The theory of evolution is the unifying theory of biology, meaning it is the framework within which biologists ask questions about the living world. Its power is that it provides direction for predictions about living things that are borne out in ongoing experiments. The Ukrainian-born American geneticist Theodosius Dobzhansky famously wrote that “nothing makes sense in biology except in the light of evolution.” He meant that the tenet that all life has evolved and diversified from a common ancestor is the foundation from which we approach all questions in biology.

This chapter outlines information on the regulation of gene expression in both prokaryotes and eukaryotes.  This includes transcriptional, post-transcriptional, translational and post-translational regulation.  

IntroductionThis chapter covers the details of the Central dogma including transcription and translation.  Prokaryotic and eukaryotic transcription are compared. Eukaryotic RNA processing is described.  Protein synthesis is outlined including protein folding and modifications of the newly created proteins.  

Animal evolution began in the ocean over 600 million years ago with tiny creatures that probably do not resemble any living organism today. Since then, animals have evolved into a highly diverse kingdom. But what is an animal? While we can easily identify dogs, birds, fish, spiders, and worms as animals, other organisms, such as corals and sponges, are not as easy to classify. Animals vary in complexity—from sea sponges to crickets to chimpanzees—and scientists are faced with the difficult task of classifying them within a unified system. They must identify traits that are common to all animals as well as traits that can be used to distinguish among related groups of animals. The animal classification system characterizes animals based on their anatomy, morphology, evolutionary history, features of embryological development, and genetic makeup. This classification scheme is constantly developing as new information about species arises. Understanding and classifying the great variety of living species help us better understand how to conserve the diversity of life on earth. 

Meiosis is the process of cell division that produces haploid gametes.  In sexual reproduction haploid gametes combine through fertilization to form a genetically recombined diploid zygote.  Meiosis includes two successive divisions and processes such as crossing over and independent assortment that increase genetic variability in gametes produced.  Life cycles detail the events between meiosis and fertilization that vary for different multicellular organisms.

Genetics is the study of heredity. Johann Gregor Mendel set the framework for genetics long before chromosomes or genes had been identified, at a time when meiosis was not well understood. Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. Because of Mendel’s work, the fundamental principles of heredity were revealed. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. Not all genes are transmitted from parents to offspring according to Mendelian genetics, but Mendel’s experiments serve as an excellent starting point for thinking about inheritance.

The cellular processes of life require energy.  How do living organism obtain energy and how is it used?  This Chapter answers these questions by exploring forms of energy and energy transfer within and between living organisms, as well as the role of enzymes and adenosine triphosphate (ATP) in chemical reactions in cells.

This chapter begins with the details of the Chromosome Theory of Inheritance and moves onto discuss homologous recombination and the creation of new chromosomes.  It also describes genetic linkage maps and how to calculate distances of genes on chromosomes.  The second part of this chapter is focused on karyotypes, nondisjunction and creation of individuals with abnormal numbers of chromosomes. 

Virtually all life on Earth depends on Photosynthesis. Photosynthesis uses energy in sunlight to form organic molecules such as glucose.  This transformation of light energy to chemical energy provides fuel for the metabolic processes in all organisms.  Photosynthesis also produces oxygen required for aerobic cellular respiration. This chapter covers light energy as part of the electromagnetic spectrum, basic structures involved in photosynthesis and the metabolic pathways of photosynthesis divided into the light-dependent reactions and the Calvin cycle.

In scientific terms, phylogeny is the evolutionary history and relationship of an organism or group of organisms. A phylogeny describes the organism's relationships, such as from which organisms it may have evolved, or to which species it is most closely related. Scientists must collect accurate information that allows them to make evolutionary connections among organisms. It is a highly dynamic field of biology because phylogenetic modeling concepts are constantly changing as new information is collected.  Over the last several decades, new research has challenged scientists’ ideas about how organisms are related. 

Carl Woese and his colleagues proposed that all life on Earth evolved along three lineages, called domains. Two of the three domains—Bacteria and Archaea—are prokaryotic. Prokaryotes were the first inhabitants on Earth, appearing 3.5 to 3.8 billion years ago. These organisms are abundant and ubiquitous; that is, they are present everywhere. In addition to inhabiting moderate environments, they are found in extreme conditions: from boiling springs to permanently frozen environments in Antarctica; from salty environments like the Dead Sea to environments under tremendous pressure, such as the depths of the ocean; and from areas without oxygen, such as a waste management plant, to radioactively contaminated regions, such as Chernobyl. Prokaryotes reside in the human digestive system and on the skin, are responsible for certain illnesses, and serve an important role in the preparation of many foods.

