biology essay the importance of diffusion

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Importance of Diffusion in Organisms

The Parts of a Firefly Bug

Diffusion is an essential function in living organisms. Diffusion is the random but directional movement of molecules from a place of high concentration to a place of low concentration. This simple concept describes the process by which cells exchange toxic gases for life-sustaining gases. It also describes how nerve cells are able to send electrical signals to each other cells. Diffusion tells embryonic cells where to crawl and when they have arrived. Diffusion also makes it possible to reduce the loss of body heat to the surrounding environment.

Gas Exchange

The lungs have tiny empty grape-like sacs that are the hub of gas exchange. The cells of the body are constantly making energy molecules to sustain their daily activities. Not only does this process, called cellular respiration, require oxygen gas in order to work, it produces carbon dioxide gas, which is toxic to cells. The carbon dioxide produced by cells throughout the body is carried in the blood to the lungs. In the lungs, the carbon dioxide diffuses out of the blood and into the grape-like sacs. Oxygen gas that was breathed into the lungs goes in the opposite direction. Oxygen enters the blood. This vital exchange of gases happens by diffusion across thin layers of cells in the blood vessels that surround the grape-like sacs.

Nerve Impulses

Nerve cells called neurons communicate with other cells by sending electrical signals along their cell membrane. At rest, the inside of the neuron’s membrane is negatively charged, while the outside is positively charged. An electrical signal is generated when the membrane lets ions from outside flow into the cell. This inflow changes the charge on the inside of the membrane from negative to positive. This switch in charge is an electrical signal that moves down the length of a neuron’s arm. The movement of ions that generates the electricity is diffusion.

Morphogen Gradients

Embryonic development is the process in which organs, limbs and wings begin developing. The process in which an embryo changes shape to start looking like an miniature adult is possible because of diffusion. Different groups of cells in different parts of the embryo release proteins called morphogens. Morphogens are like perfume, attracting cells from far away to move closer. Embryonic development is a beautiful symphony of many morphogen gradients overlapping and competing with each other. The result is that legs only develop on the body, antennas only develop in the head, and wings develop on an animal’s back. Morphogen gradients are possible because proteins diffuse.

Counter Current Heat Exchange

Homeotherms are animals that regulate their body temperature internally, as opposed to having to bathe in or run from the sun. One problem homeotherms face is the loss of heat to cold surroundings. Killer whales are an example of animals that face this problem, since they swim in cold water. The flippers and fins of killer whales are thin and lose a lot of heat to the surrounding water. Since flippers and fins are part of the whale, blood must carry oxygen and heat from the center of the body to these appendages. One way that killer whales preserve heat is that their arteries that bring warm blood to their appendages are right next to veins that bring blood back to the body. Thus, the heat that is lost from the arteries moving towards the tip of a fin is picked up by blood that is in the veins, moving back into the body.

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Importance of diffusion to living organisms

Diffusion is basically the movement of chemical species (ions or molecules) under the influence of concentration difference. The species will move from the high concentration area to the low concentration area till the concentration is consistent in the whole system. Diffusion mostly occurs in gases and liquids as these can move freely.

The main features of an efficient diffusion system would be that it has a large surface area, thin membrane and a continuous supply of substances. A large surface area is needed so that high amount of substances can be exchanged at a time while the thin membrane means that the diffusion pathway would be short so that it is more efficient. The continuous supply would help in maintaining a concentration gradient which is essential for diffusion to take place.

The 2 main types of diffusion are simple and facilitated. Simple diffusion is when a small, non-polar molecule passes through a lipid bilayer. In this type of diffusion, a hydrophobic molecule moved into the hydrophobic region of the membrane without getting rejected. A key feature is that it does not  need a carrier protein to take place. An example of simple diffusion is osmosis.

Facilitated diffusion on the other hand is dependant on carrier proteins to transport it across the membrane.

Diffusion is essential for many organisms as it is a feature of a number of processes which control and supply vital substances to the body in order for basic survival. A few of these are discussed below.

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Gas exchange is one of these processes. It is when much needed oxygen is obtained by the body in order for respiration to take place and the waste CO 2  is taken out of the body. In us mammals, the exchange takes place in the lungs which contain a large number of alveoli. These are sponge-like structures in which the diffusion takes place. They are highly adapted to diffuse the gases as they give a large surface area for exchange of the gases. Also, there is only a thin layer of cells between the alveoli and the blood capillaries meaning there is a short diffusion pathway so diffusion takes place more efficiently. There is a ventilation system which means there is continuous oxygen supply to the alveoli which again makes diffusion more efficient.

