• what is the significance of transpiration?
• what are the disadvantages of transpiration?

the method by which plants lose water in the form of water vapour through the aerial parts of the plant.

types of transpiration

stomatal transpiration

• takes place when stomata are open

• stomatal movement depends on the turgor pressure of the guard cells

• when cells are turgid [accumulaiton of k] the stomata are open

• when the guard cells lose water and become flaccid, the stomata close.

  

cuticular transpiration

epidermis of the leave secretes a waxy layer which is not permeable to water. its molecules absorb water by imbibition and the water is then slowly lost to the atmosphere

• herbaceous plants transpire by this method [50%]

• through the day and night

  

lenticular transpiration

stems of woody plants have openings on their surface known as lenticles.

• this occurs both in the day and at night

  

conditions influencing transpiration

1. sunlight ☀️

the degree of stomatal opening varies on the intensity of sunlight. on a sunny day the rate of transpiration is at its maximum

1. temperature of the air 🌡

when the temperature is high, the rate of transpiration is high as water will evaporate more easily.

1. humidity 🥵

when the atmosphere is dry, its capacity to hold air is much more in comparison to when it is humid.

1. wind or air movement 💨

transpiration is more when the wind velocity is high. this is because water vapour is quickly swept away.

adaptations of plants

• morphological- leaves are reduced to pines, leaves are folded or rolled up, may be sheed
• anomatical- stomata are sunken in nerium, thick waxy cuticle appears on evergreen trees.

experiments

#1 to show that water is given off by the aerial parts during transpiration

a colourless liquid is observed on the periphery of the glass and blue cobalt chloride paper turns pink [confirms the presence of water vapour]

• a polythene sheet covers the soil
• a control can be shown when there are no aerial parts of the plant

#2 to demonstrate that the lower surface of a dorsiventral leaf transpires more

vaseline is applied on leaf a both sides

only bottom- leaf b

on the top- leaf c

and d no vaseline

• transpiration is least where both surfaces are covered with vaseline
• after that the second least shrivelled is the one where vaseline was applied on the underside
• we can conclude that the lower surface has more stomata & greater transpiration occurs

#3 to measure the rate of transpiration in a leafy shoot and consequently knowing the rate of transpiration

• air bubble travels through the arm of the potometer.
• we can conclude that the plant absorbs water from the stem as the plant loses water by transpiration

precautions

• the potometer should be left still before taking readings again
• the light intensity must be constant for all readings

limitations

• can only measure the rate of transpiration by measuring the rate of absorption of water. which may not be accurate.
• only uses very small volumes of water.

guttation

released from pores called hydrathodes

conditions favouring the same-

• excess water in the plant
• low temperature
• all conditions that inhibit transpiration