Organisms: Shared Characteristics

Introduction

All living organisms share several fundamental characteristics that distinguish them from non-living matter. Understanding these traits is essential for studying biology at the cellular and molecular levels.

• Cells: The basic unit of life; all organisms are made up of one or more cells.

• Replication: The ability to reproduce and make copies of themselves.

• Evolution: Populations of organisms change over time through genetic variation and natural selection.

• Information: Organisms store and process hereditary information, primarily in the form of DNA within chromosomes.

• Energy: All living things acquire and use energy to maintain order and support life processes.

Example: Humans have been present on Earth for approximately 100,000 years, as determined by written and archaeological records.

Key Concepts in Biology

Three Major Theories

Modern biology is built upon three foundational theories that explain the nature and diversity of life.

• Cell Theory: All living organisms are composed of cells, and all cells arise from pre-existing cells.

• Theory of Evolution by Natural Selection: Species evolve over time due to heritable variation and differential reproductive success.

• Chromosome Theory of Inheritance: Genetic information is stored in chromosomes and passed from one generation to the next.

Additional info: These theories provide the framework for understanding biological processes and relationships among organisms.

Microscopy and Discovery of Cells

Historical Development

The invention of the microscope was pivotal in the discovery of cells and the development of cell theory.

• Robert Hooke (1664): Observed cells in cork, describing them as "cellulae" resembling monastery cells.

• Anton van Leeuwenhoek (1684): Improved microscope design and observed "animalcules" (single-celled organisms).

Example: Hooke's and Leeuwenhoek's observations laid the foundation for the understanding that all organisms are made of cells.

Cell Theory

Principles and Evidence

Cell theory states that all living things are composed of cells and that all cells arise from pre-existing cells.

• All organisms are made of cells: This was confirmed through microscopic observations.

• All cells come from pre-existing cells: Proven by Louis Pasteur's experiments, which refuted the hypothesis of spontaneous generation.

Example: Pasteur's swan-neck flask experiment demonstrated that microorganisms do not arise spontaneously but from other microorganisms.

Theory of Evolution by Natural Selection

Darwin and Wallace's Contributions

Charles Darwin and Alfred Wallace independently proposed the theory of evolution by natural selection, explaining how species change over time.

• Population: Species consist of populations of individuals with varied traits.

• Heritable Variation: Traits are inherited and can affect reproductive success.

• Natural Selection: Individuals with advantageous traits are more likely to survive and reproduce, leading to changes in populations over generations.

Example: Selective breeding in domesticated animals, such as breeding larger chickens, demonstrates artificial selection, a process analogous to natural selection.

Life Processes: Information and Inheritance

Genetic Information

Life processes depend on the storage, transmission, and expression of genetic information.

• Genes: Units of hereditary information located on chromosomes.

• Chromosomes: Structures within cells that contain DNA and carry genetic information from one generation to the next.

Additional info: The chromosome theory of inheritance was proposed in 1902 by Sutton and Boveri, linking Mendelian genetics to cellular structures.

Spontaneous Generation vs. Cell Theory

Historical Hypotheses

Spontaneous generation was the hypothesis that living organisms could arise from non-living matter. This idea was disproven by scientific experiments.

• Spontaneous Generation: Hypothesis that life could arise from non-living materials (e.g., maggots from meat).

• Disproven by Pasteur: Demonstrated that microorganisms arise from other microorganisms, not spontaneously.

Example: Pasteur's experiment with broth in swan-neck flasks showed that sterilized broth remained free of microorganisms unless exposed to existing microbes.

Summary Table: Major Theories in Biology

Key Equations and Concepts

• Natural Selection: Change in frequency of traits in a population over time.

• Genetic Information: Transmission of DNA from parent to offspring.

Equation:

Additional info: This equation is a simplified representation of how trait frequencies can change due to selection.