Transport and Exchange
Mechanisms
cells need to receive metabolites
from surrounding metabolic processes
- e.g. glucose (respiration)
- nitrates for plants + synthesis amino acids
waste products need to be
removed from cells
- e.g. CO2 from respiration
- urea - waste product
Types of
Organisms
unicellular
use cell membrane as
exchange surface
multicellular
specialised exchange surfaces
to exchange substances
complex
organisms
need transport system to
link exchange surface to all cells
Surface Area
D: can be represented as the total
number of cells in direct contact with
surrounding environment
absorptive surface area - measure of
rate of supply of metabolites to tissue
Volume
D: the total 3D space occupied by
metabolically active tissues
a measure of an organisms
demand for metabolites
Surface Area to
Volume Ratio
as surface area
INCREASES,
SA:V DECREASES
CUBE
as side of cube
increase, SA:V
ratio decrease
Small
Organisms
can gain ALL metabolites +
remove all waste via body surface
large SA:V ratio
Large
Organisms
small SA:V ratio
greater metabolic needs so
requirement of metabolites
higher
multicellular animals so majority
of cells not in direct contact
with surrounding environment
have SPECIALISED
EXCHANGE SURFACES
Features of Exchange
Surfaces
Increased Surface
Area
Thin Separating
Surface
Large
Conc.
Gradients
will INCREASE
overall SA:V ratio
FLATTENED
SHAPE
SPECIAL EXCHANGE
SURFACES
e.g. flatworm
increases SA:V ratio
decreases diffusion
distance
need to be MOIST
EXTERNAL
INTERNAL
e.g. gills of
young tadpole
e.g. fish gills +
alveoli in mammals
need to be thin so RATE
of DIFFUSION is MAXIMISED
conc. gradient necessary for
diffusion to occur
Small organism - constantly
use oxygen for respiration
Large organisms - ventilation systems
e.g. breathing in mammals
Mass Flow
internal
transport
system
D: allows transport of substances in
larger organisms
- All molecules swept along
in SAME direction. - Brought about by pressure difference within organism
SOURCE - Pressure
generated
SINK - Pressure
much less
Examples
Xylem tissue
transports water + mineral ions
from the root to the leaves
water evaporation from leaf
creates tension (negative pressure)
that pulls water up through xylem
via transpiration system
Phloem
tissue
transports sucrose (translocation)
to roots (for storage of carbohydrates)
and to growing regions (energy for growth)
- energy expenditure involved
moving sucrose into phloem. - ATP used move sucrose from
companion cell to phloem sieve tube
Circulatory system
High pressure generated
by pumping of heart
transports substances - O2, CO2, glucose,
amino acids, lipids, urea in blood system
around body
Ventilation (breathing)
in mammals
- reduction of pressure in thorax
causes air to enter lungs (inhalation) - increased pressure in thorax
causes air to be expelled from lungs
(exhalation)
brings in O2 rich air into lungs and removes
air with raised CO2 levels.
Ensures diffusion of respiratory gases
can take place between alveoli and capillaries