Transport In Plants

Question 1

What are adaptations of xerophytes and how do they help to reduce water loss

Answer 1

Rolled leaves - Reduces SA
Hairy Leaves - Traps water vapour
Less stomata - Reduces diffusion
Thick waxy layer of epidermis - Reduced water loss by evaporation as layer is waterproof
Spines instead of leaves - Reduces SA

Question 2

Where is xylem located in the stem

Answer 2

On the edge and inner part of stem

Question 3

Where is xylem found in roots

Answer 3

Center of the roots

Question 4

How does lignified cell wall help xylem with its function

Answer 4

Adds strength to xylem wall and is involved in waterproofing and improves adhesion of water molecules

Question 5

How is no end plates and no protoplasm on the xylem adapted to its function

Answer 5

Doen not impede the mass flow of H20 and dissolved solutes

Question 6

How do pits in walls of xylem help xylem with its function

Answer 6

Prevents xylem from collapsing and reduces lateral loss of water

Question 7

What are the key differences in Xylem and Phloem

Answer 7

Xylem has no living cells wheras Phloem has companion cells
Xylem transports water and mineral ions upwards and is involved in translocation wheras Phloem transports assimilates both ways in the plant
Xylem does not have end plates wheras phloem has sieve plates w/ sieve pores
Xylem is impregnated w/ lignin

Question 8

How is sieve plates w/ sieve pores adapted to its function

Answer 8

Allows continous movement of organic compounds

Question 9

What is the function of celluose cell wall in Phloem

Answer 9

Strengthens wall to withstand hydrostatic pressure that moves assimilates

Question 10

What is the function for no nucleus vacuole or ribosomes in mature cells

Answer 10

Maximises space for the translocation of assimilates

Question 11

Why are carbohydates not transported in the form of glucose and starch

Answer 11

Starch - Not soluble/ does not affect W.P of cell
Glucose - Less likely to leave S.T.E AND less reactive

Question 12

What is the first step of how assimilates are loaded into sieve tube elements

Answer 12

H+ moves out of companion cells via active transport which creates a concentration gradient

Question 13

What happens after Hydrogen ions are actively transported into the cell wall of companion cell

Answer 13

Hydrogen ions move back down the conc. gradient via facilitated diffusion through a cotransporter protein back into the companion cells and Sucrose moves with the Hydrogen Ions

Question 14

What happens after sucrose is in the companion cells

Answer 14

Sucrose moves into the sieve tube element by diffusion via plasmodesmata

Question 15

How is sucrose unloaded from companion cells into sink

Answer 15

Sucrose is actively transported out of companion cells out of phloem and to maintain a conc. gradient sucrose is converted into other molecules

Question 16

Why is transpiration unavoidable

Answer 16

As stomata open for gaseous exchange in order to undergoe photosynthesis to produce sugars

Question 17

State the steps of transpiration

Answer 17

Water vapour evaporates out of stomata on leaves –> loss of water creates lower hydrostatic pressure at the top of the plant and when water is lost by transpiraton more water moves into xylem down water potential gradient via apoplastic pathway to replace it. There is high hydrostatic pressure at bottom and low H.P at top thus water moces down pressure gradient and is pulled up the xylem under tension by mass flow column of water also pulled up (cohesion & adhesion)

Question 18

How do the properties of xylem help it move up the transpiration stream

Answer 18

Cohesion occurs / Adhesion occurs (Water sticks to Xylem Wall Vessels)
Water moves up by capillary action
Water acts as a solvent and dissolves sucrose in translocation

Question 19

State the similarities betwen xylem and phloem

Answer 19

Both are complex tissues
Both are hollow tubes