Morphology and characteristics of early life on earth. The earliest life form on earth is very simple. A cell is an individual. It has no nucleus. We call it prokaryote. It survives by directly absorbing nutrients from the surrounding environment on the cell surface. This lifestyle is called heterotrophy. At that time, their living environment was anoxic, which was called anaerobic. So the earliest prokaryotes were heterotrophic and anaerobic. Its shape is spherical at first, then it becomes oval, arc, sticky rice strip, then it becomes spiral, slender and filiform, and so on. From the development direction of morphological changes, it is to increase the surface area of the body in contact with the outside world and increase its own volume. Bacteria and cyanobacteria living on the earth now belong to prokaryotes. The occurrence and development of cyanobacteria has accelerated the increase of oxygen content on the earth. Since more than 2 billion years ago, there has been a large amount of oxygen not only in water but also in the atmosphere. The appearance of nucleus is an important event in biological evolution. Prokaryotes have evolved for/kloc-0.5 billion years. The nuclear substances that were originally dispersed uniformly in their cells are relatively concentrated and covered with a membrane called nuclear membrane. The nuclear membrane of a cell separates the nuclear matter in the membrane from the cytoplasm outside the membrane. This is how the nucleus of a cell is formed. Organisms with nuclei are called eukaryotes. Since then, cells are no longer simply divided into two cytoplasm during reproduction and division, and the nucleus inside is also divided into two. Eukaryotes (there were no animals at that time, so to speak, they were actually just eukaryotic plants) appeared about 2 billion years ago. The emergence of gender is another important event in the process of biological evolution, because gender promotes the eugenics of biology and accelerates the development of biology in a more complicated direction. Therefore, after the appearance of eukaryotic unicellular plants, it took hundreds of millions of years for eukaryotic multicellular plants to appear. Not long after the appearance of eukaryotic multicellular plants, the division of labor of plants appeared. A group of cells in plants mainly play the role of fixing plants and become fixed organs, which is the origin of modern algae plant fixators. From then on, organ differentiation began to appear, and the internal cell morphology of different functional parts also began to differentiate. It can be seen that the appearance of nucleus and sex has greatly accelerated the development of the morphology and function of the organism itself.
The origin of life
For a long time, there are various explanations about the origin of life. In recent decades, according to the new achievements of modern natural science, people have made a comprehensive study on the origin of life and made great progress.
According to scientific calculations, the earth has a history of about 4.6 billion years since its birth. The early earth was very hot, and all the elements on the earth were in a gaseous state. At that time, there would never be life. The initial life evolved step by step from inanimate matter through extremely complicated chemical processes in an extremely long time after the earth's temperature dropped. At present, this view that the origin of life is through the chemical evolution process has been recognized by most scholars, and that this chemical evolution process can be divided into the following four stages.
It is speculated that the chemical evolution of the origin of life began under the conditions of the primitive earth. At that time, the surface temperature of the earth had dropped, but the internal temperature was still very high and volcanic activity was extremely frequent. The gas ejected from the volcano formed the primitive atmosphere (below). It is generally believed that the main components of primitive atmosphere are methane (CH4) and ammonia, which is an imaginary map of primitive earth.
(left) primitive atmosphere (right) organic matter formation
(NH3), water vapor (H2O), hydrogen (H2), in addition to hydrogen sulfide (H2S) and hydrogen cyanide (HCN). Under the action of cosmic rays, ultraviolet rays and lightning, these gases may naturally synthesize a series of relatively simple organic small molecules such as amino acids, nucleotides and monosaccharides. Later, the earth's temperature dropped further, and these small organic molecules flowed through lakes and rivers with the rain, and final gathering was in the primitive ocean.
This speculation has been confirmed by scientific experiments. 1935, American scholar Miller and others designed a set of sealing device (below). They pumped the air out of the device, then simulated the atmospheric composition on the primitive earth and introduced methane, ammonia, hydrogen and water into the Miller experimental device.
Steam and other gases, and simulated lightning and continuous spark discharge under primitive earth conditions. Finally, amino acids were detected in the U-tube. Amino acid is the basic unit of protein, so it is of great significance to explore the production of amino acids on earth.
