Foundations of Biology
Foundations and Fundamental Questions of Biology
Biology is defined as the science that studies life.
Determining the exact nature of life involves addressing several fundamental questions:
Identification of shared properties that characterize an entity as "alive."
Understanding how various living things function internally and externally.
Organizing the remarkable diversity of life into a structured system for better understanding.
Investigating the origins of life's diversity and the mechanisms through which it continues to evolve.
The field of virology focuses on viruses. Although viruses can attack living organisms, cause diseases, and reproduce, they lack certain characteristics required by biologists to be classified as living entities.
As new organisms are discovered daily, biologists continuously seek to refine the answers to these core questions.
The Eight Propeties of Life
All living organisms share eight key characteristics or functions that collectively define life:
Order
Organisms are highly organized structures consisting of one or more cells.
Even single-celled organisms are remarkably complex, with atoms forming molecules that compose organelles and other cell components.
Multicellular organisms may consist of millions of cells. These cells have the advantage of specialization to perform specific functions.
In some instances, specialized cells can be sacrificed for the benefit of the organism as a whole.
Specialized cells coordinate to form complex organs such as the heart, lungs, or skin.
Sensitivity or Response to Stimuli
Organisms respond to various environmental stimuli.
Plants exhibit phototropism (bending toward light) and thigmotropism (responding to touch).
Bacteria exhibit chemotaxis (movement toward or away from chemicals) and phototaxis (movement toward or away from light).
Movement toward a stimulus is termed a positive response, while movement away is termed a negative response.
Reproduction
Single-celled organisms reproduce by duplicating their DNA (genetic material) and dividing it equally to form two new cells.
Multicellular organisms often produce specialized reproductive cells to form new individuals.
DNA containing genes is passed to offspring, ensuring they belong to the same species and possess similar characteristics to the parents, such as blood type or fur color.
Adaptation
This refers to the "fit" between an organism and its environment, a result of evolution by natural selection.
Adaptation operates in every lineage of reproducing organisms and enhances reproductive potential and survival.
Examples include heat-resistant Archaea living in boiling hot springs and nectar-feeding moths with tongue lengths matching specific flower sizes.
Adaptations are not constant; as environments change, natural selection causes population characteristics to track those changes.
Growth and Development
Organisms grow according to specific instructions coded in their genes.
These genetic instructions ensure that the young of a species will develop characteristics similar to those of their parents.
Regulation and Homeostasis
Even small organisms require regulatory mechanisms to coordinate internal functions such as nutrient transport and response to environmental stresses.
Homeostasis (meaning "steady state") is the maintenance of a relatively stable internal environment required for life.
Organ systems, such as the circulatory or digestive systems, assist in homeostasis by delivering nutrients, removing wastes, carrying oxygen, and cooling the body.
Energy Processing
All organisms require energy for metabolic activities.
Some organisms capture energy from the Sun to convert into chemical food energy, while others utilize chemical energy from molecules they ingest.
Evolution
The diversity of life is the result of mutations, or random changes in hereditary material, over time.
Mutations allow organisms to adapt to changing environments.
Characteristics fit for an environment lead to greater reproductive success through natural selection.
The Cell as the Basic Unit of Life
The cell is the fundamental unit of life; all living things are composed of one or more cells.
Unicellular Organisms (Prokaryotes): Organisms made of a single cell, such as bacteria and protozoa. These are mostly microscopic, requiring a microscope to be seen.
Multicellular Organisms (Eukaryotes): Organisms made of many cells, such as plants and animals. These are macroscopic and can be seen with the unaided eye.
A microscope is a specialized instrument used to magnify and view objects that are otherwise invisible to the unaided eye.
The History and Invention of the Microscope
Early Optics: During the first century, Romans experimented with glass samples. They discovered that glass with a thick middle and thin edges made small objects appear larger. This was the earliest form of a lens.
Etymology: The word "lens" is derived from the Latin word "lentil," due to the similarity in shape to the lentil bean.
13th Century: Lenses began to be utilized in the production of eyeglasses, offering magnification between and .
Late 16th Century: Zacharias Janssen (1580–1638), likely with help from his father Hans, invented the first compound microscope by combining several lenses to further enlarge objects.
Robert Hooke (1635–1703): In 1665, Hooke used a self-built microscope to examine a thin slice of cork. He observed small compartments he called "cellula" (meaning "little rooms" in a monastery). His findings were published in the famous work Micrographia.
Antonie van Leeuwenhoek (1632–1723): Created a microscope with significantly higher magnification than Hooke's. He was the first to observe:
Bacteria, blood cells, and protists (which he termed "animalcules").
Sperm cells and egg cells in both humans and animals.
The process of fertilization, which provided early evidence against spontaneous generation.
Development of the Cell Theory
Following improvements in microscope technology over a century, two scientists established the foundation of the cell theory:
Matthias Jakob Schleiden: A botany professor at the University of Jena, Germany. In 1838, after years of studying various plants, he published research concluding that all plants are made of cells.
Theodor Schwann: A physiology professor at the University of Louvain, Belgium. In 1839, he published research based on animal cell slides.
The First Two Postulates:
All organisms are made up of cells.
The basic unit of life is the cell.
The Third Postulate:
Proven by Rudolf Ludwig Karl Virchow in 1858. While studying diseases in organs and tissues, he noted that diseases originate from affected cells.
He stated "Omnis cellula e cellula," meaning all cells arise from preexisting cells.
It is believed Robert Remak, a Jewish scientist, originally made this discovery in 1855 by hardening the cell membrane to observe cell division.
Disproving the Theory of Spontaneous Generation
Spontaneous generation was the belief that living organisms could arise from nonliving sources. This theory was widely accepted until the 19th century when it was disproved by several key experiments:
Francesco Redi (1668): Experimented with fresh meat in jars. He used an open jar, a jar covered with gauze, and an airtight sealed jar. Maggots only appeared on the meat in the open jar. Maggots appeared on the gauze of the covered jar but not the meat. He concluded maggots come from living things (flies), not the meat itself.
John Needham (1745): Attempted to support spontaneous generation. He boiled chicken broth and sealed it. When microorganisms grew anyway, he claimed they arose spontaneously. In reality, the broth was likely contaminated by air after boiling or before sealing.
Lazzaro Spallanzani (1729–1799): Challenged Needham by sealing the flask before boiling the broth. No microorganisms grew. Believers in spontaneous generation argued that by sealing the flask, he prevented the "vital force" of air from entering.
Louis Pasteur (1859): Conducted the definitive experiment using S-shaped (swan neck) flasks that allowed air to enter but trapped dust particles in the bottom bend.
In one flask, he broke the neck, allowing dust (and microbes) to reach the broth, which quickly became cloudy.
In the intact S-shaped flask, the broth remained sterile despite being open to the air, as microbes were trapped in the bend.
This proved that microorganisms are introduced via dust particles and do not arise spontaneously from the broth. This finalized the rejection of spontaneous generation and supported the third postulate of Cell Theory.