The act or process of assimilating; the state of being assimilated. In biology, it is associated with the photosynthesis in autotrophs and the digestive process in heterotrophs.
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Assimilation in biology is referred to as the process in which the living organisms integrate the nutrients from various external resources in their body and utilizes them to satisfy the energy demands required to stay alive. In another definition, assimilation is described as the absorption of vitamins, minerals, and other chemicals from food within the intestinal tract. Furthermore, the breakage of complex molecules available in the food into the simpler particles, and then the movement of those modest units in those destinations in the living body where they are required such as active cells is often cited as assimilation. The process of photosynthesis, nitrogen fixation, conversion of magnesium supplements, and the formulation of biological tissues and fluids via adsorption of nutrients into the human body after the digestion in the intestine are some of the practical applications of biological assimilation. Moreover, the growth, the renewal of the organisms, the structural developments, their reproduction, and the restoration of energy reserves in the body are supported by assimilation. It is often cited in thermodynamics that the human bodies are an open system that means that they can only exist and survive with the uninterrupted input of energies from the external resources supplied and hence, that supports the significance of assimilation in biology.
Impact of Assimilation in Living Organisms
Solar irradiation is the primary source of energy for all living creatures in the universe. The living organisms found in the earth, based on their use of various forms of nutrition to fulfill the energy demands (c.f. Fig 1) are divided into two types:
The organisms that are capable of producing their food via light, water, carbon dioxide, and other chemicals are known as autotrophic organisms. The whole process in which the inorganic compounds in the form of various oxides of carbon are converted into organic compounds such as carbohydrates, amino acids, proteins, and other useful components is called carbon fixation also referred to as carbon assimilation. The autotrophic organisms are further classified into photoautotrophs and litho autotrophs based upon the utilization of sunlight and inorganic oxidation processes respectively. On the other side, heterotopic organisms are those kinds of creatures that are not capable of producing their own food and for the energy supplies, they solely rely on obtaining energy from external resources by assimilating the organic matter present in the food they eat. Thus, during assimilation, the complex proteins and carbohydrates are converted into glucose and amino acids. Therefore, in respiration, the glucose is employed while the amino acids are acquired in the building of new proteins. It is very important to understand that the process of dissimilation (the renewal of components parts due to destruction) and assimilation take part continually. Thus, it can be perceived from the above discussion that assimilation is a very vital phenomenon for the movement of digested food particles into various cells of the body where energy is required.
Examples of Assimilation
The process of assimilation occurs in nearly all forms of living organisms in the world. Generally, the living is characterized in three categories i.e. plants, invertebrates, and humans. Hence, the process of assimilation in all three groups is explained below as:
Nitrogen is the basic ingredient for the survival and growth of plants. The nitrogen is supplied to the plants either by numerous fertilizers or when it is absorbed by the soil from the atmosphere. The process of assimilation in the plants starts when the bacteria present in the soil convert the nitrogen into ammonium and then the ammonia is again converted into nitrates that can be easily absorbed by the roots of the plants . Later, after the cycle of absorption, amino acids, nucleic acids, and chlorophyll are all built around those absorbed nitrates. Furthermore, the process of assimilation is also utilized in the process of carbon fixation described above in autotropic organisms. Hence, carbon assimilation and nitrogen assimilation are found in plants and is being illustrated in Fig 2 captioned as assimilation in plants.
Eating and digestion are two of the most important processes in assimilation in invertebrates. Although assimilation is a very easy process in some invertebrates in many, it is referred to as a tedious procedure. The nutrients are absorbed straight away from the host digestive system by tapeworms. The sponges and corals directly take the food particles through a process called phagocytosis. There is a single, long digestive tract extending from mouth to anus in nematodes. Hence, it can be concluded that all forms of invertebrates take energy from the nutrients in one way or another, they all employ assimilated nutrients for growth and energy .
Human Digestion Assimilation
The digestive system of humans is relatively complex as compared to plants and insects to assimilate food and water. Food injected in the mouth travels all the way to the stomach where the process of digestion starts. The infectious bacteria are killed by hydrochloric acid and the larger food particles are converted assimilated into smaller ones that are transported into cells. The food after the stomach is pushed into the small intestine, where it is mixed with liver bile and pancreatic juices. The nourishment is digested properly and then the nutrients in the food are supplied to various cells in the body where the energy is required. Later after the distribution of nutrients, the remaining mesh is forwarded to the large intestine. Hence, it can be concluded that the process of assimilation in human bodies occurs in the small intestine also referred to as bowl.
Assimilation of Nutrients
It is a very well-known fact that the food we eat regularly in the form of various meals reaches from our plate directly to our cells via assimilation as the body breaks down the food into simpler particles, digests it, and then distributes it to required destinations. Moreover, as described earlier, assimilation takes down the nutrients from the food to cells where it is used for growth and reproduction. To understand the concept of assimilation of nutrients, it is very vital to go through the cycle of food digestion.
