The principle of biogenesis is a basic tenet of modern cell theory which states that all cells only come from other cells.

Principle of Biogenesis

Although cells were first observed by Robert Hooke in the 1660s, cell theory was not widely accepted in the scientific community for approximately 200 years. The subsequent work and observations of scientists like Matthias Schleiden, Theodor Schwann, Robert Remak, and Rudolf Virchow were critical in establishing its general acceptance.

Acceptance of Cell Theory

Developed in the 17th century following early observations of microscopic life, the cell theory is a foundational scientific principle. It posits three main claims: the cell is the fundamental unit of life, all living organisms contain at least one cell, and new cells can only arise from pre-existing cells.

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The cell is the fundamental unit of life. While cells vary significantly in size, shape, structure, and function—categorized primarily into prokaryotic and eukaryotic cells—they all share a few fundamental components at their simplest level of construction. The internal structures of a cell are analogous to the organs inside a human body, with unique components suited to specific functions.

Cell

Any living thing that functions as a singular entity

Organism 

- Genetics
- Cell theory
- Evolution
- Homeostasis

Foundations of Modern Biology

Microscopes are fundamental tools in microbiology that produce magnified images of specimens generally too small to be seen with the naked eye. By manipulating the physical properties of light—such as contrast, size, and color—microscopes allow researchers to examine microbial cells in high detail. This capability is crucial for both clinical and research applications, including the identification of specific microbial species and the diagnosis of diseases. Before microscopes, theories about microorganisms were strictly hypothetical.

Microscopes

Wikipedia

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Tissue

Molecular and cellular biology studies the molecular structures and cellular processes that underlie the function, reproduction, and development of living organisms.

Molecular and Cellular Biology

The (metabolic) center of a neuron. It is in charge of keeping the cell alive

Cell body

Cell-cell interactions describe the process in which one cell influences the differentiation of neighboring cells during the development of the nervous system. This process is a key reason why vertebrate brains are less hardwired and more susceptible to environmental cues and experience. In contrast, invertebrate development, such as in C. elegans, is more hardwired and relies less on cell-cell interactions, making their mitotic lineages strictly predictable and easier to trace.

Cell-Cell Interactions

Although cells share certain fundamental characteristics, they exhibit remarkable variety in their structure, function, and metabolic activity. The two primary categories of cells are prokaryotic cells, which lack a nucleus, and eukaryotic cells, which possess a well-organized, membrane-bound nucleus.

Types of Cells

Animal cell organelles are specialized sub-cellular structures that perform specific functions necessary for the cell's survival, growth, and homeostasis. These include membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, as well as non-membrane-bound structures like ribosomes.

Animal Cell Organelles

An ecosystem describes the interactions between groups of organisms from all biological domains and nonliving things in a shared geographical space.

Ecosystem

Symbiosis is any close relationship shared by two biological organisms of different species (called symbionts).

Symbiosis (long term interspecific interactions)

The process in which physical/behavioral changes of a population occur over long periods of time. Evolution is a scientific theory that for over the last 150 years, scientists have gathered an overwhelming amount of evidence that supports this theory.  

Evolution 

The scientific field of study of traits and their passage from parents to offspring. Humans inherit 23 chromosomes from the father, and 23 from the mother. These 23 pairs of chromosomes consist of 22 autosomal chromosome pairs and one sex chromosome pair. The physical unit of inheritance is a gene, comprised of DNA (Deoxyribonucleic acid) segments.

Genetics and Inheritance in Humans

The Earth is estimated to be approximately 4.6 billion years old. For its first 2 billion years, its atmosphere lacked oxygen, which is necessary to support life as it is currently known.

The Earth's Early Atmosphere

The primordial soup hypothesis proposes that life on Earth began in a body of water. According to this idea, metals and gases from the atmosphere combined with an energy source—such as lightning or ultraviolet light—to form the organic carbon compounds that serve as the chemical building blocks of life.

Primordial Soup Hypothesis

In 1952, Stanley Miller and Harold Urey conducted an experiment to test the primordial soup hypothesis by simulating the early Earth's atmosphere. They combined water ($$\text{H}_2\text{O}$$), methane ($$\text{CH}_4$$), hydrogen ($$\text{H}_2$$), and ammonia ($$\text{NH}_3$$) in a sealed, sterile flask, heated the mixture to generate water vapor, and introduced electrical sparks to simulate lightning. After one week, they analyzed the contents and discovered amino acids, which are the structural units of proteins.

