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Section 1 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 interior of the volcano forms the primitive atmosphere (Figure 76). It is generally believed that the main components of primitive atmosphere are methane (CH4), ammonia (NH3), water vapor (H2O) and 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. 1953, American scholar miller and others designed a set of airtight devices (fig. 77). They pumped the air out of the device, then simulated the atmospheric composition on the primitive earth, and introduced methane, ammonia, hydrogen, water vapor and other gases to simulate the continuous spark discharge of lightning under the 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 the chemical process of synthesizing organic matter from inorganic substances is completely possible in the origin of life.

How did organic macromolecules such as protein and nucleic acid form from small organic molecules 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 protein and nucleic acid formed in the primitive earth, but it has provided some clues for people to study the origin of life, and it is possible to produce these organic polymers under the primitive earth conditions.

Judging from the multi-molecular system composed of organic polymers, protein, nucleic acid and other organic polymers are accumulating more and more in the ocean, and their concentrations are 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.

It is the most complicated and decisive stage in the origin of life, which is directly related to 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.

Biological classification system During the 1 100 million years after the formation of the earth, primitive life appeared on the earth. After a long time, primitive life gradually evolved into such an extremely colorful biological world. According to the basic structural characteristics of various organisms, biologists have scientifically classified various organisms from the perspective of biological evolution. With the development of natural science, the biological classification system is constantly changing. Now briefly described as follows.

At first, biologists divided the living things on the earth into plants and animals. Later, some scholars put forward a new classification system based on the double-boundary system. For example, some scholars have proposed a five-realm system, namely monera realm and Protozoa realm (some species extracted from animals and plants, including gymnosperms, Chrysophytes, Myxomycetes, Trichinella, Carnipoda and so on). ), plants, fungi and animals. Others believe that adding virus realm to the five-realm system forms a six-realm system.

However, for a long time, people have divided the biological world into the plant kingdom and the animal kingdom. This classification method has been used for more than 200 years and is still widely used today.

In the second quarter, the evolution of living things

How do all kinds of creatures on the earth come from now? This issue has been debated since ancient times. Creationists believe that all kinds of creatures on the earth were created by God. According to creationism, the number of creatures is only the number originally created, and all these creatures are created at one time, and there is no kinship between them. Evolutionists believe that all kinds of creatures on the earth were not created by God, but gradually evolved from ancestors after a long time, so there is a distant or close kinship between all kinds of creatures. Because evolutionists cite a lot of facts when demonstrating biological evolution, the once popular creationism is less and less believed by people, while evolutionism is recognized by more and more people.

Evidence of biological evolution

There is a lot of evidence of biological evolution. Only three evidences of paleontology, embryology and comparative anatomy are introduced here.

Evidence of Paleontology Paleontology is a science that studies the occurrence, development, classification, evolution and distribution of organisms in geological history. Its research object is the remains, remains or relics of ancient creatures preserved in the stratum-fossils.

In the process of studying fossils, paleontologists found that fossils of various organisms appeared in the strata in a certain order, that is, the earlier the strata were formed, the simpler and lower organisms became fossils; The later the stratum is formed, the more complex and higher the fossils become. This not only proves that all kinds of modern organisms evolved gradually through a long geological age, but also reveals the evolutionary order of organisms from simple to complex, from low to advanced, from aquatic to terrestrial. Fossils of various organisms appear in a certain order in the stratum, which is one of the most reliable evidences of biological evolution.

Through the study of horse fossils, we know the evolution process of horses. This is an outstanding example of paleontology confirming biological evolution.

The ancestors of modern horses are called ancestor horses (Figure 78). According to the stratum where archaeopteryx fossils were buried, archaeopteryx lived in warm and humid grass and bushes 50 million years ago. It is as big as a modern fox, with a curved back, a flexible body and four toes on its forelimbs.

In the recent strata, the fossil of the horse's close relative, the three-toed horse, was found. Three-toed horses live in the vast grassland, with larger body and longer limbs than their ancestors. Its forelimb has only three toes, and its middle toe is developed, making it the only toe that touches the ground.

