Life Organisms

Inquiring About Life Organisms are adapted to the environments they live in. These adaptations are the result of evolution, the fundamental organizing principle of biology and the core theme of this book. 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. What is life? O The phenomenon of life defies a simple, one-sentence definition. Owe recognize life by what living things do. Concept 1. 1 The themes of this book make connections across different areas of biology. Eight unifying themes will help you organize and make sense of biological information. Theme 1: 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 he 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. Ocells 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, properties that are not present at the preceding level. O Emergent properties are created by new arrangements and interactions of parts as complexity increases. O For example, photosynthesis can take place only when molecules are arranged in a specific way in an intact hloroplast. J It a serious head injury disrup ts the intricate architecture ot a human brain, the mind may cease to function properly even though all of the brain tissues are still present. O The cycling of chemical elements at the ecosystem level depends on a network of diverse organisms interacting with each other and with the soil, water, and air. Emergent properties are not unique to life: a set of bicycle parts won’t take you anywhere, but if they are arranged in a certain way, you can pedal to your chosen destination on a working bicycle.

O Compared to such nonliving xamples, however, the unrivaled complexity of biological systems makes the emergent properties of life especially challenging to study. Reductionism is a powerful strategy in biology. Reductionism is the approach of reducing complex systems to simpler components that are more manageable to study. O Biologists must balance the reductionist strategy with the larger-scale, holistic objective of understanding the emergent properties of life”how all the parts of biological systems are functionally integrated. Biologists are beginning to complement reductionism with new strategies for studying whole systems.

O The ultimate goal of systems biology is to model the dynamic behavior of whole biological systems based on a study of the interactions among the system’s parts. O Successful models allow biologists to predict how a change in one or more variables will affect other components as well as the whole system. The systems approach enables scientists to pose new kinds of questions. O How might a drug that lowers blood pressure affect the functions of organs throughout the human body? O How might increasing a crop’s water supply affect processes in the plants, such as the storage of molecules essential for human nutrition?