Miller-Urey Experiment

-Brightfield Microscopes  
-Darkfield Microscopes  
-Phase Contrast Microscopes  
-Differential Interference Contrast Microscopes (DIC)    
-Fluorescence Microscopes  
-Confocal Microscopes  
-Two-Photon Microscopes  
-Electron Microscopy  
-Scanning Probe Microscopy

Types of Microscopes 

Antonie van Leeuwenhoek, sometimes hailed as 'the Father of Microbiology,' was a Dutch cloth merchant who began his work in obscurity but became the first to develop innovative lens-making techniques for simple microscopes powerful enough to view microbes definitively. Using his simple microscope, which passed light through just one lens, he observed microorganisms as no one had before. His friend, the prominent physician Reinier de Graaf, helped bring attention to his powerful microscopes by writing to the Royal Society of London. From $${}1673$$ onward, van Leeuwenhoek regularly submitted letters to the society detailing his observations. In $${}1674$$, he described his groundbreaking observations of single-celled organisms. He described these organisms—which we now know were bacteria and protists observed in rain water—as 'animalcules' or 'wee little beasties.' His $${}1674$$ report initially produced controversy in the scientific community, but his claims were soon verified when the society sent a delegation to investigate his findings. He subsequently became a celebrated figure, at one point even entertaining a visit by the czar of Russia.

Antonie Van Leeuwenhoek

The invention of microscopes allowed scientists to observe microorganisms and realize their enormous diversity, noting variations in size, appearance, and rates of reproduction. To effectively study this vast array of organisms, researchers recognized the need to systematically organize and classify them.

Discovery of Microbial Diversity

Microscopy is widely utilized in clinical settings to analyze patient samples and diagnose potential infections. For example, if a patient presents with an increasingly painful, swollen wound oozing pus, a medical professional can collect a swab from the site. This sample is then sent to a medical laboratory and examined under a microscope, allowing scientists to identify the specific pathogen causing the aggressive infection.

Clinical Applications of Microscopy

Galileo Galilei was an Italian astronomer who contributed to the early development of microscopy. Prior to the widespread discovery of microorganisms, Galileo used a compound microscope, which was more sophisticated than simple microscopes because it passed light through two sets of lenses. He utilized this compound microscope to closely examine the parts of insects.

Galileo Galilei

Robert Hooke ($${}1635$$–$${}1703$$) was an English scientist who made critical early contributions to microscopy. He used a microscope of his own design to make numerous observations, which he published in his famous book, Micrographia, in $${}1665$$. While viewing a thin sample of cork tissue, Hooke became the first to observe distinct, honeycomb-like structures. He described them as 'small Boxes or Bladders of Air' and coined the term 'cell' (from the Latin for 'small room') to name them. At the time, Hooke was not aware that the cork cells were long dead and, therefore, lacked the internal structures found within living cells.

Robert Hooke

The development of the microscope involved contributions from multiple inventors prior to the discovery of microorganisms. Notably, eyeglass makers in the Netherlands during the late $${}1500$$s played a foundational role in creating early optical instruments that eventually led to the microscopes used by later scientists.

Early Microscope Development

In microscopy, a specimen refers to the specific item, organism, or sample that is being viewed. It is typically placed on a glass slide and secured onto the microscope's stage for observation.

Microscope Specimen

Proper microscope maintenance is essential to preserve delicate components and ensure high-resolution images, as dirty or scratched lenses will refract light in unintended ways. Routine care includes cleaning lenses with specialized lens paper, protecting the bulb from breakage, and covering the instrument when not in use. To avoid physical damage during operation, users must never push an objective into a slide, should not use the coarse focusing knob with $${}40	imes$$ or greater objective lenses, must only apply immersion oil with specialized objectives (typically $${}100	imes$$), and must meticulously clean immersion oil from all lenses immediately after use.

Microscope Maintenance and Care

In light microscopy, the z-plane refers to the specific depth or distance from the observer at which an image is maximally focused. While traditional forms of light microscopy create an image focused at a single z-plane, more advanced instruments like confocal microscopes can scan multiple z-planes successively to construct a three-dimensional image.

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