3.1 Exchange and transport Flashcards
Why plants need transport systems
Need substances e.g. water, minerals and sugars
Need to get rid of waste e.g. oxygen
Some materials only obtained from specific parts of plant e.g. minerals in soil
Xylem functions
Transport water and dissolved minerals up the plant
Support
Phloem functions
Transports sugars (glucose) and other assimilates in solution up and down the plant
vascular system positions in roots
xylem (in cross / star shape) at the centre
phloem surrounds xylem’s arms
provides support for the root
vascular system in stems
near the outside
xylem closer to the centre and separated from phloem by cambium
provides “scaffolding” to reduce bending of stem
vascular system in leaves
forms veins
xylem at the top of leaf
phloem under the leaf
factors affecting organisms needing specialised exchange surfaces
size
SA:V ratio
level of activity
how size affects need for specialised exchange surfaces
multicellular organisms have several layers of cells diffusion too slow to enable sufficient supply to innermost cells
how SA:V ratio affects need for specialised exchange surfaces
lower in larger organisms
diffusion not sufficient and will not meet requirements due to larger relative volume
how level of activity affects need for specialised exchange surfaces
cells of active organisms need to respire more
needs a more sufficient supply of nutrients and oxygen to keep up rate of respiration
features of good exchange surfaces
large surface area (more space for molecules to pass through)
thin permeable barrier (reduce diffusion distance)
good constant blood supply (maintains a steep concentration gradient so diffusion occurs rapidly all the time)
cartilage functions and location
prevents airways from collapsing during inspiration
tracheal cartilage is C-shaped to allow flexibility and space for food to pass down oesophagus
found in trachea and bronchi
ciliated epithelium functions and location
lines airways
“wafts” to and fro to move mucus up and out of trachea and down oesophagus
found in trachea, bronchi and bronchioles
goblet cell functions and location
secretes mucus (traps microbes and removed to prevent infection) found in trachea, bronchi and larger bronchioles
smooth muscle functions and location
contracts around airways to control size of lumen
prevents harmful substances from entering lungs
found in trachea, bronchi and bronchioles
elastic fibres functions and location
provides recoil when smooth muscles relax, helps airway to open again
stretches when smooth muscles contract
in alveoli, stretch during inspiration (more volume = more air)
in alveoli, provide recoil to help push out air
rib cage function and location
protects organs in thoracic cavity e.g. lungs and heart
surrounds lungs and heart
internal and innermost intercostal muscles functions and location
can contract during expiration to reduce volume of thorax and lungs (only during exercise or coughing and sneezing)
pressure increases over atmospheric pressure
air rushes out of lungs
found between ribs
external intercostal muscles functions and location
elevates ribs (via contracting) during quiet and forced inhalation
increases thoracic volume
decreases pressure lower than atmospheric pressure
air rushes into lungs
found between ribs
diaphragm functions and location
contracts and flattened during inhalation, allowing lungs to move down
increases thoracic volume
decreases pressure lower than atmospheric pressure
air rushes into lungs
found under lungs
inspiration method
diaphragm contracts and moves down and becomes flatter (displaces digestive organs downwards)
external intercostal muscles contract and raise ribs
volume of chest cavity increased
pressure in chest cavity drops below atmospheric pressure
air moves into lungs
expiration method
diaphragm relaxes and pushed up by displaced digestive organs underneath
external intercostal muscles relax and ribs fall
internal intercostal muscles may contract to help (only during exercise or coughing/sneezing)
volume of chest cavity decreased
pressure in lungs rises above atmospheric pressure
air moved out of lungs
vital capacity definition
maximum volume of air they can be moved by the lungs in one breath
dependant on size of person (height), age, gender and level of regular exercise
tidal volume definition
volume of air moved in and our with each breath
normally at rest
usually sufficient to supply all oxygen required in body at rest
residual volume definition
volume of air that remains in the lungs even after forced expiration
breathing rate
how many breaths per minute
oxygen uptake
how much oxygen is used up per minute
can be assumed as the oxygen used up in spirometer
spirometer safety precautions
medical grade oxygen used (there is enough oxygen, no microbes)
water level not too high (doesn’t enter tubes)
disinfect equipment (microbes)
check patients health (e.g. no lung problems)
soda lime (absorb CO2 from chamber)
spirometer validity precautions
nose clip (all air breathed comes from chamber) make sure everything is airtight (no oxygen lost through leaks)
buccal cavity definition
the mouth
countercurrent flow definition
where two fluids flow in opposite directions
maintains constant concentration gradient throughout gill lamellae
gill filament definition
slender branches of tissue that make up gill (primary lamellae)
gill plates definition
folds of the gill filaments to increase surface area (gill plates)
operculum definition
bony flap that covers and protects gills
gills structure
thin gill filaments located on gill arch
surface of gill filaments folded into gill plates
