Introduction: Themes in the Study of Life
Overview: Inquiring About the World of Life
• Organisms are adapted to the environments they live in.
• These adaptations are the result of evolution, the fundamental organizing principle of biology.
• Posing questions about the living world and seeking science-based answers are the central activities of biology, the scientific study of life.
• Biologists ask a wide variety of ambitious questions.
o They may ask how a single cell becomes a tree or a dog, how the human mind works, or how the living things in a forest interact.
• Biologists can help answer questions that affect our lives in practical ways.
• Research breakthroughs in genetics and cell biology are transforming medicine and agriculture.
o Molecular biology is providing new tools for anthropology and criminal science.
o Neuroscience and evolutionary biology are reshaping psychology and sociology.
o New models in ecology are helping society evaluate environmental issues, such as the causes and biological consequences of global warming.
• What is life?
o The phenomenon of life defies a simple, one-sentence definition.
Concept 1.1 Themes help connect the concepts of biology.
• Seven unifying themes will help you organize and make sense of biological information.
Theme 1: Evolution is the core theme of biology, the one idea that makes sense of everything we know about living organisms.
• Life has been evolving on Earth for billions of years, resulting in a vast diversity of past and present organisms.
• At the same time, living things share certain features.
• The scientific explanation for this unity and diversity is evolution: the idea that the organisms living on Earth today are the modified descendants of common ancestors.
• In other words, scientists can explain traits shared by two organisms with the idea that they have descended from a common ancestor, and scientists can account for differences with the idea that heritable changes have occurred along the way.
Theme 2: New properties emerge at each level in the biological hierarchy.
• Each level of biological organization has emergent properties.
• Biological organization is based on a hierarchy of structural levels, each building on the levels below.
o At the lowest level are atoms that are ordered into complex biological molecules.
o Biological molecules are organized into structures called organelles, the components of cells.
o Cells are the fundamental unit of structure and function of living things.
• Some organisms consist of a single cell; others are multicellular aggregates of specialized cells.
• Whether multicellular or unicellular, all organisms must accomplish the same functions: uptake and processing of nutrients, excretion of wastes, response to environmental stimuli, and reproduction.
• Multicellular organisms exhibit three major structural levels above the cell: Similar cells are grouped into tissues, several tissues coordinate to form organs, and several organs form an organ system.
• For example, to coordinate locomotory movements, sensory information travels from sense organs to the brain, where nervous tissues composed of billions of interconnected neurons—supported by connective tissue—coordinate signals that travel via other neurons to the individual muscle cells.
o Organisms make up populations, localized groups of organisms belonging to the same species.
o Populations of several species in the same area combine to form a biological community.
o Populations interact with their physical environment to form an ecosystem.
o The biosphere consists of all the environments on Earth that are inhabited by life.
• As we move from the molecular level to the biosphere, novel emergent properties arise at each level that are not present at the preceding...
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