Transpiration

Question 1

Name the plant tissue shown in the photograph

Answer 1

Xylem

Question 2

Name the chemcial found in the ring labelled A and describe its function

Answer 2

Lignin

Waterproof and embedded in the xylem wall to prevent water loss

Structural - prevent xylem imploding when under high tension

Question 3

Describe how water is moved through a plant by cohesion tension theory

Answer 3

Water evaporated from the mesophyll cells
Reduces the water potential in cells
Water is drawn out of xylem vessels by osmosis
Creates tension between water molecules held together by hydrogen bonds
Water is pulled up the xylem vessels

Question 4

The diameter of a tree is less during the day is than it is at night.

Explain how this supports cohesion tension theory

Answer 4

Water evaporates from surface of mesophyll cells and diffuses through stomata
Creates tension in the column of water in xylem vessels

This tension causes the xylem vessels to be pulled inwards

Cuasing the girth of the tree to decrease

Question 5

Give 4 adaptations shown by xerophytes

Answer 5

Stomata in pits
Rolled leaves
Thick waxy cuticle
Hairs on surrounding stomata
Reduced number of stomata
Spines/fewer leaves

Question 6

Why do some xerophytes have hairs on their leaves?

Answer 6

Trap layer of water vapour around leaf (boundary layer)
Increases water potential around leaf
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of the leaf

Question 7

Why do some leaves have stomata in pits?

Answer 7

Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf

Question 8

Why do some leaves have a thick waxy cuticle?

Answer 8

Hydrophobic waxy substances impede movement of polar water molecules
Increases diffusion distance
Decreases diffusion/transpiration of water molecules

Question 9

Why do some leaves have rolled leaves?

Answer 9

Traps water vapour around the stomata
Decreases water potential gradient between internal and external environment of leaf
Reduces diffusion/transpiration of water out of leaf

Question 10

Why do some plants have spines or fewer leaves

Answer 10

Reduced surface area
Reduced water loss by diffusion/transpiration

Question 11

Why might the rate of water uptake by a plant NOT be the

same as the rate of transpiration?

Answer 11

Water used for turgidity
Water used in photosynthesis
Water used in hydrolysis
Water produced by condensation reactions
Water produced by respiration

Question 12

Name this piece of apparatus

Answer 12

Potometer

Question 13

In which direction would you expect the bubble to move?

Answer 13

To the left

Towards the plant

Question 14

List 4 environmental factors that increase the rate of transpiration

Answer 14

Increased temperature
Increased wind/air movement
Increased light intensity
Decreased humidity

Question 15

Explain how an increase in temperature increases the rate of transpiration

Answer 15

Increased rate of evaporation of water
Increased rate of diffusion due to increased KE of water molecules out of leaf

Question 16

Explain how an increase in wind increases the rate of transpiration

Answer 16

Air movement removes water molecules that have left the leaf
Maintains a steep diffusion gradient between internal and external surface of the leaf.
More water moves by diffusion through the stomata

Question 17

Explain how an increase in light intensity increase the rate of transpiration

Answer 17

Stomata open to allow carbon dioxide to enter the leaf for photosynthesis
Increases number of water molecules moving through stomata and out of the leaf

Question 18

Explain how an increase in humidity decreases the rate of transpiration

Answer 18

Increased number of water molecules in external atmosphere.
Reduces the water potential gradient between the internal and external environment
Decreases diffusion of water out of the leaf

Question 19

How would you calculate the surface area of a leaf?

Answer 19

Draw round leaf on a piece of graph paper.
Count the number of squares inside the outline
Multiple by 2 (top and bottom surface of leaf)

Question 20

Namre the type of plant that has leaf adapations shown on the diagram

Answer 20

Xerophyte

Question 21

A potometer can be used to calculate the rate of water uptake by a shoot .

List 3 measurements needed to calculate the rate of water uptake

Answer 21

Distance travelled by the air bubble
Time taken
Diameter/radius of the capillary tube lumen

Question 22

Name the tissue used to transport water in the stem and leaves of a plant

Answer 22

Xylem

Question 23

Why is a mass transport system needed for the movement of water in a plant

Answer 23

Maintains the diffusion gradient needed to bring water to and from the cell membrane of individual cells
Surface area to volume ratio too low to deliver the water required by every cell directly from the environment

Question 24

Describe how you woudl set up this piece of apparatus

Answer 24

Cut the plant stem under water - to prevent air bubbles entering the xylem

Push plant stem into bung and keep the stem in water at all times

Submerge all the apparatus in a bowl of water and eliminate any air bubbles

Fill the reservoir with water

Attach the bung to the potometer

Remove from bowl of water nd chekc for leaks