The plasma membrane, the cell membrane, has many functions, but the most basic one is to define the cell's borders and keep the cell functional. The plasma membrane is selectively permeable. This means that the membrane allows some materials to freely enter or leave the cell, while other materials cannot move freely, but require a specialized structure, and occasionally, even energy investment for crossing.

Elements in various combinations comprise all matter, including living things. Some of the most abundant elements in living organisms include carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. These form the nucleic acids, proteins, carbohydrates, and lipids that are the fundamental components of living matter. Biologists must understand these important building blocks and the unique structures of the atoms that comprise molecules, allowing for cells, tissues, organ systems, and entire organisms to form. All biological processes follow the laws of physics and chemistry, so in order to understand how biological systems work, it is important to understand the underlying physics and chemistry. For example, the flow of blood within the circulatory system follows the laws of physics that regulate the modes of fluid flow. The breakdown of the large, complex molecules of food into smaller molecules—and the conversion of these to release energy to be stored in adenosine triphosphate (ATP)—is a series of chemical reactions that follow chemical laws. The properties of water and the formation of hydrogen bonds are key to understanding living processes. Recognizing the properties of acids and bases is important, for example, to our understanding of the digestive process. Therefore, the fundamentals of physics and chemistry are important for gaining insight into biological processes.

An animal’s endocrine system controls body processes through the production, secretion, and regulation of hormones, which serve as chemical “messengers” functioning in cellular and organ activity and, ultimately, maintaining the body’s homeostasis. The endocrine system plays a role in growth, metabolism, and sexual development.

People did not understand the mechanisms of inheritance, or genetics, at the time Charles Darwin and Alfred Russel Wallace were developing their idea of natural selection. Scholars rediscovered Mendel’s work in the early twentieth century, and over the next few decades scientists integrated genetics and evolution in what became known as the modern synthesis—the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s. Natural selection can affect a population’s genetic makeup, and, in turn, this can result in the gradual evolution of populations. In the early twentieth century, biologists in the area of population genetics began to study how selective forces change a population through changes in allele and genotypic frequencies.  Adaptive evolution is the process by which natural selection increases the frequency of beneficial alleles in the population, while decreasing the frequency of deleterious alleles.

The environment consists of numerous pathogens, usually microorganisms, that cause disease in their hosts. Components of the immune system constantly search the body for signs of these pathogens. Mammalian immune systems evolved for protection from such pathogens. These systems are composed of an extremely diverse array of specialized cells and soluble molecules that coordinate a rapid and flexible defense system. 

A nervous system is an organism’s control center. It processes sensory information from outside and inside the body and controls all behaviors, from fundamental to complex. Although nervous systems throughout the animal kingdom vary in structure and complexity, each functions to maintain homeostasis. 

Viewed from space, Earth offers no clues about the diversity of life forms that reside there. Scientists believe that the first forms of life on Earth were microorganisms that existed for billions of years in the ocean before plants and animals appeared. The mammals, birds, and flowers so familiar to us are all relatively recent, originating 130 to 250 million years ago. The earliest representatives of the genus Homo, to which we belong, have inhabited this planet for only the last 2.5 million years, and only in the last 300,000 years have humans started looking like we do today.  The study of life is a vast field that delves into the past, present, and future.  This module will provide an introduction into the science of Biology as well as a look into its major themes and concepts.

This chapter begins with the evolution of viruses, viral morphology and classification. Steps in viral infection are covered along with various host and virus types. Prevention and treatment of viruses is outlined in this chapter. Finally prions and viroids are covered at the conclusion of the chapter. 

All living organisms need nutrients to survive. While plants can obtain the molecules required for cellular function through the process of photosynthesis, most animals obtain their nutrients by the consumption of other organisms. At the cellular level, the biological molecules necessary for animal function are amino acids, lipid molecules, nucleotides, and simple sugars. However, the food consumed consists of protein, fat, and complex carbohydrates. Animals must convert these macromolecules into the simple molecules required for maintaining cellular functions, such as assembling new molecules, cells, and tissues. The conversion of the food consumed to the nutrients required is a multistep process involving digestion and absorption. This module will explore these ideas as well as the components of various digestive systems found in the animal kingdom.