aqa biology essay the importance of diffusion in organisms

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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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Adam Roberts

*** This piece of writing discusses diffusion in the right way with a good range of relevant examples. However, it does not gain a higher star rating because of a lack of detail. Examiners want to see evidence that candidates have learned new content at AS and A level and that they can use A level terminology correctly and in the right context. If particular terms are used it is important that a candidate shows that they really understand what those terms mean.

Document Details

• Word Count 946
• Page Count 2
• Level AS and A Level
• Subject Science

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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

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