Transcript Exchange and transport File

DIFFUSION, OSMOSIS,
ACTIVE TRANSPORT
Outline for
revision
SIMPLE DIFFUSION
 SIMPLE DIFFUSION (or just diffusion) is a PASSIVE PROCESS
 requires no outside energy, using KINETIC ENERGY in SOLUTES
 Solutes move from a region of HIGH concentration to a region of
LOW concentration (along a concentration gradient)
 A difference in the concentration of a substance between two places is
called a concentration gradient or in this case a diffusion gradient
 NET movement of solutes continues until equilibrium is reached
 Once molecules have distributed evenly the system reaches equilibrium
and diffusion stops
 Molecules still move but equal numbers move in each direction
 Diffusion can occur in open systems or across membranes
THE RATE OF DIFFUSION
 Is DIRECTLY proportional to the
 SURFACE AREA of the membrane
 CONCENTRATION gradient
 TEMPERATURE
 Is INVERSELY proportional to the
 DISTANCE (e.g. thickness of the exchange surface)
EXAMPLES OF DIFFUSION:
 Oxygen diffusing from the alveoli in the lungs into the red blood
cells in the capillaries
 Oxygen diffusing from the red blood cells into the muscles
 Oxygen diffusing from air spaces in the soil into root hair cells
 Carbon dioxide diffusing from the air around leaves into the
leaf for photosynthesis
 Oxygen produced by photosynthesis moving from the leaf into
the air
 Carbon dioxide produced by respiration diffusing from the
muscles into the red blood cells
ACTIVE TRANSPORT
 ACTIVE TRANSPORT (or just diffusion) is a ACTIVE PROCESS that
requires energy from respiration
 Solutes move from a region of LOW concentration to a region of
HIGH concentration (i.e. against a concentration gradient)
EXAMPLES OF ACTIVE TRANSPORT:
 Mineral ions are absorbed from soil water, where they are at
low concentrations, into root hair cells where there are at high
concentration.
 Oxygen in the soil is needed to the cells do aerobic respiration
to provide energy for this process.
 Active transport is also needed in the kidney to reabsorb
glucose into the blood
OSMOSIS
 OSMOSIS (or just diffusion) is a PASSIVE PROCESS that requires
no outside energy, using only KINETIC ENERGY in WATER
 Is the net movement of water from a region of higher water
potential to lower water potential across a semipermeable
membrane.
 High water potential: where a solution is dilute, in other words is
relatively little solute.
 Low water potential: resolution is concentrated, in other words as a
large amount of solute.
TONICITY
 Hypertonic = lower water potential, more solute
 Isotonic = same water potential, same solute concentration
 Hypotonic = higher water potential, less solute
EXAMPLES OF OSMOSIS:
 Root hair cells
 have a higher concentration of minerals than the soil water around
them. In other words, they are hypertonic to the soil water
 the soil is hypotonic (higher water potential)
 so water moves from the soil into the root hair cell.
 Vacuoles in plant cells, for example leaf palisade cells,
 contain cell sap, which contains a high solute concentration.
 Water fills the cell by osmosis to maintain turgor – making the cells
stiff enough to support the leaf
TURGOR & PLASMOLYSIS
 TURGOR
 The hypertonic vacuole fills with
water, pressing the cytoplasm
against the cell wall.
 FLACCIDITY
 When the plant cells receive too little water, the surroundings do not have
as much water potential as they did.
 the vacuoles are no longer hypertonic to their surroundings.
 The vacuoles do not absorb water and the cells lose their turgor.
 the cells become soft – or flaccid – and no longer support the tissues of
the plant, so it wilts.
 PLASMOLYSIS
 When the vacuoles shrink extremely, the cytoplasm pulls away from the
cell wall, showing gaps.
 The cell is now in a plasmolysed state.
OSMOREGULATION
 In animals (including humans), if the blood is more dilute than
the tissues (is hypotonic, i.e higher water potential) water
moves into the tissues from the blood.
 Keeping tissue and blood concentration normal is important and is called osmoregulation
(The mechanism shown for
controlling the concentration
of the blood comes in the
section about homeostasis and
the kidney)