In addition, some scholars simulate the atmospheric composition of the primitive earth and make other organic substances in the laboratory, such as purine, pyrimidine, ribose, deoxyribose, fatty acids and so on. These studies show that in the Origin of Life, the chemical process of inorganic synthesis of organic matter is completely possible.
How were organic polymers such as protein and nucleic acid formed by small organic molecules formed under primitive earth conditions? Some scholars believe that in the primitive ocean, small organic molecules such as amino acids and nucleotides, after long-term accumulation and interaction, formed primitive protein molecules and nucleic acid molecules through condensation or polymerization under appropriate conditions (such as adsorption on clay).
Now, some people imitate the conditions of primitive earth and make substances similar to protein and nucleic acid. Although there are some differences between these substances and protein and nucleic acid, it is not certain whether the formation process of protein and nucleic acid on the primitive earth is like this, but it has provided some clues for people to study the origin of life; Under the conditions of primitive earth, it is possible to produce these organic polymers.
According to the multi-molecular system composed of organic polymers, it is speculated that protein, nucleic acid and other organic polymers accumulate more and more in the ocean, and the concentration keeps increasing. Due to various reasons (such as evaporation of water and adsorption of clay), these organic polymers are concentrated and separated, and they interact and condense into droplets. These droplets float in the primitive ocean, and the outer layer has the most primitive boundary film, which is isolated from the surrounding primitive marine environment, thus forming an independent system, that is, a multi-molecular system. This multi-molecular system has been able to carry out primitive material exchange activities with the external environment.
The evolution from multi-molecular system to primitive life and from multi-molecular system to primitive life is the most complex and decisive stage in the process of life origin, which directly involves the occurrence of primitive life. At present, people can't verify this process in the laboratory. However, we can speculate that some multi-molecular systems have evolved for a long time, especially the interaction between protein and nucleic acid, and finally formed primitive life with primitive metabolism and reproduction. Later, from the chemical evolution stage of the origin of life to the biological evolution stage after the emergence of life.
Although a large number of simulation experiments have been carried out on the chemical evolution process of the origin of life, most of them are only concentrated in the first stage, and some stages are limited to hypothesis and speculation. Therefore, we must continue to study and discuss the origin of life.
Protein and nucleic acid are the most important substances in organisms. Without protein and nucleic acid, there would be no life. 1965, China scientists synthesized crystalline bovine insulin (a protein containing 5 1 amino acid). 198 1 year, China scientists synthesized yeast alanine transport ribonucleic acid (a kind of ribonucleic acid) artificially. These works reflect China's great achievements in exploring the origin of life.
Biology is a subject that studies the species, structure, development, origin and evolution of organisms at all levels and the relationship between organisms and their surrounding environment. Man is a creature and the object of biological research.
Biology is a branch of natural science. Study the structure, function, occurrence and development of living things. According to the research object, it is divided into zoology, botany, microbiology and so on. According to the research content, it is divided into taxonomy, anatomy, physiology, genetics, ecology and so on. It is a science that studies the species, structure, function, behavior, development, origin and evolution of organisms at all levels and the relationship between organisms and their surrounding environment. In ancient times before the development of natural science, people were puzzled by colorful creatures. They often regard life and inanimate objects as two completely different and unrelated fields, and think that life is not dominated by the laws of motion of inanimate objects. Many people also attribute all kinds of life phenomena to an immaterial force, that is, the role of "vitality". These groundless speculations have been gradually abandoned with the development of biology and have no place in modern biology.
Since the 20th century, especially since the 1940s, biology has absorbed the achievements of mathematics, physics and chemistry, and gradually developed into an accurate, quantitative and molecular science. People have realized that life is a form of material movement. The basic unit of life is the cell, which is a material system composed of protein, nucleic acid, lipid and other biological macromolecules. Life phenomenon is the expression of the comprehensive movement and transmission of matter, energy and information in this complex system. Life has many characteristics that inanimate matter does not have. For example, life can synthesize a variety of organic compounds at normal temperature and pressure, including complex biological macromolecules; It can make use of substances in the environment, so that all kinds of substances in the body far exceed the production efficiency of the machine, without discharging harmful substances that pollute the environment; Can efficiently store and transmit information; It has self-regulation function and self-replication ability; Individual development and species evolution are carried out in an irreversible way. It is of great theoretical and practical significance to reveal the mechanism in the process of life.
