CHƯƠNG V: SINH QUYỂN 1/ What is Life? In a recent issue of the journal Science (March 22, 2002), molecular biologist Daniel E. Koshland Jr. was asked to write a special essay where he would set out to define life. In this article, he suggested that something could be considered “alive” if it meets the following seven conditions. (1). Living things must have a program to make copies of themselves from generation to generation. This program would describe both the parts that make up the organisms and the processes that occur between the various parts. These processes are of course the metabolic reactions that take place in a living thing allowing it to function over time. In most living systems, the program of life is encoded in DNA. (2). Life adapts (thích nghi) and evolves (tiến hóa) in step with external changes in the environment. This process is directly connected to life’s program through mutation (sự đột biến) and natural selection. This condition allows life-forms to be optimized for gradual changes in the environment. (3). Organisms tend to be complex, highly organized, and most importantly have compartmentalized (chia thành ngăn) structures. Chemicals found within their bodies are synthesized through metabolic processes into structures that have specific purposes. Cells and their various organelles (cơ quan tế bào) are examples of such structures. Cells are also the basic functioning unit of life. In multi-cellular organisms, cells are often organized into organs to create higher levels of complexity and function. • (4). Living things have the ability to take energy from their environment and change it from one form to another. This energy is usually used to facilitate their growth and reproduction. We call the process that allows for this facilitation (sự thuận lợi) metabolism. • (5). Organisms have regeneration (sự tái sinh) systems that replace parts of themselves that are subject to wear and tear. This regeneration can be partial or it can involve the complete replacement of the organism. Complete replacement is necessary because partial replacements cannot stop the unavoidable decline in the functioning state of the entire living system over time. In other words, all organisms degrade into a final non-functioning state we call death. • (6). Living creatures respond to environmental stimuli through feedback mechanisms. Cues from the environment can cause organisms to react through behavior, metabolism, and physiological change. Further, responses to stimuli generally act to increase a creature’s chance for day-to-day survival. • (7). Organisms are able to maintain numerous metabolic reactions even in a single instance in time. Living things also keep each of these reactions separated from each other. 2/ Origin of Life • The Sun and its planets formed between 5 and 4.6 billion years ago as matter in our solar system began to coalesce because of gravity. By about 3.9 billion years ago, the Earth had an atmosphere that contained the right mix of hydrogen, oxygen, carbon, and nitrogen to allow for the creation of life. Scientists believe that the energy from heat, lightning, or radioactive elements caused the formation of complex proteins and nucleic acids into strands of replicating genetic code. These molecules then organized and evolved to form the first simple forms of life. At 3.8 billion years ago, conditions became right for the fossilization of the Earth's early cellular life forms. These fossilized cells resemble present day cyanobacteria. Such cells are known as prokaryotes. Prokaryote cells are very simple, containing few specialized cellular structures and their DNA is not surrounded by a membranous envelope. The more complex cells of animals and plants, known as eukaryotes, first showed up about 2.1 billion year ago. Eukaryotes have a membrane-bound nucleus and many specialized structures located within their cell boundary. By 680 million years ago, eukaryotic cells were beginning to organize themselves into multicellular organisms. Starting at about 570 million years ago an enormous diversification of multicellular life occurred known as the Cambrian explosion. During this period all but one modern phylum of animal life made its first appearance on the Earth. Figure 9a-1 describes the approximate time of origin of the Earth' s major groups of plants and animals. Figure 9a-1: Important events in the evolution of life. Dates for many of the events shown are based on fossil evidence. Figure 9a-2: This fish fossil from Wapiti Lake in British Columbia, Canada was alive during the geologic period known as the Triassic (208-245 million yrs BP). Fish first appear on our planet during the Ordovician Period about 500 million years ago. h). Species Diversity and Biodiversity- các loại đdsh Table 9h-1: Major extinction events during the Phanerozoic. Date of the Extinction Event Percent Species Lost Species Affected 65 Million Years Ago (Cretaceous) 85% Dinosaurs, plants (except ferns and seed bearing plants), marine vertebrates and invertebrates. Most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians were unaffected. 