Transpiration

what are 6 factors that effect the rate of transpiration (and do they increase it or decrease it)?

• high wind speed - increase

• high humidity - decrease

• high temperature - increase

• low water supply - decrease

• larger leaves (more stomata) - increase

• thicker waxy cuticle - decrease

how would we set up an experiment to change the conditions for high wind speed, high humidity, high temperature and low water supply?

• high wind speed - fan at different settings

• high humidity - clear plastic bag/box over plant and spray with water

• high temperature - heater at different settings

• low water supply - water it less

what is the explanation for high wind speed increasing the rate of transpiration?

• Moving air sweep away the water vapour outside the stomata, increasing the water vapour potential gradient between inside and outside the leaf.

• An increases in wind speed therefore increases the rate of transpiration

what is the explanation for high humidity decreasing rate of transpiration?

• An increase in humidity means there is more water vapour in the air. This decreases the difference in water vapour potential between inside and outside the leaf

what is the explanation for high temperature increasing rate of transpiration?

• As temperature increases, water molecules have more kinetic energy so there is an increased rate of diffusion and evaporation from the cell surfaces, leading to an increased rate of transpiration

what is the explanation for low water supply decreasing rate of transpiration?

• Shortage of water leads to wilting and closure of stomata, thereby decreasing the rate of transpiration

what is the explanation for larger leaves increasing the rate of transpiration?

• More stomata available for transpiration to occur from

what do potometers do?

measure the rate of transpiration

how is the rate of transpiration measured?

• The way of measuring the rate of transpiration is to measure the rate of water uptake

• This is an approximation as not all of the water taken up by the plant is lost in transpiration (99% is lost so it is a good approximation)

• It is also very difficult to measure the volume of water evaporating off a leaf's surface

• Rate of water uptake = distance moved by air bubble (mm) / time taken (s)

• this can be seen using a potometer

what are the 2 types of potometer called?

• volume (bubble) potometer

• mass potometer

why is a control used when using a mass potometer?

the control will show any mass that is lost due to the plant

why when using a mass potometer will we out a polythene bag over the pot?

to stop evaporation of water from the soil or surface of water