the new supersedes the old(xīn chén dài xiè)

the new supersedes the old

This entry is reviewed by the project of "science popularization China" science encyclopedia entry compilation and application.

Metabolism includes material metabolism and energy metabolism. Metabolism is composed of assimilation and dissimilation, two opposite and simultaneous processes. There are obvious differences and close relations between assimilation and dissimilation. If there is no assimilation, the organism will not be able to produce new protoplasm, nor be able to store energy, so dissimilation cannot be carried out; on the contrary, if there is no dissimilation, there will be no energy release, and the material synthesis in the organism will not be carried out. It can be seen that assimilation and dissimilation are both opposite and unified, and jointly determine the existence and continuity of organisms.

type

In the long-term evolution process, organisms constantly interact with their environment, and gradually form different types of metabolism. According to the different processes of assimilation and dissimilation in nature, the basic types of metabolism can be divided into assimilation and dissimilation. On the one hand, biological organisms transform the substances they absorb from the environment into their own substances through a series of chemical reactions. This process is called assimilation, that is, matter from the outside to the body, from small molecules to large molecules. Therefore, assimilation is a process of absorbing energy. For example, green plants use photosynthesis to convert water and carbon dioxide into starch and cellulose. On the contrary, it is dissimilation, that is, from the body to the external environment, the process of substances changing from large molecules to small molecules, which is a process of releasing energy, and at the same time expelling substances that the organism does not need or cannot use.

Assimilation and alienation are two aspects of contradiction, which are both opposite and unified. They restrict, relate and depend on each other, and both of them take their opposites as their existence conditions. Dissimilation provides energy for assimilation, which in turn provides material basis for dissimilation. For example, the metabolism of the human body is different at different ages. In childhood and adolescence, more nutrients are needed to promote the growth of the body. Assimilation plays a dominant role in this stage, and the metabolism is vigorous. On the contrary, in the old age, the human body function gradually declines, and the metabolism is gradually slow. At this time, the primary and secondary relationship between dissimilation and assimilation has also changed.

assimilation

According to the way of assimilation, organisms can be divided into autotrophic and heterotrophic types. People call heterotrophic organisms which can absorb the ready-made organic matter and assimilate the simple inorganic matter into the complex organic matter from the environment; they call autotrophic organisms. According to the different energy and carbon sources, organisms can be divided into four types.

1. Photoautotrophic type

Photoautotrophic organisms are those that use light as energy and CO < sub > 2 < / sub > or carbonate as main carbon source. These organisms usually have photosynthetic pigments, which use light as energy for photosynthesis, water or other inorganic substances as hydrogen donors, reduce CO < sub > 2 < / sub >, and synthesize cell substances. For example, higher plants, algae and some bacteria with photosynthetic pigments all belong to this type. The way of assimilating CO < sub > 2 < / sub > can be summarized by a general formula. In the general formula, a is oxygen in higher plants and algae, and sulfur or other inorganic sulfide in bacteria. In the process of photosynthesis, higher plants absorb light energy, assimilate carbon dioxide and water, produce organic matter, and release oxygen.

CO₂+2H₂A→(CH₂O)+2A+H₂0

The mechanism of photosynthesis is complex, including a series of optical steps and material transformation. It can be expressed as follows:

6CO₂+6H₂0→C₆H₁₂O₆+6O₂

2. Light heterotrophic type

The organisms that use light as energy and organic matter as the main carbon source are called heterotrophic main substance. Some bacteria have photosynthetic chromophores and can carry out photosynthesis. They use organic matter as hydrogen donor, assimilate organic matter to form their own matter, which is a kind of photosynthesis without oxygen production.

3. Chemoautotrophic type

The main energy source of chemoautotrophic substance is chemical energy, and the main carbon source is CO < sub > 2 < / sub > which can oxidize some inorganic substances such as NH < sub > 3 < / sub > and H < sub > 2 < / sub > s% to obtain chemical energy to reduce CO < sub > 2 < / sub > and synthesize organic substances. For example, nitrobacteria can oxidize ammonia to nitrous acid to obtain energy. Ammonia oxidation and CO < sub > 2 < / sub > reduction are coupled in bacterial cells.

