Mass Transport In Plants

Question 1

What is transpiration

Answer 1

The loss of water vapour in the stomata via evaporation

Question 2

What are the 4 factors of transpiration

Answer 2

1.light=more light causes more stomata to open
2.temperature=more kinetic energy so faster moving molecules so more evaporation
3.humidity=more water potential in the air so water potential more outside leaf- reduces water potential gradient
4.wind=more wind blows humid air containing water vapour maintains water potential gradient

Question 3

Describe the cohesion theory of water transporting in the xylem

Answer 3

-water molecules lost from leaf because of transpiration and diffusion of water through stomata
-lowers water potential of leaf cells
-water pulled from xylem creating tension
-water molecules cohere together by hydrogen bonds
-forming continuous water column
-adhesion of water molecules to walls of xylem

Question 4

Describe root pressure and how that forces water upwards

Answer 4

-as water moves into the root by osmosis it increases volume of liquid inside the root
-pressure in the root increases forcing water above it upwards

Question 5

What does the xylem transport in plants

Answer 5

-water

Question 6

What does the phloem transport in plants

Answer 6

-organic ions ie sucrose

Question 7

What are the 2 key cells in the phloem

Answer 7

-sieve plates
-companion cells

Question 8

Describe the sieve plate elements of the phloem

Answer 8

They’re living cells with no nucleus to provide metabolic support

Question 9

Describe the companion cells elements of the phloem

Answer 9

-beside sieve plates to provide metabolic support
-provides ATP for active transport of organic ions

Question 10

Describe the mass hypothesis for the mechanism of translocation in plants

Answer 10

-in the source of the leaf sugars are actively transported into phloem by companion cells
-this lowers water potential of sieve cells and the tube
-water enters by osmosis
-this creates an increase in hydrostatic pressure causing mass movement towards sink and root
-the sugars used are converted in root for respiration

Question 11

How is transpiration measured in xylem

Answer 11

Using a potometer

Question 12

Using understanding of mass flow hypothesis to explain how pressure is created in phloem tube

Answer 12

-sucrose actively transported in phloem
-lowering water potential
-from the xylem water is transported In the phloem by osmosis

Question 13

What are the 2 methods of investigating translocation

Answer 13

-ringing experiments
-tracer experiments

Question 14

Describe the tracer experiment

Answer 14

-using radioactive 14C in carbon dioxide the flow of sugars can be traced within plant
-the carbon dioxide is absorbed over time into the Plant by photosynthesis
-this allows stems to be viewed under a x ray film and sugars turn into black
-shows sugars move only in phloem plant

Question 15

Describe the ringing experiment of translocation

Answer 15

-a ring of Bark is removed from tree removing phloem
-trunk swells above the removed section- showing the tissue above swells
-shows that once phloem is removed sugars can’t be transported