There are two schools of biology from the beginning, one is called natural history school, and the other is called experimental school. The natural history school is represented by ecology, and the experimental school is represented by genetics and molecular biology.
Since the 1940s, biology has absorbed the achievements of mathematics, physics and chemistry, and gradually developed into an accurate, quantitative and molecular science.
Biologists divide organisms into several fields according to their development history, morphological and structural characteristics, nutritional methods and their functions in the ecosystem. At present, it is generally understood that the biological world on earth is divided into five realms: prokaryotes such as bacteria and cyanobacteria are monera realms; Single-celled eukaryotes are protozoa; Photoautotrophic plant kingdom; The fungal world that absorbs heterotrophy; Swallow the kingdom of heterotrophic animals.
Virus is a cell-free life form, which consists of a long nucleic acid chain and a protein shell. Viruses do not have their own metabolic mechanism and enzyme system. So when the virus leaves the host cell, it becomes a chemical substance that has no life activity and cannot reproduce on its own. Once it enters the host cell, it can use the material and energy in the cell and the ability of replication, transcription and translation to produce a new generation of viruses like it according to the genetic information contained in its own nucleic acid.
Viral genes, like those of other organisms, can mutate and recombine, so they can also evolve. Because the virus has no independent metabolic mechanism and cannot reproduce independently, it is considered as an incomplete life form. In recent years, a virus-like virus that is simpler than a virus has been discovered. It is a small RNA molecule without protein shell, but it can cause diseases in animals. The existence of these incomplete life forms shows that there is no insurmountable gap between inanimate and living.
Prokaryotic cells and eukaryotic cells are two basic forms of cells, which reflect two stages of cell evolution. It is a great progress in modern biology to divide organisms with cellular morphology into prokaryotes and eukaryotes. Prokaryotic cells are characterized by no modular organelles such as mitochondria and plastids, and the chromosome is just a circular DNA molecule, with no protein such as histone and no nuclear membrane. Protozoa and organisms are mainly bacteria.
Eukaryotic cells are cells with more complex structures. It has membrane organelles, such as mitochondria, and a nucleus with a double membrane, which separates the genetic material in the nucleus from the cytoplasm. DNA is a synthetic chromosome of long-chain molecules, jailer proteins and other protein. This nuclear cell can undergo mitosis and meiosis, and the result of division is that the copied chromosomes are evenly distributed to daughter cells. Protozoa are the most primitive eukaryotes.
Plants are eukaryotes with light and autotrophic as their main nutritional forms. Typical plant cells contain vacuole nucleus and cell wall, and cellulose is the main component. Cytoplasm is composed of chloroplasts, which are organelles for photosynthesis. Photosynthesis in plants uses water as an electron donor. Photosynthetic autotrophy is the main nutritional mode of plants. A few higher plants are parasitic, and even fewer plants can catch small insects for heterotrophic absorption.
Plants have developed from unicellular green algae to angiosperms adapted to photosynthesis. In higher plants, roots (fixing and absorbing organs), stems (supporting organs) and leaves (light and organs) differentiate. Petiole and many branched stems support the flaky leaves to spread in all directions to obtain the maximum light and absorption area, and the cells gradually differentiate into various tissues specially used for photosynthesis, transportation and covering. Through sexual reproduction, most plants form the life history of alternate generations of gametophyte and sporophyte. Plants are the most important producers in the ecosystem and the main source of oxygen on the earth.
Fungi are eukaryotes whose main nutrition is absorption. Fungi have cell walls which contain chitin and cellulose. Chitin is a polysaccharide containing glucosamine, which is the main component of animal bones such as insects, and plant cells do not contain chitin. Fungi have no plastids and photosynthetic pigments. Fungi have strong reproductive ability and various reproductive modes, mainly taking spores produced by asexual or sexual reproduction as reproductive units. Fungi are widely distributed and are important decomposers in the ecosystem.
Animals are eukaryotes and feed on swallowing. Swallowing heterotrophy includes a series of complex processes such as capture, swallowing, digestion and absorption. The structure of animal body develops in the direction of adapting to swallowing heterotrophy. Single-celled animals swallow food to form food vacuoles. Food is digested in food vacuoles, then enters the cytoplasm through the membrane, and lysosomes in the cytoplasm fuse with it, which is intracellular digestion.
In the evolution of multicellular animals, intracellular digestion was gradually replaced by extracellular digestion. After food is caught, it is digested by enzymes secreted by digestive glands. After digestion, small molecules of nutrients are absorbed through the digestive tract and transported to various cells of the body through the circulatory system.
Correspondingly, multicellular animals gradually formed a complex excretory system, external respiratory system and complex sensory system, nervous system, endocrine system and motor system. Of all living things, only the animal's body structure has developed to such a complicated and advanced degree. In the ecosystem, animals are consumers of organic food.
In the early stage of life development, ecosystem is a double-loop system composed of producers and decomposers. With the appearance and development of eukaryotes, especially animals, the double-ring ecosystem has developed into a three-ring system composed of producers, decomposers and consumers. Today's colorful biological world has emerged.
From viroids and viruses to plants and animals, there are many different types of organisms. There are a series of intermediate links between each type, forming a continuous pedigree. At the same time, the three evolutionary directions determined by nutritional methods present an interactive spatial relationship in the ecosystem. Therefore, evolution is both a time process and a spatial development process. From the historical origin of time and the life relationship of space, biology is a whole.
biological property
Biology is not only diverse, but also has some characteristics and attributes of * * *.
