Diffusion is the movement of molecules or ions down a concentration gradient i. e. from an area of high concentration to an area of low concentration. For a diffusion system to be efficient, it should have a large surface area so that high amount of substances can be exchanged at a time. It should also have a thin membrane and a continuous supply of substances, as a thin membrane means that the diffusion pathway would be short, and the continuous supply helps maintain a concentration gradient, which is essential for diffusion to take place.

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There are two main types of diffusion; simple and facilitated. Simple diffusion is when a small, non-polar molecule such as CO2 and Oxygen passes through the phospholipid bilayer. A carrier protein is not needed for this type of diffusion to take place. Facilitated diffusion, however, requires carrier proteins transport molecules across the membrane, as the molecules are polar or are too large to pass through the lipid bilayer. Examples of these molecules are sodium and potassium ions, and glucose.

Diffusion is essential for living organisms as it is a feature of a number of processes which control and supply vital substances to the body. It occurs throughout the human body, and without it, cells and body tissue could not get important nutrients for survival. In humans and animals, diffusion is needed during respiration. It is the way oxygen travels from the lungs to the red blood cells in the blood and the way carbon dioxide travels from the blood to the lungs from where it can be exhaled.

In the oxidative phosphorylation stage of aerobic respiration, diffusion is vital in getting the protons across the potential gradient from the inter-membranal space to the inner membrane to phosphorylate ADP and an inorganic P to ATP which is the universal energy carrier. Without this, we will be unable release energy in respiration and therefore will die. Oxygen continues down the concentration gradient into mitochondria organelles as the final electron acceptor and is reduced to water. The cells in our body also take up nutrients from the blood by diffusion.

Humans and animals cannot make nutrients, so they get the nutrients from the food they eat. Once a nutrient arrives at a cell, it is still inside a blood vessel while the cell lies outside. The lack of nutrients inside the cell, and between the cell and the blood vessel, creates a concentration gradient between the blood vessel and the cell. Due to the lower concentration in the cell, the nutrient diffuses through the blood vessel wall and into the cell. Diffusion is essential in water reabsorption in the kidney for the removal of excess Na and Cl ions. If this process is not done, the osmotic state would be affected.

Diffusion is also extremely important in excretory systems of human beings. For example in a urinary system, if the body doesn’t consume enough water, then water is diffused back in the body and vice versa. Diffusion is responsible for our nerves to function as the neurotransmitter diffuses across the synaptic cleft, so that the next nerve cell can pick up the signal and pass it along. In the case of plants, diffusion is the very important process because plants transfer food particles from the phloem and water particles from the xylem through the process of diffusion and osmosis.

When there’s excess water in the plants, this water needs to be removed, and this is done by the process of transpiration, which requires diffusion. Also, diffusion is an essential process in exchange of gases. Plants get carbon dioxide and release oxygen through diffusion. Photosynthesis also requires diffusion in a number of steps. Moreover, roots absorb water and salts from the soil which is transferred from roots to leaves through the process of diffusion. Diffusion is an important process in the lives of plants.

Water is an important component of all cells, and water moves into plant cells by the process of osmosis. Osmosis is the diffusion of water across a semipermeable membrane. When there’s excess water in the plants, this water needs to be removed by transpiration. In this process, water vapour evaporates from the surface of a leaf by diffusion through the open stomata. Many plant nutrients reach the root surface via diffusion through the soil solution. Some nutrient molecules diffuse across root cell membranes into the cytoplasm or from the cytoplasm of the endodermal cells into the xylem tissue.

Also, diffusion is an essential process in exchange of gases. During photosynthesis, carbon dioxide diffuses from the atmosphere through the stomata and into the air spaces of leaves and oxygen is also released via diffusion. In photoynthesis water must diffuse into the plant or bacterial cell. It is then destroyed in what is commonly called the light dependent reactions. It is separated into Hydrogen ions and oxygen. The oxygen is released into the air via diffusion and the Hydrogen ions are used to

Produce ATP and reduced NADP. Since the water is used up, more is needed to keep the process up, so more water diffuses into the cell. In order for the plant to produce sugars from the carbon dioxide that has diffused into the cell as, it must enter the chloroplast. This is where the light independent reactions occur. The carbon dioxide is used up along with some of the ATP to make sugar. As the sugar is made and relocated this creates a carbon dioxide deficit in the chloroplast, causing more Carbon dioxide to diffuse into it.

Diffusion also plays a role in the movement of photosynthetic products such as sugars into the phloem for transport throughout the plant. Because cellular membranes are composed of a lipid bilayer, lipid-soluble materials use simple diffusion to cross the membrane surface. Substances with low lipid solubility can move across membranes via facilitated diffusion. In this process, the substance binds to a transporter molecule, which transports the substance across the membrane and down its concentration gradient.

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