Fish are adapted to exchange gases as the gills have many lamellae which are covered with plates. These give a large surface area while also they are very thin to give a short diffusion pathway. There is a counter flow blood system meaning it flows in the opposite direction of the water. This maintains a concentration gradient in order for diffusion to take place.

The main feature of the mechanism in insects is that they have an extensive tracheole system that gives a large surface area. These are permeable to CO 2 and O 2  in order to allow the exchange of gases.

Plants require CO 2  for the purpose of photosynthesis. Therefore they have thin cell walls and membranes to allow gases to diffuse through. There are stomata which control the entry and exit of gases while there are large air spaces for circulation so that diffusion is efficient.

The transport of glucose to cells is by facilitated diffusion and this is needed as all cells need to respire therefore glucose is vital.

Diffusion also plays a part in the human digestive system as after the carbohydrates and other substances are processed through digestion, the substances that are wanted and are small enough are reabsorbed through the gut wall through diffusion. These can then be used for energy and growth purposes.

The process of osmosis (or osmoregulation) is classed as a type of diffusion. This is due to the fact that the substance (which is water in the case of osmosis) moves from an area of high concentration to an area with lower concentration.

One example of when osmosis takes place is when water is taken up by the roots of plants. Firstly, the water enters the root hair from an area of high water potential. As the water builds up in the cell, it has a higher potential than that of the next cell up, meaning that once again the water moves to the next cell by osmosis. This process carries on transporting the water up through the roots. The system of the roots is called the symplast pathway.

An instance of osmosis in mammals is the reabsorption of water from the kidney tubules back into the blood. A function of the kidney is to control the water level in the blood. The water is absorbed in the descending limb of the loop of henle. This is the part which is permeable to water. The water potential in the descending limb is higher than in the surrounding tissues meaning that water diffuses through into the tissues by osmosis. This is vital for mammals as it controls water loss to a degree by keeping it to a minimum (although water is lost by other means such as perspiration).

The occurrences of diffusion discussed above give us a basic insight into the importance of diffusion in organisms. The majority of living organisms require diffusion to take place in order for main systems to function. These key systems such as gaseous exchange and water control would be unable to function without diffusion taking place. . Without diffusion there would be no respiration of the cells which is the central process in all the biological systems, thus we can say safely state that it is probably the most important process for organisms as without it, there would be no chance of survival whatsoever.

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Revision note.

Biology Lead

Diffusion & Facilitated Diffusion

• Diffusion is a type of transportation that occurs across the cell membrane
• It can be defined as:
• The molecules or ions move down a concentration gradient
• The random movement is caused by the natural kinetic energy of the molecules or ions

Diffusion across the cell membrane

• As a result of diffusion, molecules or ions tend to reach an equilibrium situation (given sufficient time), where they are evenly spread within a given volume of space
• The rate at which a substance diffuses across a membrane depends on several factors

Diffusion Factors Table

Facilitated diffusion

• Large polar molecules such as glucose and amino acids
• Ions such as sodium ions (Na + ) and chloride ions (Cl - )
• These substances can only cross the phospholipid bilayer with the help of certain proteins
• This form of diffusion is known as facilitated diffusion

Channel proteins

Carrier proteins.

• They are highly specific (they only allow one type of molecule or ion to pass through)
• Channel proteins are water-filled pores
• They allow charged substances (eg. ions) to diffuse through the cell membrane
• The diffusion of these ions does not occur freely, most channel proteins are ‘gated’, meaning that part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
• This allows the channel protein to control the exchange of ions

A channel protein (open and closed)

• Unlike channel proteins which have a fixed shape, carrier proteins can switch between two shapes
• This causes the binding site of the carrier protein to be open to one side of the membrane first, and then open to the other side of the membrane when the carrier protein switches shape
• The direction of movement of molecules diffusing across the membrane depends on their relative concentration on each side of the membrane
• Net diffusion of molecules or ions into or out of a cell will occur down a concentration gradient (from an area containing many of that specific molecule to an area containing less of that molecule)

A carrier protein changing shape during facilitated diffusion

Remember – the movement of molecules from high concentration to low concentration is diffusion. If this movement requires the aid of a protein (for example because the molecule is charged and cannot pass directly through the phospholipid bilayer) this is facilitated diffusion.

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• Biology Article

Table of Contents

What is Diffusion?

Types of diffusion, factors affecting diffusion, examples of diffusion, causes of diffusion, significance of diffusion, diffusion definition.

“Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.”

Read on to explore what is diffusion and the different types of diffusion.

