READ 1 1 The Science of Life Biology unifies much of natural science The study of biology is a point of convergence for the information and tools from all of the natural sciences Biological systems are the most complex chemical systems on Earth and their many functions are both determined and constrained by the principles of chemistry and physics Put another way no new laws of nature can be gleaned from the study of biology but that study does illuminate and illustrate the workings of those natural laws The intricate chemical workings of cells are based on everything we have learned from the study of chemistry And every level of biological organization is governed by the nature of energy transactions learned from the study of thermodynamics Biological systems do not represent any new forms of matter and yet they are the most complex organization of matter known The complexity of living systems is made possible by a constant course of energy the Sun The conversion of this energy source into organic molecules by photosynthesis is one of the most beautiful and complex reactions known in chemistry and physics Life defies simple definition In its broadest sense biology is the study of living things the science of life Living things come in an astounding variety of shapes and forms and biologists study life in many different ways They live with gorillas collect fossils and listen to whales They read the messages encoded n the long molecules of heredity and count how many times a hummingbird s wings beat each second What makes something alive Anyone could deduce that a galloping horse is alive and a car is not but why We cannot say If it moves it s alive because a car can move and gelatin can wiggle in a bowl They certainly are not alive Although we cannot define life with a single simple sentence we can come up with a series of seven characteristics shared by living systems Cellular organization All organisms consist of one or more cells Often too tiny to see cells carry out the basic activities of living Each cell is bounded by a membrane that separates it from its surroundings Ordered complexity All living things are both complex and highly ordered Your body is composed of many different kinds of cells each containing many complex molecular structures Sensitivity All organisms respond to stimuli Plants grow toward a source of light and the pupils of your eyes dilate when you walk into a dark room Growth development and reproduction All organisms are capable of growing and reproducing and they all possess hereditary molecules that are passed to their offspring ensuring that the offspring are of the same species Homeostasis All organisms maintain relatively constant internal conditions that are different from their environment a process called homeostasis For example your body temperature remains stable despite changed in outside temperatures Evolutionary adaptation All organisms interact with other organisms and the nonliving environment in ways that influence their survival and as a consequence organisms evolve adaptations to their environements Living systems show hierarchical organization The organization of the biological world is hierarchical that is each level builds on the level below it 1 The Cellular Level At the cellular level atoms the fundamental elements of matter are joined together into clusters called molecules Complex biological molecules are assembled into tiny structures called organelles within membrane bounded units we call cells The cell is the basic unit of life Many independent organisms are composed of only single cells Bacteria are single cells for example All animals and plants as well as most fungi and algae are multicellular composed of more than one cell 2 The Organismal Level Cells in complex multicellular organisms exhibit three levels of organization The most basic level is that of tissues which are groups of similar cells that act as a functional unit Tissues in turn are grouped into organs body structures composed of several different tissues that act as a structural and functional unit Your brain is an organ composed of nerve cells and a variety of associated tissues that form protective coverings and contribute blood At the third level of organization organs are grouped into organ system The nervous system for example consists of sensory organs the brain and spinal cord and neurons that convey signals 3 The Populational Level Individual organisms can be categorized into several hierarchical levels within the living world The most basic of these is the population a group of organisms of the same species living in the same place All populations of a particular kind of organism together form a species its members similar in appearance and able to interbreed At a higher level of biological organization a biological community consists of all the populations of different species living together in one place 4 The Ecosystem Level At the highest tier of biological organization a biological community and the physical habitat within which it lives together constitute an ecological system or ecosystem For example the soil water and atmosphere of a mountain ecosystem interact with the biological community of a mountain meadow in many important ways 5 The Biosphere The entire planet can be thought of as an ecosystem that we call the biosphere As you move up this hierarchy novel properties emerge These Emergent properties result from the way in which components interact and they often cannot be deduced just from looking at the parts themselves Examining animal You and all the living define life individual cells for example gives little hint about the whole humans have the same array of cell types as a giraffe It is because world exhibits many emergent properties that it is difficult to The previous descriptions of the common features and organization of living systems begins to get at the nature of what it is to be alive 1 2 The Nature of Science At its core science is concerned with developing an increasingly accurate understanding of the world around us using observation and reasoning To begin with we assume that natural forces acting now have always acted that the fundamental nature of the universe has not changed since its inception and that it is not changing now A number of complementary approaches allow understanding of natural phenomena there is no one scientific method Scientists also attempt to be as objective as possible in the interpretation of the