Modern biology is a huge knowledge system with many branches. This paper focuses on the objects, branches, methods and significance of biological research. The essence of life and the history of biological development will be elaborated in "life" and "biological history" respectively.
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Cheng Jian | Floor 6
Genetic law of pea
Mendel chose pea for genetic experiment. The specific reasons are as follows: Mendel found that pea is a closed-pollinated plant. Because of long-term closed pollination, the purity of pea is guaranteed, that is to say, a pea variety with red flowers will also open red flowers, and the offspring of high-stem peas will never have short stems; In peas, red flowers and white flowers, tall stems and short stems, round grains and wrinkled grains are so distinct. These different pea colors and grain shapes are called relative traits. It is precisely because the genetic relative traits of pea are distinct, and the characteristics of closed pollination make its genetic relative traits very stable. When studying plants with this characteristic, it is easy to observe the influence of heterogeneous pollen. Although pea is a closed-flowered plant, its flower shape is relatively large. It is easy to remove stamens from pea flowers by artificial means and send pollen to female flowers.
Mendel confidently started a genetic experiment that had never been carried out before. He carefully picked the male flowers of red peas and sent the pollen of white peas to get the hybrid generation (F). Peas grown from the first generation seeds are red flowers, and the second generation seeds are pollinated by closing flowers. When the plants grown from the second generation seeds bloom, besides 3/4 plants are red flowers, 65,438+0/4 plants are white flowers. He called the parental traits that appeared in the first generation as dominant traits, and the parental traits that did not appear as recessive traits. The phenomenon that the characters of two parents appear at the same time in the second generation is called "separation phenomenon". When Mendel made a hybridization experiment with peas, he carefully observed the following seven pairs of completely different characters:
Color of flowers: red and white;
Seed shape: round and wrinkled;
Color of leaves: yellow and green;
Flowering position: axillary (that is, branched) terminal;
The shape of mature pods: full and shrinking;
Height of plants: height and height.
The initial experiment was to cross two peas (parents) with obvious differences in the above single traits, and the above seven groups of related traits were crossed seven times respectively. The results of seven crosses were surprisingly consistent. That is, the hybrid generation has only one parental trait. For example, when a plant with red flowers crosses a plant with white flowers, the hybrid offspring always have the same red flowers. Peas with yellow cotyledons are crossed with peas with green cotyledons, and the first generation (F) always has the characteristics of yellow cotyledons. The phenomenon that only one parent of this hybrid appears in the first generation is no exception in the hybridization of 7 pairs of relative traits observed by Mendel. In addition, when the first hybrid is self-pollinated, the seeds of the second hybrid are obtained. In the second generation of seven crosses, the characters of two hybrid parents appeared, that is, both of them were separated. More interestingly, in the second generation of hybrid, the traits that parents appeared in the first generation (that is, dominant traits) and the traits that parents did not appear in the first generation (that is, recessive traits) were both 3: 1.
It can be seen that the genetic traits of organisms are influenced by their parents, but they will not be completely "copied", so the inheritance of biological genes is continued through generations of life, thus preserving a complete gene pool!
Genetic law of pea
Mendel chose pea for genetic experiment. The specific reasons are as follows: Mendel found that pea is a closed-pollinated plant. Because of long-term closed pollination, the purity of pea is guaranteed, that is to say, a pea variety with red flowers will also open red flowers, and the offspring of high-stem peas will never have short stems; In peas, red flowers and white flowers, tall stems and short stems, round grains and wrinkled grains are so distinct. These different pea colors and grain shapes are called relative traits. It is precisely because the genetic relative traits of pea are distinct, and the characteristics of closed pollination make its genetic relative traits very stable. When studying plants with this characteristic, it is easy to observe the influence of heterogeneous pollen. Although pea is a closed-flowered plant, its flower shape is relatively large. It is easy to remove stamens from pea flowers by artificial means and send pollen to female flowers.
Your brother is more stupid than 2.
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