Pure Bio Chp 3 Movement of Substances PPT

Movement of Movement of SubstancesSubstancesChapter 3

Movement of Substances Diffusion Osmosis Active Transport

Learning Objectives...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

What are these What are these items???items???



What happens when What happens when you spray air you spray air

freshener in one freshener in one corner of the room?corner of the room?


Movement of air Movement of air particles...particles...

The gas particles spread

out from the source to the rest of the

room.



The gas particles

spread from a region of

higher concentration to a region

of lower concentratio

n.



• 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.

concentratio

n

gradient



• 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.


Defining Diffusion...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.


Defining Diffusion...Defining Diffusion...DIFFUSION is

the NET MOVEMENT of particlesfrom a region of HIGHER CONCENTRATION

to a region of LOWER CONCENTRATIONdown a CONCENTRATION GRADIENT.

Diffusion stops when particles reach DYNAMIC EQUILIBRIUM.

Diffusion of a Dissolved Diffusion of a Dissolved SubstanceSubstance

Place a drop of potassium permanganate solution at the bottom of a beaker of water. Observe the changes in the colour of the water.

Investigation 3.1 TB Pg 32

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.



Question!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 .


Question!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.


Question!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?


Diffusion across a Diffusion across a MembraneMembrane

• Diffusion can occur across a permeable membrane.

• At the end, there will be equal concentrations of all ions on both sides of the membrane.


Diffusion across a Diffusion across a MembraneMembrane

• Sugar molecules diffuse across the membrane to the right side.

• Water molecules will diffuse across the membrane to the left side.


An amoeba

Diffusion in CellsDiffusion in CellsDiffusion 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


Diffusion in CellsDiffusion in CellsIn 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


A root hair cell

Diffusion in CellsDiffusion in CellsIn 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


What affects the RATE of What affects the RATE of diffusion?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.


What is Osmosis?What is Osmosis?


• 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


Defining Osmosis...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.


What is Water What is Water Potential?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


What is Water What is Water Potential?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


Demonstrating Demonstrating OsmosisOsmosisExpected

Observation:• The liquid level

inside the thistle funnel rises.


thistle funnel

water

sucrose solution

cellophane paper(partially permeable membrane)


Demonstrating Demonstrating OsmosisOsmosisExpected

Observation:• The liquid level

inside the thistle funnel remains the same.


thistle funnel

water

water

cellophane paper(partially permeable membrane)


Test Yourself!Test Yourself!TB Pg 36


3 Types of Solutions3 Types of Solutions• If two solutions have the same water

potential, they are isotonic.


3 Types of Solutions3 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 applyonly to animalsystems and notplant systems


Osmosis in Living Osmosis in Living OrganismsOrganisms

• 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.


Osmosis in Animal Osmosis in Animal CellsCells

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



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.



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


Osmosis in the HagfishOsmosis 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.


Osmosis in Plant CellsOsmosis in Plant CellsWhen 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.


Osmosis in Plant CellsOsmosis in Plant CellsWhen placed in a solution of high water

potential...

• The turgidity of the cell with water is called turgor.

• The pressure exerted by the water on the cell wall is the turgor pressure.

in solution with high water potential

cell becomes turgid,cell wall prevents cell

from bursting


Osmosis in Plant CellsOsmosis in Plant CellsWhen 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.


Osmosis in Plant CellsOsmosis in Plant CellsWhen 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.


Osmosis in Plant CellsOsmosis in Plant CellsWhen placed in a solution of low water

potential...

• If not too badly damaged, the cell can be restored by placing it in water or in a solution with high water potential.

in solution with low water potential

plasmolysed cell


Turgor in PlantsTurgor 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?


Turgor in PlantsTurgor 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.


Turgor in PlantsTurgor 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.


Test Yourself!Test Yourself!TB Pg 37


Exchange of Materials Exchange of Materials in Cellsin 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.


Surface Area to Surface Area to Volume RatioVolume Ratio

A B C

Cube

Surface area /m2

Volume /cm3

Surface area :

volume

A

B

C



• 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.



• 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.


Cells for AbsorptionCells 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.


Cells for AbsorptionCells 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.


Active TransportActive TransportLiving 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.


Active TransportActive 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.

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Pure Bio Chp 3 Movement of Substances PPT