mass transport Flashcards
what is transported in the xylem and phloem?
xylem: water and mineral ions
phloem: organic substances eg sucrose/sugars
adaptations of xylem
end walls broken = continuous column
strengthened with lignin = support
no cytoplasm/organelles = doesn’t obstruct continuous flow
cohesion tension theory
water evaporates from mesophyll cels in leaf
water vapour diffuses out of leaf through stomata
down concentration gradient between leaf and air
creates tension which pulls more water into the leaf
water moves out of xylem into leaf cells
creates tension on column of water in xylem
water molecules cohesive, joined by hydrogen bonds
moves upwards
water enters root hair cells by osmosis
as water pulled upwards
evidence for cohesion tension
change in trunk diameter
- increased transpiration = narrower trunk as xylem pulled in by cohesion
translocation (mass flow)
at source
Sucrose actively transported into phloem
By companion cells
decreases water potential in phloem
so water moves in by osmosis from xylem
creates high hydrostatic pressure
at source
sugars used in respiration or stored
lower water potenial
so water moves out by osmosis into xylem
low hydrostatic pressure
creates pressure gradient
= mass transport from source to sink
evidence for mass flow
higher concentration of sucrose in sap nearer source than sink
- suggests osmosis would occur to move sugars
radioactive tracers to track movement of sugars
puncture phloem
sap flows out fast (faster nearer leaves then stem)
suggests there’s a pressure (gradient)
metabolic inhibitor (stops ATP production) stops translocation
suggests active transport involved
evidence against mass flow
sugar moves to many sinks
not just ones with lower water potential
sieve plates create a barrier
its of pressure needed to get solutes through fast enough
what is transpiration?
loss of water vapour from stomata by diffusion
due to water potential gradient between leaf and air
factors affecting transpiration
light - positive correlation
- stomata open when light for photosynthesis, allow transpiration
temperature - higher = faster
- warmer water molecules have more kinetic energy so evaporate faster, creates gradient so water diffuses out leaf faster
humidity - lower = faster
- air dry, concentration gradient between leaf and air increased, faster
wind - windier = faster
- blows water molecules from around stomata, increases concentration gradient
potometer
measures water uptake (assumes same as transpiration)
cut the shoot underwater
(stops air entering xylem)
cut at slant
(increase surface area)
assemble underwater so no air can enter
remove but keep end of capillary tube submerged in beaker
make sure water and air tight
shut tap (attached to resevoir, used to reset water bubble if needed)
remove end of capillary tube from beaker until air bubble formed before replacing it
record starting position and time
distance moved per unit time
rate of movement is estimate of rate of transpiration
how are radioactive tracers used to investigate translocation?
supply plant with organic substance that has a radioactive label
eg carbon dioxide (with radioactive isotope)
will be incorporated with organic substances in leaf and move around by translocation
movement tracked using autoradiography
- placed on photographic film
- turns black where radioactivity is
gas exchange in single celled organisms
absorb and release gas by diffusion through outer surface
large surface area to volume ratio
thin surface and short diffusion distance
gas exchange in fish
water enters fish through mouth
passes out through gills
each gill made of thin plates called gill filaments
- give large surface area for exchange
gill filaments covered in lamellae
- increase surface area more
lamellae have thin surface layer of cells and many blood capillaries to aid diffusion
by the counter current system
outline the counter current system
blood flows through lamellae in one direction and water flows in the opposite direction
maintains large concentration gradient between water and blood along whole lamellae
allows as much oxygen as possible to diffuse into blood
gas exchange in insects
air moves into tracheae through spiracles (pores)
oxygen travels down concentration gradient to cells
branch into tracheoles - have thin permeable walls straight to cells
carbon dioxide from cells move down its own concentration gradient to be released
gases not carried in blood
use rhythmic abdominal pumping to move air in and out of spiracles
gradient created as oxygen used by respiring cells
adaptations of insects gas exchange system
tracheoles have thin walls = short diffusion distance
highly branched and have many tracheoles = large surface area
and short diffusion distance
abdominal pumping moves air in and out to maintain concentration gradient
spiracles controlled by muscles, can close to reduce water loss
gas exchange in dicotyledonous plants
needs CO2 for photosynthesis and O2 for respiration, release
surface of mesophyll cells in leaf
- main gas exchange surface
- large surface area
- inside leaf
- contains many air spaces so co2 diffuses in
- used in photosynthesis by nearby chloroplasts = maintains concentration gradient
gases move in and out through stomata in epidermis
- open to allow gas exchange
- close to reduce water loss
- controlled by guard cells
adaptation of plants
large surface area - maintained by air spaces in leaf
short diffusion distance - thin tissues
large concentration gradient - gases used quickly in photosynthesis
how do insects reduce water loss?
