Module 3: Plant Transport Systems

Question 1

What is transpiration?

Answer 1

Evaporation of water from the surface of a leaf (1),

Question 2

What is the Transpiration Stream?

Answer 2

The transpiration stream is the flow of water moved up from the soil into the root hair cell and through the root cortex by osmosis. Then up the xylem and stem to the leaves.

Question 3

Structure of Xylem:

Answer 3

Long tubes joined end to end. No walls- Allows for uninterrupted flow. No cytoplasm. Walls thickened with lignin to prevent collapse. Water and ions enter and leave through non-lignified pores. Annular lignin rings and lignin spirals.

Question 4

Structure of Phloem:

Answer 4

Transports solutes. Sieve tubes joined end to end, separated by sieve plates. Companion cells on the side of sieve tubes.

Question 5

Suggest how water can be lost from a cut stem when all leaves have been treated with petroleum jelly? (Petroleum covering the bottom of leaves)

Answer 5

Stomata are located in the stem as well as the leaves and so water loss by transpiration can still occur.
Water can evaporate from the upperside of the leaves.

Question 6

4 examples of adaptions to reduce water loss in plants:

Answer 6

The surface covered in reflective hairs (reduce diffusion gradient of water by keeping air surrounding plant moist)
The ability to store carbon dioxide so stomata only need to open at night.
Leaves are reduced to spines to prevent damage from animals.
Small leaves - smaller surface area - reduces water loss
Sunken Stomata

Question 7

At the endodermis, water has to enter _______

Answer 7

the symplast pathway

Question 8

Most water moves across the root cortex by the ____________

Answer 8

apoplast pathway

Question 9

What is adhesion?

Answer 9

The attraction of water molecules to its surroundings (e.g impermeable walls of the xylem tissue)

Question 10

Translocation occurs through____ by _______

Answer 10

Translocation occurs through sieve elements by mass flow

Question 11

Sucrose is actively loaded into the phloem at regions known as ____________

Answer 11

Sources

Question 12

Sucrose ________ the water potential of the cell it’s in .

Answer 12

decreases

Question 13

What are the adaptions of hydrophytes?

Answer 13

• No waxy cuticles
• thin leaves
• flexible stem + roots
• little to no roots ~ direct diffusion into stem
• lots of stomata
• Aerenchyma ~ made from apoptotic parenchyma -provide air spaces - low resistance transportation pathway + buoyancy
• Large leaves (on the surface of water) - maximise site of gaseous exchange.

Question 14

Why do plants need transport systems?

Answer 14

• Metabolic demand - provide for photosynthesis for aerobic respiration and active transport
• Size - long distance for nutrients to travel - transport system allows fast transport
• Surface Area : volume ratio - can’t rely on simple diffusion.
• Water aids thermoregulation and turgidity(Structural aid)

Question 15

Difference between sap and dew?

Answer 15

The sap is in the phloem and dew is the water lost by transpiration.

Question 16

Evidence of cohesion tension theory?

Answer 16

Trunk diameter changes due to the rate of transpiration.

Question 17

Hydrophytes

Answer 17

Live either partially or completely submerged in water.

Question 18

Xerophytes

Answer 18

Live where water loss by transpiration (due to hot and dry conditions) is greater than water uptake.

Question 19

What are the two methods of calculating the number of stomata?

Answer 19

Method 1: drop water on microscope slide - place ripped leaf - examine
Method 2: Paint a leaf’s surface with nail vanish - allow to dry -peel off a place on a dry microscope slide.

Question 20

Xerophyte adaptations:

Answer 20

• deep horizontal roots
• waxy cuticle - waterproof to reduce loss
• sunken stomata - create local humidity - reduce conc. gradient of water out of plant.
• Hairs and spikes ^^ + prevent damage from animals
• Thick leaves - Reduce SA:Vol area

Question 21

Describe active translocation:

Answer 21

Solutes are produced at sources and are transported into the phloem using proton pumps.
The active loading causes a higher solute concentration, which decreases the water potential. This causes water to flow into the phloem from the xylem by osmosis.
This causes the source to become an area of high pressure (because of the incompressibility of water) - this creates a pressure gradient that will move the solutes by mass flow.
Solute leaves at sink, increasing water potential, causing water to exit into the xylem.

Question 22

How can translocation rate be measured?

Answer 22

Using aphid stylets - once aphids penetrate the phloem sever stylets - collect sap at different distances. Provide the tree with radioactive C02 to form radioactive sucrose. The time taken for the radioisotopes to reach each stylet and their distance from the source can be used to calculate the rate.

Question 23

Tracheary elements:

Answer 23

Tracheids and vessel elements

Question 24

Tracheids:

Answer 24

Smaller tubes with tapering end walls overlap adjacent tracheids, providing the plant with mechanical strength. Water passes between tracheids through empty lumens, pits in cell walls, and unlignified cell walls.

Question 25

Vessel Elements:

Answer 25

Larger lumens - more effective at transporting water in xylem.

Question 26

Angiosperm:

Answer 26

Flowering plant

Question 27

Why do flowering plants require more efficient transport tissue?

Answer 27

They are large and therefore need greater water flow to provide water and ions to all areas of the plant.

Question 28

What is the metaxylem?

Answer 28

Metaxylem is mature xylem.

Question 29

True or false: Metaxylem can’t grow

Answer 29

True - it can’t grow due to its extensive lignification.

Question 30

What are the 3 types of pathways for water movement in a plant’s roots?

Answer 30

Symplast, Vacuolar and Apoplast.

Question 31

What is the casperian strip?

Answer 31

A band of waxy suberin that surrounds endodermal cells - It waterproofs the cell which forces water from the apoplast pathway to enter the cytoplasm.

Question 32

Why is it important water from the apoplast pathway is forced into the cytoplasm at the casperian strip?

Answer 32

To filter the water through a partially permeable membrane to remove toxins.

Question 33

Apoplast pathway:

Answer 33

Water moves through non-living areas in the cell wall and intracellular spaces. Water is pulled by cohesion and tension forces.

Question 34

Vacuolar pathway:

Answer 34

Water moves between vacuoles in different cells.

Question 35

Symplast pathway:

Answer 35

Movement of water in living space, moving from cell to cell in the cytoplasm through the plasmodesmata by osmosis. Water moves by cohesion-tension and a gradient in water potential.

Question 36

What happens when water potential is lower outside a plant cell.

Answer 36

They are plasmolysed.

Question 37

Affect of cyanide on root pressure:

Answer 37

Mitochondria halted ~ Root pressure decreases ~ proves transport is partially active.

Question 38

Affect of temperature on root pressure:

Answer 38

Root pressure increases as temp increases ~ enzyme controlled reaction is occurring.

Question 39

Active Loading:

Answer 39

Hydrogen ions act as co-transporters, moving across the membrane of companion cells, the sucrose from surrounding tissues is attracted to the hydrogen ions (through hydrogen bonding) - when the hydrogen ions return, the sucrose molecules are pulled across the membrane before the hydrogen ions periodically bind to cotransport proteins.

Question 40

What is the name of the central cavity in a xylem or phloem?

Answer 40

Lumen

Question 41

What is the name of the “gaps” between lignified xylem cells/vessels

Answer 41

Pits

Question 42

Similarities between the structure of the xylem and phloem:

Answer 42

Both are made of cells joined end to end.
Xylem and phloem sieve tube elements both lack nuclei
Both are complex tissues made of multiple tissue types