The digestive system primarily starts from the mouth where the food is chewed. The saliva produced by the salivary glands moistens the food and thus it is passed to the stomach via the esophagus. The starches are also broken down into simpler particles by saliva. As the food enters the stomach, very strong acids and enzymes break the food further into various nutrients such as carbohydrates, proteins, and fatty acids. Hence, the digestion of food is partially complete and then it is pushed into the small intestine where the assimilation of nutrients occurs. For instance, the complete cycle of digestion of food is illustrated in Fig 3.After partial digestion of food in the stomach, a mixture of food, liquids, and digestive juices are passed in the small intestine also termed as a bowl in a very regulated and controlled manner. The small intestine is a tightly folded tube that connects the stomach on the top-notch and large intestine in the bottom (cf Fig 4). It is very well written by scientists that much of the digestion occurs here and the prime task of the small intestine is the absorption and assimilation of the nutrients present in the food. In adults, the average length of the bowl/small intestine is around 7 meters. The small intestine has been further divided into three segments by doctors mentioned as duodenum, jejunum, and ileum as shown in Fig 4 which are covered by omentum anteriorly . Each part of the intestine has its own distinct role in the absorption of the nutrients. It can be seen in Fig 4, that the food first enters in the duodenum where it is mixed with various secretions such as bicarbonate, digestive enzymes, and bile salts that boost the process of digestion. The duodenum is divided into four parts that are inferior, superior, ascending, and descending altogether around 25 cm long. The fats available in the food are often digested by bile salts from the liver. The carbohydrates and fats are digested via pancreatic enzymes. The acid that arrives with the food from the stomach is neutralized by bicarbonate from the pancreases. It is worth mentioning here that the proper digestion of food and its conversion into nutrients is associated with the healthy working of the liver and pancreas. After the proper digestion of the chyme in the duodenum, it is passed into the jejunum, and around 90% of the assimilation of nutrients including protein, carbohydrates, vitamins, and minerals is achieved here. The small intestine is equipped with very minute projections written as microvilli. The only responsibility of these cells is to take the nutrients from the jejunum and pump it to blood or cells where the energy is required. Lastly, the absorption of water, bile salts, and some excessive vitamins are completed in the ileum, after which the extra food particles are pushed in the large intestine or colon .
Malabsorption and Assimilation
The major role of the small intestine in the digestion process is to absorb the nutrients from the food that is eaten and to deliver them to the cells via the bloodstream. There may be a variety of syndromes due to which the smooth working of the bowl is in effect. Hence, those diseases are called malabsorption syndromes. In malabsorption disorders, the intestine is unable to absorb and assimilate both micronutrients (minerals and vitamins) and macronutrients (fats, carbohydrates, and proteins). Damage in the intestine, excessive use of medicines, lactose deficiency, peracetic diseases, radiation therapy, and injured intestine lining are some of the factors that cause malabsorption syndrome. Doctors believe that the said disorder can be predicted via stool, blood, breathe, imaging tests, and biopsy. Moreover, malabsorption disorder can be treated by altering the diet, taking vitamin and enzyme supplements, and avoiding dairy products. It is believed that the adsorption of nutrients is badly affected in the human body due to malabsorption syndrome .
Factors Affecting Assimilation
Many factors affect the assimilation of nutrients. Some of the key factors that have been dedicated by the doctors that affect the assimilation of organic matter are temperature, the composition of the food intake, the time gap between two meals, the age of culture, and the change in cell concentration and structure. On the other hand, the researchers believe that the human body behaves differently in the assimilation process truly based on the kind of food taken. Moreover, it has also been published in various research articles that daily consumption of green tea and occasional fasting improves the digestion system that results in an advanced assimilation process.
It can be concluded from the above discussion that the distribution of nutrients to various cells is mandatory for their growth, health, and reproduction. The dispersal of nutrients to required destinations from the small intestine is accomplished by assimilation. It is believed that the said process is generally found in both autotrophic organisms and heterotrophic organisms. Moreover, in the small intestine, the complete digestion process occurs in the duodenum, followed by 90% of the assimilation of nutrients including protein, carbohydrates, vitamins, and minerals is achieved in the jejunum. Later, the absorption of water, bile salts, and some excessive vitamins are completed in the ileum. It is believed that the process of assimilation is affected by various factors including quantity and composition of the food eaten, the time gap between two meals, the age of culture, and the change in cell concentration and structure. Moreover, the smooth execution of assimilation is severely disturbed by malabsorption syndromes, a disorder that occurs due to malfunctioning of the small intestine due to damage in the intestine, excessive use of medicines, lactose deficiency, peracetic diseases, radiation therapy and injured intestine lining.
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