Unit 3 - Transport In Plants Flashcards
What distinguishes stems from other parts of the plant?
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 carbohydrates
Absorb water and minerals
Role of the Parenchyma
Involved in respiration, photosynthesis, storage and secretion
Heavily lignified
What is Collenchyna tissue made of?
Pectin
Cellulose
Collenchyna Cells
Role of Collenchyna?
Provide support
Expands as the stem grows
Role of endodermal cells?
Regulate the substances enter
What is pericycle made of?
Parenchyma
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
What is the cortex made of?
Parenchyma
Transpiration
Loss of water from leaves of a plant, occurs from the underside of the leaf, stomata.
Water moves from areas of high hydrostatic pressure to areas of low hydrostatic pressure
Functions of water in plants
Turgidity dash keep stems and leaves Richard
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 vacuoles
Factors affecting rate of transpiration
Temperature
Humidity
Light intensity
Wind
Lignin
Causes spirals in xylem
Allows cells to stretch and 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
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 lubricate roots movement
Meristem in roots
Increase height of pants
Meristem in stem
Increases plant girth
Stele
Section in the middle of transverse section of dicotyledonous route
– Endodermis
– xylem tissue
– Phloem tissue
Water uptake
Water enters capillaries from soil by osmosis
Apoplast and symplast pathways
Water leaves Apoplast at endodermis and enter from symplast
Water enters xylem under root pressure then travels in the tracheids and vessel elements
Water carried to mesophyll through small veins
Evaporate in leaf air spaces and stomata
Pith
Made from parenchyma cells
Forms inner cortex
Epidermis in plants
Protect moist under tissues from desiccation an invasion of pathogen
Translocation
Movement of dissolved Solutes ( sucrose) from sources to sinks ( tissues that need them ) through the phloem
What is translocation bidirectional?
Roots can act as a sink by releasing carbohydrates and also as a store depending on the time of year
Process of translocation
Glucose formed in photosynthesis and condensed
Moves into companion cell by active transport
Reduces water permeability allowing HT water moving
Create high hydrostatic pressure – maths floor
Sucrose diffuses out of phloem to where it’s needed for growth and storage
Mass flow
Assimilates enter sieve tube and lower water potential
Water enters through osmosis and increases hydrostatic pressure
Assimilate leave at sink and increase water pressure
Water leaves and lowers hydrostatic pressure
High hydrostatic pressure forces sap through vessels towards regions of low hydrostatic pressure
How does the process of translocation reoccur?
Sink remove sugar which increases water potential H2O leaves tubes keeping hydrostatic pressure low
Tonoplast
Membrane around cell wall
Function of endodermis
Controls amount of H2O coming in
What is the Caspian strip made of?
Suberin- Impermeable to water, lipid
What does Casperian strip stop?
Movement of water through the Apoplast
Sources to sink
Sugar moving from where it’s made to where it stored
Possible sinks
Seeds
Fruit
Meristems
Fruit
Possible sources
Leaves
Food stores in seeds
Storage organs
How does water get up the xylem?
Root pressure
Capillary action
Transpirational pull
H20 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 water potential in xylem and medulla H2O moves across endodermis into medulla
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 H2O through leaves must be replaced by H2O in the xylem
H2O moves up xylem as a result of tension, created by loss of water in leaves
H2O moves out of the 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 the Mesophyll and air space in spongy Mesophyll
H2O vapour collect water potential rises, when higher in the leaf
Mesophytes
Plants adapted to a habitat with adequate water
Halophytes
Plants adapted to a salty habitat
Xerophytes
Plants adapted to dry habitats
Adaptions of xerophytes
Rolled leaves – Reduces surface area
Reduced number and size of stomata – reduces diffusion
Sunken stomata - creates pockets 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
Arenchyma- parenchyma with many air spaces, buoyancy
Allows O2 to diffuse to roots for aerobic respiration
Reduced root system – water can directly into leaves, feathered 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 or cell organelles – little resistance to flow of water
Lignified waterproofing and strengthening
Boarded 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 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?
Assimilate such as sucrose and amino acids
What are assimilates?
Products of photosynthesis
Why does the wind affect transpiration?
Favour around the stomata is blown away
Reduces water vapour around stomata
Create a steeper water potential gradient
Why is water loss from the leaves unavoidable ?
Stomata open for gas exchange for photosynthesis
Photosynthesis is necessary to make sugars
Water loss through the cuticle
Why is sucrose transported in translocation 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 pieces membranes denaturing the 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 decreases
Root pressure increases with a rising temp and decreases with a fall in temperature
It’s O2 levels fall or raspatory substrates so does root pressure
Evidence for cohesion tension theory
Changes in diameter of trees – when transpiration is that its highest as is the tension, diameter shrinks
When is xylem vessel is broken air is drawn in rather than water leaking out
Plant can no longer move water of the stem as continuous stream is broken
Evidence for translocation
Microscopy has allowed us to see the adaptions of Companion cells active transport
If the mitochondria of companion cells are poisoned, translocation stops
Flow of sugars in phloem is 10,000 times faster than diffusion
Why is water stop from entering the apoplast through the Casparian strip?
Ensures water and dissolved mineral ions have to pass into the cell through the plasma membrane so the water and ions are in the cytoplasm
Prevent water from cortex going back to Medulla
