There are about 500,000 kinds of plants and 1.5 million kinds of animals on the earth. The existing animals are only one tenth of those on the original earth. All kinds of creatures not only maintain the sustainable development of nature, but also are the basic conditions for human survival and development.
Life span is one of the basic parameters of living things. Some creatures can only live for one day, while others, such as some plants, can live for thousands of years. Cell senescence is very important for determining the life span of organisms, bacteria, viruses and even prions. At present, the scientific community generally believes that telomere, a special DNA sequence at the end of a cell chromosome, has a great relationship with the life span of the cell. Normally, every time a cell divides, telomeres become shorter. With the gradual shortening of telomeres, the meaningful DNA sequence in the middle section of chromosome DNA is finally missing. Because normal physiological activities cannot continue at this time, cells will experience a programmed death controlled by themselves-apoptosis. In addition, the telomere structure in tumor cells usually does not shorten, which is one of the reasons why tumor cells can divide indefinitely.
For a long time, boundary is the highest category in biological science classification. At the beginning, people only divided living things into two realms: animals and plants. After being discovered, microorganisms have been classified as animals or plants for a long time: active microorganisms are classified as animals, pigments (algae) or bacteria are classified as plants, and some are even put into two fields at the same time. Later, bacteria without nuclei separated into a world, then fungi separated from the plant world and became an independent world, and finally archaea stood on its own feet.
The latest genetic research found that this classification is not very correct, so domain was introduced as the highest category of organisms. Existing organisms are divided into acellular domain, eukaryotic domain or prokaryotic domain, and organisms (bacteria and archaea) that have not formed nuclei are divided into prokaryotes. Only in eukaryotes will there be boundaries. Eukaryotes are divided into four realms: protozoa, fungi, plants and animals.
There are nine realms: viroid, virus, archaea, bacteria, cyanobacteria, protozoa, fungi, plants and animals.
The chemical composition of cells mainly refers to various compounds that constitute cells. These compounds include inorganic substances and organic substances. Generally speaking, hydrocarbon-containing compounds and their derivatives are called organic substances (except carbonate), such as starch, amino acids, amino acid salts, nucleic acids, etc. Inorganic substances are mainly water, inorganic salts and gaseous elements. The normal order of the contents of various substances in living cells from less to more is: sugars and nucleic acids (accounting for 1~ 1.5%), inorganic salts (accounting for 1~ 1.5%), lipids (accounting for 1~2%) and
In the production practice of cultivating plants and domesticating animals, the ancients accumulated knowledge about the morphology, structure and living habits of organisms, noticed the changes of organisms and the relationship between organisms and the environment, and gradually formed a simple idea of biological evolution. Aristotle in ancient Greece systematically sorted out the knowledge about animals in his time, and divided 540 kinds of animals into two categories: bloody and bloodless, and each category was divided into several categories. He further put forward the concept of biological grade, that is, biological ladder, and thought that all creatures in nature formed a continuous series, that is, a straight line series from plants to people. Erya, a book collected by China during the Warring States Period, recorded the changes of biological types. Huai Nan Zi in the early Han Dynasty not only made a preliminary classification of animals and plants, but also proposed that all kinds of creatures developed from primitive types.
Cloning is an epoch-making breakthrough in the field of biotechnology. With the birth of Dolly the cloned sheep in Britain, people all over the world attach great importance to it. Scientists believe that it indicates that "mankind will enter the era of cloning in an all-round way in 2 1 century". Dolly successfully gave birth to her first lamb in April, 1998, which indicated that sheep cloned from mature cells could be pregnant and give birth to healthy lambs at full term.
The scientist who cloned Dolly said that cloning can produce healthy offspring, which is very important for the commercialization of nuclear transplantation technology. The advantages of adopting cloning technology are: it can speed up the reproduction of improved livestock, which may lead to a revolution in animal husbandry; Can cultivate batches of high-quality cattle and sheep varieties to meet people's needs; Can save endangered wild animals and maintain ecological balance; It can mass-produce many precious drugs that people in the medical field urgently need. In addition, using cloning technology, cells, tissues or organs of plants can be cloned, and the traditional agriculture of "depending on the weather" in the past can be changed. In short, at the turn of the century, the development of science and technology in Chengdu will change the living environment of mankind and greatly benefit mankind.
The Book of Rites: "If the soil is poor, the vegetation will not grow, if the water is annoying, the fish and turtles will not grow, and if the gas is weak, biology will not succeed." Tang Yuanzhen's poem "With Wind and Evening" said: "Life is limited, and peace is better than stone." Zou Taofen's General Answer to Questions: "As you all know, all living things are inseparable from the environment."
"Zhuangzi on Earth": "A husband keeps a tiger, but he doesn't know it. He doesn't dare to bring creatures, so he is angry when he kills them." Qing Li Dou's Record of Yangzhou Painting Boat and Little Qinhuai Record: "When you enter the market at ordinary times, you pay for everything you see. If you don't have money, you will put your hands together and worship, all of which are based on the wish to let go when you see creatures. "
"Xunzi Book of Rites": "Heaven can be a creation, but not a thing; The land can carry people, but it cannot cure people. " Han Dong's book "The Story of the Spring and Autumn Period Yang Zun Yin Bei": "Love life, be strict with success, be happy with life, mourn death, and aspire to heaven." "History of the Ming Dynasty, Biography of Foreign Countries, Ryukyu": "Heaven and earth take biology as their heart, and emperors can be unique!" It also refers to planting crops. Song and Ming Ying Xing's Heavenly Creations: "All creatures that rule the earth use hoes and hoes."
Song Yuwenbao's Collection of Sword Blowing: "Tang Liuyuan is eighty years old and strong. People asked him and said, but he didn't use air to cool things and cooked creatures ... but he was a creature without fireworks. "
About 15000 BC, in the following 5000 years, the French made cave paintings in Las Cox, which shows that our ancestors have been observing the biological world. There are bison, deer and other animals in these paintings.
Around 2650 BC, it was confirmed that Egyptian doctor Imhotep looked for the causes of diseases from natural phenomena.
About 2000 BC, papyrus documents found in the Nile valley have recorded information on the treatment of trauma and disease.
About 65438 BC+0750 BC, King Hammurabi of Babylon made laws related to medical practice and carved them on stone pillars. These laws specify the expenses and severe penalties for treatment errors, such as amputation of both hands due to the death of 65,438+0 patients due to treatment accidents.
About BC 1500, China raised silkworms to make exquisite clothes. Farmers put bags containing ants on citrus trees to protect fruits from insects-this is the earliest record of using biological control.
About 802 BC, Europe first introduced and planted rose trees from Asia.
In 570 BC, Anacker Simande, an ancient Greek philosopher, suggested that animals were first born in water and then became land animals.
In 500 BC, Heraclitus of Eiffel proposed that the tension between opposing forces is crucial to life. In addition, he believes that fire is the basic element.
For more than 90 years after about 460 BC, the Greek doctor Hippocrates lived and taught on the Greek island of Kos.
In the twentieth century, human beings have a new view of life. Biologists' main energy has shifted from catching and distinguishing new species to studying the inner mysteries of biology; By observing various cells under a microscope and then entering them, we begin to understand the various molecules that make it up. Based on the existing knowledge of biological phenomena, scientists explore how they echo the life mechanism. Since then, the mystery of the inheritance of life has been revealed by human beings bit by bit, and artificial genetic food has begun to appear, which poses less and less threat to human health. Biology has enabled human beings to see the dawn in their struggle with nature and their efforts to control their own life laws.