Flashcards in Transport In Plants Deck (54):
2 seed leaves
Branching pattern of veins
vascular tissues distributed throughout plant
xylem and phloem found together in vascular bundles that may also contain other types of tissues that give the bundle strength and help support plant.
Layer of dividing cells
Xylem contents travel...
Phloem contents travel...
Up and down
The way the vascular bundle is arranged in a young root...
provides strength to withstand the pulling forces to which roots are exposed
Endodermis in young root
special sheath of cells around the vascular bundle
gets water into xylem vessels
inside is layer of meristem cells called pericycle
In stems of non-woody plants the bundles are....
In in stems of woody plants the bundles are...
separate and discrete
separate in young stems and become continuous ring in older stems.
The way the vascular bundle is arranged in stems...
provides strength, and flexibility for the bending forces of the stem
In stems, between the xylem and phloem is a layer of _______ which is...
a layer of meristem cells that divide to produce the vascular bundle
In a leaf, the vascular bundle forms...
the midrib and veins, which get smaller as they spread
in veins, the xylem is on top of the phloem
Describe the structure and function of the xylem.
vessels to carry water/dissolved mineral ions
fibres to support plant
living parenchyma cells which act as packing tissue to separate and support the vessels
How do xylem vessels form?
lignin deposited on the walls makes them waterproof, strengthens vessel walls, and prevents vessel from collapsing, but kills cells, so the end walls and cell contents decay which forms long columns of dead cells with no contents.
Lignin thickening forms....
if ____________ is not complete then....
patterns in cell wall which may be spiral, annular (rings), or reticulate (broken rings)
prevents vessel being too rigid and allows flexibility
it leaves gaps in the cell wall which form bordered pits that allow water to pass between adjacent vessels and to the rest of the living part of the plant.
How are xylem vessels adapted?
made from dead cells in columns (carry stuff)
narrow tubes (so water column doesn't break easily and capillary action is effective
bordered pits (water can move sideways)
lignin in spiral/annular/reticulate (xylem can stretch as it grows)
no cross-walls, no cell contents, lignin prevents collapse (so water flow isn't stopped)
What is capillary action?
ability of fluid to flow in narrow spaces without external forces.
Describe the structure and function of phloem.
contains sieve tubes which are made of sieve tube elements and companion cells
sieve tubes have very thin walls
carries sap (sucrose dissolved in water)
Sieve tube elements?
lined up to form sieve tubes
has little cell contents to allow mass flow of sap
the ends have sieve plates (cross-walls) that have holes in them to allow sap movement
sieve plates keep lumen open and block tube when infected (with callose)
in between sieve tubes
large nucleus, dense cytoplasm
lots mitochondria (ATP for active processes)
help load sucrose actively into sieve tubes
What are the cytoplasmic bridges/cell junctions/gaps in cell walls that plant cells' cytoplasms are joined by?
(plasmodesma : singular)
water passes through cell walls and between cells by mass flow not osmosis
water passes through cell cytoplasm, plasma membrane and plasmodesmata
water passes through cytoplasm and vacuoles
What is water potential?
the tendency of water to move from one place to another
What is pressure potential?
What happens as pressure potential increases?
when the water in the cell exerts pressure on the cell wall
when cell full of water and turgid
reduces the flow of water into cell
What happens after water loss?
What is the tissue called now?
cytoplasm and vacuole shrink so no longer pushes against cell wall
plasma membrane loses contact with wall (plasmolysis)
What is TRANSPIRATION?
loss of water vapour from upper plant from stomata in leaves (open for gaseous exchange)
During transpiration, some water vapour leaves from where? but why does very little leave here?
through upper leaf surface
but waxy cuticle stops evaporation
In transpiration, where does the water evaporate from?
cell wall of spongy mesophyll
In transpiration, water vapour is lost...... gradient
as it is lost.....
this is useful because it...
down water vapour potential gradient
it has to be replaced so it draws water up the stem
transports mineral ions up plant, maintains turgidity, supplies water (growth, photosynthesis, evaporates and keeps plant cool)
5 environmental factors that affect transpiration
What is a potometer?
device that measures the rate of water uptake as a leafy stem transpires.
Precautions while using potometer to ensure valid results
set up under water to make sure no air bubbles in apparatus
cut stem under water to prevent air entering xylem
cut stem at angle to provide large SA in contact with water
What is the outermost layer of cells of a root called?
