Plant transport

Question 1

What is the apoplast pathway?

Answer 1

Cell wall to cell wall without entering the cell cytoplasm

Question 2

What is the symplast pathway?

Answer 2

Moves into the cytoplasm by osmosis across the plasma membrane via the plasmodesmata to the xylem

Question 3

What is the vacuolar pathway?

Answer 3

Move via vacuoles but has to cross plasma membranes as resistance is to high. Little water is moved

Question 4

What is the function of the apoplast, symplast and vacuolar pathway?

Answer 4

Move water across a root

Question 5

What are tracheids?

Answer 5

Dead, tube-like cells with a tapering end

Question 6

What is the function of tracheids?

Answer 6

Transportation of water and minerals

Question 7

What four cells does the xylem contain?

Answer 7

Vessels, tracheids, fibres and parenchyma

Question 8

Where are tracheids mostly found?

Answer 8

In gymnosperm and lower angiosperm

Question 9

What is the structure of tracheids?

Answer 9

Thick lignified wall. No nucleus or cytoplasm

Question 10

What is the structure of vessels in the xylem?

Answer 10

Long cylindrical structure with a tube like appearance and lignified walls

Question 11

Where are vessels mostly found in the xylem?

Answer 11

In angiosperms

Question 12

What are vessels in the xylem?

Answer 12

Dead, large central cavity and have no cytoplasm or nucleus

Question 13

What are fibres in the xylem?

Answer 13

Dead cells with a lignified wall and a central lumen

Question 14

What is the role of fibres in the xylem?

Answer 14

Provide mechanical support

Question 15

What is the structure of the fibres in the xylem

Answer 15

Dead cell with a lignified wall and a central lumen

Question 16

What is the role of parenchyma in the xylem?

Answer 16

Assist in the short distance transportation of water and stores starch and fat

Question 17

What is the structure of the parenchyma in the xylem?

Answer 17

Only living cells in the xylem

Question 18

What is the cohesion-tension theory of transpiration?

Answer 18

1. Water uptake primarily occurs by osmosis from soil into root hair cells
2. Moves via symplast/vacuolar pathways as casparian band prevents movement through apoplast pathway
3. Water enters xylem via cohesion and osmosis
4. Water drawn up xylem through cohesion and adhesion due to the state of tension caused by transpiration
5. Water leaves the xylem via vessels (osmosis) into the leaf
6. Water moves through the leaf tissues via via the apoplast, vacuolar and symplast pathways
7. Water evaporates from surface of epidermal cells and diffuses into the atmosphere

Question 19

What is cohesion?

Answer 19

Attractive forces between the same molecules

Question 20

What is adhesion?

Answer 20

Attractive forces between molecules and other dissimilar surfaces or molecules

Question 21

What is a potometer used to measure?

Answer 21

Rate of water uptake in a leafy shoot

Question 22

How could a potometer be set up?

Answer 22

Cut healthy shoot under water
Cut shoot at a slant
Check apparatus is full of water
Insert shoot into the apparatus under water
Shut screw clip
Remove potometer from water ensuring airtight joints around the shoot

Question 23

Why should the shoot be cut under water in a potometer?

Answer 23

Stop air from entering xylem vessels

Question 24

Why should the shoot be cut at a slant in a potometer?

Answer 24

To increase SA

Question 25

What should be done while measuring the uptake of water in a leafy plant to ensure the results are valid?

Answer 25

Dry plant leaves Keep conditions constant Allow time for shoot to acclimatize Keep ruler fixed and record position of air bubble on scale

Question 26

What effect does increased temperature have on the rate of transpiration?

Answer 26

Increases transpiration

Question 27

What effect does increased humidity have on the rate of transpiration?

Answer 27

Decreases transpiration

Question 28

What effect does increased air movement have on the rate of transpiration?

Answer 28

Increases transpiration

Question 29

What effect does increased light intensity have on the rate of transpiration?

Answer 29

Increases transpiration

Question 30

Why would increased temperature result in increased transpiration?

Answer 30

Increases kinetic energy of water molecules so diffusion occurs quicker Increases kinetic energy of air and warm air holds more water

Question 31

Why would increased humidity result in decreased transpiration?

Answer 31

No/less diffusion gradient between the internal air spaces and the environment

Question 32

Why would increased air movement result in increased transpiration?

Answer 32

Diffusion gradient maintained, as humid air is blown away and fresh air which is

Question 33

Why would increased light intensity result in increased transpiration?

Answer 33

Affects the degree of opening and closing of stomata

Question 34

What is the mass flow theory?

Answer 34

Transport in the phloem - movements of water and sucrose generate a gradient of hydrostatic pressure which drives the translocation of organic solutes from leaf (source) to roots (sink)

Question 35

What happens in mass flow theory?

Answer 35

1. Companion cell actively transports H+ into mesophyll cell. Sucrose is co-transported with H+ down the proton gradient back into the companion cell 2. Sucrose moves from the companion cell into sieve tube element through the plasmodesmata 3. Sieve tube element's water potential lowers due to the sucrose entering 4. Water diffuses into the sieve tube element via osmosis 5. Sieve plates reduce the fluid volume 6. Water and sucrose move down the phloem via translocation from an area of high hydrostatic pressure to low hydrostatic pressure 7. Living cells (parenchyma) in the root actively transport sucrose out of sieve tube elements 8. Water diffuses from the sieve tube elements into the xylem vessels

Question 36

What is the evidence against mass flow theory?

Answer 36

Sieve plates would obstruct mass flow so why are they there? Sucrose and amino acids have been observed moving at different rates and in different directions in the same tissue Why are the companion cells in the middle of the stem not just at the source and sink?

Question 37

How are roots adapted for the uptake of water and mineral ions?

Answer 37

Large SA for water to enter via osmosis Many root hair cells per root - large total SA Cellulose cell wall is freely permeable to water Many mitochondria to provide ATP Many protein carriers in cells membrane for transport of mineral ions into the cell

Question 38

How does water and mineral ions enter the root?

Answer 38

Water potential of soil is higher than water potential inside of root Water enters via osmosis Ions actively transported into root cell which decreases the water potential inside the cell Steeper water potential gradient causes more water to move into the cell quicker

Question 39

What is root pressure?

Answer 39

A constant additional force that influences the upward movement of water

Question 40

How is tension generated in a plant?

Answer 40

Water molecules are evaporating through the stomata Cohesion therefore causes tension throughout the plant causing water to rise

Question 41

What is translocation?

Answer 41

The movement of sugars and other dissolved substances through the phloem