The horse fossils after the three-toed horse confirmed that the figure of the horse gradually became taller, the toes of the middle toe formed hard hooves, and the toes on both sides degenerated into relics. This kind of horse is suitable for running on the vast grassland. This series of horse fossils vividly shows that modern horses evolved from smaller ancestor horses after a long geological period.

In the study of paleontology, some fossils of intermediate animals and plants have also been found, which also provides strong evidence for the theory of biological evolution. For example, archaeopteryx fossils are important evidence that birds evolved from ancient reptiles; Fossils of seed ferns prove the evolutionary relationship between seed plants and ferns.

Geochronology Geochronology refers to the time and sequence of rock formation in different ages on the earth's crust. According to the method of paleontology, geological times can be divided into Archean, Proterozoic, Paleozoic, Mesozoic and Cenozoic, and then each generation can be divided into several periods. For the order of occurrence of various organisms in geological age, see the geological age representative on the next page (the years in the table are estimated figures).

Evidence of embryology embryology is a science that studies the formation and development of animal and plant embryos. It also provides important evidence for biological evolution.

It has long been noted that the embryonic development of all higher organisms (such as vertebrates and seed plants) starts from fertilized eggs. This situation can explain that higher organisms originated from single-celled organisms.

Let's compare the embryos of seven vertebrates and humans. As can be seen from Figure 79, the embryos of these seven animals are very similar to humans in the early stage of development, that is, they all have gill slits and tails. By the late stage of development, the gill slits of other animals and humans have disappeared, and so has the human tail. Now I want to ask: these animals are very different from people in their adult forms. Why are they similar in the early stages of embryonic development? Gill is an organ suitable for breathing in water. Why do terrestrial vertebrates and humans also have branchial cleft in the early stage of embryonic development? Since people are tailless, why do people have tails during embryonic development?

All these indicate that higher vertebrates evolved from some lower vertebrates in ancient times. In other words, both vertebrates and humans evolved from the same ancient primitive ancestor, so their embryos are very similar in the early stage of development. The primitive ancestors of ancient vertebrates lived in water, so both terrestrial vertebrates and humans will have branchial cleft during embryonic development. People evolved from animals with tails, so there will be obvious tails during embryonic development.

Evidence of comparative anatomy Comparative anatomy is a science of anatomy and comparative study of organs and systems of various vertebrates. The most important evidence provided by comparative anatomy for the theory of biological evolution is homologous organs.

Homologous organs refer to organs with the same origin, similar structure and position, but different shapes and functions. For example, the wings of birds, the wings of bats, the fins of whales, the forelimbs of horses and the upper limbs of human beings are quite different in appearance and function, but their internal structures are basically the same. That is to say, they are all composed of humerus, radius, ulna, wrist, metacarpal bone and phalanx, and the arrangement is basically the same (Figure 80), and they are all homologous organs. The existence of homologous organs proves that all organisms with homologous organs evolved from the same primitive ancestor. Only in the process of evolution, due to the different living environments, homologous organs adapt to different living environments and gradually appear different shapes and functions. So the same forelimbs, the wings of birds and bats become suitable for flying, the fins of whales become suitable for swimming in water, the forelimbs of horses become suitable for running, and the upper limbs of people become suitable for all kinds of complicated movements.

The relationship between biology and environment

1. Influence of environment on living things

The living environment of living things is varied. From the top of the mountain to the depths of the ocean, from the vast desert to the dense forest, from the city to the countryside, there are creatures everywhere. In different environments, the species of organisms vary greatly (Figures 82, 83, 84 and 85).

The concept of ecological factors no matter what kind of environment a living thing lives in, it will be influenced by various factors in the environment. Taking wheat as an example, its growth and development are not only affected by abiotic factors such as light, temperature and water, but also by biological factors such as wheat aphid, locust and mouse. The factors that affect biological morphology, physiology and distribution in the environment are called ecological factors.