213 Million Years Ago (Triassic) 44% Marine vertebrates and invertebrates. 248 Million Years Ago (Permian) 75-95% Marine vertebrates and invertebrates. 380 Million Years Ago (Devonian) 70% Marine invertebrates. 450-440 Million Years Ago (Ordovician) 50% Marine invertebrates. • Scientists developed the notion of biodiversity to overcome some of the difficulties of species concept. To accomplish this task, biodiversity describes the diversity of life at the following three biological levels: • Genetic Level or Genetic Diversity - Genetic diversity refers to the total number of genetic characteristics expressed and recessed in all of the individuals that comprise a particular species • Species Level or Species Diversity - Species diversity is the number of different species of living things living in an area. As mentioned above, a species is a group of plants or animals that are similar and able to breed and produce viable offspring under natural conditions. • Ecosystem Level or Ecosystem Diversity - Ecosystem diversity is the variation of habitats, community types, and abiotic environments present in a given area. An ecosystem consists of all living and non-living things in a given area that interact with one another. • The biodiversity found on Earth today is the product of 3.5 billion years of evolution. In fact, the Earth supports more biodiversity today than in any other period in history. However, much of this biodiversity is now facing the threat of extinction because of the actions of humans Figure 9i-1: Succession of plant species on abandoned fields in North Carolina. Pioneer species consist of a variety of annual plants. This successional stage is then followed by communities of perennials and grasses, shrubs, softwood trees and shrubs, and finally hardwood trees and shrubs. This succession takes about 120 years to go from the pioneer stage to the climax community. Abandoned Field to Oak Forest [...]... chalk; and (5) in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms Figure 9r-1: Carbon cycle Table 9r-1: Estimated major stores of carbon on the Earth Sink Amount in Billions of Metric Tons Atmosphere 57 8 (as of 1700) - 766 (as of 1999) Soil Organic Matter Ocean Marine Sediments and Sedimentary Rocks Terrestrial Plants Fossil Fuel Deposits 150 0 to 1600...j) Introduction to the Ecosystem Concept (khái niệm) - Major Components of Ecosystems • Ecosystems are composed of a variety of abiotic and biotic (vô sinh và hữu sinh) components that function in an interrelated fashion Some of the more important components are: soil, atmosphere, radiation from the Sun, water, and living organisms • Soils are much more complex... biomes Ecosystem Type Net Primary Productivity (kilocalories/meter -2 /year) Tropical Rain Forest 9000 Estuary 9000 Swamps and Marshes 9000 Savanna 3000 Deciduous Temperate Forest 6000 Boreal Forest 350 0 Temperate Grassland 2000 Polar Tundra 600 Desert < 200 p) Biogeochemical Cycling: Inputs and Outputs of Nutrients to Ecosystems • The patterns of cycling nutrients in the biosphere involves both biotic... Yet by weight, carbon is not one of the most abundant elements within the Earth's crust In fact, the lithosphere is only 0.032% carbon by weight In comparison, oxygen and silicon respectively make up 45. 2% and 29.4% of the Earth's surface rocks • Carbon is stored on our planet in the following major sinks (Figure 9r-1 and Table 9r-1): (1) as organic molecules in living and dead organisms found in the... composed of a very high percentage of water, up to and even exceeding 90% The protoplasm of a very few cells can survive if their water content drops below 10%, and most are killed if it is less than 30 -50 % Water is the medium by which mineral nutrients enter and are translocated in plants It is also necessary for the maintenance of leaf turgidity and is required for photosynthetic chemical reactions... Atmosphere 57 8 (as of 1700) - 766 (as of 1999) Soil Organic Matter Ocean Marine Sediments and Sedimentary Rocks Terrestrial Plants Fossil Fuel Deposits 150 0 to 1600 38,000 to 40,000 66,000,000 to 100,000,000 54 0 to 610 4000 s) The Nitrogen Cycle The nitrogen cycle represents one of the most important nutrient cycles found in terrestrial ecosystems (Figure 9s-1) Nitrogen is used by living organisms to produce . Million Years Ago (Permian) 75- 95% Marine vertebrates and invertebrates. 380 Million Years Ago (Devonian) 70% Marine invertebrates. 450 -440 Million Years Ago (Ordovician) 50 % Marine invertebrates. •. CHƯƠNG V: SINH QUYỂN 1/ What is Life? In a recent issue of the journal Science (March 22, 2002), molecular. during the geologic period known as the Triassic (208-2 45 million yrs BP). Fish first appear on our planet during the Ordovician Period about 50 0 million years ago. h). Species Diversity and Biodiversity-