Module 3.3

Question 1

Why do multicellular plants need a transport system

Answer 1

SA:V - diffusion distance is large and not efficient enough
Size
Metabolic rate - plants are not active but sugars cant be absorbed in the roots so must be manufactures - need transport system to move water and minerals up to the leaves and sugars from the leaves to the rest of the plant

Question 2

structure of xylem

Answer 2

lignified cell walls - waterproof and kills cells so they have no contents also strengthens and prevents collapse/closing
bordered pits - water and mineral ions can move out
no end cell walls - continuous column of water

Question 3

Phloem sieve tube element structure

Answer 3

Sieve plates - movement of assimilates
No nucleus and very little cytoplasm - space for assimilate mass flow
lined end to end to form sieve tubes

Question 4

Phloem companion cells structure

Answer 4

many mitochondria - provide ATP for active transport
Large nucleus and dense cytoplasm
carry out metabolic processes for loading of assimilates into sieve tubes

Question 5

process of transpiration

Answer 5

Water enters leaf through xylem moves y osmosis into spongey mesophyll cells
Water evaporates out of cells
Water vapour in air spaces of the leaves
Higher water vapour concentration inside the leaves
Water vapour diffuses out of the stomata

Question 6

Environmental factors effecting transpiration

Answer 6

Light intensity
Humidity
Temperature
Water availability
Wind speed

Question 7

precautions for a potometer

Answer 7

Assemble under water - prevents air bubbles from entering equipment/continuous column of water
Vaseline around bung - all water is going into xylem
Cut stem under water - xylem wont water lock
dry leaves - reduced humidity

Question 8

What is the apoplast pathway

Answer 8

Water travels in the spaces between cells along the cell walls
carried by mass flow not osmosis

Question 9

What is the symplast pathway

Answer 9

Water travels through the plasma membrane and into the cytoplasm moving through plasmodesmata between cells
Moves by osmosis

Question 10

How adhesion helps water move up the plant

Answer 10

Water hydrogen bonds to the lignin in the xylem cell walls
Water does not fall down the xylem and can be pulled up
The xylem is very narrow so the forces can pull water up the vessel

Question 11

How cohesion helps water move up the plant

Answer 11

Water molecules are hydrogen bonded to each other
1 continuous column that can be pulled upwards

Question 12

What is the transpiration stream

Answer 12

The loss of water by evaporation from the leaves must be replaced with water coming up the xylem. Because of cohesion as one molecule is lost from the top of the chain the whole column is pulled up (cohesion-tension theory)

Question 13

Role of the xylem

Answer 13

Transport water and mineral ions from root to leaves

Question 14

Role of the phloem

Answer 14

Transport sucrose, amino acids and other assimilates around the plant

Question 15

What is root pressure

Answer 15

The endodermis actively transporting mineral ions into the medulla and xylem draws water in by osmosis. Pressure builds up forcing the water into the xylem and pushing the rest of the column up the xylem

Question 16

What are xerophytes

Answer 16

Plants adapted to live in dry conditions

Question 17

What are hydrophytes

Answer 17

Plants adapted to live in lots of water

Question 18

How large air spaces help hydrophytes

Answer 18

help the leaves float so they are exposed to sunlight and can do gaseous exchange

Question 19

How stomata on the top of the leaves help hydrophytes

Answer 19

The stomata are in contact with air and not water so gaseous exchange can occur

Question 20

How rolled leaves help xerophytes

Answer 20

increases the humidity around the stomata by trapping air decreasing transpiration

Question 21

How spikes for leaves help xerophytes

Answer 21

Reduces surface area for transpiration

Question 22

How fleshy stems help xerophytes

Answer 22

Can act as water storage

Question 23

How wide roots help xerophytes

Answer 23

when it does rain they collect more water

Question 24

How tap roots help xerophytes

Answer 24

Can reach down to ground water

Question 25

How sunken stomata help xerophytes

Answer 25

Increases humidity and reduce wind around the stomate reducing transpiration

Question 26

How hair around stomata help xerophytes

Answer 26

capture water vapour and hold it around the stomata increasing humidity and reducing transpiration

Question 27

What is translocation

Answer 27

An active process requiring ATP for the transport of assimilates especially sucrose around the plant between sources and sinks

Question 28

What are sources

Answer 28

Areas of the plant that produce assimilates to be transported in the phloem e.g. sucrose produced in the leaves

Question 29

What are sinks

Answer 29

Areas of the plant that require assimilates transported in the phloem e.g. roots and meristem

Question 30

Active loading at sources

Answer 30

H+ ions actively transported out of companion cells increasing the concentration outside of the cell and decreasing the concentration inside the cell (concentration gradient)
H+ ions diffuse back into the companion cells through cotransporter proteins which will only allow the movement of hydrogen if it is accompanied by sucrose
Creates high concentration of sucrose in the companion cell than sieve tube
Sucrose diffuses through plasmodesmata into sieve tube elements

Question 31

Removal of assimilates at sinks

Answer 31

Where sucrose is being used the cells have a lower concentration
Sucrose diffuses into the cells through the plasmodesmata
This makes the water potential higher in the sieve tubes so water moves out
The reduces the hydrostatic pressure at the sinks making assimilates flow towards them

Question 32

Where are the vascular bundles in the stem

Answer 32

Around the outer edge - provides flexibility and strength to withstand bending forces

Question 33

Where are the vascular bundles in the leaf

Answer 33

Form the midrib

Question 34

Where are the vascular bundles in the root

Answer 34

Inside the endodermis in X shape - withstand pulling forces

Question 35

Adaptations of the xylem

Answer 35

cells aligned end to end to form continuous column
Narrow tubes so water column does not easily break
Bordered pits allow water to move out of the vessels
Lignin in patterns allows the xylem to stretch with growth and bend

Question 36

Role of the endodermis

Answer 36

mineral ions are actively transporting into the medulla and xylem - water potential decreases - water osmoses into the medulla and xylem
Contains the casparian strip

Question 37

Role of the casparian strip

Answer 37

suberin strip around the outside of endodermis cells which acts as a water proof barrier
Stops the apoplast pathway to ensure all the water travels into the medulla and xylem vessels

Question 38

How thick waxy cuticles help xerophytes

Answer 38

Reduce evaporation from the leaves

Question 39

How dense spongey mesophyll helps xerophytes

Answer 39

Less surface area for the evaporation of water

Question 40

How sucrose moves along the phloem

Answer 40

Mass flow
caused by different hydrostatic pressures at either ends of the tube.
sinks have low HP sources have High HP