section 3: transport in plants - topic 1: xylem & phloem

Question 1

what are the 2 transport systems a plant has?

Answer 1

xylem
phloem

Question 2

why do plants need transport systems?

Answer 2

• need water, minerals, and sugars to live
• need to get rid of waste substances
• direct diffusion is too slow to meet their metabolic needs (relatively big = high metabolic rate)

need transport systems to move substances to and from individual cells quickly

Question 3

what are the 2 types go tissue involved in transport in plants?

Answer 3

xylem tissue
phloem tissue

Question 4

what does xylem tissue transport?
in which direction?

Answer 4

water and mineral ions (in solution)
up the plant - from roots to leaves

Question 5

what does phloem tissue transport?
in which direction?

Answer 5

mainly sugars (in solution)
both up and down the plant

Question 6

what is the other function of xylem?

Answer 6

support

Question 7

where are the xylem and phloem found in roots? function?

Answer 7

they are in the centre to provide support for the root as it pushes through the soil

Question 8

where are the xylem and phloem found in stems? function?

Answer 8

they are near the outside to provide a sort of ‘scaffolding’ that reduces bending

Question 9

where are xylem and phloem found in leaves? function?

Answer 9

they make up a network of veins which support the thin leaves

Question 10

what part of xylem tissue actually transports the water and ions?

Answer 10

xylem vessels

Question 11

what are xylem vessels?

Answer 11

very long, tube-like structures formed from cells (vessel elements) joined end to end

Question 12

why can water pass through the middle of xylem vessels easily?

Answer 12

they have no end walls, making an uninterrupted tube

Question 13

why do the xylem vessels not contain any cytoplasm?

Answer 13

because they are dead

Question 14

what are the cell walls thickened by?

Answer 14

lignin

Question 15

what is the function of lignin?

Answer 15

it helps to support the walls and stops them from collapsing inwards

Question 16

what are the 2 ways in which lignin can be deposited in xylem walls?

Answer 16

spiral
distinct rings

Question 17

what does lignin being deposited in these patterns allow?

Answer 17

flexibility and prevents the stem from breaking

Question 18

does the amount of lignin increase or decrease as the cell gets older?

Answer 18

increases

Question 19

how do water and mineral ions move into and out of the vessels?

Answer 19

through small pits in the walls where there’s no lignin

Question 20

what is phloem formed from/

Answer 20

cells arranged in tubes

Question 21

how does phloem differ from xylem?

Answer 21

it is purely a transport tissue - it is not used for support as well

Question 22

what does phloem tissue contain?

Answer 22

phloem fibres
phloem parenchyma
sieve tube elements
companion cells

Question 23

what are the most important cell types in phloem for transport?

Answer 23

sieve tube elements and companion cells

Question 24

what are sieve tube elements?

Answer 24

living cells that form the tube for transporting sugars through the plant

Question 25

sieve tube elements are joined end to end to form what?

Answer 25

sieve tubes

Question 26

what are the ‘sieve’ parts of sieve tube elements? function?

Answer 26

they are the end walls
they have lots of holes in them to allow solutes to pass through

Question 27

what is unusual about sieve tube elements?

Answer 27

they have no nucleus, a very thin cytoplasm, and few organelles

Question 28

why do sieve tube elements need companion cells?

Answer 28

sieve tube elements can’t survive on their own due to their lack of a nucleus and other organelles

Question 29

what do companion cells do?

Answer 29

they carry out the living functions for both themselves and their sieve cells

for example, they provide the energy for the active transport of solutes