C7: Transport In Plants Flashcards
What is the plant vascular system?
It is a complicated network of conducting tissues that interconnects all organs and transports materials
What does xylem transport and from where to where?
water and mineral ions from roots to the rest of the plant
What does phloem transport and from where to where?
sugar (sucrose) from source to sink
What direction(s) do xylem and phloem move in?
- xylem moves up
- phloem can move up and down
Describe the structure/location of the vascular bundles in a dicot root.
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)
Describe the structure/location of the vascular bundles in a dicot stem.
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)
Describe the structure/location of the vascular bundles in a dicot leaf.
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
What are the main transport organs in plants?
stems, roots, and leaves
What two broad categories can flowering plants be classified into?
monocotyledons & dicotyledons
What are the dermal tissues in plants?
epidermis and stomata
What are the ground tissues in plants?
parenchyma, collenchyma, and sclerenchyma
What does TS and LS stand for?
transverse sections and longitudinal sections
What are some structural characteristics of parenchyma cells?
- packing tissue
- thin cellulose cell walls
- vary in size
- makes up cortex
What are the four functions of parenchyma?
- food storage
- aids in water movement / storage
- support and gas exchange
- contain chloroplast for photosynthesis
What are some structural characteristics of collenchyma cells?
- thick pectin and hemicellulose walls
- located below epidermis on outside of stems & midrib of leaves
What is the function of collenchyma?
support
What are some structural characteristics of sclerenchyma cells?
- dead cells
- cell walls contain lignin
- empty inside
- form fibers
- no intracellular spaces
What is the function of sclerenchyma?
support and strength
What is lignin?
a hard material made by plants for support (strengthens xylem vessels and sclerenchyma cells)
Describe the overall path / flow of water in the root.
- root hairs/epidermis
- cortex (parenchyma)
- endodermis
- pericycle
- root xylem
How are mineral ions and organic compounds transported throughout the plant?
they are transported by being dissolved in water (mineral ions -> xylem; organic compounds -> phloem)
What is the purpose of root hairs?
to increase the surface area for absorption of water
uptake of water VS uptake of minerals
- uptake of water is passive and occurs by osmosis
- uptake of minerals occurs by diffusion or active transport
What is transpiration?
the process in which the plants lose water due to evaporation in the leaves and stem
What are the two pathways that water and the dissolved solutes can take to move across the cortex?
- Apoplastic: water moves through the cell walls
- Symplastic: water moves from cell to cell via the plasmodesmata
What cells make up xylem?
tracheids and xylem vessel elements
vessel elements VS tracheids (structural)
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
How do xylem vessel elements die?
as lignin increases, the contents of the cell die, leaving an empty space (lumen)
Why do pits form?
lignin is not laid down where there are groups of plasmodesmata
Why are pits important?
pits link together with neighboring pits and provide water flow between the conducting elements
How is mass flow accomplished?
through cohesion (water attracted to water) and adhesion (water attracted to lignin and cellulose)
When does an air lock occur?
when air bubbles form in the column of water (in the xylem), the water stops moving due to the blockage
How can water get through an air lock?
water can escape through pits
How is water able to move from the root to the leaves via osmosis?
The leaves have lower water potential due to transpiration
Describe some features of the apoplast pathway.
- 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
What happens when water taking the apoplastic pathway reaches the Casparian strip (waterproof layer)?
water must go through the symplastic pathway (this helps control flow of mineral ions and generate root pressure)
What material makes the Casparian strip waterproof?
suberin
Describe some features of the symplast pathway.
- water travels through the cytoplasm and plasmodesmata or vacuole of cells
- water moves by osmosis
- movement of water is slower than apoplastic pathway
What are some features of the root cap?
- tip of root
- not permeable to water
- provides protection
What is the source and the sink?
- source: where assimilates are made
- sink: where the assimilates are stored and developed
What are the cells that make up phloem?
sieve tube elements and companion cells
sieve tube elements VS companion cells (structural)
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
What is translocation in phloem tissue?
transport of assimilates from source to sink (requires energy)
List some common sources where assimilates are made.
- leaves and stem
- storage organs (tubers and tap roots)
- food stores in seeds
List some common sinks where assimilates are required.
- meristems that are dividing
- roots that are absorbing
What are the two types of meristems?
- apical meristem (primary growth: top tip of plant and roots)
- lateral meristem (secondary growth: widening of plant)
What is the mass flow hypothesis?
there is a passive movement of sucrose from the source to the sink
What two factors cause a buildup of hydrostatic pressure at the source?
- water is incompressible (occupies fixed volume)
- the walls of the sieve tubes are rigid