Diffusion is the process of movement of molecules under a concentration gradient. It is an important process occurring in all living beings. Diffusion helps in the movement of substances in and out of the cells. The molecules move from a region of higher concentration to a region of lower concentration until the concentration becomes equal throughout.

Liquid and gases undergo diffusion as the molecules are able to move randomly.

Take water in a beaker. Add a few copper sulfate crystals in one place and leave it as it is for some time without disturbing it. After some time we can see that the beaker contains a uniformly coloured solution. Here, both water and copper sulfate diffuse independently. With this experiment, we can infer that solutes move from a higher concentration to a lower concentration in a solution.

Also Read:  Diffusion in Plants

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Diffusion is widely used in various fields such as biology, physics, chemistry, etc. Diffusion can be classified into two main types: Simple diffusion and facilitated diffusion.

Simple diffusion

A process in which the substance moves through a semipermeable membrane or in a solution without any help from transport proteins.  For example, bacteria deliver small nutrients, water and oxygen into the cytoplasm through simple diffusion.

Facilitated diffusion

Facilitated diffusion is a passive movement of molecules across the cell membrane from the region of higher concentration to the region of lower concentration by means of a carrier molecule.

Dialysis:  It is the diffusion of solutes across a selectively permeable membrane. A selectively permeable membrane is one that allows only specific ions and molecules to pass through, while it obstructs the movement of others.

Osmosis:  It is the movement of solvent molecules from the region of lower concentration to the region of higher concentration through a semipermeable membrane.    Since water is solvent in every living being, biologists define osmosis as the diffusion of water across a selectively permeable membrane. For example, plants take water and minerals from roots with the help of osmosis.

Also Read:  Facilitated Diffusion

There are a few factors that affect the process of diffusion, which individually and collectively alters the rate and extent of diffusion. These factors include:

• Temperature.
• Area of Interaction.
• Size of the Particle.
• The steepness of the concentration gradient.
• A tea bag immersed in a cup of hot water will diffuse into the water and change its colour.
• A spray of perfume or room freshener will get diffused into the air by which we can sense the odour.
• Sugar gets dissolved evenly and sweetens the water without having to stir it.
• As we light the incense stick, its smoke gets diffused into the air and spreads throughout the room.
• By adding boiling water to the dried noodles, the water diffuses causing rehydration and making dried noodles plumper and saturated.

Diffusion is a natural and physical process, which happens on its own, without stirring or shaking the solutions. Liquid and gases undergo diffusion as the molecules are able to move randomly. The molecules collide with each other and change their direction.

Diffusion is an important process, which is involved in the different life processes . As mentioned above, it is the net movement of particles, ions, molecules, solution, etc. In all living species, diffusion plays an important role in the movement of the molecules during the metabolic process in the cells.

Diffusion is important for the following reasons:

• During the process of respiration, this process helps in diffusing the carbon dioxide gas out through the cell membrane into the blood.
• Diffusion also occurs in plant cells. In all green plants, water present in the soil diffuses into plants through their root hair cells.
• The movement of ions across the neurons that generates electrical charge is due to diffusion.

Also Read:  Difference between diffusion and osmosis

Frequently Asked Questions

1. what is diffusion.

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.

2. List the types of diffusion.

Diffusion can be divided into two main types, namely, simple diffusion and facilitated diffusion.

3. What is simple diffusion?

Simple diffusion is defined as the process in which a substance moves through a semipermeable membrane or in a solution without any help from transport proteins.

4. State an example of simple diffusion.

In a cell, water, oxygen and carbon dioxide molecules can pass directly through the cell membrane without requiring any energy along the concentration gradient. This is a form of simple diffusion.

5. What is facilitated diffusion?

Facilitated diffusion can be defined as the passive movement of molecules across the cell membrane from a region of higher concentration to a region of lower concentration by means of a carrier molecule.

6. Provide an example of facilitated diffusion.

In the human body, glucose molecules, sodium and potassium ions use carrier proteins to pass through the cell membranes.

7. How does dialysis work?

Dialysis works through the diffusion of solutes across a selectively permeable membrane. A selectively permeable membrane is the one that allows only specific ions and molecules to pass through while obstructing the movement of other molecules.

8. What are the factors affecting diffusion?

Temperature, area of interaction, size of the particle and the steepness of the concentration gradient are all factors that affect the process of diffusion.

9. State the significance of diffusion.

Diffusion is a very important process occurring in all living beings. All living organisms exhibit one or the other form of diffusion, allowing the movement of the molecules during various metabolic or cellular processes.

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What is the purpose of diffusion?

