Rate of transpiration

Question 1

What are the 2 types of factors effecting rate of transpiration?

Answer 1

Plant physiology and environmental

Question 2

What are plant physiology factors?

Answer 2

Number, size and position of stomata, number of leaves and presence of cuticle

Question 3

What are environmental factors?

Answer 3

Air movement/wind speed, relative humidity, temperature, light, soil water availability and carbon dioxide levels

Question 4

What is light used for?

Answer 4

As an energy store for photosynthesis

Question 5

How does light affect stomata?

Answer 5

Stomata open in light for gas exchange to get carbon dioxide in and oxygen out

Question 6

What is te effect of increase is light intensity?

Answer 6

More stomata open

Question 7

What is the effect of rate of transpiration with increased light intensity?

Answer 7

Diffusion of water vapour out increases so rate of transpiration increases

Question 8

How is light intensity drawn?

Answer 8

It plateaus at a certain point as maximum rate of photosynthesis is reached

Question 9

What is relative humidity?

Answer 9

Total amount of water vapour in the air of possible max water vapour air can hold

Question 10

What is the effect of increased relative humidity?

Answer 10

More water vapour molecules therefore remain in air spaces inside the leaf

Question 11

How does increased humidity affect rate of transpiration?

Answer 11

Transpiration rate decreases

Question 12

What is the effect of increased temperature?

Answer 12

Increases kinetic energy so they infuse out more quickly

Question 13

What is the effect of increased kinetic energy?

Answer 13

Increases rate of evaporation of after vapour molecules from spongy mesophyll cells into air spaces as the temperature increases, energy provided to break hydrogen bonds

Question 14

What is the effect of temperature on relative humidity?

Answer 14

Temperature increases which increases max saturation of the air with water vapour molecules

Question 15

What is still air?

Answer 15

Leaf/stomata has a layer of still air trapped by shape/hairs

Question 16

What is the effect of still air?

Answer 16

Water vapour molecules diffuse out of the leaf and are trapped in still air so water vapour around stomata increases and air becomes more saturated

Question 17

What is the effect of saturated air?

Answer 17

It decreases the water vapour diffusion gradient

Question 18

How does air movement affect transpiration?

Answer 18

Increased air movement increases the rate of transpiration by maintains diffusion gradient

Question 19

How do you measure transpiration?

Answer 19

A potometer

Question 20

What is a potometer?

Answer 20

A device used for measuring the rate of water uptake of a leafy shoot

Question 21

What is the cause of water uptake?

Answer 21

99% of water taken up is lost by transpiration

Question 22

What is the stages of setting up a potometer?

Answer 22

1. A cut plant stem is sealed into the potometer using a rubber bung.
2. Air bubble is introduced to capillary tube and the distance the bubble travels shows how much water has been taken up

Question 23

How can potometers measure effects on rate of transpiration

Answer 23

They can be set up in different environmental conditions

Question 24

What are issues with setting up a potometer?

Answer 24

Air can enter the stem when its cut or air leaks in tubing

Question 25

What are ways of reducing air entering set up?

Answer 25

Cut stem at angle under water and join to rubber tubing under water, seal the join between rubber bung and tubing with vaseline and use waterproof tape to seal the join between plant stem and rubber tubing

Question 26

How can rate of transpiration be calculated?

Answer 26

By timing how long it takes the bubble of air to move a set distance (or vice versa)

Question 27

How a the volume of water be calculated?

Answer 27

V = π x r² x l

Question 28

Why does the potometer only gives an estimate of the rate of transpiration?

Answer 28

It measures water uptake and not all water taken up is lost as some is used in photosynthesis or making cells turgid