The structure and function of biomacromolecules that make up organisms are the same in principle. For example, the monomers of protein in various organisms are all amino acids, but there are only about 20 kinds, and their functions are the same for all organisms; The basic metabolic pathways of different organisms are the same and so on. This is biochemical identity. Identity profoundly reveals the unity of biology.
Biology has a multi-level structural model. All living things except viruses are composed of cells, and cells are heterogeneous systems composed of a large number of atoms and molecules.
Structurally, the cell is a multi-molecular dynamic system composed of protein, nucleic acid, lipid and polysaccharide. From the point of view of information theory, cells are the transmission system of genetic information and metabolic information; From a chemical point of view, cells are complex macromolecules synthesized from small molecules; Thermodynamically, cells are open systems far from equilibrium. ...
Besides cells, living things have other structural units. There are organelles, molecules and atoms under cells, and there are tissues, organs, organ systems, individuals, ecosystems, biosphere and so on above cells. Various structural units of organisms are arranged into a series of levels according to the complexity and the relationship of step-by-step combination, which is the structural hierarchy. There will be many higher-level properties and laws that the lower levels do not have.
There are many others, such as the order and dissipative structure of living things, the stability of living things, the continuity of life, the development of individuals, the evolution of living things, the interrelationships in ecosystems and so on.
All these show that although the biological world has amazing diversity, all creatures have the same material basis and follow the same laws. Biology is such a unified and diverse material world.
Biology, like other disciplines, has some basic research methods according to its own research objects, such as observation and description, comparison and experiment, and all of them have their own characteristics. For biology, it is necessary not only to have accurate experimental analysis, but also to observe life from a holistic and systematic perspective. Biology has accumulated a lot of information about all levels of life systems and their components. Today, the quantitative theoretical research on the law of life system has been put on the agenda, and the system theory method, as a new research method, will be valued.
The branch of biology.
Early biology is mainly the observation and description of nature, and it is the study of natural history and morphological classification. So biology was originally divided into disciplines according to groups, such as botany, zoology, anthropology and so on. Due to the diversity of biological species and people's more and more understanding of biology, the division of disciplines is becoming more and more detailed, and a discipline is often divided into several disciplines.
Dividing disciplines according to biological groups is conducive to understanding the biological characteristics and regularity of a natural group from all sides. But no matter what the research object is, it is nothing more than classification, morphology, physiology, biochemistry, ecology, heredity, evolution and so on.
Biology has a long history of development in the history of the earth. About150,000 species are extinct, and their remains are preserved in the stratum to form fossils. Paleontology specializes in studying historical organisms through fossils;
There are so many groups of organisms that a special discipline is needed to study the division of groups, which leads to taxonomy;
Morphology is a subject in biology that studies the morphological structure of animals and plants. With the use of microscope, morphology has penetrated into the field of ultrastructure, and histology and cytology have been established accordingly.
Physiology is a subject that studies biological functions, and the research method of physiology is mainly experiment;
Genetics is a subject that studies the inheritance and variation of biological characters and clarifies their laws;
Embryology is a subject that studies the individual development of organisms;
Ecology is a subject that studies the relationship between organisms and between organisms and the environment. The research scope includes individuals, populations, communities, ecosystems and biosphere. Reveal the relevant laws of food chain, productivity, energy flow and material circulation in the ecosystem;
Biochemistry is a subject that studies the chemical composition of organisms and various chemical processes of organisms, and has developed rapidly since the 20th century. The achievements of biochemistry have improved people's understanding of the nature of life. Biochemistry mainly studies the chemical process of life and the action mechanism of substances, products and enzymes involved in this process. Molecular biology developed from the study of the structure of biological macromolecules, and now more attention is paid to the relationship between the structure and function of biological macromolecules and the mechanism of gene expression and regulation.
Biophysics is a subject that studies the physical and physicochemical processes of biological structures and life activities with the concepts and methods of physics. Early biophysical research began with bioluminescence, bioelectricity and other issues. With the development of biology and physics and the appearance and intervention of new concepts, the research scope and level of biophysics have been deepened and broadened. Small branches such as quantum biology, crystal structure of biological macromolecules and biological cybernetics have emerged.
Biomathematics is the product of the combination of mathematics and biology, and its task is to study the mathematical laws in the process of life.
Biology is a multi-level complex system. In order to reveal the law of a certain level and its relationship with other levels, disciplines divided by levels have emerged and attracted more and more attention. For example: molecular biology, cell biology, individual biology, group biology and so on.
In short, some new disciplines in biology are constantly dividing, while others are constantly merging. This availability of biology reflects the extremely rich content of biology and its vigorous development.
Significance of learning biology
Biology is closely related to many aspects of human life. Biology, as a basic science, is traditionally the foundation of agriculture and medicine, involving planting, animal husbandry, aquaculture, medical care, pharmacy, health and so on. With the continuous progress of biological theory and method, its application field is also expanding. Now, the influence of biology has extended to food, chemical industry, environmental protection, energy, metallurgy and other fields. If bionics is considered, it will also affect the development of machinery, electronic technology, information technology and many other fields.
A branch of biology.
Botany, Palynology, Zoology, Microbiology, Cell Biology, Molecular Biology, Taxonomy, Habitology, Physiology, Bacteriology, Microbial Physiology, Microbial Genetics, Soil Microbiology, Cytochemistry, Cytogenetics, Immunology, Embryology, Eugenics, Biology, Genetics, Molecular Genetics, Ecology, Biophysics, Biology.