Diffusion is the way of passive transport of substances in and out of the cell across the cell membrane. Diffusion occurs down the concentration gradient, i.e. from higher concentration to lower concentration.

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Diffusion: Meaning, Types, Causes, Examples, and Factors

Subhajit Halder

| Updated On - Jun 28, 2024

“Diffusion is the net movement of substances like atoms, ions, molecules, or energy from a region of higher concentration to one of lower concentration.”

Key Terms: Diffusion , Concentration Gradient, Facilitated diffusion, Semi permeable Membrane, Osmosis

What is Diffusion?

[Click Here for Sample Questions]

The movement of molecular level chemicals or particles from a location of higher concentration to a region of lower concentration is defined as diffusion. Diffusion is a natural and physical phenomenon that occurs without the use of any kind of energy . Diffusion occurs in liquids and gases because molecules can move around at random . The molecules clash and shift direction , resulting in a passive mode of transportation. Diffusion is a stochastic process due to the inherent randomness of the diffusing entity.

When perfume is sprayed , its fragrance diffuses into the air and spreads throughout the room because the perfume bottle carries a higher concentration of the ingredient. The chemical diffuses into the atmosphere when air is dispensed from the bottle because the ambient air has a lower concentration than the bottle. The odour of the perfume is disseminated across the area thanks to the diffusion mechanism.

Types of Diffusion

Diffusion is a vital biological and chemical process. Diffusion can be divided into two main types: Simple diffusion and Facilitated diffusion.

Simple diffusion

Simple diffusion is the unassisted movement of molecules, atoms, or ions that pass directly through spaces in a semipermeable membrane from an area of higher concentration to an area of lower concentration. The simple diffusion rate is comparably slower than the facilitated diffusion rate.

Diffusion of oxygen, carbon dioxide, water , and other small molecules across cell membranes.

Facilitated diffusion

Facilitated diffusion involves the movement of larger or polar molecules through a membrane with the help of transport proteins . It's also a selective process , in that the membrane only permits certain types of molecules to flow through while preventing others from doing so. This is significant because enhanced diffusion allows plants to segregate different minerals from the soil through their roots. Facilitated diffusion occurs at a faster rate than simple diffusion. However, depending on the sort of carrier contributing to the diffusion, this form of diffusion might be passive or active.

Diffusion of glucose and water across cell membranes.

Osmosis is a special type of diffusion where water molecules diffuse through a semipermeable membrane from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration) .

The main difference between simple and facilitated diffusion is that simple diffusion occurs passively and without assistance , whereas facilitated diffusion requires transport proteins to promote the movement of molecules that cannot cross the membrane on their own.

Causes of Diffusion

The primary cause of diffusion is the random thermal movement of particles. Because of this kinetic energy, there are collisions, which cause the particles to disperse from areas of higher to lower concentration. It is a natural and physical process that occurs without the need to mix or shake the solutions.

Examples of Diffusion

Following are some examples of Diffusion:

• When you put a teabag in a cup of hot water, the tea will diffuse into the water and change color.
• The scent of a perfume or room freshener will be spread into the air, and we will be able to detect it.
• Sugar dissolves evenly in the water and sweetens it without the need to stir it.
• The smoke from the incense stick is diffused into the air and travels over the room when we light it.
• When you pour boiling water over dry noodles, the water diffuses, rehydrating them and making them plumper and more saturated .

Diffusion Pressure

Diffusion pressure refers to the pressure imposed by particles' tendency to spread from areas of higher concentration to areas of lower concentration. It is proportional to diffusing particle concentration. A permeable pot is attached to a glass tube with one end submerged in water.

A hydrogen-filled gas jar is inverted over the porous pot. The ability of hydrogen to diffuse into porous pots is faster than the ability of air to diffuse out of porous pots. This creates pressure inside the porous pot, pushing air into the water in the form of air bubbles from the glass tube's tip.

Factors Affecting Diffusion

Diffusion is a somewhat slow process that happens largely in gases and liquids. This energy-free mode of transportation does not require any energy. However, the rate of diffusion is influenced by several factors, including those listed below:

• Density : Graham's Law states that the rate of diffusion of a material is inversely related to the square root of its relative density.
• Permeability of Medium: The rate of diffusion decreases with the density of the medium.
• Temperature : The rate of diffusion increases as the temperature rises, with Q10 = 1-2-1-3. Sugar crystals do not dissolve as easily in ice-cold water as they do in warm water as a result of this.
• Diffusion Pressure Gradient: The difference in diffusion pressure at the two extremities of a system determines the rate of diffusion, which is inversely proportional to the distance between them.

