Xylem + Phloem

Question 1

Why do plants need transport systems?

Answer 1

• Small SA:V ratio
• High metabolic rate

Question 2

What does xylem transport?

Answer 2

Water + mineral ions (in solution)

Question 3

What is transported in phloem tissue?

Answer 3

Sugars (in solution)

Question 4

Which direction does transpiration occur?

Answer 4

UP ONLY

Question 5

Where are xylem and phloem found in the root of a plant?

Answer 5

• Central xylem with phloem around it
• Supports root

Question 6

Where are xylem and phloem found in the stem?

Answer 6

• Vascular bundle creates ‘scaffolding’
• Inner xylem, outer phloem
• Reduces bending in the stem

Question 7

Where are phloem and xylem found in the leaf?

Answer 7

• Network of separate veins
• Xylem above phloem

Question 8

What are xylem vessels?

Answer 8

• Long, tube-like structures joined together
• Lignin thickens walls, supporting vessels

Question 9

What is the role of lignin?

Answer 9

• Supports xylem vessels
• Prevents xylem collapsing inwards

Question 10

How do water + mineral ions move out of xylem vessels?

Answer 10

Through border pits in the cell wall

Question 11

What cells are phloem tissue made from?

Answer 11

• Parenchyma cells + Companion cells

Question 12

Why do sieve tube elements in phloem need companion cells?

Answer 12

• Sieve tube elements have no nucleus, few organelles so need a companion cell to carry out living functions

Question 13

What are sieve tube elements?

Answer 13

They are continuous tubes that transport assimilates up an
down the cell

Question 14

How do ‘sieve’ ends allow solutes to pass through?

Answer 14

They have small holes in them

Question 15

How does water enter root hair cells?

Answer 15

• H20 moves down water potential gradient
• Travels by osmosis into root hair cell

Question 16

Define osmosis

Answer 16

The diffusion of water molecules across a partially permeable membrane down a concentration gradient

Question 17

What are the 2 different pathways water moves to xylem through?

Answer 17

Symplast and Apoplast

Question 18

What occurs when water moves through the symplast pathway?

Answer 18

H20 moves through cytoplasm’s of cells and moves between cells through plasmodesta

Question 19

What occurs when water moves through the apoplast pathway?

Answer 19

• H20 travels through cell walls
• H20 diffuses through them

Question 20

What are Caspian strips?

Answer 20

Waxy strips that block water from travelling with the apoplast pathway (cell walls)

Question 21

Where are Caspian strips found?

Answer 21

In the endodermis cell layer

Question 22

Why do leaves have Caspian strips?

Answer 22

• They force water to travel through cell membranes which allows plants to control which substances can move on

Question 23

Which pathway does water move to in leaves?

Answer 23

• Water leaves xylem and moves into cells (apoplast pathway)

Question 24

What is the transpiration stream?

Answer 24

The movement of water from roots to leaves

Question 25

State 3 mechanisms that help water move

Answer 25

Cohesion, tension and adhesion

Question 26

How does cohesion and tension aid the movement of water in plants?

Answer 26

- Cohesion allows water to move in a continuous column, against gravity

Question 27

How does adhesion aid the creation of the transpiration stream?

Answer 27

Adhesion allows for H20 molecules to be attracted to xylem vessel walls

Question 28

Explain the formation of the transpiration stream

Answer 28

- Water evaporates from leaves at the top of plant - This creates tension which pulls H20 molecules into leaf due to cohesion - Water column created pulling water through the plant

Question 29

Why do plants open stomata?

Answer 29

CO2 is allowed in so glucose can be produced by photosynthesis

Question 30

Why does opening stomata let out water from the plant?

Answer 30

Higher concentration of water inside so water diffuses out of the leaf

Question 31

State the 4 main factors affecting rate of transpiration

Answer 31

Light Intensity!!, Temperature, Humidity and Wind

Question 32

How does light intensity affect rate of transpiration?

Answer 32

Light intensity increases rate as stomata only open in light

Question 33

Explain how temperature affects rate of transpiration

Answer 33

- Warmer H20 molecules have more energy so evaporate inside the leaf faster - Increased water potential gradient causes H20 to diffuse out of leaf

Question 34

How does humidity affect rate of transpiration?

Answer 34

If air around plant is drier, water potential gradient is increased so rate increases

Question 35

Explain how wind intensity affects rate of transpiration

Answer 35

- H20 molecules in air are blown away so high concentration gradient is maintained

Question 36

What climates are xerophytic plants adapted to?

Answer 36

- Dry climates

Question 37

Why do marram grasses have stomata that are sheltered from the wind?

Answer 37

Slows the rate of transpiration so less water is lost

Question 38

How do layers of 'hairs' on xerophytic plants help them adapt?

Answer 38

They trap moist air around stomata, reducing water potential gradient, slowing transpiration rate

Question 39

Why do marram/cacti have a thick waxy layer?

Answer 39

The layer reduces water loss from evaporation

Question 40

Why do cacti have spines instead of leaves?

Answer 40

Reduced SA for water loss

Question 41

What are hydrophytes adapted to?

Answer 41

Aquatic habitats so low O2 levels

Question 42

How do air spaces allow hydrophytes to survive in aquatic habitats?

Answer 42

Air spaces in tissues help plants float, store O2 and access sunlight

Question 43

How is the location of stomata important for hydrophytes?

Answer 43

Stomata present on upper surface of floating leaves to maximise gas exchange

Question 44

Why do hydrophytes have flexible leaves?

Answer 44

Prevents damage from strong water currents

Question 45

What is translocation?

Answer 45

The movement of dissolved substances in a plant

Question 46

Is translocation passive?

Answer 46

NO, it requires energy

Question 47

Why are sugars transported as sucrose during translocation?

Answer 47

Sucrose is soluble + metabolically inactive so doesn't get used up in transport

Question 48

Explain how sugars move from source cells to phloem vessels

Answer 48

- ATP is used to actively transport H+ ions out of cell into companion cell - H+ ion (+ sucrose) binds to transport protein and enters companion cell - Sucrose then diffuses from companion cell to phloem cell as low conc. in phloem vessel

Question 49

How does sucrose move to sink cell, after it enters phloem?

Answer 49

- High conc. of sucrose lowers water potential so water molecules enter tubes by osmosis from xylem - Water in area of high conc. moves to area of low conc., moving sucrose in the process (soluble) - High hydrostatic pressure at the source end of the tube forces water to move back into xylem

Question 50

How does sucrose get from sink end of the phloem into sink cell?

Answer 50

- Solutes move through active transport into sink companion cell - ATP used to actively transport H+ ions into sink cells as H+ ions bind to co-transport protein (along with sucrose) and is carried into sink cell