Transcript Detailed movement of substances

Movement of Substances
Chapter 3
Learning Objectives...
DIFFUSION
• define diffusion
• discuss its importance in nutrient uptake and gaseous
exchange in plants and humans.
OSMOSIS
• define osmosis
• discuss the effects of osmosis on plant and animal tissues.
ACTIVE TRANSPORT
• define active transport
• discuss its importance as an energy-consuming process by
which substances are transported against a concentration
gradient,
– E.g.: ion uptake by root hairs
– E.g.: uptake of glucose by cells in the villi
Movement of Substances
Diffusion
Osmosis
Active Transport
What are these items???
Movement of Substances
Diffusion
Osmosis
Active Transport
What happens when you
spray air freshener in one
corner of the room?
Movement of Substances
Diffusion
Osmosis
Active Transport
Movement of air particles...
The gas
particles spread
out from the
source to the
rest of the
room.
Movement of Substances
Diffusion
Osmosis
Active Transport
Movement of air particles...
The gas
particles spread
from a region
of higher
concentration
to a region of
lower
concentration.
Movement of Substances
Diffusion
Osmosis
Active Transport
Movement of air particles...
• Air freshener particles spread from a
region of higher concentration to a region
of lower concentration.
• The two regions of different concentrations
form a concentration gradient.
Movement of Substances
Diffusion
Osmosis
Active Transport
Movement of air particles...
• Air freshener particles will keep moving
down the concentration gradient until the
particles are evenly spread out.
• The particles are then said to be in
dynamic equilibrium
– The particles are in constant random motion
– But there is no net movement of particles
This movement of particles down the
concentration gradient is known as
DIFFUSION.
Movement of Substances
Diffusion
Osmosis
Active Transport
Defining Diffusion...
DIFFUSION is
the NET MOVEMENT of particles
from a region of HIGHER CONCENTRATION
to a region of LOWER CONCENTRATION
down a CONCENTRATION GRADIENT.
Movement of Substances
Diffusion
Osmosis
Active Transport
Defining Diffusion...
DIFFUSION is
the NET MOVEMENT of particles
from a region of HIGHER CONCENTRATION
to a region of LOWER CONCENTRATION
down a CONCENTRATION GRADIENT.
Diffusion stops when particles reach
DYNAMIC EQUILIBRIUM.
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion of a Dissolved Substance
Investigation 3.1 TB Pg 32
Place a drop of potassium permanganate solution at
the bottom of a beaker of water. Observe the
changes in the colour of the water.
OBSERVATIONS
• Potassium permanganate
particles move up the water
from a region of higher
concentration to regions of
low concentration.
• Over time, a homogeneous
solution will be obtained.
Movement of Substances
Diffusion
Osmosis
Active Transport
Question!
Copy and complete the sentence...
Diffusion is the NET movement of particles
from a
HIGHER
concentration to a
LOWER
concentration until they
reach DYNAMIC EQUILIBRIUM, whereby the
particles are spread out
EVENLY
.
Movement of Substances
Diffusion
Osmosis
Active Transport
Question!
Answer on a sheet of foolscap paper...
“You can smell food when molecules from the
food enter your nose.”
Explain how the molecules get from the food
to your nose.
Movement of Substances
Diffusion
Osmosis
Active Transport
Question!
Moths emit chemicals (called pheromones) to
attract a mate.
a) Which process is responsible for the
distribution of these chemicals through the
air?
b) If a moth detects pheromones, how might it
work out which direction they are coming
from?
c) What would be the advantage of a moth
releasing the pheromones on a night when
there was little wind?
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion across a Membrane
• Diffusion can occur across a permeable
membrane.
• At the end, there will be equal concentrations
of all ions on both sides of the membrane.
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion across a Membrane
• Sugar molecules diffuse across the membrane to the
right side.
• Water molecules will diffuse across the membrane to
the left side.
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion in Cells
Diffusion is an important way by which oxygen
and carbon dioxide move into and out of cells.
food and oxygen
diffuse in
carbon dioxide and
waste products
diffuse out
An amoeba
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion in Cells
In the lungs,
• Oxygen diffuses from the lungs into blood
vessels
• Carbon dioxide diffuses out of the blood vessels
into the lungs
Gaseous exchange in the lungs
Movement of Substances
Diffusion
Osmosis
Active Transport
Diffusion in Cells
In the root hair cell,
• Oxygen diffuses into the root hair cell
• Carbon dioxide diffuses out of the root hair
cell
oxygen diffuses in
carbon dioxide
diffuses out
A root hair cell
Movement of Substances
Diffusion
Osmosis
Active Transport
What affects the RATE of diffusion?
