Lets Define Science

1.6 Biology Is Studied at Many Levels of Organization Life’s properties emerge when DNA and other molecules are organized in cells. Energy flows through all the biological levels shown here    The internal hierarchy of the individual organism is matched by the external hierarchy of the biological world (Figure 1.6). Organisms do not live in isolation. A group of individuals of the same species that interact with one another is a population, and populations of all the species that live and interact in the same area are called a community. Communities together with their abiotic environment constitute an ecosystem. Individuals in a population interact in many different ways. Animals eat plants and other animals (usually members of another species) and compete with other species for food and other resources. Some animals will prevent other individuals of their own species from exploiting a resource, whether it be food, nesting sites, or mates. Animals may also cooperate ...

1.5 Energy Can Be Used Immediately or Stored (A) Animal cells break down and release the energy contained in the chemical bonds of food molecules to do mechanical work—in this kangaroo’s case, to jump. (B) The cells of this Arctic ground squirrel have broken down the complex carbohydrates in plants and converted their molecules into fats, which are stored in the animal’s body to provide an energy supply for the cold months.    Cells use nutrients to supply energy and to build new structures Living organisms acquire nutrients from the environment. Nutrients supply the organism with energy and raw materials for carrying out biochemical reactions. Life depends on thousands of biochemical reactions that occur inside cells. Some of these reactions break down nutrient molecules into smaller chemical units, and in the process some of the energy contained in the chemical bonds of the nutrients is captured by high-energy molecules that can be used to do different kinds of cel...

Biological information is contained in a genetic language common to all organisms Cells are the basic building blocks of organisms, but even a single cell is complex, with many internal structures and many functions that depend on information. The information required for a cell to function and interact with other cells—the “blueprint” for existence—is contained in the cell’s genome , the sum total of all the DNA molecules it contains. DNA (deoxyribonucleic acid) molecules are long sequences of four different subunits called nucleotides . The sequence of the nucleotides contains genetic information. Genes are specific segments of DNA encoding the information the cell uses to make proteins ( Figure 1.4 ). Protein molecules govern the chemical reactions within cells and form much of an organism’s structure. By analogy with a book, the nucleotides of DNA are like the letters of an alphabet. Protein molecules are the sentences. Combinations of proteins that form structures and control b...

All of life shares a common evolutionary history Evolution —change in the genetic makeup of biological populations through time—is the major unifying principle of biology. Charles Darwin compiled factual evidence for evolution in his 1859 book On the Origin of Species . Since then, biologists have gathered massive amounts of data supporting Darwin’s theory that all living organisms are descended from a common ancestor. Darwin also proposed one of the most important processes that produce evolutionary change. He argued that differential survival and reproduction among individuals in a population, which he termed natural selection , could account for much of the evolution of life. Although Darwin proposed that living organisms are descended from common ancestors and are therefore related to one another, he did not have the advantage of understanding the mechanisms of genetic inheritance. Even so, he observed that offspring resembled their parents; therefore, he surmised, such mechanis...

We lay the chemical foundation for our study of life in the next three chapters, after which we will turn to cells and the processes by which they live, reproduce, age, and die. Some organisms are  unicellular, consisting of a single cell that carries out    all the functions of life ( Figure 1.1A–C ). Others are multicellular ,  made up of many cells that are specialized for different functions ( Figure 1.1D–G ). Viruses are acellular , although they depend on cellular organisms.  The discovery of cells was made possible by the invention of the microscope in the 1590s by the Dutch spectacle makers Hans and Zaccharias Janssen (father and son). In the mid- to late 1600s, Antony van Leeuwenhoek of Holland and Robert Hooke of England both made improvements on the Janssens’ technology and used it to study living organisms. Van Leeuwenhoek discovered that drops of pond water teemed with single-celled organisms, and he made many other discoveries as he progressiv...

A mphibians—frogs, toads, and salamanders—have been around for a long time. They watched the dinosaurs come and go. But today amphibian populations around the world are in dramatic decline, with more than a third of the world’s amphibian species threatened with extinction. Why? Biologists work to answer this question by making observations and doing experiments. A number of factors may be involved, and one possible cause may be the effects of agricultural pesticides and herbicides. Several studies have shown that many of these chemicals tested at realistic concentrations do not kill amphibians. But Tyrone Hayes, a biologist at the University of California at Berkeley, probed deeper. Hayes fo cused on atrazine, the most widely used herbicide in the world and a common contaminant in fresh water. More than 70 million pounds of atrazine are applied to farmland in the United States every year, and it is used in at least 20 countries. Atrazine is usually applied in the spring, w...

blue dragonfly Biology is the scientific study of living things. Biologists define “living things” as all the diverse organisms descended from a single-celled ancestor that evolved almost 4 billion years ago.Because of their common ancestry, living organisms share many characteristics that are not found in the nonliving world. Living organisms:  • consist of one or more cells • contain genetic information • use genetic information to reproduce themselves • are genetically related and have evolved • can convert molecules obtained from their environment into new biological molecules • can extract energy from the environment and use it to do biological work • can regulate their internal environment This simple list, however, belies the incredible complexity and diversity of life. Some forms of life may not display all of these characteristics all of the time. For example, the seed of a desert plant may go for many years without extracti...