Module 3.3 - Transport in Plants

Question 1

Why do plants need transport systems? (3)

Answer 1

• Oxygen and glucose is required to internal/ underground organelles that do not photosynthesis
• Size: move water up and down the plant from the roots to the leaves of large trees
• Have a relatively low SA: V ratio therefore cannot rely on diffusion which can’t sustain the plant

Question 2

What is the Structure of the vascular system of roots, stems and leaves include xylem vessels, sieve tube elements and companion cells? (3)

Question 3

Xylem vessels? (3)

Answer 3

• Non-living Long hollow structures made by several columns of cells fusing together end to end
• Xylem vessels are lignified providing mechanical strength
• Un-lignified pits allow water to move out the vessel

Question 4

Sieve tube elements? (3)

Answer 4

• Living long hollow structures made by several columns of cells fusing together end to end
• Areas between the cells are sieve plates which allow phloem contents to flow through
• Companion cells act as a life support system for sieve tube cells

Question 5

Xerophytes? (7)

Answer 5

• A thick cuticle – minimise water lose by transpiration
• Sunken stomata – reduces air movement, creating humid microclimate, decreasing diffusion concentration gradient
• Reduced stomata - minimise water lose by transpiration
• Reduced leaves - minimise water lose by transpiration
• Hairy leaves – humid microclimate
• Curled leaves – humid microclimate
• Longer roots – more water from soil

Question 6

Hydrophytes (5)

Answer 6

• More stomata – maximise gas exchange for photosynthesis
• Wide flat leaves – more area to catch light for photosynthesis
• Small roots – water can diffuse directly into the stem
• Thin cuticle – conservation of water is not an issue
• Reduced structure – water supports the plant

Question 7

What is the process for transpiration? (4)

Answer 7

• Water enters the roots of the plant by osmosis and is transported up in the xylem until is reaches the leaves
• Moves into the spongy mespophyll of cells through osomosis
• Evaporotates from the cell walls via the apoplast pathway
• Water vapour then moves out the cell through the stomata along a diffusion gradient

Question 8

What are the environmental factors that affect the rate? (5)

Answer 8

• Light intensity – at greater intensity the higher the transpiration rate
• Humidity – higher humidity decreases the rate of diffusion
• Water availability
• Air flow – greater air flow allows water vapour to be carried away, increasing diffusion gradient
• Temperature

Question 9

How is water transported into the plant? (4)

Answer 9

• Root hair cells are the exchange surfaces in plants where water is taken into the body of the plant form the soils
• Has a large SA:V ratio
• Each hair has a thin surface layer therefore diffusion and osmosis can take place quickly
• The water potential of soil water is lower than inside the root hair cell, therefore water moves into the root hair cell via osmosis

Question 10

The symplast pathway? (3)

Answer 10

• The root hair cell has a higher water potential than the next cell along, therefore water moves from the root hair cell to the next cell along
• This process continues until the xylem is reached
• As water leaves the root cell, water potential falls again, maintaining osmosis gradient

Question 11

The apoplast pathway (2)

Answer 11

• Water moves through the cellulose cell wall into the xylem, pulling more water molecules into the apoplast due to cohesive forces
• This creates a continuous flow of water through the cell wall

Question 12

Transpiration and translocation