1: Non-cell life form Viruses do not have a cell morphology, and are generally composed of a long nucleic acid chain and a protein shell (long nucleic acid chains include RNA and DNA. When viruses replicate, there is direct transcription of DNA, and viruses containing RNA need to be reverse transcribed into DNA and then replicated. ). Based on the number of nucleotides that make up a nucleic acid, the maximum number of genes per virus particle is 300. Viruses that are parasitic on bacteria are called bacteriophages. The virus does not have its own metabolic mechanism, no enzyme system, and it cannot produce adenosine triphosphate (ATP). Therefore, when the virus leaves the host cell, it becomes a chemical substance that has no life activity and cannot reproduce on its own. Only after entering the host cell, it can use the material and energy in the living cell, as well as a full set of equipment for replication, transcription and translation, according to the genetic information contained in its own nucleic acid to produce a new generation of virus like it. Virus genes can be mutated and recombined just like the genes of other organisms, so they can evolve. Because the virus has no independent metabolic mechanism and cannot reproduce independently, it is considered to be an incomplete life form. Regarding the origin of the virus, some people think that the virus is a highly degenerated organism due to parasitic life; some people think that the virus is a part of nucleic acid and protein particles detached from eukaryotic cells; more people think that the virus is a lower level before cell morphogenesis Life form. Viruses that are simpler than viruses have been discovered in recent years. They are small RNA molecules with no protein shell. In addition, a type of prion, which has only protein but no nucleic acid, has been found to cause chronic diseases in mammals. The existence of these incomplete life forms narrows the distance between lifelessness and life, indicating that there is no insurmountable gap between lifelessness and life. Therefore, under the prokaryotes, it is more reasonable to open up another world, namely the virus world. 2: Prokaryotes Prokaryotic cells and eukaryotic cells are the two basic types of cells, and they reflect the two stages of cell evolution. The division of organisms with cell morphology into prokaryotes and eukaryotes is a major advance in modern biology. The main feature of prokaryotic cells is that there are no membrane organelles such as mitochondria and plastids. The chromosome is just a circular DNA molecule, which does not contain histones and other proteins and has no nuclear membrane. Prokaryotes include bacteria and cyanobacteria, which are solitary or group of single-cell organisms. Bacteria are prokaryotes that can only be seen through a microscope. Most bacteria have cell walls, and the main component is peptidoglycan instead of cellulose. The main nutritional mode of bacteria is absorption of heterotrophic bacteria, which secretes hydrolase enzymes outside the body, breaks down large molecules of organic matter into small molecules, and then absorbs small molecule nutrients into the body. Bacteria are almost ubiquitous on the earth, they multiply very quickly and are extremely large in number. They are important decomposers in ecosystems and play an important role in the nitrogen cycle and other element cycles in nature (see Soil Mineral Transformation ). Some bacteria can oxidize inorganic substances and obtain energy from them to make food; some bacteria contain bacterial chlorophyll and can carry out photosynthesis. But the electron donor for bacterial photosynthesis is not water but other compounds such as hydrogen sulfide. Therefore, the photosynthesis of bacteria is photosynthesis without oxygen production. The reproduction of bacteria is asexual reproduction, in some species there is a primitive sexual process of exchange of genetic material between two cells-bacterial conjugation. Mycoplasma, Rickettsia and Chlamydia are bacteria. Mycoplasma has no cell wall, the cells are very tiny, even smaller than some large virions, can pass through bacterial filters, and is the smallest life form that can independently carry out growth and metabolic activities. The enzyme system of Rickettsia is incomplete. It can only oxidize glutamic acid, but not glucose or organic acids to produce ATP. Chlamydia has no energy metabolism system and cannot make ATP. Most Rickettsia and Chlamydia cannot carry out metabolic activities independently, and are considered as organisms between bacteria and viruses. Cyanobacteria are prokaryotic organisms that are self-supporting for photosynthesis. They are solitary, or group, and multicellular. Like bacteria, the main component of the cyanobacterial cell wall is peptidoglycan, and the cell has no nuclear membrane and organelles, such as mitochondria, Golgi apparatus, and chloroplast. But cyanobacteria cells have photosynthetic sheets composed of membranes, which are not found in bacteria. The cyanobacteria contain chlorophyll a, which is also a kind of chlorophyll which is not contained in bacteria but also contained in higher plants. Cyanobacteria also contain carotenoids and blue pigment phycocyanin, and some species have red pigment phycoerythrin, these photosynthetic pigments are distributed on the plasma membrane and photosynthetic sheet. The photosynthesis of cyanobacteria is the same as the photosynthesis of green plants. It is used to reduce the H + produced by CO2. Therefore, molecular oxygen is also produced along with the synthesis of organic matter, which is completely different from the photosynthesis of photosynthetic bacteria. The earliest life occurred in a reducing atmospheric environment free of free oxygen (see Origin of Life), so they should be anaerobic and heterotrophic. From anaerobic to aerobic, from heterotrophic to autotrophic, are two major breakthroughs in the history of evolution. Cyanobacterial photosynthesis changes the earth's atmosphere from anoxic to aerobic, which changes the entire ecological environment, creates conditions for the occurrence of aerobic organisms, and opens up new prospects for biological evolution. In the modern earth ecosystem, cyanobacteria are still one of the producers. The proto-green algae discovered in recent years contain chlorophyll a, chlorophyll b and carotenoids. Judging from the composition of their photosynthetic pigments and their cell structure, they are very similar to the chloroplasts of green algae and higher plants, so they have been valued by biologists. 