Origin Of Life PDF

THE ORIGIN OF LIFE  Evolving Concept of Life Based on Emerging Pieces of Evidence  It took Earth nearly one billion years to cool enough for the first life forms to appear. Scientists have been studying living things and the world around us for several hundred years. This chapter int...

THE ORIGIN OF LIFE  Evolving Concept of Life Based on Emerging Pieces of Evidence  It took Earth nearly one billion years to cool enough for the first life forms to appear. Scientists have been studying living things and the world around us for several hundred years. This chapter introduces how life originated, how certain species came into existence and then became extinct, and how the diversified environment in the present world came about.  The information and evidence gathered through the work of researchers over hundreds of years of study can help to understand the many aspects of life science. This knowledge can foster better understanding of the interactions between organisms and lead to the realization to value life by taking care not only of oneself but all the living organisms around. The Concept of Life Earth is much older than life. Based on radioactive decay studies of rocks, it was revealed that earth is around 4.5 billion years old – 1 billion year older than the oldest fossils. There are many theories about the origin of life. Some believed that living organisms were put to Earth by some divine forces. Others say that life did not originate from Earth but from other planets. According to the primordial soup theory proposed by Alexander Oparin and John Haldane, life started in a primordial soup of organic molecules. Some form of energy from lightning combined with the chemicals in the atmosphere to make the building blocks of protein known as the amino acids. Traces of bacteria found in rocks indicate their prehistoric existence Bacteria separated into two groups First group is called Eubacteria, also known as the true bacteria. Most living bacteria, including those that cause disease and decay, are eubacteria. Second group is called Archaebacteria, or ancient bacteria – and these bacteria are rare. These are found mainly in hostile environment where conditions resemble those of early Earth (e.g. salty lakes, hot springs, swamps, and ocean floor) Eubacteria Archaebacteria Today, biologist believed that the oxygen of early Earth’s atmosphere was produced by bacteria. About 3 BYA, a group of photosynthetic bacteria known as cyanobacteria, evolved. As they carried out photosynthesis, oxygen gas is released into the oceans. Cyanobacteria are believed to have evolved from Eubacteria Life was only able to travel to land because of a change in the environment. When cyanobacteria introduced oxygen to the atmosphere, a significant amount of oxygen started to disperse to the upper atmosphere, creating ozone. Before ozone was created, all life was limited to the oceans. But because of the new ozone layer that served as a barrier that blocked ultraviolet radiation levels on Earth's surface, it went down to a level that allowed life to move to dry land. More complex life-forms appeared in the fossil record. These organisms, known as eukaryotes, were much larger than prokaryotes, and they contained a central nucleus and a complicated internal structure. Over the past 1.5 billion years, eukaryotic cell have evolve into organisms that are composed of many cells. The first living things to populate the surface of the land were plants and fungi. The solution to the challenge of living on dry land was a unique mutualistic partnership between plants and fungi called mycorrhizae. Plants supply the fungi with food, while the fungi supply the plants with nutrients obtained from organic matter. Mycorrhizae is a strong connection between the roots of the plants and the fungi. Fungi actually grow on or into the root of the plant and then branch out into the rock or soil. Fossil records reveal that plants covered the surface of Earth within 80 million years of their initial invasion. Animals soon followed plants onto land. The fist animals to leave the water were the arthropods – animals with hard body covering and jointed legs. The first arthropods to live on land were scorpions. They are carnivorous relatives of spiders with two large pincers on their front legs and a venomous stinger at the end of their tails. Scorpions were the first terrestrial animals Today there are more than 200 million insects alive at any one time for each person on Earth. In addition, more than 70 percent of the animal species discovered are insects. Based on the fossil records and studies, insects were the first animals to develop wings. More complex animals began to evolve. Fossils showed that worm-like animals, the earliest known animals with notochords, existed. The notochord, however, exists only for a short time during the embryonic development and is replaced by the vertebral column or backbone. Chordates, or animals with notochords and vertebral column are called vertebrates. The early vertebrates were jawless fish with bone skeletons. Jawless fish have been the only vertebrates for more than 100 million years. Nowadays, jawless fishes are eel-like, parasitic lampreys, and scavenging hagfishes. Eventually, some 400 MYA evolved from the jawed fish. These are the sharks and bony fish that we encounter today. The first vertebrates on land were the amphibians, which evolved from bony fishes about 350 MYA. Reptiles evolved from amphibians about 300 MYA. The massive reptiles, known as dinosaurs, arose about 220 MYA. Although most dinosaurs are now extinct, descendants of small insect-eating dinosaurs still exist: The birds. Birds, mammals, and dinosaurs coexisted until the sudden extinction of the dinosaurs 65 million years ago during the Cretaceous period. This caused birds and mammals to diverge rapidly and fill the nearly-empty Earth. Dinosaurs were the dominant life forms on Earth for over 150 million years  Unifying Themes in the Study of Life Show the connections among living things and how they interact with each other and with their environment. The six general themes 1. Levels of Organization There is hierarchy of increasing complexity within cells, from the molecular level of DNA (where the chemistry of life occurs), to the organelle level (where the cellular activities are organized), to the cellular level (the smallest level of organization). 2. The Flow of Energy Energy is used by organisms to grow and do work. Without it, life stops. Almost all energy that living things need is obtained from the sun. Plants capture the energy from sunlight and use it to make complex molecules in a process called photosynthesis. These molecules then serve as the source of fuel for animals that eat them. The flow of energy among organism helps determine how organisms interact within their environment. Animals eat to get the energy 3. Evolution The theory of evolution helps explain how all kinds of organisms came into existence. It explains why organisms look the way they do and how organisms of the past are related to the organisms alive today. Charles Darwin – proposed the theory of evolution by natural selection, which presumes that organisms with more favorable traits would be more likely to survive and reproduce in a certain environment. This favorable traits are called adaptation. Example: cactus plant is adapted to desert environment. The leaves of a cactus plant are reduced to thin spines that enable it to live in a dry, arid environment 4. Interacting Systems Living things interact with each other and with the environment. Example: animal cells that descended from symbiotic possess organelles, and symbiotic fungi helped plants move from sea to land. Flowering plants and insects have been coevolving through cooperation 5. Structure and Function In biology, structure is always related to function. Example: hummingbird sucks nectar from a deep flower through its long tongue. The hummingbird has a long tongue that is used to suck nectar easily 6. Ecology Biologist have recognized and studied the interdependence of organisms with each other and with the environment. This branch of biology is called ecology. Ecology is the study of complex communities of organisms in relation to their environment. Organisms need the physical environment to survive. They need substances like water, nutrients, and gases from the environment. Example: all organisms depend on the oxygen-carbon dioxide cycle, which releases vital gases in the atmosphere. All organisms in an ecosystem coexist, and energy and matter have a natural cycle What’s the connection? Describe each unifying theme illustrated below.