3.1.3 - Transport in Plants Flashcards
What distinguishes stems from other parts of the plants
Presence of nodes and internodes
Role of vascular cambium
Responsible for secondary growth and contains meristematic tissue
Functions of roots
Anchor the plant in the ground
Store excess carbs
Absorbs water and minerals
Role of parenchyma
Involved in respiration, photosynthesis, storage and secretion
Heavily lignified
What is collenchyna tissue made of
Collenchyma cells
Pectin
Cellulose
Role of collenchyma
Provide support
Expands as the stem grows
Role of endodermal cells
Regulates the substances that enter
What is pericycle made of
Parenchyma and sclerenchyma
Role of pericycle
Maintains meristematic activity
What is xylem tissue made of
Tracheids
Vessel elements
Parenchyma
Sclerenchyma
Embolisms
Air bubbles formed in plant capillaries
Ions needed by plants
NO3 ^2- Mg ^2+ PO4 ^3- K ^+ SO4 ^2-
What is the cortex made of
Parenchyma
Transpiration
Loss of water from leaves of a plant, occurs from underside of leaf (stomata)
Water moves from areas of high hydrostatic pressure to areas of low hydrostatic pressure
Functions of water in plants
Turgidity - keep stems and leaves rigid
Photosynthesis
Enzyme reactions - metabolic processes occur in solution
Transport - ions absorbed in solution and transported in xylem
Apoplastic pathway
Water moving from soil solution to root hair and across cortex to the xylem in the cell walls
Symplastic pathway
Water moving from soil solution to root hair and across cortex to the xylem through the cytoplasm and plasmodesmata
Vacuolar pathway
Water moving from soil solution to root hair and across cortex to the xylem through the vacuoles
Factors affecting rate of transpiration
Temperature
Humidity
Light intensity
Wind
Lignin
Causes spirals in xylem
Allows cells to stretch/expand
Adaptations of vessel elements
Hollow lumen
Perforated cell ends
Lignin for rigidity
Casparian strip
Controls amount of water coming in the endodermis
Factors affecting transpiration
Temperature Humidity Light intensity Air movement Soil water availability
Control variables when using potometer
Cut at an angle to increase SA of lumen
Bung to stop water evaporating
Assemble potometer underwater - prevents air from entering
Dry leaves - no water molecules blocking stomata
Functions of roots
Anchor the plant in the ground
Store excess carb reserves
Absorb water and minerals
Purpose of root hairs
Provide a very large surface area for uptake of water and ions
Why is the root tip covered by a cap of cells
Protects dividing cells of the top and lubricates root movement
Meristem in roots
Increase height of plants
Meristem in stem
Increase plant girth
Stele
Section in middle of transverse section of dicotyledonous root
Endodermis
Xylem tissue
Phloem tissue
Water uptake
Water enters capillaries from soil (osmosis)
Apoplast and symplast pathways (root hair cells to cortex)
Water leaves apoplast at endodermis and enter from symplast
Water enters xylem under root pressure then travels in tracheids and vessel elements
Water carried to mesophyll through small veins
Evaporates in leaf air spaces and from stomata
Pith
Made of parenchyma cells
Forms inner cortex
Epidermis in plants
Protects moist under tissues from desiccation and invasion of pathogens
Transpiration
Loss of water from a plant
H2O moves from an area of high hydrostatic pressure to areas of low
What is transpiration affected by
Gravity
Electrostatic forces
Water potential
How does water enter the xylem from the soil
H2O moves into cell as active transport transports inorganic ions into the cell (ATP)
Lowers H2O potential –> higher conc. of solute; conc. gradient
H2O can moves from an area of high WP (soil) to an area of low WP (cell) - osmosis
Translocation
Movement of dissolved solutes (sucrose) from sources to sinks through the phloem
Why is translocation bidirectional
Roots can act as a sink by releasing carbs and also as a store depending on time of year
Process of translocation
Glucose formed in photosynthesis and condensed (sucrose)
Moves into companion cell by active transport (active loading)
Reduces WP allowing H2O to move in (osmosis)
Creates high hydrostatic pressure - mass flow
Sucrose diffuses out of phloem to where it’s needed for growth and storage
Mass flow
Assimilates enter sieve tube and lower wp
Water enters through osmosis and increases hydrostatic pressure
Assimilates leave at sink and increase wp
Water leaves and lowers hydrostatic pressure
High hydrostatic pressure, forcing sap through vessels towards regions of lower pressure
How does the process of translocation reoccur
Sink removes sugar, increases WP –> H2O leaves tubes (osmosis) keeping hydrostatic pressure low
Tonoplast
Membrane around cell wall
Function of endodermis
Controls amount of H2O coming in (casparian strip)
What is the Caspian strip made of
Suberin - impermeable to water, lipid
What does Casparian strip stop
Movement of water through the apoplast
Source to sink
Sugar moving from where its made to where its stored
Possible sinks
Seeds
Fruit