blood capillaries carry deoxygenated blood close to surface of fill plates where exchange takes place
countercurrent flow in fish
blood flows along gill arch and our along filaments to gill plates
blood flows through capillaries in opposite direction to flow of water over gill plates
creates countercurrent flow
maximises amount of oxygen from water (maintains steep concentration gradient)
gas exchange in insects
air-filled tracheal system (air directly to all respiring tissue)
air enters system via spiracle
transported into body via tracheae then tracheoles
gas exchange occurs between air in tracheole and tracheal fluid
also across thin walls of tracheoles
tracheal fluid can be withdrawn into body fluid so increase SA of tracheole wall exposed to air (more O2 can be absorbed when active)
ventilation in insects
tracheal system expanded and have flexible walls
become air sacs (squeezed by action of flight muscles)
repetitive expansion and contraction ventilates tracheal system
movement of wings alter volume of thorax
thorax volume decreases, air in tracheal system out under pressure and pushed out
thorax volume increases in pressure, pressure inside drops and air rushes into system
abdomen expands, spiracles at front end of body opens
abdomen reduces in volume, spiracles at rear end open
dicotyledonous plants
two seed leaves
characterised distribution of vascular tissues (in vascular bundles)
xylem structure
vessels (carries water and dissolved mineral ions)
fibre (helps support plant)
living parenchyma cells (packing tissues to separate and support vessels)
xylem vessels structure
lignin impregnates walls of cells as vessels develops
(leaves cell dead with no contents, prevents cell from collapsing, leaves cell open at all times)
lignin forms in patterns (not too rigid, allows flexibility)
bordered pits (allows water to move between vessels in case of blockage or pass into living part of plant)
adaptations of xylem
dead cells aligned end to end with no end walls (forms continuous column)
tubes narrow (water column doesn’t break easily, capillary action more effective)
bordered pits (allows water to move between vessels in case of blockages)
lignin deposited in spiral, annular or reticulate pattern (allows for stretching for growth, bending for stem or branch)
why flow of water is not impeded in xylem
no cross walls
no cell contents, nucleus or cytoplasm
lignin thickening prevents walls from collapsing
phloem structure
sieve tube (carries assimilates in solution up and down plant) companion cell (pumps sucrose into siege tube elements)
sieve tube structure
made up of sieve tube elements
no nucleus, very little cytoplasm (space allows mass flow to occur)
sieve plates at ends of elements (allows movement of sap from one element to next)
companion cell structure
between sieve tubes
numerous mitochondria (more ATP production for active loading)
large nucleus (genetic information for own and sieve tube element)
dense cytoplasm
pathways taken by water
apoplast pathway (passes through cell wall and between cells, carries mineral ions, moves via mass flow) symplast pathway (enters cell cytoplasm through membrane, passes through plasmodesmata to next cell) vacuolar pathway (symplast pathway but also through vacuole)
water uptake of plant cell in pure water
water molecules move into cell (down water potential gradient)
won’t burst because strong cellulose cell wall
water inside cell exerts pressure on cell wall (pressure potential)
reduces influx of water
cell is turgid
water loss in plant cell
placed in solution with very negative water potential
water moves out of cell (moves down water potential gradient)
vacuole and cytoplasm shrink
cytoplasm no longer pushes against cell well (no longer turgid)
plasma membrane loses contact with wall (plasmolysis)
cell is now flaccid
transpiration definition
loss of water vapour from upper parts of plant (though leaves)
pathway of water in leaves
water enters leaf through xylem
moves into cells in spongy mesophyll (osmosis or apoplast pathway)
evaporates from cell walls of spongy mesophyll
moves through stomata (down water vapour potential gradient)
lowers water potential in leaf and draws more water from xylem
importance of transpiration
transfers mineral ions up plant
maintains cell turgidity
supplies water for growth, cell elongation and photosynthesis
cools down plant on hot day (supplies water)
environmental factors of transpiration
light intensity temperature relative humidity air movement (wind) water availability
how light intensity affects transpiration rate
stomata opens in light
allows for gaseous exchange for photosynthesis
higher light intensity = faster transpiration rate
how temperature affects transpiration rate
increases rate of evaporation from cell surfaces in spongy mesophyll (water vapour potential in leaf rises)
increases rate of diffusion as water molecules have more kinetic energy
decreases relative water vapour potential in air (steeper water vapour potential gradient)
how relative humidity affects transpiration rate
increases water vapour potential in air (less steep water vapour potential gradient)
slows rate of diffusion
how air movement affects transpiration rate
wind carries water vapour away from leaf
maintains steep water potential gradient
how water availability affects transpiration rate
if insufficient water in soil
plant cannot replace lost water
stomata close and leaves wilt
potometer uses
measures water uptake in shoots
estimate transpiration rate
potometer precautions for validity
set up under water (no air bubbles in apparatus)
shoot is healthy
cut stem under water (no air bubbles in xylem)
