loss

  35. Investigation #2:Investigating stomatal distribution in a leaf by using cobalt chloride paper

  36. cobalt chloride paper sellotape Which piece of cobalt chloride paper will turn pink first? Ans: The piece of cobalt chloride paper attached to the lower epidermis of the leaf will turn pink first.

  37. Investigation #3: Comparing the abundance of stomata on the upper and lower surfaces of a leaf

  38. Introduction to Investigation • This investigation allows us to compare the amount of stomata present on the upper and lower surfaces of a leaf by putting the leaf in hot water and observing the amount of bubbles appeared

  39. forceps hot water leaf Procedure

  40. Discussions 1) Which surface has more air bubbles coming off? Ans: There should be more air bubbles appearing on the lower surface of the leaf

  41. Discussions 2) Why do air bubbles appear on the leaf surfaces? Ans: Air in the air spaces between the mesophyll cells in leaf expands on heating and passes out through stomata of the leaf, forming air bubbles

  42. Discussions 3) What does the result show? Ans: The result shows that more stomata are present on the lower epidermis of a leaf

  43. Investigation #4: Comparing the abundance of stomata on the upper and lower surfaces of leaves by weighing

  44. Introduction to Investigation • As water is lost by evaporation, the weight of a detached leaf will decrease with time. In this investigation, leaves will be treated differently (with vaseline) and the loss in weight will then be compared among the leaves.

  45. Procedure A B C D Smear with vaseline on both surfaces of the leaf Smear with vaseline on lower surface of the leaf only Smear with vaseline on upper surface of the leaf only Do not apply vaseline on the leaf

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