chapter 3 - diffusion & osmosis
TRANSCRIPT
Chapter 3
Chapter 3
Diffusion and
Osmosis
Diffusion and
Osmosis
By the end of the lesson, you should be able to• define and describe diffusion, osmosis and active
transport• to describe the idea of a partially permeable
membrane• assess the importance of water potential gradient in
water uptake by plants• explain the effects of osmosis in plant and animal
tissues• define and discuss importance of active transport in
ion-uptake by root hairs and glucose uptake by cells in the villi
OBJECTIVES
Introduction
• Recall:~ A cell is the basic unit of life~ Many complex reactions take place inside the cell~This means that many raw materials must be
brought into the cell~ And new products formed by the chemical
reactions, and waste materials, must exit the cell.
How?
• How do the raw materials get into the cell?• How do the new products leave the cell?• How are the waste materials removed from the
cell?
Answer:• Materials move across the partially permeable
cell membrane• By processes called _________, _________ and
_______________
diffusion osmosisactive transport
Diffusion
Diffusion is the net movement of ions or solute molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient
conce
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ati
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gra
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nt
region of low concentration of
molecule Xregi
on o
f hi
gh c
once
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molecule moves from a region of high concentration to that of low concentration
Diffusion
Diffusion in gases
Gas molecules move from a region of higher concentration to that of a lower concentration
The movement continues until they are evenly spread
A. B.
Diffusion
Diffusion in liquids
Dissolved particles of a substance in a liquid move from a region where they are more concentrated to a region where they are less concentrated.
The particles continue to move until they are evenly distributed.
A. B.
Diffusion
Importance of Diffusion
Initially, the concentration of a substance outside the cell is higher than inside the cell.
The particles diffuse across the cell membrane.
Later, an equal concentration of the substance inside and outside the cell is attained.
Diffusion
Importance of Diffusion• Living cells continuously use up oxygen during aerobic respiration.
• The concentration of oxygen inside the cell falls.
• Oxygen molecules diffuse into the cell until the oxygen concentration is raised again.
• During respiration, carbon dioxide is produced.
• The concentration of carbon dioxide rises and creates a concentration gradient.
oxygencarbon dioxide
Oxygen is supplied to Amoeba by diffusion. Diffusion enables metabolic wastes such as carbon dioxide to be excreted out.
Diffusion
1. Temperature: An increase in temperature results in a higher rate of diffusion.1. Temp Molecules move faster Rate of diffusion
2. Size of particles: Small molecules or ions diffuse faster than large ones.1. Particle size Energy to move particle Rate of diffusion
3. Thickness of the barrier: Membranes of plant and animal cells are of about the same in thickness and permeability. Plant cell walls vary in their thickness. The thicker the cell walls, the slower the rate of diffusion.1. Thinner membrane Higher rate of diffusion
4. Concentration gradient: The greater the concentration gradient, the higher the rate of diffusion1. Steeper concentration gradient Higher rate of diffusion
5. Surface area: The rate of diffusion into a cell depends on the total surface area of the cell membrane. 1. surface area rate of diffusion.
Factors which Affect the Rate of Diffusion
Lungs
Diffusion in our body
• Recall: Our cells have a partially permeable membrane
• Partially permeable membrane
Allows some substance through and not others
• How do these substances pass through?
via DIFFUSION
Practical Application
• Kidney dialysis
• Waste products are removed from the blood by diffusing across artificial membrane in the machine
• Blood cells and other large protein are retained
Osmosis
Osmosis is the diffusion of water across a selectively permeable membrane, from a high water potential to a low water potential.
The selectively permeable membrane on the side of the water is being continuously bombarded by water molecules which pass through.
This causes an increase in the volume of sucrose solution and a decrease in the volume of water.
sucrose solutionwater
water molecules
sucrose molecule
selectively-permeable membrane
Osmosis
Water Potential
The water potential of a solution is a measure of the tendency of
water molecules to move from one place to another
A dilute solution has a higher water potential than
a concentrated solution
The difference in water potential between two solutions is known as the water potential gradient
Osmosis
Osmosis and Plant Cells
Turgor pressure – The outward pressure
which the cell sap exerts against the
inside wall of the cell
In plant cells, the cell sap contains dissolved salts and sugar. If the cell sap has a lower water potential than that of the surrounding fluids, water from the
outside enters by osmosis.
Turgor – A state when a cell is firm or turgid due to water entering the cell,
causing it to swell.
Importance of Turgor in Plants
2. Changes in turgor of the guard cell causes the opening of the stomata
Turgor (II)
3. Changes in turgor of the pulvinus (small swelling at the base of the leaflets) causes the folding of leaflets in the Mimosa
Osmosis
Osmosis and Plant Cells
Turgid cells. The cytoplasm is pressed against the cell wall. The cell swells up and is prevented from bursting by the cellulose cell wall.
Plasmolysed cells. Water is lost from its vacuole, the cytoplasm shrinks and is withdrawn from the cell wall.
water enters by osmosis
cell sap more concentrated than outside solution
cellulose cell wall
cell sap less concentrated than outside solution
plasma membrane
water leaves by osmosis
cytoplasm
Plasmolysis leads to wilting
Fertilizer - Good or Bad?
• Too much fertilizer added will cause the plant to wilt
• Soil solution becomes very concentrated
• Water moves out of root
• Plant will wilt
• Sufficient water must be added to ensure plant survival
OsmosisOsmosis and Animal Cells
Changes observed under a microscope when blood is dropped into hypertonic and hypotonic solutions.
cell shrinks
in hypertonic solution
in hypotonic solution
cell swells
cell becomes crenated
cell bursts and cell is said to be haemolysed
normal red blood cell
Active Transport
Active transport is an energy-consuming process by which substances are transported from regions of low concentration to regions of high concentration against a concentration gradient.
substrate molecule
carrier protein
restorationcarrier protein changes shape
substrate released
energy from ATP used
OUTSIDE
INSIDE
binding site
cell membrane
binding
Active Transport
soil particle
high concentration of ions
low concentration of ions
Direction of active transport
Plants need to absorb mineral salts from the soil. They are present as charged ions which cannot diffuse across partially-permeable membranes.
Ion uptake by root hair is facilitated by active transport
Active Transport
Active transport enables absorption of glucose and amino acids through the inner surface of the small intestine.
microvillus
glucose molecule
direction of active transport
cell lining the villus
Uptake of glucose by cells in the villi
The presence of microvilli increases the surface area over which active transport occurs.