• Steepness of concentration gradient
– The steeper the concentration gradient, the
faster the rate of diffusion
• Heat
– Heat causes particles to gain kinetic energy
and move faster.
– The higher the temperature, the faster the
rate of diffusion.
Movement of Substances
Diffusion
Osmosis
Active Transport
What is Osmosis?
Movement of Substances
Diffusion
Osmosis
Active Transport
• Solute molecules cannot diffuse across a partially
permeable membrane.
• Water molecules move from the left arm to the
right arm of the U-tube.
• Level of solution in the left arm falls, while the
level of solution in the right arm rises.
• Net result: both arms contain the same
concentration of solution
Movement of Substances
Diffusion
Osmosis
Active Transport
Defining Osmosis...
OSMOSIS is
the NET MOVEMENT of WATER MOLECULES
from a solution of HIGHER WATER POTENTIAL
to a solution of LOWER WATER POTENTIAL
through a PARTIALLY PERMEABLE MEMBRANE.
Movement of Substances
Diffusion
Osmosis
Active Transport
What is Water Potential?
• Water potential is a measure of the
tendency of water to move from one place
to another.
– A dilute solution has more water molecules
per unit volume than a concentrated
solution, thus it has a higher water potential
Movement of Substances
Diffusion
Osmosis
Active Transport
What is Water Potential?
• When a partially permeable membrane separates 2
solutions of different water potentials, a water
potential gradient is established.
• Water always moves down a water potential
gradient.
partially permeable
membrane
Movement of Substances
Diffusion
Osmosis
Active Transport
Demonstrating Osmosis
Investigation 3.2 TB Pg 35
Expected Observation:
• The liquid level
inside the thistle
funnel rises.
thistle funnel
water
sucrose solution
cellophane paper
(partially permeable membrane)
Movement of Substances
Diffusion
Osmosis
Active Transport
Demonstrating Osmosis
Investigation 3.2 TB Pg 35
Expected Observation:
• The liquid level
inside the thistle
funnel remains the
same.
thistle funnel
water
water
cellophane paper
(partially permeable membrane)
Movement of Substances
Diffusion
Osmosis
Active Transport
3 Types of Solutions
• If two solutions have the same water potential,
they are isotonic.
Movement of Substances
Diffusion
Osmosis
Active Transport
3 Types of Solutions
• If one solution has a higher water potential than
another, it is hypotonic.
• The solution with lower water potential is
hypertonic.
Note:
The terms apply
only to animal
systems and not
plant systems
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Living Organisms
• Plant and animal cells are surrounded by a
living, partially permeable cell surface
membrane.
• The enclosed nucleus and cytoplasm are a
complex mixture of various dissolved
substances.
• Osmosis occurs in and out of the cell across
the cell surface membrane.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Animal Cells
When placed in a solution of high water potential...
• Cell cytoplasm has a lower water potential than
that of the solution outside the cell.
• Water enters the cell by osmosis.
• The animal cell will swell and may even burst.
in solution with high
water potential
cell expands
and bursts
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Animal Cells
When placed in a solution of the same water
potential...
• There will be no net movement of water across the
cell surface membrane.
• There will be no change in size or shape.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Animal Cells
When placed in a solution of low water potential...
• Cell cytoplasm has a higher water potential than
that of the solution outside the cell.
• Water leaves the cell by osmosis.
• The animal cell shrinks, forming spikes on the cell
surface membrane. This process is known as
crenation.
in solution with lower
water potential
crenated cell
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in the Hagfish
• The hagfish lives in sea water.
• To prevent water leaving or entering the
fish, its body fluid is as salty as the sea
water in which it lives.
• Its body fluid is considered to be isotonic to
its surrounding fluid.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Plant Cells
When placed in a solution of high water potential...
• Cell sap has a lower water potential than that of
the solution outside the cell.
• Water enters the cell by osmosis.
• The vacuole increases in size and pushes the cell
contents against the cell wall.
• The cell wall is strong and inelastic. It exerts an
opposing pressure as water enters the cell,
preventing it from over-expansion.
• The plant cell expands and becomes turgid. The
cell does not burst because it is protected by the
cell wall.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Plant Cells
When placed in a solution of high water potential...
in solution with high
water potential
cell becomes turgid,
cell wall prevents cell
from bursting
• The turgidity of the cell with water is called
turgor.