Abiotic factors There are many abiotic factors. The following is only about the influence of sunlight, temperature and water on living things.

Without sunlight, plants can't carry out photosynthesis and survive. Therefore, sunlight plays a decisive role in the physiology and distribution of plants. On land, some plants can only grow well under strong light, such as pine, fir, willow, locust, wheat, corn and so on. During wheat filling, continuous rainy weather will cause wheat yield reduction. Some plants can only grow well in the dark under dense forests, such as ginseng, notoginseng and other medicinal plants. In the ocean, with the increase of depth, the light gradually weakens and the distribution of plant species is different. Someone investigated a bay and found that there were more green algae in shallow water, more brown algae in a little deeper and more red algae in a little deeper. The limit that sunlight can reach is 200 meters below the sea surface, so it is difficult for plants to survive in waters below 200 meters. In addition, the length of sunshine also affects the flowering period of plants. Some plants need long sunshine to blossom, but these plants only bloom in late spring and early summer, such as alfalfa, iris and spinach. Some plants need a short sunshine to bloom. These plants bloom in autumn, such as Compositae. There are also some plants that are not strict about the length of sunshine and can bloom in different seasons.

The influence of sunlight on animals is also obvious. Sunlight can affect the body color of animals. For example, the back of fish is dark, but the abdomen is white, which is related to the influence of sunlight. Sunlight can affect the vision of animals. Some animals can hardly see anything at night, such as chickens; Some animals have good eyesight at night, such as owls. The length of sunshine has an effect on animal reproduction. Trout often lays eggs in 65438+February, because its reproductive organs can only mature under the stimulation of short sunshine. Sunlight can also affect the growth and development of animals. Someone has done such an experiment: under the condition of continuous illumination or continuous non-illumination, most of the individuals produced have no wings; When aphids are cultivated under alternating light and dark conditions, most of the individuals produced have wings. In life habits, some animals have phototaxis, such as moths. Moths are very sensitive to ultraviolet rays, so people often use black lights to trap and kill such agricultural pests at night.

The temperature in the temperature universe varies greatly, and the temperature range in which organisms can live is very narrow. Overheating or supercooling will make the metabolism of organisms unable to proceed normally, and even make organisms die. Take animals for example. Most animals live in the temperature range of -2 ~ 50℃. If the ambient temperature exceeds this range, many animals will find it difficult to survive.

Temperature has an important influence on the distribution of plants. There are many coniferous forests in the forests in cold areas. Among the forests in the warm zone, there are more broad-leaved forests. Apple, pear and other fruit trees are not suitable for planting in tropical areas, and oranges are not suitable for planting in the north, all because of temperature restrictions.

Temperature will affect the shape of animals. It is found that mammals of the same kind living in cold areas are relatively large in size, but their tails, ears and noses are relatively short, which can reduce the surface area of their bodies and thus minimize the loss of heat. For example, foxes living in the Arctic have much smaller ears than foxes living in African deserts (Figure 86).

Temperature also has obvious influence on the living habits of animals. In hot summer, birds are mainly active in the cooler hours of morning and evening, and are dormant at noon. Some animals, such as snails, lurk in caves in summer. When the temperature drops below 24℃, cicadas (commonly known as cicadas) stop singing. When winter comes, many warm animals go into hibernation, such as snakes and lizards.

Water We know that all living things can't live without water. Among the various chemical components in living organisms, most of them are water. Therefore, water is also an important ecological factor affecting biological survival.

For animals, water shortage is more serious than food shortage. Animals live longer without food than without water.

The total precipitation in one year and the distribution of rainy season are important factors limiting the distribution of terrestrial organisms. In arid desert areas, only a few drought-tolerant animals and plants survive; However, in tropical rain forest areas with abundant rainfall (such as Hainan Island in the south of China), there are dense forests and various kinds of animals and plants.

Biological factors Every living thing in nature is influenced by many living things around it. Among these creatures, there are both homogeneous and heterogeneous. Therefore, biological factors can be divided into two types: intraspecific relationship and interspecific relationship.