4. Chemotrophic type

This kind of biological energy comes from the chemical energy produced by the oxidation of organic matter, and the carbon source mainly comes from organic matter, such as sugars, organic acids and so on. Therefore, organic carbides are both carbon source and energy source. Animals, fungi and most bacteria belong to this type.

Dissimilation effect

According to the way of biological dissimilation (i.e. respiratory type), it can be divided into aerobic and anaerobic organisms.

1. Aerobic substance

Most organisms have to live in an oxygen rich environment. They can obtain free oxygen from the atmosphere to decompose organic matter in the body and obtain energy.

2. Anaerobic organisms

This kind of organisms can not absorb free oxygen from the atmosphere and obtain energy by oxidation in the body. The main aerobic substance is aerobic respiration, which makes the organic substance release energy through a series of reactions, and finally forms CO < sub > 2 < / sub > and H < sub > 2 < / sub > O and other substances. Anaerobic respiration can release much less energy than aerobic respiration because of incomplete decomposition of organic matter and incomplete release of energy.

But the distinction between aerobic and anaerobic organisms is not absolute. Aerobic organisms can also carry out anaerobic respiration under certain conditions. For example, if the oxygen supply of human muscles is insufficient during strenuous exercise, anaerobic respiration can be used to supply energy. For another example, yeasts and some intestinal microflora can grow under aerobic or anoxic conditions, but they can obtain energy in different ways of oxidation. In anoxic condition, yeast ferments ethanol and accumulates ethanol and CO < sub > 2 < / sub >. In aerobic condition, it carries out aerobic respiration and oxidizes organic matter to CO < sub > 2 < / sub > and H < sub > 2 < / sub > o.

function

① Obtain nutrients from the external environment, material and energy;

② To transform the material absorbed by the outside world into its own components;

③ The structural elements are assembled into proteins, nucleic acids and lipids;

④ Decomposition of organic nutrients;

⑤ It provides all the energy for the life activities of organisms.

Material metabolism and energy metabolism

Metabolism includes material metabolism and energy metabolism. Material metabolism refers to the process of material exchange and material transformation between the organism and the external environment. Energy metabolism refers to the process of energy exchange and energy transformation between the organism and the external environment. They are interrelated and coupled. For example, after eating too much energy intake, fat synthesis increases; while in hunger, fat mobilization releases energy for the body to use.

(1) Material metabolism

The decomposition of old substances and the synthesis of new substances are carried out at the same time. The metabolic changes of all substances in organisms are collectively referred to as material metabolism, which includes anabolism and catabolism. Anabolism refers to the synthesis of all substances in the organism, which belongs to the category of assimilation, such as the synthesis of protein by amino acids and nucleic acids by nucleotides; catabolism refers to the decomposition of all substances in the organism, which belongs to the category of dissimilation, such as the complete decomposition of sugars into carbon dioxide and water through the tricarboxylic acid cycle.

(2) Energy metabolism

① Changes in energy metabolism

In the process of material exchange accompanied by energy exchange is called energy metabolism. The body absorbs nutrients from the external environment for anabolism and energy from the outside world. This part of energy mainly comes from the chemical energy contained in nutrients. When these nutrients are catabolized in the body, they release chemical energy for the needs of life activities. Chemical energy is not only used to synthesize other components in the body, but also used in various life activities. However, if the chemical energy can not be completely converted into work energy, some of it will inevitably be released in the form of heat and become scattered heat (q). The energy used to do work is called free energy (Δ f), and the total energy of transformation is called reaction heat (Δ h). According to the law of conservation of energy, the heat of reaction is equal to the sum of the free energy of transformation and the heat of emission, i.e. △ H = △ F + Q

② Basal metabolism

Basal metabolism refers to the minimum energy required by all organs of human body to maintain life. That is, the lowest energy metabolism required to maintain basic life activities such as heartbeat and respiration when the human body is awake and extremely quiet and not affected by muscle activity, environmental temperature, food and mental stress. In order to compare the energy metabolism level of different individuals, the basic metabolic rate (BMR) can be expressed by the heat emitted by the body per square meter of body surface area per hour. Basal metabolic rate (BMR) varies with different physiological conditions such as gender and age

Chinese PinYin : xīn chén dài xiè