Transport in Plants

Question 1

Why is there a need for a transport system?

Answer 1

• Metabolic demands: glucose needed in other parts of the plants
• Size: need a transport system for transpiration across
• SA: V: diffusion alone can not meet the metabolic demand to supply their cells

Question 2

Learn the structures of the vascular system

Answer 2

yeah mate draw them alr

Question 3

How is the transport system arranged?

Answer 3

-into vascular bundles

Question 4

What are the structure and the function of the xylem?

Answer 4

• non-living tissue
• involved with the water and mineral ions
• long reinforced with lignin spirals

Question 5

What is the structure and function of the phloem?

Answer 5

-living tissue that transports food in organic solute around the plant

Question 6

What is the function of the sieve tube elements?

Answer 6

-to allow for the sucrose to move both ways

Question 7

Why is water transport in plants important?

Answer 7

• The loss of water by evaporation helps cool the plant

- Water is needed for photosynthesis

Question 8

How are root hair cells adapted for their function?

Answer 8

• microscopic size means they can penetrate easily through soil
• Large SA:V
• Thin layer so less diffusion distance
• concentration of solutes maintains a water potential gradient

Question 9

What are the three different pathways water can take across the root?

Answer 9

• Symplast pathway
• Apoplast pathway
• Vacuolar pathway

Question 10

What is the symplast pathway?

Answer 10

• water moves through the symplast
• the cytoplasm is connected by the plasmodesmata
• the root hair cell has a higher water potential than the cells connected to it
• so water moves via osmosis
• a water potential gradient is maintained along the way

Question 11

What is the Apoplast pathway?

Answer 11

• movement of water through the apoplast (between the cell walls and intracellular spaces)
• the water is pulled along by cohesive forces
• this means there is a continuous flow of water with very little resistance
• This is the FASTEST PATHWAY

Question 12

How does water from the Apoplast pathway join the cytoplasm?

Answer 12

• when the water reaches the endodermis it is forced into the cytoplasm of the cell
• this waterproof layer is called the CASPARIAN STRIP

Question 13

What is the function of the Casparian strip?

Answer 13

• prevents any toxic solutes in the apoplast water from entering the plant
• because there are no carrier proteins to let them in

Question 14

Transpiration (transpiration stream)

Answer 14

• water evaporates from the surface of the leaves
• this creates a low water potential at the surface of the leaves
• so water moves to the adjacent cell via osmosis
• this is repeated across the leaf to the xylem
• cohesion and adhesion in water molecules help pull the water up the xylem in a chain (hydrogen bonds)
• this combined effect is called capillary action

(cohesion tension theory)

Question 15

What is transpiration pull?

Answer 15

-water being drawn up from the roots in a continuous stream to replace the water lost by evaporation

Question 16

Evidence for the cohesion tension theory

Answer 16

• changes in tree diameter (due to water loss at different points in the day)
• air drawn in when xylem is cut
• water not being able to move up when the xylem vessel is cut

Question 17

What can be used to measure transpiration?

Answer 17

-potometer

Question 18

What cell controls transpiration?

Answer 18

-guard cells (opening and closing due to turgor pressure)

Question 19

Factors effecting the rate of transpiration

Answer 19

• Light intensity
• relative humidity
• temperature
• wind speed
• water availability

Question 20

What is translocation?

Answer 20

• the transport of organic solutes from source to sink
• bi directional
• requires ATP energy
• translocation occurs in phloem vessels

Question 21

Is translocation passive or active?

Answer 21

-active as it require ATP energy

Question 22

What are the main sources of assimilates?

Answer 22

• leaves and green stems

- food stores

Question 23

what are the main sinks?

Answer 23

• roots
• meristems
• food stores

Question 24

What is phloem loading?

Answer 24

• sucrose is actively loading into the phloem cells by companion cells
• requires ATP energy and co-transporter proteins

Question 25

Explain Active loading at the source

Answer 25

1. H+ ions are pumped out of the companion cells (proton pumps)
2. This increases the hydrogen ion concentration outside the companion cell
3. The hydrogen moves back into the companion cell via co transporter proteins by facilitated diffusion
4. sucrose also gets transport alongside the H+ ions
5. sucrose diffuses across the plasmodesmata into the sieve tube elements

Question 26

Explain the Mass flow of sucrose

Answer 26

1.the active loading of the sucrose into the phloem makes the sap solution hyper tonic
2.this causes water to be drawn in from the xylem through delignified pits
3.This causes an increase in the hydrostatic pressure
4.This means the sucrose (through water) will be transported to areas of lower hydrostatic pressure
5.This transports the sucrose from source to sink
This is called MASS FLOW

Question 27

What is the main process of phloem unloading?

Answer 27

-sucrose diffuse across to the sink

Question 28

Evidence for translocation

Answer 28

• aphids
• flow of sugar is faster than diffusion alone
• When mitochondria is poisoned translocation stops

Question 29

What Xerophytes do we need to know?

Answer 29

• Cacti

- Marram Grass

Question 30

What adaptations do Xerophytes have?

Answer 30

• Thick waxy cuticle (prevent water loss from cuticle)
• Sunken stomata (creates humid air around stomata)
• Reduced number of stomata
• Reduced Leaves
• Long roots
• hairy leaves