3: Eukaryotes Compared with prokaryotic cells, eukaryotic cells are cells with a more complex structure. It has various membrane organelles such as mitochondria, with a nucleus surrounded by a double membrane, separating the genetic material located in the nucleus from the cytoplasm. DNA is a long-chain molecule that combines with histones and other proteins to form a chromosome. The division of eukaryotic cells is mitosis and meiosis. As a result of the division, the copied chromosomes are evenly distributed to the daughter cells. Protozoa are the most primitive eukaryotes. The primitiveness of protists not only appears at the structural level, that is, stays at the level of single cells or their groups, and does not differentiate into tissues; it also manifests in the diversity of nutritional methods. Protozoa are autotrophic, heterotrophic and mixed nutrition. For example, Euglena can photosynthesize and absorb organic matter dissolved in water. In addition to autotrophic and saprophytic nutrition, Golden Trichomonas can swallow organic food particles like animals. So these organisms have not clearly differentiated into animals, plants or fungi. Based on these characteristics, RH Whitaker absorbed the opinions of E. Haeckel of the last century and listed protists as the first realm in his five-world system, the protist world. However, some scientists advocate the abolition of this world. Their reason is that the species contained in the protozoa are too complex. Most protozoa can obviously be classified as animals, plants, or fungi. Those intermediate organisms are not difficult to use classification The analytical method of learning appropriately determines the attribution. Plants are eukaryotes with photosynthetic autotrophic as the main nutritional method. Typical plant cells contain vacuoles and cell walls with cellulose as the main component. In the cytoplasm, there are organelles for photosynthesis, that is, the plastids containing photosynthetic pigments, chloroplasts. In addition to chlorophyll a, there are chlorophyll b in the chloroplasts of green algae and higher plants. Many kinds of aquatic algae show different colors due to the different composition of auxiliary photosynthetic pigments. The photosynthesis of plants uses water as the electron donor, so they all emit oxygen. Photosynthetic autotrophic is the main nutritional method in the plant kingdom. Only certain low-grade single-cell algae are used for mixed nutrition. A small number of higher plants are parasitic, with secondary absorption of heterotrophs, and few higher plants can capture small insects and absorb heterotrophic. The plant kingdom developed from unicellular green algae to angiosperms along the direction of adapting to photosynthesis. In higher plants, plant bodies undergo differentiation of photosynthetic organs (leaves), supporting organs (stems), and organs (roots) for fixation and absorption. The petiole and many branched stems support the flaky leaves spreading out on all sides to obtain maximum light and CO2 absorption area. The cells also gradually differentiate to form various tissues specifically for photosynthesis, transduction and covering. The reproduction of most plants is sexual reproduction, forming a life history of gametophyte and sporophyte alternate generations. In higher plants, sporophytes continue to develop and differentiate, while gametophytes tend to simplify. Plants are the main producers in the ecosystem and the main source of oxygen on earth. Fungi are eukaryotes with absorption as the main nutrient. Fungal cells have cell walls, at least at some stage in life history. The cell walls mostly contain chitin, and some also contain cellulose. Chitin is a polysaccharide containing glucosamine, which is the main component of animal bones such as insects, and the plant cell wall is never chitinous. Fungal cells lack plastids and photosynthetic pigments. A few fungi are single-celled, such as yeast. The basic structure of multicellular fungi is branched or unbranched hyphae. A whole mass of mycelium is called mycelium. Some hyphae are divided into multiple cells with a septum, each cell has one or more nuclei, and some hyphae are multinucleated bodies without a septum. Mycelium has the function of absorbing water and nutrients. Mycelium is often loose like a cobweb to expand the absorption area. The reproductive capacity of fungi is very strong, and the modes of reproduction are diverse, mainly using various spores produced by asexual or sexual reproduction as the breeding unit. Fungi are widely distributed. In the ecosystem, fungi are important decomposers, and the scope of decomposition may be larger than that of bacteria. Slime mold It is a special fungus. One section of its life history is fungal, while the other section is animal. Its structure, behavior and feeding method are similar to amoeba. Slime molds are considered to be between fungi and animals. Animals are eukaryotes that devour as a nutrient. Heterotrophic swallowing includes a series of complex processes such as capture, swallowing, digestion and absorption. The structure of the animal body develops along the direction of adapting to eating heterotrophic. Single-celled animals form food bubbles after swallowing food. Food is digested in the food bubble, and then enters the cytoplasm through the membrane. The lysosome in the cytoplasm is fused with it for intracellular digestion. During the evolution of multicellular animals, intracellular digestion is gradually replaced by extracellular digestion. After the food is captured, it is digested by digestive glands in the digestive tract. Digested small-molecule nutrients are absorbed by the digestive tract and passed through The system is delivered to cells in various parts of the body. In response to this, multicellular animals gradually formed a complex excretory system, an external respiratory system for gas exchange, and a complex sensory organ, nervous system, endocrine system, and motor system. The nervous system and endocrine system constitute a complex self-regulating and self-controlling mechanism that regulates and controls all physiological processes. Among all living things, only the animal's body structure has developed to such a high level of sophistication. In the ecosystem, animals are consumers of organic food. In the early days of life, when there were only blue bacteria and bacteria on the earth, the ecosystem was a two-ring system composed of producers and decomposers. With the emergence and development of eukaryotes, especially animals, the two-ring ecosystem has developed into a three-ring system consisting of producers, decomposers, and consumers. The colorful biological world of today appears. From viruses, viruses to plants and animals, organisms have many distinctive types. There is a series of intermediate links between various types, forming a continuous lineage. At the same time, the three evolutionary directions determined by the nutritional methods show the spatial relationship of interaction in the ecosystem. Therefore, evolution is both a time process and a spatial development process. Biology is a whole in terms of the historical origin of time and the living relationship of space. The Compactor Pedal Trash Bin is not ordinary trash unit. 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