transport in plants

Question 1

why do plants need a transport system

Answer 1

1. metabolic demands
   co2, hormones, nutrients etc need to be transported
2. size
   can grow v tall so need a transport system up and down
3. SA:Vol ratio
   leaves adapted to have high sa:v ratio but stems, trunks etc have a low ratio so cant rely on diffusion alone

Question 2

what is a vascular bundle

Answer 2

a series of transport vessels

2 main types of transport tissues: xylem and phloem

Question 3

function of xylem

Answer 3

transport water and minerals from roots to rest of plant

Question 4

how is the xylem adapted

Answer 4

1. made from dead cells, end to end –>
   hollow cells reduce resistance to flow of water
2. narrow tubes –>
   ensure water column doesnt break easily, efficient capillary action
3. pits in walls –>
   lateral movement of water from one vessel to another
4. lignified walls –>
   mechanical strength/support, ensures less water is absorbed by cell walls

Question 5

transport of water through plant: the transpiration stream

Answer 5

1. water moves in from soil via osmosis (down water potential gradient)

2, root hair cells are specialised, have a high SA:V, and are thin, increasing rate of uptake of water

3. water enters xylem vessels through mass flow

Question 6

what processes help move water up stem

Answer 6

1. root pressure - root hair cells move mineral ions into root, water moves in, raising hydrostatic pressure, forcing water into xylem
2. transpirational pull - water is cohesive, when water is evaporated, it pulls the whole column up
3. capillary action - water is adhesive, attracted to walls of xylem vessels which pulls water up