Introduction to Biology

Biology

The study of living organisms including their origin, distribution, evolution, structure and function.

Microbiology, Botany, Zoology

The three main branches of biology

Taxonomy

Classification and identification of organisms

Physiology

Study of the normal physical, mechanical, and biochemical functions of living organisms and their bodily systems.

Anatomy

Study of the bodily structure of living organisms. Derived from the Greek word for "dissection".

Genetics

Studies genes, heredity, and the variation of inherited traits in organisms.

Cytology

Study of cells, focusing on their structure, composition, and function.

Evolutionary Biology

Studies the processes—such as natural selection, genetic drift, mutation, and gene flow—that drive the diversity and adaptation of life over time.

Ecology

Study of how living organisms interact with each other and their physical surroundings.

Biogenesis

the foundational biological principle that living organisms develop only from pre-existing living matter through reproduction.

Spontaneous Generation Theory or Abiogenesis

Was an archaic theory proposing that living organisms could arise from non-living matter. Promoted by Aristotle, it suggested that environmental elements like "vital heat" could produce creatures such as flies from rotting meat or mice from dirty rags. This idea was debunked in the 19th century.

Aristotle (350 BC)

Played a pivotal role in establishing the theory of spontaneous generation, because he observed phenomena like maggots appearing on decaying meat, and rats in stored grains. He remained unchallenged for 2,000 years.

Francesco Redi (1668)

Disproved Aristotle's theory by conducting an experiment that concluded maggots arise from fly eggs, not the meat.

Anton/ie Van Leeuwenhoek (1676)

“Father of Microbiology”, discovered microorganisms through his own powerful microscope made up of single lenses.

John Needham (1748)

Supported spontaneous generation. He observed microbial growth in heated meat broth, and concluded that they originated from the meat. His sterilization methods were inadequate, because he boiled it for a short time, which allowed microbes to grow.

Lazzaro Spallanzani

Challenged Needham by boiling broth in a sealed flask for a longer time, and observed no growth of microbes. He concluded that the air carried germs in Needham’s study.

Theodor Schwann

Passed air through a red-hot tube in a flask of sterilized broth. The heat killed the microbes in the air, and no microbial growth was observed.

Georg Schroeder and Theodor Von Dusch

Conducted the “Cotton-Plug Filtration Experiment”. Concluded that microorganisms in the air cause contamination, and cotton traps them, preventing microbial growth in the broth.

Louis Pasteur (1861)

Provided the definitive disproof of spontaneous generation through his “Swan-Neck Flask Experiment”. Concluded that life does not form spontaneously, microorganisms come from microogranisms.

Cell

The basic structural and functional unit of life forms.

Prokaryotic and Eukaryotic Cells

The two types of cells

Prokaryotic Cell

Simpler, smaller, and lack a membrane-bound nucleus and specialized organelles. Are unicellular (single-celled), example: bacteria

Eukaryotic Cell

Contain a membrane-bound nucleus and specialized organelles. Are multicellular, examples: animals, plants, humans.

Cells - Tissue - Organ - Organ System - Body

The Levels of Biological Organization (smallest to largest)

Robert Hooke (1665)

Discovered cells while examining a cork under a compound microscope. He named these tiny, hollow, honeycomb-like compartments "cells" because they reminded him of the small, simple rooms monks lived in at a monastery.

Antonie Van Leeuwenhoek (1676)

Discovered the first living cells by using powerful, single-lens microscopes of his own design. He observed single-celled organisms (protozoa) in pond water, which he called "animalcules". He also famously documented bacteria, red blood cells, and sperm cells, proving cells were alive.

Robert Brown (1831)

Most famous for discovering the cell nucleus. While examining orchid tissues under a microscope, he identified a distinct, opaque, circular structure within the cells and coined the term "nucleus".

Matthias Schleiden (1838)

He concluded that all plants are composed of cells and that the cell is the basic building block of all plant matter.

Theodor Schwann (1839)

A botanist who concluded that all animals are made of cells.

Rudolf Virchow (1839)

A physician who did research on cancer cells and concluded “Omnis cellula e cellula” → “All cells come from pre-existing cells”.

Classical Cell Theory

A foundational biological principle stating that all living organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

All living organisms are made of one or more cells.

The first principle of the Classical Cell theory.

The cell is the basic structural and functional unit of life.

The second principle of the Classical Cell theory.

All cells arise from pre-existing cells.

The third principle of the Classical Cell theory.

Modern Cell Theory

Add onto the Classical Cell Theory with biological advancements.

The hereditary material contained in the cell is passed on from one cell to another.

The fourth principle of the Modern Cell theory.

The chemical composition and the metabolic processes are generally similar in all cells.

The fifth principle of the Modern Cell theory.

The general chemical and biological functions of cells are intracellular.

The sixth principle of the Modern Cell theory.

The functions that a cell can do rely on the processes and subcellular structures present inside the cell.

The seventh principle of the Modern Cell theory.

Swan-Neck Flask Experiment by Louis Pasteur (1861)

This experiment definitively disproved the theory of spontaneous generation. By boiling nutrient broth in flasks with long, S-shaped necks, he sterilized the liquid while allowing fresh air to enter. Airborne microbes became trapped in the curve, proving that life only arises from pre-existing life.

Francesco Redi’s experiment (1668)

This experiment disproved spontaneous generation. He placed rotting meat in jars: one open (control), one sealed with a cork, and one covered with porous gauze. Maggots only appeared on the meat in the open jar, proving they hatched from fly eggs.

Cotton-Plug Filtration Experiment by Georg Schroeder and Theodor Von Dusch

Introduced the use of cotton-wool plugs to filter air entering microbial culture vessels. Their experiment dealt a powerful blow to the theory of spontaneous generation by proving that dust and microbes could be physically filtered from the air.