C7: Transport In Plants

Question 1

What is the plant vascular system?

Answer 1

It is a complicated network of conducting tissues that interconnects all organs and transports materials

Question 2

What does xylem transport and from where to where?

Answer 2

water and mineral ions from roots to the rest of the plant

Question 3

What does phloem transport and from where to where?

Answer 3

sugar (sucrose) from source to sink

Question 4

What direction(s) do xylem and phloem move in?

Answer 4

• xylem moves up
• phloem can move up and down

Question 5

Describe the structure/location of the vascular bundles in a dicot root.

Answer 5

the VB forms a central stele with cross-shaped xylem on inside and phloem on outside (helps roots withstand the pulling strains due to water transport and growth)

Question 6

Describe the structure/location of the vascular bundles in a dicot stem.

Answer 6

the VB are located on the outside and form a ring with the xylem on the inside and phloem on the outside (xylem closer to stem’s center for help support the plant)

Question 7

Describe the structure/location of the vascular bundles in a dicot leaf.

Answer 7

the VB form the midrib and veins and spread from the center of the leaf in a parallel line; xylem is found on upper side of the VB while phloem is found on the lower side

Question 8

What are the main transport organs in plants?

Answer 8

stems, roots, and leaves

Question 9

What two broad categories can flowering plants be classified into?

Answer 9

monocotyledons & dicotyledons

Question 10

What are the dermal tissues in plants?

Answer 10

epidermis and stomata

Question 11

What are the ground tissues in plants?

Answer 11

parenchyma, collenchyma, and sclerenchyma

Question 12

What does TS and LS stand for?

Answer 12

transverse sections and longitudinal sections

Question 13

What are some structural characteristics of parenchyma cells?

Answer 13

• packing tissue
• thin cellulose cell walls
• vary in size
• makes up cortex

Question 14

What are the four functions of parenchyma?

Answer 14

• food storage
• aids in water movement / storage
• support and gas exchange
• contain chloroplast for photosynthesis

Question 15

What are some structural characteristics of collenchyma cells?

Answer 15

• thick pectin and hemicellulose walls
• located below epidermis on outside of stems & midrib of leaves

Question 16

What is the function of collenchyma?

Answer 16

support

Question 17

What are some structural characteristics of sclerenchyma cells?

Answer 17

• dead cells
• cell walls contain lignin
• empty inside
• form fibers
• no intracellular spaces

Question 18

What is the function of sclerenchyma?

Answer 18

support and strength

Question 19

What is lignin?

Answer 19

a hard material made by plants for support (strengthens xylem vessels and sclerenchyma cells)

Question 20

Describe the overall path / flow of water in the root.

Answer 20

1. root hairs/epidermis
2. cortex (parenchyma)
3. endodermis
4. pericycle
5. root xylem

Question 21

How are mineral ions and organic compounds transported throughout the plant?

Answer 21

they are transported by being dissolved in water (mineral ions -> xylem; organic compounds -> phloem)

Question 22

What is the purpose of root hairs?

Answer 22

to increase the surface area for absorption of water

Question 23

uptake of water VS uptake of minerals

Answer 23

• uptake of water is passive and occurs by osmosis
• uptake of minerals occurs by diffusion or active transport

Question 24

What is transpiration?

Answer 24

the process in which the plants lose water due to evaporation in the leaves and stem

Question 25

What are the two pathways that water and the dissolved solutes can take to move across the cortex?

Answer 25

- Apoplastic: water moves through the cell walls - Symplastic: water moves from cell to cell via the plasmodesmata

Question 26

What cells make up xylem?

Answer 26

tracheids and xylem vessel elements

Question 27

vessel elements VS tracheids (structural)

Answer 27

**vessel elements** - short cells arrange in rows forming large tubes - large inner diameter and thinner cell walls - small and abundant pits - perforated plates **tracheids** - long cells with overlapping ends - small inner diameter and thicker cell walls - large and less abundant pits - no perforated plates

Question 28

How do xylem vessel elements die?

Answer 28

as lignin increases, the contents of the cell die, leaving an empty space (lumen)

Question 29

Why do pits form?

Answer 29

lignin is not laid down where there are groups of plasmodesmata

Question 30

Why are pits important?

Answer 30

pits link together with neighboring pits and provide water flow between the conducting elements

Question 31

How is mass flow accomplished?

Answer 31

through cohesion (water attracted to water) and adhesion (water attracted to lignin and cellulose)

Question 32

When does an air lock occur?

Answer 32

when air bubbles form in the column of water (in the xylem), the water stops moving due to the blockage

Question 33

How can water get through an air lock?

Answer 33

water can escape through pits

Question 34

How is water able to move from the root to the leaves via osmosis?

Answer 34

The leaves have lower water potential due to transpiration

Question 35

Describe some features of the apoplast pathway.

Answer 35

- most water travels through this route - water runs through cellulose walls, dead cells, and xylem hollow tubes - water moves by diffusion - apoplastic pathway occurs more rapidly than symplastic pathway

Question 36

What happens when water taking the apoplastic pathway reaches the Casparian strip (waterproof layer)?

Answer 36

water must go through the symplastic pathway (this helps control flow of mineral ions and generate root pressure)

Question 37

What material makes the Casparian strip waterproof?

Answer 37

suberin

Question 38

Describe some features of the symplast pathway.

Answer 38

- water travels through the cytoplasm and plasmodesmata or vacuole of cells - water moves by osmosis - movement of water is slower than apoplastic pathway

Question 39

What are some features of the root cap?

Answer 39

- tip of root - not permeable to water - provides protection

Question 40

What is the source and the sink?

Answer 40

- source: where assimilates are made - sink: where the assimilates are stored and developed

Question 41

What are the cells that make up phloem?

Answer 41

sieve tube elements and companion cells

Question 42

sieve tube elements VS companion cells (structural)

Answer 42

**sieve tube elements** - elongated - joined end to end with perforated end plates - walls made of cellulose - reduced cytoplasm - no nucleus & ribosomes **companion cells** - walls made of cellulose - has all the typical cell organelles

Question 43

What is translocation in phloem tissue?

Answer 43

transport of assimilates from source to sink (requires energy)

Question 44

List some common sources where assimilates are made.

Answer 44

- leaves and stem - storage organs (tubers and tap roots) - food stores in seeds

Question 45

List some common sinks where assimilates are required.

Answer 45

- meristems that are dividing - roots that are absorbing

Question 46

What are the two types of meristems?

Answer 46

- apical meristem (primary growth: top tip of plant and roots) - lateral meristem (secondary growth: widening of plant)

Question 47

What is the mass flow hypothesis?

Answer 47

there is a passive movement of sucrose from the source to the sink

Question 48

What two factors cause a buildup of hydrostatic pressure at the source?

Answer 48

- water is incompressible (occupies fixed volume) - the walls of the sieve tubes are rigid