DIFFUSION Summarized Notes

This Should Take You 2 Hours To Study, If You Spend Here More Than Expected It Still Is Okay As We Study At Different Paces.

Diffusion

if you are a non-smoker, you can often smell tobacco smoke from a person who Is Smoking some distance away from you. How does the smoke reach you? The answer is by diftusion. You know that solids, Iiquids and gases are made up of tiny particles, these particles are always moving around at random because they have energy the energy tor diffusion comes from the kinetic energy of random movements of molecules and ions. You can see evidence of this when you look at smoke particles moving in the air. The smoke particles move because they are being bumped into and pushed around by the particles of air. In this way, the smoke particles spread from where the smoke is concentrated, around the person who is smoking, to where there is less smoke, or even no smoke, just where you are! After some time, the smoke spreads out evenly throughout the room.

Let us look at another example of how diffusion works:

• The molecules that have been dissolved in a solution are in a constant random movement due to their kinetic energy. This results in the molecules being evenly distributed throughout the solution.

• When you mix potassium permanganate crystals and water, you cannot see the molecules, but they are there. The tendency of molecules to spread out is an example of diffusion. You may want to ask how these molecules come to be evenly distributed. Let us start with a beaker of distilled water only.

• What do you think will happen if we now add a lump of potassium permanganate crystals (purple colour)?

• When the lump is dropped into the water, it begins to dissolve. This random movement of particles from where they are more concentrated to where they are less concentrated is called diffusion. Even when diffusion stops, particles still move randomly, but they move equally in all directions. Therefore, diffusion is the movement of molecules, atoms or ions from a region of high concentration to a region of low concentration, down a concentration gradient.

Facilitated Diffusion

Some molecules, Such as oxygen and carbon dioxide (gases), diffuse very fast through cell membranes in solution. lons and small polar molecules diffuse much more slowly, because they are insoluble in the lipid part of the cell membrane. Facilitated diffusion is a modified form of diffusion in which protein carriers transport ions and molecules across the cell membrane.

The molecules are picked up on one side of the membrane where they are in higher concentrations and then deposited on the other side where they are in lower concentrations

These special carrier molecules that form the protein channel bind only to a specific molecule, such as a particular sugar or amino acid. Once the molecule binds to the carrier protein, this protein helps or facilitates the diffusion process by changing shape and moving the molecules down its concentration gradient, through the membrane and into the cell where it is released.

Facilitated diffusion can occur in either direction depending on the concentration gradient. If there is a higher concentration of the particular molecule inside the cell, the same carrier protein would then transport the molecules out of the cell. You may have asked yourself the question, 'Is there a difference between passive/simple diffusion and facilitated diffusion? Simple diffusion is a type of passive transport where no energy is required for molecules to move out or into the cell. However, there are times when large molecules cannot, on their own, cross the plasma membrane and are helped across the membrane by carrier proteins. This process is known as facilitated diffusion.

Summarized Difference Between Passive And Facilitated Diffusion 

Passive/Simple Diffusion

• Molecules move randomly; they do not require a protein carrier 

• Do not require specific facilitator for specific molecule

• The process of simple dittusion occurs only in prokaryotes

• Diffusion occurs in all states of matter: solid, liquid and gas

Facilitated Diffusion

• Movement of molecules requires a protein carrier channels/pores to help move the molecules in the cell surface

• Requires specific facilitator for specific molecule, which Is not the case with simple diffusion

• Facilitated diffusion is seen only in eukaryotes 

• An example is the movement of glucose molecules into red blood cells

Similarities of simple diffusion and facilitated diffusion

• Passive processes

• No expenditure of energy is required

• Molecules move down the concentration gradient

• Does not take place against the Concentration gradient

Try Out This Experiment To Understand Diffusion Better

EXPERIMENT

(Diffusion With A Tea Bag)

You will need to leave this activity set up for at least a day. What happens when you add a tea bag to water?

