Lecture 4: Vascular system, to fetch a pail of water Flashcards
Are parenchyma cells alive at maturity?
yes
Are collenchyma cells alive at maturity?
yes
Are scelernchyma cells alive at maturity?
No
What are the functions of parenchyma
photosynthesis
regeneration
secretion
storage
What is the functions of collenchyma
supports the plants growing organs; as it is able to develop thick flexible walls
What is the function of sclerenchyma?
strengthens and supports plant organs that are no longer growing
What does it mean by vascular system?
transports nutrients throughout a plant
- such transport may occur over long distances more than 100m in the tallest plants
What are the properties of water
surface tension
adhesion
cohesion
What are the three stages of water transport in a tree
- ) water uptake of soil (roots)
- ) cohesion and adhesion in the xylem (trunk)
- ) transpiration (leaves)
How is the vascular system formed?
from the meristematic cells in young shoots and roots
What must divide to make xylem and phloem?
procambium
Where is the phloem located? outside or inside?
outside
Where is the xylem located? outside or inside
inside
Where does wood come from? xylem or phloem
xylem
what does the vascular system supply to the plant
water
minerals
sugars
What hormones are required for the development of xylem and phloem from the procambium
auxin and cytokinin
What is the function of the xylem?
conducts.. water and minerals absorbed from the roots upwards - principal water conducting tissue - also conducts minerals - contains cells that store food
What kind of tissue is the xylem (simple/complex?)
complex
true or false; the xylem makes continuous pipes?
true
What are the organisation types of xylem?
vascular bundles
vascular cylinders
Which is made first the metaxylem or the protoxylem?
protoxylem
true or false; the protophloem is crushed against the side of the epidermis of the plant because the xylem continues to increase in girth
true
What are the 3 cell types that the xylem is composed of?
tracheary elements
fibers
parenchyma
What do the tracheary elements do?
water conduction
What do fibers of the xylem do?
storage and support
What do the parenchyma of the xylem do?
storage
What are the types of tracheary elements?
tracheids
vessels
What are the characteristics of tracheary elements?
dead at maturity
long, narrow cells
have lignified secondary cell walls
confer strength and rigidity
What is the first type of tracheary elements formed?
protoxylem (rings/ annular thickenings)
What is the second type of tracheary elements formed?
metaxylem (spiral or reticulate thickenings)
Describe tracheids (all vascular plants)
pits in side walls
sealed at ends
water passes across cell sides
What are vessels (angiosperms)
shorter than tracheids
perforations at end of walls as well as pits at sides
PERFORATIONS HAVE NO SECONDARY OR PRIMARY CELL WALL
vessel may comprise several cells end on end
water moves freely in continuous tubes
pits are also present
Why do vessels need perforations?
during hot/windy weather; rapid transpiration
What are the downsides of using vessels to conduct water?
- susceptible to embolisms (pockets of air & water vapour)
- embolisms break the cohesion of water molecules (cavitation)
What are the effects of embolism?
break the continuity of water in xylem
- perforation contain air bubbles
- and water moves sideways through pits and continues upwards
What is apoptosis?
programmed cell death
how is the water transported up a plant? What physical changes must occur?
- root pressure (push)
- transpiration stream (pull)
How is transpiration increased?
eg. at noon the rate of transpiration increases as it is hotter
What happens at night?
- at night, transpiration is low; root cells continue to pump mineral ions into xylem of the vascular cylinder; lowering the water potential
Where does water flow in?
flow in from the root cortex
- generating root pressure
What does root pressure sometimes result in?
guttation
What is guttation
the exudation of water droplets on tips of grass blades or the lead margins of some small, herbaceous eudicots
What are the functions of the phloem?
- principal food conducting tissue; many succrose; other sugars eg. mannitol, sorbitol; amino acids, micronutrients, lipids
- major signaling superhighway (hormones,protein, RNA)
- transport up to 1m/hr in either direction
- osmotic pressure drives flow
- links all other cells
How does the phloem conduct the assimilate (food)
source to sink
What is a sugar source?
- is a plant organ that is a NET PRODUCER of sugar, such as mature leaves
What is a sugar sink?
- is an organ that is a net consumer or storer of sugar, such as tuber or bulbs, fruits, roots and shoots
What is an assimilate?
food
- must be transported from mature leaves to growing points( roots, shoots, fruits)
How is the plant body regulated?
regulation signals are transported via the growing points
What are the 3 cells of the phloem
sieve elements
sclerenchyma
parenchyma
What is the main function of the sieve elements of the phloem?
food conduction
What is the main function of the sclerenchyma of the phloem
support
What is the main functionof the parenchyma of the phloem?
off loading, storage
What are sieve elements
- highly specialized elongated cells
- living cells with no nucleus at maturity
- primary cell wall
- associated with companion cells and albuminous cells (specialized parenchyma cells)
What are the two types of sieve elements?
sieve cells
sieve tube members
What is the sieve cell?
- in gymnosperms
- narrow pores on all walls
- allow transport ACROSS CELLS
- no sieve plates
What is the pair of the sieve cell?
albuminous cell
What is the albuminous cell?
- parenchyma cell
- associated with the sieve cells
- similar function to companion cells
- don’t share precursor with sieve cell
- AID LOADING ON/OFF
What is a sieve tube member?
- in angioserms
- have narrow pores plus sieve plates
- more efficient transport
What is the pair of sieve tube members?
companion cells
What are companion cells?
- parenchyma cell
- associated with sieve tube members
- share precursor cell with sieve tube member
- aid loading and off loading
what happens when cells mature; damaged; what are the pores blocked by?
(P-protein) slime
callose (beta 1-4 glucan)
How do aphids retrieve phloem from a tree?
turgor pressure forces sieve tube sap through aphid (honeydew is exuded)
true or false; do ants farm aphids so that they can harvest honeydew from them?
true
How are aphids examined in the lab
stylet is severed
anesthetize aphid
harvest phloem in microlitres
Why are aphids examined in the lab?
so that signaling molecules in the phloem can be identified (RNA, protein, hormones, viruses)
