Transport In Plants

Question 1

Structure of xylem

Answer 1

F: transport water and ions in plants
1) long tube like structures formed from dead cells joined end to end
2) no end walls = create an uninterrupted tube allow water to pass up in middle easily = increase sA for water to transport
3) thick cell wall made of lignin(a sugar) = keeps vessels rigid and strengthen

Question 2

Cohesion tension theory in transpiration

Answer 2

1) water evaporates from leaves at the top
2) creates tension = causes upwards pull on water column
3) as water pass along= tension pulls in xylem walls making vessel narrower= increase action of capillarity
4) cohesion causes polar water molecules to stick together in the vessel tube = allow the continuous column of water to move up the continuous tube

Question 3

What is the effect on diameter of xylem vessel causes it to change ?

Answer 3

• tension of water = in day more transpiration = more tension= narrow diameter = allow continuous flow along the column
• night= less transpiration/ tension = diameter increase = limit water loss

Question 4

What is the effect of root pressure on transpiration ?

Answer 4

• more water moves into xylem by osmosis from soil = increase volume of vessel =PRESSURE increase TOO inside the root = higher pressure forces water moves upwards= faster transpiration rate

Question 5

4 factors affect transpiration Rate

Answer 5

• light intensity
• temperature
• humidity
• wind /air flow

Question 6

How does light intensity affect transpiration ?

Answer 6

• the more light = faster rate
• stomata opens to allow CO2 in for photosynthesis, when it’s dark, stomata closes to limit water loss= so less transpiration when less light

Question 7

Effect of temperature on rate of transpiration ?

Answer 7

• higher temperature = faster rate
• warmer causes molecules gain more KE to vibrate around = causes quicker evaporation from inside leaf
  = cause an increase in w.p gradient between inside and outside of leaf, causes more water to evaporate diffuse out of the leaf down the conc.grad

Question 8

How does humidity affect rate of transpiration ?

Answer 8

• lower the humidity = drier = faster rate
• negative correlation = if air is dry= causes increase in w.p grad between leaf and air = water easier to diffuse out by osmosis high to low conc = increase transpiration

Question 9

How does wind affect transpiration ?

Answer 9

• more wind= more transpiration= increase rate
• lots of air movement causes water molecules to vibrate more around the stomata = increases w.p gradient= faster rate

Question 10

Explain why diameter of branch decreased when rate of water flow increase ? (2)

Answer 10

1) increase transpiration = produce a greater tension
2) reduce adhesive forces between xylem and water

Question 11

Describe and explain the changes in rate of water flow in branch from day to night hours (3)

Answer 11

1) rate of flow increases to max at mid day then decreases
2) because increase transpiration
3) transpiration creates tension= increases transpirational pull = allow water to pull up of continuous column of xylem