You will need:

• Some clean water

• a container, such as a glass or jar, about 10 cm deep, which you can see through

• a tea bag

Method:

1) Pour some hot water into your container, to about the height of the width of your hand. Leave it for about 1 minute, until the water is completely still.

2) Very gently put a tea bag into the water. Watch what happens.

3) Write down in your notebook what you see:

• in the next few minutes

• after about one hour

• the next day

When you did the practical investigation, you saw the molecules of the tea colour moving in all directions. The molecules of water were also moving randomly. The light-brown 'tea' molecules eventually spread out evenly through the water. The molecules moved from a region of higher concentration to a region of lower concentration. We say that they moved down a concentration gradient. You can see this in the graph below.

Diffusion in living organisms

Most of the gases that move into, around, and out of animals and plants do so by diffusion. Remember that diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient Oxygen in the air is at a concentration of about 21%, inside your body, the concentration is much lower because oxygen is being continuously used up by our cells. Oxygen enters your body by diffusion. When you breathe in, air is drawn into tiny air-filled sacs in your lungs. The air in these sacs is separated from the red blood cells (which transport oxygen) only by the thin wall of the air sac and the wall of the blood vessel carrying the blood. A concentration gradient of oxygen exists between the air sac and the blood vessels, down which oxygen diffuses into the blood. In a similar way, carbon dioxide gas, needed by the palisade cells of the leaf to make food, passes into these cells through tiny openings in the leaf surface called stomata. This process also occurs by diffusion. As the plant continuously uses up carbon dioxide in daylight, this ensures that a concentration qradient exists betvween air outside the leat and air inside the leaf. Movement of carbon dioxide will take place into the leaf.

Factors Affecting The Rate Of Diffusion

The speed with which a molecule diffuses through a cell wall or cell surface membrane will depend on temperature, concentration gradient, distance and surface area

1) Temperature -a higher temperature means more kinetic energy, so a faster rate of diffusion. The relationship is directly proportional.

2) Concentration gradient - the greater the difference in concentration of molecules, the faster the rate of diffusion. The relationship is directly proportional.

3) Distance - the shorter the distance that the molecules will have to travel, the faster the rate of diffusion. The relationship is inversely proportional. Gas diffuses faster through a thin wall than a thick wall.

4) Surface area - the greater the surface area of the cell, the faster the rate of diffusion. The relationship is directly proportional. As the surtace area increases, more particles can spread as there is more area to travel.

The Relatively Sizes Of Atoms In Comparison To A Human

The Importance Of Diffusion Of Gases And Solutes

Now you know the definition of diffusion and how it works or takes place. in this Section, We are going to discuss why diffusion is important in both plants and animals. The diffusion of molecules, such as oxygen, carbon dioxide and water, down the Concentration gradient makes it possible for the cells to obtain substances they need and to get rid of waste products and toxic substances. Let us start with the example of qaseous exchange in plants. The palisade cells of the leaves need carbon dioxide as raw material for photosynthesis. Plants obtain their carboon dioxide from the air, but how does it get into the palisade cells where it is needed? There is a higher concentration of carbon dioxide in the air surrounding the leaves than inside; therefore it will diffuse into the leaves through the stomata. Oxygen is produced inside the cells as a by-product of photosynthesis, and becomes highly concentrated there; therefore it diffuses out into the air down the concentration gradient. This is called gaseous exchange. In animals, oxygen is needed for aerobic respiration inside all living cells. How does it get there? The air that you breathe in contains a higher concentration of oxygen than the blood in the capillaries surrounding the alveoli. As a result, oxygen diffuses from the alveoli, where it is highly concentrated, into the bloodstream down the concentration gradient. When the blood circulates throughout the whole body, it takes food, such as glucose and oxygen, to the cells where they are needed for aerobic respiration. When the blood reaches the capillaries surrounding the tissues, oxygen and glucose diffuse from the blood into the cells. At the same time, carbon dioxide and other waste products, such as.urea diffuse from the cells, where they are highly concentrated as products of metabolism, into the bloodstream. The blood takes the waste products to the excretory organs to be removed from the body.

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