• The pressure exerted by the water on the cell wall
is the turgor pressure.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Plant Cells
When placed in a solution of the same water
potential...
• There will be no net movement of water across the
cell surface membrane.
• There will be no change in size or shape.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Plant Cells
When placed in a solution of low water potential...
• Cell sap has a higher water potential than that of
the solution outside the cell.
• Water leaves the cell by osmosis.
• The vacuole decreases in size.
• The rigid cell wall does not change its shape.
• The cytoplasm shrinks away from the cell wall.
This is known as plasmolysis. The cell is said to be
plasmolysed.
Movement of Substances
Diffusion
Osmosis
Active Transport
Osmosis in Plant Cells
When placed in a solution of low water potential...
in solution with low
water potential
plasmolysed cell
• If not too badly damaged, the cell can be restored
by placing it in water or in a solution with high
water potential.
Movement of Substances
Diffusion
Osmosis
Active Transport
Turgor in Plants
• If the cell is plasmolysed, its tissues
become flaccid.
• Cells will be killed if they remain
plasmolysed for too long.
• Question: why is it not advisable to add too
much fertiliser around the roots of the
plant?
Movement of Substances
Diffusion
Osmosis
Active Transport
Turgor in Plants
• Turgor is important in maintaining the
shape of soft tissues in plants.
• Most leaves and stems are able to remain
firm and erect because of the turgor
pressure within their cells.
• When there is high rate of evaporation of
water from the cells, they lose their
turgidity and the plant wilts.
Movement of Substances
Diffusion
Osmosis
Active Transport
Turgor in Plants
• Movements of certain plant parts are due
to changes in turgor.
– Certain flowers open during the day and
close at night (and vice versa)
– The leaves of the Mimosa plant fold when
they are touched. Caused by changes in
turgor of the cells.
– Changes in turgor of the guard cell to cause
the opening and closing of stomata.
Movement of Substances
Diffusion
Osmosis
Active Transport
Exchange of Materials in Cells
• Surface area to volume ratio is important
for cell efficiency.
• Cells exchange materials across their cell
surface membranes:
– Enter cell: oxygen, nutrients
– Leave cell: carbon dioxide, waste
• If cells do not exchange materials quickly
enough, they will die.
Movement of Substances
Diffusion
Osmosis
Active Transport
Surface Area to Volume Ratio
A
Cube
B
Surface area
/m2
C
Volume /cm3
Surface area :
volume
A
B
C
Movement of Substances
Diffusion
Osmosis
Active Transport
Surface Area to Volume Ratio
• As the cell becomes bigger, surface area to
volume ratio decreases.
• The largest cell of the same shape has the
smallest surface area to volume ratio.
• The rate of movement of a substance
across the surface of a cell depends on how
big the area of cell surface membrane is.
• The greater the surface area to volume
ratio, the faster the rate of diffusion for a
given concentration gradient.
Movement of Substances
Diffusion
Osmosis
Active Transport
Surface Area to Volume Ratio
• The activities that the cell carries out for
survival is known as metabolism.
• Actively growing (or metabolizing) cells are
usually small
– Large surface area to volume ratio
• As the cells grow in size, their metabolism
slows down.
• Cells stop growing when they reach a
maximum size.
Movement of Substances
Diffusion
Osmosis
Active Transport
Cells for Absorption
• Some cells are specifically adapted to
absorb materials.
• Root hair cell has a long protrusion to
increase absorption of water and mineral
salts from the soil.
• The red blood cell has a flattened
biconcave shape increases surface area to
volume ratio which increases the rate of
oxygen uptake.
Movement of Substances
Diffusion
Osmosis
Active Transport
Cells for Absorption
• Epithelial cells in the small intestine have
microvilli to increase surface area to volume
ratio of the cell for absorbing digested food
substances.
Movement of Substances
Diffusion
Osmosis
Active Transport
Active Transport
Living cells are able to absorb substances
against a concentration gradient.
Definition:
Active transport is the process in which
energy is used to move particles of a
substance against a concentration gradient.
Movement of Substances
Diffusion
Osmosis
Active Transport
Active Transport
• Only occurs in living cells:
– Living cells respire and release energy which
is used in active transport.
• In plants:
– Root hairs take in dissolved mineral salts by
active transport
– Water enters the cell by osmosis
• In animals:
– Glucose and amino acids are quickly
absorbed by the small intestine by active
transport.
Movement of Substances
Diffusion
Osmosis
Active Transport