close spiracles using muscles
reduce evaporation (less water lost)
- waterproof waxy exoskeleton
- hairs around spiracles, traps moist air
how do plants reduce water loss?
open stomata during the day
water enters guard cells making them turgid, stomata kept open
if dehydrated, guard cells lose water and become flaccid, closes stomata
xerophytes and their adaptations (5)
plants adapted to warm, dry or windy conditions, where water loss is an issue
stomata sucks in pits, trap moist air
- reduces concentration gradient of water so less water moves out of leaf
hairs on epidermis - trap moist air around stomata
curled leaves with stomata inside - protect them from wind (wind moves moist air, increasing concentration gradient and therefore evaporation)
reduce stomata, less to escape from
waxy cuticles, reduce evaporation
gas exchange in humans
air enters trachea
splits into 2 bronchi (one to each lung)
branches into bronchioles
end in alveoli (where exchange happens)
ribcage, intercostal muscles and diaphragm work to move air in and out
inspiration
external intercostal muscles contract
(internal relax)
diaphragm contracts
ribcage moves up and out
diaphragm flattens
increases volume of thoracic cavity
so decreases pressure (below atmospheric)
air flows down pressure gradients into lungs
inspiration active - requires energy
expiration
external intercostal muscles relax
(internal contract)
diaphragm relaxes
ribcage moves down and in
diaphragm domes again
decreases volume in thoracic cavity
so increases pressure (above atmospheric)
air flows down pressure gradient out of lungs
normal expiration passive - no energy
forced expiration active - internal and external intercostal muscles work together, decrease volume further, muscles antagonistic
gas exchange in the alveoli
alveoli surrounded by network of capillaries
- oxygen moves down concentration gradient into blood (in haemoglobin)
- carbon dioxide diffuses into alveoli and in breathed out
flow of blood in capillaries maintain concentration gradient
arrives as deoxygenated from heart and then carries oxygenation back to the heart
adaptations of alveoli
thin exchange surface
- epithelium one cell thick, creates short diffusion pathway
large surface area
- millions of them
steep concentration gradient
- maintain by blood flow
- allows quicker diffusion
how do you calculate pulmonary ventilation rate?
tidal volume x breathing rate
what is tidal volume?
volume of air in each breath
ventilation rate
number of breaths per minutes
forced expiratory volume
max volume of air breathed out in 1 second
forced vital capacity
max volume of air to be forcefully breathed out
TB
infection with bacteria
causes damage to gas exchange surface
= decreased tidal volume
smaller efficient surface area
fibrosis
formation of scar tissue in lungs
thicker and less elastic than normal
less able to expand
= reduced tidal volume
larger diffusion distance
reduced rate of gas exchange
= slower diffusion rate
asthma
airways become inflamed
muscle lining bronchioles contracts and lots of mucus produced
constriction so harder to breathe
= air flow restricted, less o2 in blood
emphysema
particles trapped in alveoli
causes inflammation, attracts phagocytes
produce enzyme that breaks down elastin
- makes alveoli elastic so loss means they cant recoil to expel air
- also damages walls so reduces surface area
= decreased rate of gas exchange
what do organism exchange with their environment?
take in oxygen and nutrients
excrete waste products such as CO2 and urea
exchange heat to maintain temperature
SA : V
smaller animals =
larger SA:V ratio
larger animals =
smaller SA:V ratio
affect of SA:V on heat and water loss
larger SA compared to V = increased heat loss
smaller animals
larger SA:V ratio
= lose heat and water more easily
therefore need higher metabolic rate to remain warm
- need adaptations if living in cool, eg eat high energy foods
- have kidney adaptations to produce small volumes of urine to retain water
larger animals
smaller SA:V ratio
= harder to lose heat and water
- need adaptation if living in heat eg large ears or in water to cool