What does the epidermis of a root contain?
root hair cells which increase SA to absorb water/mineral ions from soil
What is the endodermis? (starch sheath)
layer of cells surrounding the medulla and xylem and contains granules of starch
What does the Casparian strip do?
blocks the apoplast pathway so mineral ions and water have to pass through the plasma membrane into cell
also stops water in medulla passing back into the cortex
Where does the water and mineral ions move?
How are mineral ions actively transported?
from the soil to root cortex to endodermis of vascular bundle to medulla (mineral ions actively transported, water follows by osmosis because of water potential difference)
by apoplast till endodermis then symplast (Casparian strip blocks apoplast)
transporter proteins in membrane pump them from cytoplasm of cortex cells to medulla and xylem
Describe the process of water moving up the stem.
transpiration pull and cohesion-tension theory?
pressure in root medulla builds when mineral ions in, so forces water into xylem and up (root pressure)
water molecules are attached by cohesion (hydrogen bonds) so when water is lost at the top, the column of water pulled up (cohesion-tension theory)
if water is broken in 1 xylem vessel, maintained through other vessel via bordered pits (all paragraph=transpiration pull)
adhesion attracts water to side of xylem vessel so pulls water up (capillary action)
when water leaves the xylem to the leaf, it creates low hydrostatic pressure and so tension
How does water evaporate from stomata?
evaporates from cells lining the cavity immediately above guard cells
What are terrestrial plants?
What are they adapted for?
To reduce water loss and replace water
How are terrestrial plants adapted? (4)
Waxy cuticle (reduce evaporation through epidermis)
Stomata located under surface (reduce E from direct sun heating)
Stomata close at night
Deciduous plants lose leaves in winter when water is less available (frozen?) and temp is too low for photosynthesis
What is Marram grass?Where does Marram grass grow?
Why do they need to adapt to this environment?
Xerophyte (needs little water)
Place lacks water
How is Marram grass adapted? (4)
Leaf rolled longitudinally (air trapped inside to reduce water loss)
Thick waxy cuticle on outer of rolled leaf
Stomata on inner of rolled leaf (protected) / in pits in lower epidermis (folded, in hairs)
Spongy mesophyll is dense (few air spaces so less SA for evaporation)
What are cacti?
Succulents (water in stems that are fleshy and swollen)
How are cacti adapted? (3)
Spines as leaves (reduce SA so less loss by transpiration)
Stem green (for photosynthesis)
Widespread roots (take up any rain)
What other features do xerophytes have?
Low water potential in leaf cells to reduce evaporation (maintained by high salt concentration)
Water potential between cells is reduced and leaf air spaces are reduced
What are hydrophytes?
What do they need for this environment?
Live in water
Need oxygen to float to keep leaves in light
How are hydrophytes adapted? (4)
Large air spaces in leaves (float to absorb sunlight)
Stomata on upper epidermis (exposed to air for gaseous exchange)
Stem has large air spaces (for buoyancy and oxygen to diffuse quickly to roots for respiration)
Tips or margins of leaves are hydathodes and they release water droplets then evaporate from leaf surface
What is translocation?
Transport of assimilates throughout the plant that occurs in the phloem
What is the source and sink?
The source is the part that loads assimilates to phloem sieve tubes.
The sink is the part that removes them
What is active loading?
Describe the process
Using energy from ATP in companion cells
-Energy is used to transport hydrogen ions out of companion cells to create a concentration gradient
-hydrogen ions diffuse back into companion cells through cotransporter proteins which only allow H if with sucrose molecules (cotransport)
-the concentration of sucrose increases in companion cells so diffuses through the plasmodesmata into sieve tubes.
Describe the movement of sucrose.
Sucrose moves by mass flow along the phloem which is caused by the difference in hydrostatic pressure between the ends of the tubes (pressure gradient).
Water enters at the source, which increases pressure and leaves at the sink which reduces pressure.
This causes the sap to flow from source to sink.
What happens when the sucrose enters sieve-tube elements?
The water potential decreases and water moves in by osmosis so increases hydrostatic pressure at the source
What happens at the sink when sucrose is present?
What if it's used in cells?
What happens when sucrose is removed from sap?
The sucrose is used for respiration, growth in meristem and is converted to starch to store in roots
It diffuses out of the sieve tubes via plasmodesmata or by active transport
The water potential decreases and water moves out so hydrostatic pressure decreases