Significance of Diffusion

Diffusion is an essential function that affects how molecules move throughout a cell's metabolic process. Diffusion is a natural phenomenon that occurs in liquids and gasses without using energy.

Diffusion is an essential process for the following reasons:

• Diffusion helps in the exchange of gases like oxygen and carbon dioxide during respiration.
• The diffusion is important for pollination  as it spreads the aroma of flowers, attracting insects and animals.
• Diffusion drives the process of transpiration .
• Diffusion keeps the cell walls of internal plant tissues moist by allowing water molecules to move between cells.

Things to Remember 

Following are some important points:

• Diffusion keeps the inside plant tissues' cell walls wet.
• It's a way for ions and other chemicals to spread throughout the protoplast.
• Diffusion is the process of water loss in the form of vapour.
• Diffusion is the process by which gases (CO2 and O2) are exchanged between the plant interior and the outside air.
• Water diffuses over a semi-permeable membrane through osmosis, a unique type of diffusion.
• The fragrance of flowers comes from the diffusion of volatile aromatic molecules that attract pollinators .

Sample Questions 

Ques: What is facilitated diffusion? (3 Marks)

Ans: Facilitated diffusion is the passive transport of molecules across the cell membrane with the aid of a carrier molecule from an area of higher concentration to a region of lower concentration. Molecules that are unable to freely cross the phospholipid bilayer (for example, big, polar molecules and ions) make use of it. Glucose molecules, sodium ions, and potassium ions all use carrier proteins to travel across cell membranes in the human body.

Ques: Does facilitated diffusion produce ATP? (3 Marks)

Ans: Because it is the passive flow of substances such as glucose and amino acids across the cell membrane, it does not require ATP. Because glucose is such a large molecule, it does so with the help of a membrane protein. Because it is passive, assisted transport does not require chemical energy from ATP hydrolysis in the transport stage; instead, molecules and ions move along their concentration gradient, reflecting the diffusive nature of the process.

Ques: Why does diffusion not use energy? (3 Marks)

Ans: Molecules are believed to flow down a concentration gradient spontaneously. This form of diffusion takes place without the need for any energy. Small, uncharged molecules can freely flow through a cell membrane by simple diffusion. They easily pass through the membrane of the cell. Diffusion is known as the movement of various molecules from a higher level of concentration to a lower level of concentration.

Ques: What is the main cause of the diffusion process in plants? (3 Marks)

Ans: Diffusion happens in plant cells as well. Water from the soil diffuses into the roots of all green plants via their root hair cells. Diffusion is the passage of ions across neurons that generates electrical charges. During photosynthesis, plants consume carbon dioxide. During photosynthesis, the concentration of carbon dioxide inside a leaf is this low. The increasing carbon dioxide content in the air around the plant allows the gas to diffuse into the leaf.

Ques: Is diffusion active or passive? (2 Marks)

Ans: Diffusion is a type of passive transport. A single chemical will tend to travel from a high-concentration location to a low-concentration area until the concentration is uniform throughout the space. You've heard of stuff diffusing through the air. Simple diffusion and osmosis, both of these methods are passive and they do not use ATP energy of cells.

Ques: How does distance affect diffusion? (2 Marks)

Ans: Diffusion occurs more quickly when the diffusion distance is modest since the particles do not have to go as far. Diffusion can happen quickly over short distances but take a long time over big distances. A molecule of glucose, for example, can diffuse across a 50-micrometre diameter cell in 2.5 seconds, while it takes 32 years to diffuse a distance of one meter.

Ques: How can you speed up diffusion? (2 Marks)

Ans: The faster the rate of diffusion, the higher the concentration difference. This is due to the higher kinetic energy of the particles due to higher temperature and this results in quick movement of them. The faster the rate of diffusion, the larger the surface area. Because heavier molecules move slower, they diffuse more slowly. For lighter molecules, the opposite is true.

Ques: Is diffusion always from high to low concentration? (3 Marks)

Ans: Diffusion is a type of passive transport. When a single substance moves from a high-concentration area to a low-concentration area, this is referred to as "moving solutes down the concentration gradient." The end outcome is an equal concentration of molecules on both sides of the membrane or equilibrium. Movement of molecules cannot stop till the system is in equilibrium. You've heard of stuff diffusing through the air.

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The importance of diffusion essay

Subject: Biology

Age range: 16+

Resource type: Other

Last updated

24 May 2021

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A-Level biology ’ the importance of diffusion’ essay

22/25 marks

written by me

the sections written in purple are out of spec and can be used to gain higher marks once you are in the top band already.

Tes paid licence How can I reuse this?

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