3.3 Transport in plants

Question 1

Why do plants need transport systems

Answer 1

Small sa:v

Simple diffusion would be too slow

Question 2

What do xylem and phloem transport?

Answer 2

Xylem- water minerals

Phloem- dissolved solutes like sugars

Question 3

Name 3 ways that xylem vessels are adapted for their function

Answer 3

No end walls-water can pass through easily
Dead-no cytoplasm-water can pass through easily
Lignin walls-support xylem vessles stop them collapsing
Boardered pits- no lignin so water and ions can move in

Question 4

How is phloem tissue adapted for transporting solutes? (3)

Answer 4

Sieve plates have holes to allow solutes to pass through
Sieve tube elements have no nucleus, very thin layer of cytoplasm and few organelles to allow space
Companion cells many mitochondria atp active transport solutes

Question 5

Where is the vascular bundle located in 1)roots 2)stems 3) leaves, and why? (6)

Answer 5

1) centre of root to support as it pushes through soil
2) near outside for support to reduce bending
3) make veins which support thin leaves

Question 6

What is the difference between the apoplast symplast and vacuolar pathways (when water moves from the root to the xylem)?

Answer 6

apoplast- diffuses through cell walls

symplast- through cytoplasm (+plasmodesmata)

Question 7

What does the casparian strip do?

Answer 7

Blocks apoplast pathway when water gets to endodermis in root cell, so water has to go through cell membrane

Question 8

What are the three mechanisms called that aid the transpiration pull? What do these mean? (6)

Answer 8

Cohesion- attraction between water molecules caused by hydrogen bonds
Tension- produced by the ‘pull’ of water bein lost by evapouration from the leaves
Adhesion- attraction between water molecules and xylem vessel walls

Question 9

Describe the transpiration stream (6)

Answer 9

water evaporates from the leaves at ‘top’ of xylem (transpiration)
this creates tension (suction) that pulls more water into the leaf
water molecules are cohesive, so when some are pulled into the leaf, others follow.
Adhesion means water molecules are also attracted to xylem walls as well as eachother, helps water rise up
So whole column of water in the xylem moves upwards

Question 10

Define transpiration.

Answer 10

The loss of water VAPOUR from a plant, mostly through the stomata in the leaves

Question 11

Why does transpiration occur?

Answer 11

Gaseous exchange
(stomata need to be open to let in CO2 to make glucose in photosynthesis, but this also lets water out down its water potential gradient)

Question 12

What apparatus can we use to estimate transpiration rate? Why is this not fully accurate?

Answer 12

Potometer

It only measures the water uptake by a plant, and not all of this is lost through transpiration

Question 13

Define translocation.

Answer 13

the transport of assimilates throughout the plant

Question 14

Briefly describe the process of active loading of sucrose being loaded into the sieve tube (4)

Answer 14

H+ ions actively pumped out of companion cell using energy from ATP
High conc of H+ causes facilitated diffusion back into companion cell.
Sucrose is carried with the H+ through cotransport proteins in companion cell plasma membrane
sucrose diffuses into sieve tube element down concentration gradient

Question 15

Why does water enter a the root hair cells?

Answer 15

Down water potential gradient

Question 16

State and explain the four main factors that affect transportation rate (8)

Answer 16

Light- as light inc transpiration inc- bc stomata open when it’s light and close when it’s dark
Temp- as temp inc transpiration inc- bc warmer water mols have more kinetic energy so evaporate faster this inc WP grad making water diffuse out faster
Humidity- the lower the humidity the faster the transpiration rate-bc if the air around plant is dry the WP grad inc so inc transpirstion
Wind- the windier it is the faster transpiration rate- bc air blows away water molecules from stomata, inc WP grad so inc transpiration

Question 17

Name 4 of the 6 ways xerophytic plants are adapted to reduce water loss. (12)
(Also state briefly why this reduces water loss)

Answer 17

Stomata in sunken pits- sheltered from wind
Hairs- trap moist air reduces WP grad
Curled leaves- traps moist air/ lowers SA exposed for losing water/ shelters stomata from wind
Spines instead of leaves- reduces SA for water loss
Thick waxy layer on epidermis- reduces evaporation bc waterproof so water cant move through it
Reduced number of stomata- fewer places where water can be lost

Question 18

What is the difference between the source and sink?

Answer 18

Source- part of plant that loads materials into the transport system e.g. leaves photosynthesize and the sugars are moved to other parts of the plant
Sink- part of plant where those materials are removed from transport system e.g. roots receive sugars and store them as starch. (roots my convert starch back to sugars and transport it to growing stem, so roots can be sources too)

Question 19

What is the mass flow of sucrose caused by?

Answer 19

Different hydrostatic pressures between the two ends of the tube producing a pressure gradient. (water enters at source, inc pressure, leaves at sink, reduces pressure, so sap flows from source to sink)

Question 20

Which direction can phloem transport assimilates.

Answer 20

Both, xylem only upwards.

Question 21

Describe the process of active loading.

Answer 21

ATP actively trasnport hydrogen ions out of companion cell
high conc outside, low conc inside, conc grad created
bind to sucrose mols
back into cell through co transporter proteins (cotransport)
sucrose diffuses through plasmodesmata into sieve tube as conc increases