Lecture 1 Introduction to Biology

The Diversity of Life Biology is the study of living things Living things can be divided into six kingdoms Protista Archaea Bacteria Animalia Fungi Plantae

What is Life? Biology is the study of life - but what does it mean to be alive? Ludwig von Bertalanffy – life is a system where the whole is greater than the sum of the parts Modern physiology – life is an electron in search of a resting place Living organisms and many non-living things share three properties Complexity Movement Response to stimulation

Properties of Life All living organisms share five basic properties Cellular Organization All living organisms are composed of at least one cell Metabolism All living organisms use energy Homeostasis All living organisms maintain stable internal conditions Growth and reproduction All living organisms grow and reproduce Heredity All living organisms possess a genetic system that is based on DNA (Deoxyribonucleic acid)

The Organization of Life Living organisms function and interact with each other at many levels These levels are organized in a hierarchy of increasing complexity: Cellular Level Organismal Level Population Level 1. 3. 2.

Life is an Emergent Property Each higher level of organization contains novel properties not present at the simpler level of organization Birth rate & death rate – populations NOT individuals Evolution – populations evolve biologically NOT individuals These properties are termed emergent properties They are a consequence of the structural organization that is the hallmark of life They characterize many aspects of the living world

Five Themes That Unify Biology Evolution The gene frequencies change in a species over time Causes include: Genetic drift Natural & artificial selection Founder effects The Flow of Energy All living organisms require energy The sun is the source of energy for most ecosystems Plants capture energy via photosynthesis They then act as an energy source for other organisms Interaction Interaction between organisms is critical for evolution Social behavior occurs when organisms of the same species live in direct contact Community dynamics occur when organisms of different species live in direct contact (Competition, Predation, Symbiosis) Structure Determines Function Biological structures are well suited to their function This is true at every level of organization Homeostasis All living organisms act to maintain a relatively stable internal environment Maintaining homeostasis requires energy and a lot of signaling back-and-forth between cells

How Scientists Think Inductive Reasoning Deductive Reasoning Is used by scientists to develop hypotheses about how the world works Deductive Reasoning Uses accepted general principles as a “guide” to explain specific observations

Inference vs. Observation An observation is limited to a description of actions or events without interpretation An inference is a conclusion we draw based on what we observe Inference or observation? Example 1 (The cat is happy) Example 2 (The cat is chewing on the plant leaves) Example 3 (The cat is sleeping) Example 4 (The cat is a female)

Theory and Certainty in Science A theory is a set of hypotheses that have been tested many times and not rejected It indicates a high degree of certainty However, there is no absolute truth in science So the acceptance of a theory is always provisional Note: To the general public, the word theory is often used to mean what a scientist would call a hypothesis, a lack of knowledge or a guess To scientists, a theory represents that of which they are most certain, explanations supported by a wealth of evidence and experimental data

The Limitations of Science Science is limited to organisms and processes that can be observed and measured Spiritual and religious phenomena are beyond the scope of science Most religious explanations do not allow formation of a realistic null hypothesis There are also practical limits Science can provide options and understanding Science cannot be relied upon to solve all problems For example, what constitutes “acceptable risk” cannot be answered by science!

Four Theories Unify Biology & This Class The Gene Theory The information that determines what an organism is like is encoded in its genes Genes are located along DNA molecules The entire set of DNA instructions that specifies a cell is termed its genome The Cell Theory All living organisms are composed of cells Cells are the basic units of life All cells come from other cells The Theory of Heredity Genes represent traits of an organism and are inherited as discrete units Chromosomal theory of inheritance: Genes are physically located on chromosomes The Theory of Evolution All living organisms are related to one another in a common tree of life Diversity of the living world is the result of natural selection