Chapter 1 Human Biology is a Science

What is Science? Science is one of many approaches to learning about the truth of the natural world. It is a systematic approach to gathering knowledge using reason, logic and rational thinking.

Biology is the scientific study of life Biology, like all sciences, pursues a methodical search for information that reveals the secrets of the natural world and to scientifically study the life of Homo sapiens. Living organisms are classified in to hierarchical groupings: Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species. Genus names are always capitalized, species names are always lower case. Scientific names are always in italics (or underlined).

The scientific method Explanations are sought using an approach known as the scientific method: Observe some aspect of the natural world and ask a question. Develop hypotheses (educated guesses) using all known information. Predict what the outcome would be if the hypothesis is true or valid. Test the hypothesis by experiments, models, and observations. Repeat the tests for consistency. Analyze and report objectively on the tests and conclusions.

Scientific experiments Experiments involve scientific tests in which there is a careful accounting of all of the conditions that may influence outcome. Control groups do not get the treatment so can be used as a basis of comparison for the treated or experimental group. The experimental group experiences all of the same conditions as the control except for the independent variable being studied (e.g. fertilizer). The dependent variable changes with the treatment (e.g. crop yield).

Experimental sampling error The sample size must be large enough to be representative of the whole. If the sample size is too small, sampling error abounds (e.g., counting green and black jelly beans). Science undergoes continual re-evaluation. Single experiments rarely provide truthful answers to complicated questions. Not all science is performed by conducting experiments in the laboratory. Observations & hypotheses can be done in the field, where “mother nature” is the laboratory & the life forms being studied become the experimental subjects.

Scientific hypotheses vs. theories A scientific theory explains a large number of observations. A theory is a related set of hypotheses that form a broad-ranging explanation of many phenomena. Theories are accepted or rejected on the basis of tests and are subject to revision. Scientists must be content with relative certainty, which becomes stronger as more repetitions are made. Scientists must be prepared to change their minds in light of new evidence.

Some theories.... Physics Chemistry Biology Gravity. Yes, gravity is “just a theory”. Big Bang origin of the universe. Relativity. Chemistry Atomic. Molecular. Quantum. Biology Evolution. Germs cause disease. All cells come from pre-existing cells.

Science is measurement Science has limits. Science is limited to questions that can be tested; subjective questions do not readily lend themselves to scientific analysis or experiments. Science has the potential to be used for controversial endeavors, which means that all of society must commit to responsible use of scientific knowledge.

Critical Thinking in Science and Life Critical thinking is an objective evaluation of information. Consider the source. Let credible scientific evidence, not opinions or hearsay, do the convincing. Question credentials and motives. Evaluate the content. Be able to distinguish between cause and correlation. Separate facts from opinions.

The Characteristics of Life Living and nonliving things share common characteristics, such as being composed of atoms, the smallest units of elements. Water and the earth’s crust are inorganic materials. But living things are organic and composed of one or more cells that do a unique kind of chemistry called metabolism.

The Characteristics of Life All living things: Consist of one or more cells that conduct coordinated chemical reactions using enzymes = metabolism. Take in and use energy and materials so they can reproduce and grow. Have genetic information that changes in species over time = evolution. Sense and respond to stimuli. Many life forms can move. Maintain homeostasis ( a dynamic balance to keep internal environment relatively constant despite changes in external world).

Our Place in the Natural World Like all living things, humans have evolved over time. Humans are mammals belonging to the animal kingdom, one of the four kingdoms of life in the domain Eukarya. We are mammals because we nurse our young with mammary glands, give live birth, are endothermic and have hair.

Life’s Organization Life is organized on many levels. Atoms and molecules are nonliving materials from which all of nature is built. Organelles are found inside cells and each has a specific structure and function. Cells are grouped together to form tissues. Tissues are found in organs and these organs cooperate to form organ systems in an organism. Many organisms of the same species are called populations and these are assembled into biological communities which interact with their environment to form ecosystems in the biosphere.

Levels of Organization in Nature

Flow of Energy and Cycling of Materials in the Biosphere

Life’s Organization Organisms are connected through the flow of energy and cycling of materials. Energy flows from the sun. Plants (producers) trap this energy by photosynthesis. Animals (consumers) feed on the stored energy in plants, using cellular respiration. Bacteria and fungi (decomposers) break down the biological molecules of other organisms in order to recycle raw materials. All organisms are part of webs that depend on one another for energy and raw materials. We are all interconnected.