In all the organisms nutrients keep on circulating and are transported from one part to another. In plants also the same process is essential so that all the parts and cells receive the required amount of nutrition. This movement can take place to the immediate surrounding or to far of body parts.When the substances need to move for shorter distances then diffusion is beneficial. During diffusion, molecules move down the concentration gradient. If the concentration gradient is high, it will result in a higher diffusion rate. Diffusion is impossible when the concentration gradients of both regions are the same. For diffusion, we will have to create differentiation between the concentration gradients of two cells. Some factors affecting diffusion are the size of the molecule, concentration gradient, temperature, state of matter. Diffusion promotes cellular respiration and distributes nutrients among cells and others.
Diffusion does not require any semipermeable membrane. Diffusion depends on the presence and concentration of other particles.It can occur in all the states of matter i.e.,solids ,liquids and gases. This process can be observed happening inside the living organisms as well as in the physical world. This process is neither stopped nor reversed. Diffusion occurs between similar and dissimilar types of solutions. Example- Water vapour moves out of the stomata during transpiration, sugar particles dissolve in a glass of undisturbed
Passive diffusion occurs when molecules move across a semipermeable membrane without the help of protein channels.
There are the following kinds of passive transport listed below:-
1) Simple diffusion
2) Facilitated diffusion
3) Channel diffusion
1. Simple Diffusion:-
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Simple diffusion is an example of passive transport. It occurs when electrochemical potentials on both sides of a permeable barrier vary.
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In this type of diffusion, very small molecules can move through gaps.
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Location- between the various phospholipid molecules in the cell membranes.
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SmallInhibitor molecules do not inhibit simple diffusion
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This does not require any energy. The speed of simple diffusion is very low.
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Inhibitor molecules do not hinder simple diffusion.
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In this type of diffusion, the movement of particles takes place with the direction of a concentration gradient.
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Example:- water, oxygen and carbon dioxide, etc.
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More examples of simple diffusion are:-
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Steroid hormones can move freely across different membranes down their concentration gradient. So, this is an excellent example of simple diffusion.
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At the time of food digestion, oxygen is transferred into the blood from the lungs. Also, oxygen is transferred into the muscles from the blood cells.
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Another simple diffusion example- In the body of pregnant women, food and oxygen travel from the mother’s body into the fetus.
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Bacteria have single-celled microorganisms. Bacteria deliver water, oxygen, and nutrients to the cytoplasm. No specialized organelles in bacteria perform this type of activity.
2. Facilitated diffusion:-
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This type of diffusion is the transport of substances or molecules across a permeable membrane through a concentration gradient. Only large polar molecules pass through this type of diffusion. Examples- Amino acid, glucose, etc.
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This allows for the flow of molecules down a concentration gradient and across the cell’s membrane.
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Simple diffusion does not require protein’s help. But, this process requires support from a protein. Two types of proteins help in this type of diffusion.
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a) carrier proteins can shuffle the molecules from one side of the membrane to the other side. b)channel proteins, which create a hole across the cell or plasma membrane. Now the channels open, which allow the molecules to flow through them.
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Carbon dioxide and oxygen can diffuse across the plasma membrane directly. But, other molecules need assistance to cross other substances.
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Facilitated diffusion occurs through transmembrane proteins.
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These transports are large or polar particles.
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It happens through specific facilitator molecules.
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In this type of diffusion, the kinetics of carrier-mediated transport affects diffusion rate.
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Examples of this type of diffusion are:-
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Glucose (sugar molecule) is the main energy source for cells. Outside of a cell, the bloodstream is constantly supplying glucose, but glucose is continuously consumed inside of the cell. The glucose molecule is too big to get through the plasma membrane. So, the cell provides glucose-specific carrier proteins. These proteins stick to glucose molecules and allow the molecule or substances to enter the cell.
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Molecules flow from high to low- Some molecules cannot enter/exit a cell during diffusion. So, this type of diffusion can check some of these molecules while passing through the plasma membrane. They bind the molecules to special carrier proteins by opening channels located between the cells.
3. Channel Diffusion:-
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It involves the ions and charged particles moving through a specific channel protein/pore in the cell wall. In this case, no limits to the number of particles that travel through each of those channels exist.
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The channels are very selective and will accept only one type of molecule for transportation. A protein channel carries out this diffusion. It allows the compounds or molecules to go into/out of the cell.
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This type of diffusion is regulated very easily by the proteins.
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When the materials pass through one end, the ion channels open in channel diffusion. This diffusion is carried out by a protein channel. This is called “channel-mediated diffusion.”
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Proteins that are embedded in the membrane act as a doorway for diffusion.
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The molecules will move down a concentration gradient via channel diffusion.
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Some examples of channel diffusion are:-
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The perfume is diffusing into the surrounding (air).
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When watering the plants, the water is diffused into the plant. It checks the leaves from wilting. It means the carbon dioxide is diffused from the leaves from the air (located between the mesophyll cells) and transfers to the chloroplast of leaves.
Conclusion :
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Diffusion plays a main role in cellular transport.
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The factors affecting the rate of diffusion:-
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If the temperature is high, then the rate of diffusion is faster.
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Greater the difference in concentration, the more rapid the diffusion.
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If gas is more soluble, then the diffusion will be faster.
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If the density of solvent increases, the rate of diffusion will decrease.
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If the surface area increases, the rate of diffusion will increase. But, a thicker membrane reduces the rate of diffusion.
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If the diffusion distance is small, then the diffusion will happen faster.
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If the molecule is smaller, then the rate of diffusion is faster. Similarly, If the molecules are larger, it slows down the diffusion rate.