OESWTE: Mass transport in plants

Question 1

What does the xylem transport?

Answer 1

Water and mineral ions in solution.

Question 2

What does the phloem transport?

Answer 2

Organic substances like sugars.

Question 3

Describe the structure of xylem vessels (4 points) :

Answer 3

• Very long
• Tube-like structure
• No end wall between cells
• Made from dead cells

Question 4

What are the two processes by which water moves up a plant?

Answer 4

Cohesion
Tension

Question 5

Explain how cohesion and tension allow water to move up a plant:

Answer 5

1) Water evaporates from leaves at the top of the xylem (transpiration).
2) Tension is created, pulling more water into the leaf
3) Cohesive water molecules stick together, allowing the whole column of water in the xylem (from leaves to roots) to be pulled upwards
4) Water enters the stem through the roots

Question 6

What is transpiration?

Answer 6

The evaporation of water from a plants surface.

Question 7

Where does water evaporate from?

Answer 7

Moist cell walls

Question 8

Where does water accumulate before evaporation?

Answer 8

Spaces between cells in the leaf

Question 9

What are the 4 main factors that affect the rate of transpiration?

Answer 9

• Light intensity
• Temperature
• Humidity
• Wind

Question 10

How does light intensity affect the rate of transpiration?

Answer 10

• The lighter it is the faster the transpiration rate
• Stomata open when it is light to let CO2 in for photosynthesis, and close when it is dark.

Question 11

How does temperature affect the rate of transpiration?

Answer 11

• The higher the temperature the faster the transpiration rate
• Warmer water molecules have more energy so they evaporate faster.
• Increases water potential gradient

Question 12

How does humidity affect the rate of transpiration?

Answer 12

• The lower the humidity the faster the transpiration rate.
• If the air around a plant is dry, the water potential gradient between the air and leaf is increased.

Question 13

How does wind affect the rate of transpiration?

Answer 13

• The windier it is the faster the transpiration rate
• Air movement blows away water molecules from around the stomata.
• Increases the water potential gradient

Question 14

Explain the structure of the phloem (3 points):

Answer 14

• Sieve-like tube structure
• Living cells
• Thin layer of cytoplasm between cells

Question 15

What is translocation?

Answer 15

The movement of solutes to where they are needed in a plant.

Question 16

Where are solutes mainly produced?

Answer 16

Leaves

Question 17

Where are solutes mainly used?

Answer 17

Meristems in roots, stems and leaves