Chapter 7: transport in plants

Question 1

how are xylem vessels adapted to their function?

Answer 1

• cells are joined end-to-end to form tubes
• the cells are dead
• cell walls thickened with lignin
• non-lignified areas (pits) allow water to move between cells

Question 2

how are phloem sieve tube elements adapted to their function?

Answer 2

• made of living cells
• elongated elements are joined end-to-end
• sieve elements do not contain a nucleus or ribosomes
• sieve plates at the end walls have pores to allow the movement of liquids

Question 3

how are companion cells adapted for their function?

Answer 3

• structured like a ‘normal’ plant cell
• more mitochondria and ribosomes because the cell is aerobically active
• plasmodesmata link cells to the sieve element

Question 4

what is water potential?

Answer 4

a measure of the ability of water to move freely in solution

eg high water potential is pure water

Question 5

what direction does water move (relating to water potential)?

Answer 5

DOWN the water potential gradient

Question 6

what is ‘mass flow’?

Answer 6

the movement of water and nutrients from the roots to all other areas of the plant

Question 7

define ‘cohesion’

Answer 7

the sticking together of water molecules

Question 8

define ‘adhesion’

Answer 8

the attraction of water molecules to the cellulose and lignin in the walls of the xylem vessels

Question 9

describe the apoplast pathway

Answer 9

• water only travels through cell walls

- it moves due to cohesion

Question 10

describe the symplast pathway

Answer 10

• water moves into the cytoplasm/ vacuoles of the xylem vessels by osmosis
• it moves through the xylem through plasmodesmata

Question 11

what is the casparian strip?

Answer 11

• forms an impenetrable barrier to water in the endodermis
• the apoplast pathway is blocked
• endodermis cells have suberin in their walls
• water is forced into the cytoplasm

Question 12

define transpiration

Answer 12

the loss of water from a plant to its environment, by diffusion down a water potential gradient

Question 13

why is transpiration an inevitable consequence of gas exchange?

Answer 13

opening stomata for gas exchange leads to water loss by transpiration

Question 14

what are xerophytes?

Answer 14

plants that live in places where water is in short supply

Question 15

give three examples of adaptations of xerophytes

Answer 15

• cuticle contains a waxy substance called cutin
• stomata only found in the upper epidermis
• hairs that reduce the steepness of the diffusion gradient

Question 16

how is sucrose loaded into companion/ sieve elements?

Answer 16

by active transport