Meristems
Roots
Possible sources
Leaves
Food stores in seeds when they geminate
Storage organs
How does water get up the xylem
Root pressure
Capillary action
Transpirational pull
H2O cannot return to cortex through apoplast therefore pressure builds up in cortex pushing H2O up xylem
Root pressure
Endodermis in roots uses metabolic energy to pump ions into root
Reduces WP in xylem and medulla
H2O moves across endodermis into medulla (osmosis)
Capillary action
H2O can rise up a narrow tube against the force of gravity
Cohesion
Water molecules sticking together
Adhesion
Attraction between water molecules and the walls of the xylem
Transpirational pull
Loss of H20 through leaves must be replaced by H2O in xylem
H2O moves up xylem as a result of tension, created by loss of water in leaves
As H2O moves out of xylem, the whole column gets drawn up due to cohesion
How does water move in and exit the leaf
Enters through the xylem, passes through mesophyll (osmosis) and diffuses through air space in spongy mesophyll
As H2O vapour collects WP rises, when higher in the leaf –> diffuses out of stomata
Mesophytes
Plants adapted to a habitat with adequate water
Halophytes
Plants adapted to a salty habitat
Xerophytes
Plants adapted to dry habitats
Adaptations of xerophytes
Rolled leaves - reduce SA
Reduced no. and size of stomata - reduces diffusion
Sunken stomata - creates pocket of water vapour
Thick waxy cuticle - impermeable
Hairy leaves - traps water vapour
Dense spongy mesophyll - smaller surface area for evaporation
Thick stem - stores water
Hydrophytes
Plants adapted to live in freshwater
Adaptations of hydrophytes
Aerenchyma - parenchyma with many air spaces (buoyancy and flotation): allows O2 to diffuse to roots for aerobic respiration
Reduced root system - water can diffuse directly into leaves, feathery roots hold up plant
Large thin leaves
Stomata on the upper surface only
Adaptations of xylem
End walls removed to form long tubes
No cytoplasm/cell organelles - little resistance of flow of water
Lignified (waterproofing and strengthening)
Bordered pits - allow movement of water between vessels
Adaptations of sieve tube elements
Form long tubes End walls are retained End walls contain many sieve pores (sieve plates) Thin layer of cytoplasm Very few organelles; no nucleus
Adaptations of companion cells
Closely associated with sieve tube elements
Connected to sieve tube elements by many plasmodesmata
Dense cytoplasm with many mitochondria
Large nucleus
Cohesion-Tension theory
Evaporation at top of the xylem creates tension in the xylem
Water molecules are cohesive and form a column which is then pulled up by tension
Transpiration stream
Movement of water up xylem vessels from roots to leaves (area of high hydrostatic pressure to area of low hydrostatic pressure)
Translocation occurs through the sieve elements by …
Mass flow
What gets transported in translocation
Assimilates such as sucrose and amino acids
Why is using potometer not accurate
Assumption that water uptake by plants is the same as water loss
BUT water is used photosynthesis and is produced in respiration
Why does wind affect transpiration
Vapour around stomata is blown away
Reduces water vapour around stomata
Creates steeper wpg
Active loading
H+ ions pumped out of cc using active transport
Uses conc. gradient to move back into cc w. sucrose through a cotransporter protein
Sucrose builds up and diffuses through plasmodesmata into sieve tubes
Reduces wp
Why is water loss from the leaves unavoidable
Stomata opens for gas exchange for photosynthesis
Photosynthesis is necessary to make sugars
Water lost through the cuticle
Why is sucrose transported in translocation and not glucose
Soluble so can easily travel in solution
Metabolically inactive so not used during transport
Why does low temperature cause death of cells
Ice forms and pierces membranes
Denaturing of proteins
Evidence for the role of active transport in root pressure
Some poisons affect mitochondria and prevent production of ATP, when cyanide is applied to root cells, root pressure disappears
Root pressure increases w a rise in temp and decreases w/ a fall in temp –> chem reactions
If O2 levels fall or respiratory substrates so does root pressure
Guttation
Evidence for cohesion tension theory
Changes in diameter of trees - when transpiration is at its highest as is the tension, diameter shrinks
When a xylem vessel is broken air is drawn in rather than water leaking out
Plant can no longer move water up the stem as continuous stream is broken
Evidence for translocation
Microscopy allows us to see he adaptations of cc for active transport
If mitochondria of cc are poisoned, translocation stops
Flow of sugars n phloem is 10,000x faster than diffusion —> active process
Aphids
Why is water stopped from entering the apoplast through the casparian strip
Ensures that water and dissolved mineral ions (especially nitrates) have to pass into the cell through the plasma membrane so the water and ions are in the cytoplasm
Prevents water from cortex going back to medulla