Intra-species relationship organisms have both intra-species mutual assistance and intra-species struggle in intra-species relationship.

Intraspecific mutual assistance is very common. For example, many kinds of animals often get together and live in groups during their life. There are mainly two kinds of this group life style: one is a group life dominated by social insects such as ants and bees, and there is a clear division of labor among individuals, while cooperating with each other to maintain the survival of the group. It is often seen that many ants attack a big insect together and carry it to its nest. When a bee stings an enemy, it will release a pheromone, prompting other bees to attack the enemy together. The other is different from social insects, and there is no clear division of labor among group members. This type of aggregation is often seen in some insects (such as migratory locusts), fish, birds and mammals. They gather in groups, roam along specific paths in a certain area, and look for food together. At the same time, this group life is also conducive to predation or defense of the enemy. As far as predation is concerned, wolves in groups can prey on animals bigger than themselves. As far as defending the enemy is concerned, herds of musk oxen can effectively deal with the attacks of wolves. Musk oxen are often killed by wolves when they live alone. However, when they gather in groups, if they meet a wolf, the males will form a circle with their heads facing outward, enclosing the females and their young. In this way, it is very difficult for a carnivorous wolf to succeed.

In the aspect of intraspecific struggle, there is also a phenomenon that individuals of the same species struggle because of the contradiction of food, shelter, finding a spouse or other living conditions. For example, in some water bodies, if there are no other fish except perch, then adult perch will feed on the juvenile of this species. Frog tadpoles can excrete a toxic substance from their intestines. In ponds with high density of tadpoles, the increase of this toxic substance will inhibit the growth and development of tadpoles and increase the mortality rate of young tadpoles. In some animals, males often fight with males of the same species in order to compete for females during the breeding period. The above-mentioned intra-species struggle is harmful to the failed individuals, even causing death, but it is beneficial to the survival of species, which can make the surviving individuals in the same species obtain more adequate living conditions or make their offspring be born better.

Interspecific relationship Interspecific relationship refers to the relationship between organisms of different species, including health, parasitism, competition, predation and so on.

* * * Life: Two creatures live together, depend on each other and benefit from each other; If they are separated from each other, neither side can live independently. This * * * relationship between two creatures is called * *. A typical example is lichen. Lichens are living organisms of fungi and algae (Figure 87).

Lichens belong to plants, but they are not simple plants, but are composed of fungi and algae. Algae contain chlorophyll, which can carry out photosynthesis and provide organic matter for fungi. Fungi absorb water and inorganic salts to meet the needs of algae. In lichens, the relationship between fungi and algae is mutually beneficial and interdependent.

Parasitism: the phenomenon that one organism lives in the body or surface of another organism and absorbs nutrients from it to maintain life is called parasitism. Parasitism is very common in biology, such as ascaris lumbricoides, tapeworms and schistosomiasis, lice and fleas on other animals, dodder in leguminous plants (Figure 88), bacteriophages in bacteria and so on.

Competition: The phenomenon that two creatures live together and compete for resources, space, etc. It's called competition The result of competition is often unfavorable to one party or even eliminated. For example, someone has done an experiment: large and small paramecium can grow normally when they are cultured separately, but when they are cultured together, one of them dies after 16 days, while the other one still grows normally.

Predation: Predation refers to the phenomenon that one organism feeds on another. For example, herbivorous rabbits feed on certain plants, carnivorous wolves feed on rabbits, and so on.

To sum up, organisms are influenced by many ecological factors, which isomorphically form the living environment of organisms. Living things can only survive if they adapt to the environment.

Section 2 Population and Biological Community

In nature, every creature does not exist alone, but lives with other creatures. Among these biological individuals, there are both the same species and different species, and there is an interdependent and restrictive relationship between them.

The concept of population is the sum of individuals of the same species in a certain time and space, which is called population. For example, the carp in a lake are all a population, consisting of fry, small fish and big fish; All cotton aphids in a cotton field are a population, which consists of young aphids, mature aphids with wings and without wings; All beeches in a forest are also a population, which consists of beeches of different ages.

