transport in plants

Question 1

xylem

Answer 1

Tissue that transports water in the stems and leaves of a plant

Question 2

cohesion tension theory

Answer 2

How water moves up the xylem against gravity via the transpiration stream

Question 3

Explain how the cohesion tension theory works

Answer 3

Water evaporates from the leaves via the stomata due to transpiration

this reduces water potential in the cell and increasing water potential gradient

Water drawn out of xylem

Creating tension

Cohesive forces between water molecules pull water up as a column

Water lost enters the roots via osmosis

Water is moving up, against gravity

Water is also adhesive so sticks to the walls of the xylem

Question 4

Phloem

Answer 4

Tissue that transports organic substances in plants such as glucose.

Question 5

Transolcation

Answer 5

Movement of solutes from source to sink

Question 6

What happens at the source

Answer 6

High concentration of solute

Active transport loads solutes from companion cells to sieve tubes of the phloem

Lowering the water potential inside the sieve tubes

Water enters sieve tubes by osmosis from xylem and companion cells

Increasing pressure inside sieve tubes at the source end

Question 7

What happens at the sink

Answer 7

-Low concentration of solute

• Solutes removed to be used up e.g. enzymes hydrolyse
• Increasing the water potential inside the sieve tubes
• Water leaves tubes via osmosis
• Lowering pressure inside sieve tubes

Question 8

Mass flow

Answer 8

-Pressure gradient from source to sink

• Pushes solutes from source to sink
• Solutes used or stored at the sink e.g. respiration

Question 9

Adaptations of the phloem

Answer 9

1. Sieve tube elements
   ● No nucleus / few organelles → easier flow of organic substances
2. Companion cells
   ● Many mitochondria → high rate of respiration to make ATP for active transport of solutes

Question 10

Adaptation of xylem`

Answer 10

● Cells contain no cytoplasm / nucleus → easier water flow / no obstructions
● Thick cell walls with lignin → provides support / withstand tension / prevents water loss