cut stem at angle (larger SA in contact with water)
dry leaves
allow shoot to acclimatise
adhesion definition
attraction between water molecules and other particles e.g. walls of xylem vessel
cohesion definition
attraction between water molecules due to hydrogen bonds
transpiration stream definition
movement of water from soil, through plant, to air surrounding leaves
main driving force is water potential gradient between soil and leaf air spaces
water uptake and movement across root
RHC absorb water and mineral ions from soil (osmosis and active transport)
water moves through cortex and towards vascular bundle via osmosis or apoplast pathway
water movement into xylem from root
Casparian strip blocks apoplast pathway (all mineral ions and water must go through plasma membrane of endodermis)
plasma membrane contains transporter proteins (pumps mineral ions into xylem)
water potential in xylem more negative
water moves down water potential gradient into xylem via osmosis
can’t move backwards in apoplast pathway due to Casparian strip
movement of water up stem
mass flow (flow of water and mineral ions in same direction) helped by root pressure, transpiration pull and capillary action
how root pressure moves water up stem
endodermis moving minerals into xylem vessels, draws water into xylem by osmosis
builds up pressure in xylem and forces water in and up to xylem
how transpiration pull moves water up stem
water molecules form water column due to cohesion (caused by polarity in water molecules)
pulled up as water is lost via transpiration - creates tensions (why xylem vessels need lignin to prevent from collapsing)
how capillary action moves water up stem
water molecules attracted to side of xylem vessels (adhesion due to polarity)
can pull up water as vessels are very narrow
hydrophyte definition
plant adapted to living in water or where ground is wet
xerophyte definition
plant adapted to living in very dry (arid) conditions
how most terrestrial plants reduce water loss
waxy cuticle (reduce water evaporation through epidermis)
stomata underside of leaf (reduces evaporation due to direct heating from sun)
stomata closed at night (no light for photosynthesis)
deciduous plants lose leaves (temperature and light too low for photosynthesis, ground is frozen so water scarce)
xerophytic features
rolled leaf (traps air to increase humidity around stomata)
thick waxy cuticle (reduces evaporation)
stomata in pits with hairs (reduces air movement)
dense spongy mesophyll (less SA for evaporation)
leaves = spines (reduces SA for stomata)
long tap root (reach water deep underground)
closing stomata (reduces need to take up water)
low water potential in leaf cells (less evaporation as gradient reduced between cells and air spaces)
hydrophytes features
large air spaces in leaf (keeps leaf afloat so in air and absorb sunlight)
stomata on upper epidermis (exposed to air to allow gaseous exchange)
many large air spaces in stem (buoyancy, helps oxygen diffuse quickly to roots for respiration)
hydathodes
pores at tips or margins of leaf
release water droplets (guttation)
assimilate definition
substances made by the plant, using substances absorbed from environment e.g. amino acids and sucrose
source definition
part of plant that loads assimilates into sieve tubes
sink definition
part of plant that removed assimilates from sieve tubes
active loading process
companion cell pumps out hydrogen ions (energy from ATP)
increases H+ conc. outside, decreases conc. inside (creates gradient)
H+ diffuses back into companion cell with sucrose (controlled by cotransporter proteins on membrane) - facilitated diffusion / secondary active transport
concentration of sucrose increases in companion cell and moves down gradient into siege tube via plasmodesmata
movement of sucrose
mass flow in solution (sap) in phloem
sucrose enters sieve tube at source (active transport)
decreases water potential, water moved into sieve tube, increases hydrostatic pressure
sucrose leaves sieve tube at source (osmosis)
increases water potential, water moves out of sieve tube, decreases hydrostatic pressure
how we know phloem is used for translocation
radioactively labelled CO2 appears in phloem
aphids insert mouthparts into phloem to feed
sugars collect above ring when tree is ringed to remove phloem
how we know ATP is used for translocation
companion cells have many mitochondria
translocation stopped if poison that stops ATP is given
flow of sugars very high (much faster then diffusion so ATP used for active transport)
how we know active loading is used for translocation
pH of companion cells higher than surrounding cells
concentration of sucrose higher in source than sink
evidence against translocation
not all solutes in phloem move at same rate
sucrose moves to all parts of plant at same rate (regardless of lower concentrations)
role of siege plates unclear
ventilation in fish
mouth opens, floor of mouth lowers
increases volume, lowers pressure, water enters buccal cavity
mouth closes, floor raised
decreases volume, increases pressure, pushing water through gills
operculum moves outwards, decreasing pressure at gills (helps movement)
alveoli adaptations
lots of alveoli (large SA)
surfactant produced (prevents walls from sticking and collapsing)
made up of 1 layer of cells (reduces diffusion distance)
also squamous epithelial cells thin and flat
capillaries run directly on top (maintains steep concentration gradient)
elastic (helps expel air, maintains steep concentration gradient)
Casparian strip location and function
made up of suberin (waterproof)
found in the endodermis cells
prevents apoplast pathway from occurring
