3.4.8- Xylem

Question 1

Steps in investigating transpiration rate

Answer 1

1- Cut a shoot and place inside the potometer whilst underwater
2- Remove the end of the capillary tube from the water beaker
3- Allow air bubble to form in the capillary tube
4- Place the capillary tube back into the water
5- Mark the starting position of the air bubble and start the stopwatch
6- Record the distance travelled by the air bubble in a given time period
7- Calculate rate of bubble movement

Question 2

How is the transpiration rate calculated?

Answer 2

Rate of bubble distance

Question 3

Describe the Cohesion tension theory of water transport in the xylem (5)

Answer 3

Water lost from leaf because of transpiration/ evaporation of water

Lowers water potential/ pressure of mesophyll/leaf cells

Water pulled up xylem (creating tension)

Water molecules cohere / stick together by hydrogen bonds

forming a continous water column

Adhesion of water molecules to walls of xylem

Question 4

Describe the functions of the xylem vessel (3)

Answer 4

Transports water
Transports minerals
Structural support

Question 5

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves (6)

Answer 5

• In root active transport by endodermis
• of ions salts into xylem
• Lower water potential in xylem so water enters by osmosis
• Creates cohesion/ tension H bonds between water molecules = adhesion of water
• Creates continuous water column

Question 6

List 4 factors that affect the rate of transpiration and explain how each affects the rate (4)

Answer 6

Temp- higher = more transpirtaion
Light- more light increaeses transpiration
-Humidity= less means more transpiration as increase gradient
-Wind- more wind means more transpiration

Question 7

Describe feauture of the xylem that enables the steam to pass from the heated end of the stem to the cut end (2)

Answer 7

No end wall= continuous

No organelles in way

Question 8

Define the term transpiration (3)

Answer 8

Evaporation/loss of water vapour

from plant/leaf

via stomata CREDIT loss through cuticle

Question 9

Suggest why a bunch of flowers may survive longer if the ends of the stems are removed immediately before the flowers are placed in water (1)

Answer 9

air bubbles

Question 10

Apart from the leaf pores, name 1 other part of the leaf from which water may be lost (1)

Answer 10

epidermis

Question 11

Explain why the plugging of xylem vessels will result in the leaves of the upper branches turning yellow (2)

Answer 11

No movement of water

Less chlorophyll