Biology Chapter 1: A View of Life
Biology is a natural science involved with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is an extensive subject containing many subdivisions, topics, and disciplines. Among the most important topics are five principles that can be said to be the fundamental guidelines of modern biology:
- Cells are the basic unit of life
- New species and inherited traits are the product of evolution
- Genes are the basic unit of heredity
- An organism regulates its internal environment to maintain a stable and constant condition
- Living organisms consume and transform energy.
Cell theory states that the cell is the fundamental unit of life, and that all living things are made up of one or more cells or the produced products of those cells. All cells arise from other cells through cell division. In multicellular organisms, every cell in the organism’s body originates from a single cell in a fertilized egg. Also, the occurrence of energy flow occurs in cells in processes that are part of the function known as metabolism. Finally, cells contain hereditary information called deoxyribonucleic acid (DNA) which is passed from cell to cell during cell division.
A fundamental concept in biology is that life changes and develops through evolution, and that all life-forms known have a common origin. Evolution was established by Charles Darwin as a practical theory when he showed its inspiration: natural selection. Darwin theorized that species and breeds developed through the processes of natural selection and artificial selection or selective breeding.
Now evolution is used to explain the great variations of life found on Earth. Genetic drift was accepted as an additional means of evolutionary development in the creation of the theory.
The theory of evolution proposes that all organisms on the Earth, both living and extinct, have descended from a common ancestor or an ancestral gene pool. Biologists generally consider the universality of the genetic code as great support in favor of the theory of universal common descent for all Bacteria, Achaea, and Eukaryotes.
Genes are the primary units of inheritance in all organisms. A gene is a unit of heredity and corresponds to a region of DNA that influences the form or function of an organism in specific ways. All organisms, from bacteria to animals, share the same basic machinery that copies and translates DNA into proteins. Cells transcribe a DNA gene into an RNA version of the gene, and a ribosome then translates the RNA into a protein, a sequence of amino acids. The translation code from RNA to amino acid is the same for most organisms, but slightly different for some. For example, a sequence of DNA that codes for insulin in humans also codes for insulin when inserted into other organisms, such as plants.
A chromosome is an organized structure consisting of DNA and histones. DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell and any other hereditary information found in the mitochondria, chloroplasts, or other locations is collectively known as its genome. In eukaryotes, genomic DNA is located in the cell nucleus, along with small amounts in mitochondria and chloroplasts. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the nuclei. The genetic information in a genome is held within genes, and the complete assemblage of this information in an organism is called its genotype.
Homeostasis is the ability of an open system to regulate its internal environment to maintain stable conditions by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular exhibit homeostasis.
To maintain dynamic equilibrium and effectively carry out certain functions, a system must detect and respond to physiological disturbances. After the detection of a disturbance, a biological system normally responds through negative feedback. This means stabilizing conditions by either reducing or increasing the activity of an organ or system. One example is the release of glucagon when sugar levels are too low.
The survival of a living organism depends on the continuous input of energy. Chemical reactions that are responsible for its structure and function are tuned to extract energy from substances that act as its food and transform them to help form new cells and sustain them. In this process, molecules of chemical substances that constitute food play two roles; first, they contain energy that can be transformed for biological chemical reactions; second, they develop new molecular structures made up of biological molecules.
The organisms responsible for the introduction of energy into an ecosystem are known as producers. Nearly all of these organisms originally draw energy from the sun. Plants and other phototrophs use solar energy by a process known as photosynthesis to convert raw materials into organic molecules. Some of the captured energy is used to produce biomass to sustain life and provide energy for growth and development.