Transport In Plants

Question 1

Reasons for plant transport systems

Answer 1

-Metabolic demands- internal and underground don’t photosynthesise require mineral ions to make proteins
-size - need effective transport to move sub up and down to topmost leaves
-SA:Vol ratio - stems and roots cannot rely on diffusion alone

Question 2

Dicotyledonous plants

Answer 2

Produce seeds that contain 2 cotyledons - organs that act as food stores for developing embryo

Question 3

Structure of xylem

Answer 3

Vessels made of dead cells long and hollow in structure and fused end to end
Parenchyma cells pack around xylem storing food and tannin deposits

Question 4

Tannins

Answer 4

Bitter tasting chemical which plant tissues from attack by herbivores

Question 5

Lignin

Answer 5

Mechanical strength
Can form rings spirals or solid tubes w non lignified pits for water movement out of the xylem

Question 6

Xylem function

Answer 6

Movement of water and minerals

Question 7

Turgor pressure

Answer 7

Hydrostatic pressure as a result of osmosis pressure exerted by the cell surface membrane against the cell wall
Provides a hydrostatic skeleton which supports stems and leaves

Question 8

Root hair cell adaptations

Answer 8

Large SA:Vol ratio thousands on each root tip
Thin surface layer quick diffusion
Conc of solutes maintains a water potential gradient between soil and cell

Question 9

Movement of water across the root

Answer 9

Symplast pathway
Apoplast pathway

Question 10

Symplast pathway

Answer 10

Water moves through continuous cytoplasm of the living plant cells that are connected through the plasmodesmata
As water leaves the root hair cells it drops the water potential allowing for more movement of water

Question 11

Plasmodesmata

Answer 11

Microscopic channels between neighbouring plant cell through the cell walls enabling transport

Question 12

Apoplast pathway

Answer 12

Water moves through cell walls and intercellular space
As water moves into the xylem more water is pulled through due to cohesive forces between H2O molecules
Water movement stops at the casparian strip

Question 13

Casparian strip

Answer 13

Band of waxy suberin which is hydrophobic
Endodermis surrounding vascular tissue
Diverts water moving through apoplast to be diverted through cytoplasm
Prevents toxic solutes moving any further into the plant
Once into vascular tissue water returns to apoplast pathway

Question 14

Endodermal cell function

Answer 14

Move mineral ions into xylem via active transport which lowers WP in the xylem allowing for water movement via osmosis

Question 15

Root pressure

Answer 15

Gives water a push up the xylem due to the active pumping of minerals into the xylem

Question 16

Evidence root pressure is active process

Answer 16

Increases w a rise in temp
If respiration falls RP falls
Xylem sap is forced out at night when transpiration is low

Question 17

Transpiration

Answer 17

Loss of water vapour from leaves and stems by the opening of stomata when exchanging CO2

Question 18

Transpiration stream

Answer 18

Water moves across membranes by osmosis and diffusion in apoplast pathway from the xylem through the cells of the leaf
Evaporates from cell walls of mesophyll into air spaces (lowers wp)
Moves through stomata along a diffusion gradient

Question 19

Adhesion

Answer 19

Water forms hydrogen bonds with carbohydrate walls of the xylem vessels

Question 20

Cohesion

Answer 20

Water molecules form h bonds with each other and stick together

Question 21

Capillary action

Answer 21

Combined effects of adhesion and cohesion by which water can rise up xylem against gravity

Question 22

Cohesion tension theory

Answer 22

Water drawn up the xylem in a continuous stream to replace the water lost by evaporation - transpiration pull
Results in tension in xylem which helps move water across roots from the soil

Question 23

Evidence for cohesion tension theory

Answer 23

Changes in diameter of trees - day tension is highest diameter lower
Xylem vessel breaks air drawn in rather than water drawn out

Question 24

Stomata func

Answer 24

Turgid pressure is low guard cells close the pore
When environmental conditions are favourable solutes pumped in incr turgor allowing to open
Cellulose prevent swelling in width
Inner wall less flexible

Question 25

Factors affecting transpiration

Answer 25

Light - more light longer open
Humidity higher the harder to lose water
Temp - more kinetic energy evaporate quicker and decrease of humidity
Air movement - each leaf layers of hair hold air more wind easier trans

Question 26

Phloem structure

Answer 26

Sieve tube elements
Long hollow structures no nucleus
Companion cells linked to sieve tubes by plasmodesmata- life support system
Supporting tissues of fibres and sclereids

Question 27

Phloem function

Answer 27

Transports food in the form of organic solutes around the plant from where they are made
Supplies the sugars and amino acids needed for respiration and synthesis of all useful molecules

Question 28

Translocation

Answer 28

Transportation of organic molecules in the phloem from source to sink ( tissues that need them)

Question 29

Assimilates

Answer 29

Products of photosynthesis
Main assimilate is sucrose
Main sources in a plant are green leaves and stem storage organs and stores in seeds when first germinate

Question 30

Main sinks

Answer 30

Roots that are growing
Meristems that are dividing
Any part of plant that are developing food stores eg seeds fruit etc

Question 31

Phloem loading

Answer 31

Soluble products moved into phloem via active processes
Main technique by apoplast route

Question 32

Apoplast route - phloem

Answer 32

Sucrose travels to source through cell walls and intercellular spaces to companion cells
Here H+ ions pumpe out actively and renters cotransporting a sucrose molecule
Travel through plasmodesmata to sieve tubes

Question 33

Osmosis in phloem loading

Answer 33

Due to low wp water moves in via osmosis which leads to turgor pressure
Moves into the sieve elements reducing pressure in companion cells and move up or down plant by mass flow to low pressures
Forces sap to regions of lower pressure due to turgor pressure increase

Question 34

Phloem unloading

Answer 34

Unload at any point cells need it
Diffusion of sucrose into cells from phloem
Loss of solutes leads to a rise in wp of the phloem so moves out via osmosis some enters the xylem

Question 35

Evidence of translocation

Answer 35

Advances in microscopy allow study of companion cells
If mito of comp cells poisoned translocation stops
Flow of sugars in phloem is far faster than diffusion alone - active process of mass flow
Aphids can demonstrate translocation as positive pressure forces sap out

Question 36

Xerophyte adaptations

Answer 36

• thick waxy cuticle minimise water loss from cuticle
  -sunken stomata - in pits to minimise water loss from air movement creating microclimate
• reduced number of stomata
• hairy leaves
• Curled leaves - microclimate of humid air
• succulents - store water in specialised parenchyma tissues
• leaf loss
• root adaptations shallow large sa and v deep

Question 37

Hydrophyte adaptions

Answer 37

-very thin cuticle
- many always open stomata for max gaseous exchange
- reduce structure support by H2O
- wide flat leaves - capture as much light as possible
- small roots but large SA
- air sacs to float

Question 38

Aerenchyma

Answer 38

Specialised parenchyma tissue many airspace’s for extra buoyancy and forming a low resistance movement of substances to tissues below the water