The characteristic population of a population is not a simple addition of many individuals of the same species, but an organic unit, which has the characteristics of population density, age composition, sex ratio, birth rate and death rate that a single organism does not have.

Population density Population density refers to the number of individuals in a certain group in unit space. For example, the number of African crucian carp per cubic meter of water in fish ponds; The number of Apodemus agrarius per square kilometer of farmland area.

The population density of different species often varies greatly. For example, there are less than two wild donkeys per 100 square kilometer in a certain place in China, and there are hundreds of thousands of grey hamsters in the same area.

The population density of the same species is different under different environmental conditions. For example, the population density of Locusta migratoria manilensis in farmland is high in summer, but it decreases in late autumn when the weather is cold.

The age composition of the population refers to the proportion of individuals at all ages in the population. The age composition of the population can be roughly divided into three types (Figure 93): (1) growth type: there are many young individuals and few old individuals in the population. Such a population is in a developing period, and the population density will increase. (2) Stable type: the proportion of individuals in each age group is moderate, so the population is in a stable period and the population density will remain stable for some time. (3) Declining type: there are fewer young individuals in the population, but more adults and elderly individuals. Such a population is in a declining period, and the population density will become smaller and smaller.

Sex ratio The sex ratio of the population refers to the ratio of male and female individuals in the population. The population sex ratio of different species is different, which can be roughly divided into three types: (1) male and female are equal, which is more common in higher animals, such as chimpanzees and orangutans. (2) There are more females than males, which are more common in artificially controlled populations, such as chickens, ducks and sheep. Some wild animals also have more females than males during the breeding period, such as elephant seals. (3) Males are more than females, which are more common in insects engaged in social life, such as termites. The sex ratio affects the population density to some extent. For example, the use of synthetic attractants to trap and kill male pests destroys the normal ratio of pest population, which will make many female individuals unable to complete mating, thus significantly reducing the population density of pests.

Birth rate and mortality The birth rate refers to the number of new individuals born per unit time in the population. For example, the birth rate of the peaceful bird population is 7.8 chicks per female per year. Mortality refers to the number of individuals who die per unit time in the population. For example, in a certain argali population, for every 1000 individuals who live to 6 years old, the mortality rate in the age range of 6-7 years old is 69.9. Birth rate and death rate are also important factors in determining population size and population density.

The concept of biome refers to the sum of all kinds of biological populations that live in a certain natural area and have direct or indirect relations with each other. It is called biological community, or community for short. For example, in a meadow, there are not only plants such as grass and weeds, but also animals such as insects, birds and rats, as well as microorganisms such as bacteria and fungi. All these creatures live together and are closely related to each other, thus forming a community.

Structure of biological community The structure of biological community refers to the spatial configuration of various organisms in the community, including vertical structure and horizontal structure.

Vertical structure in the vertical direction, the community has obvious stratification phenomenon. For example, in the forest, tall trees occupy the upper layer of the forest, followed by shrub layer and herb layer (Figure 94). The vertical distribution of animals in the community also has a similar stratification phenomenon. For example, in the valley forest of Mount Qomolangma in China, there is a kind of birds that always move in groups in the upper layer of the forest and eat the seeds of tall trees. Birds such as tit, yellow-waisted Ye Ying and orange stork always nest in the middle of the forest. Blood pheasant and brown-tailed rainbow pheasant are typical birds at the bottom of the forest, feeding on moss and insects on the ground.

Horizontal structure in the horizontal direction, due to topographic relief, light and shade, humidity and other factors, the biological species in different areas are often different. For example, in the forest, where the base of the tree is covered by the crown, the light is dark, which is suitable for the survival of mosses and shade-loving plants, while there are more shrubs and grasses in the gap between the crowns or other places with sufficient light.

To sum up, in a certain area, the same species form a population and different populations form a community. The characteristics of population density and community structure are closely related to various ecological factors in the environment.