HO - 01 Living organisms

Overview of Life

  • Organization and Structure: Life is organized, modular, and layered. It is composed of highly structured repeating classes of molecules and is made of one or more cells. The cell is defined as the basic unit of life.

Characteristics of Life

Energy Requirements

  • Life consumes (obtains) energy essential for maintenance, growth, and reproduction. This includes the process of metabolism.

Interaction with the Environment

  • Organisms interact with their surroundings, responding to changing environmental conditions, seeking prey, and avoiding predators.

Reproduction and Evolution

  • Reproduction: Life reproduces as a mechanism for evolution, occurring over many generations. Evolution is made possible through mutations.

Classification of Living Organisms

Major Categories

  • Flora: Includes plants that don’t move and do not eat.

  • Fauna: Comprises animals that move and consume food.

  • Discussion: Ancient classifications, dating back to Aristotle, placed humans above all creatures but beneath angels.

  • Example Question: Is Spongilla lacustris flora or fauna? Options: A. Flora B. Fauna C. Flora & Fauna D. Synthetic E. Someothing else.

Historical Discoveries in Cell Biology

Robert Hooke (1665)

  • An English polymath who first named the "cell" as the minimal unit of life. He emphasized his discovery and understanding of cells.

Antonie van Leeuwenhoek (1684)

  • Known for his drawings of bacteria in the human mouth. This laid the foundation for understanding microorganisms.

Categories of Cells

Prokaryotes vs. Eukaryotes

  • Classification: Proposed by Édouard Chatton in 1938, this was the first major division in biological systems. Differences between prokaryotes and eukaryotes include:

    • Prokaryotes: no nucleus, loose DNA, generally smaller (around 1 µm).

    • Eukaryotes: larger (at least 5X the size of prokaryotes), containing a nucleus with DNA.

Evolution of Taxonomy

Five Kingdoms of Life

  • Proposed by Robert Whittaker in 1969:

    1. Plantae

    2. Fungi

    3. Animalia

    4. Protista

    5. Monera (Prokaryotes)

Discovery of Archaea (1977)

  • Recognized as a unique group of anucleate single-celled organisms found in extreme environments, such as extremophiles. Pyrococcus furiosus is notable for its optimal growth at 100 °C.

    • Comparison of major groups:

      • Bacteria: Includes Gram-positive bacteria, purple bacteria, and cyanobacteria.

      • Archaea: Includes Methanosarcina, Methanobacterium, and Haloarchaea.

      • Eukarya: Includes animals, plants, fungi, and more.

  • Introduction of Three Domains proposed by Woese, Kandler, and Wheelis (1990):

    1. Bacteria

    2. Archaea

    3. Eukarya

    • Concept of LUCA (Last Universal Common Ancestor).

Linnaean Taxonomy

  • Developed by Carl Linnaeus in 1735. This classification system organizes life and includes hierarchies such as genus and species. For example:

    • Panthera pardus (leopard)

    • Panthera onca (jaguar)

    • Panthera tigris (tiger)

    • Panthera leo (African lion)

Human Evolution

Ancestors

  • Homo neanderthalensis: Commonly known as Neanderthal.

  • Homo sapiens neanderthalensis: A subspecies designation.

  • Homo erectus: Commonly referred to as "upright man".

  • Homo sapiens: Known as "wise man"; modern humans have about 3-4% Neanderthal genes.

Exam Content

  • Key areas to review:

    1. Properties of all living organisms.

    2. Major differences between prokaryotes and eukaryotes.

    3. The five kingdoms of life.

    4. The three domains of life.

    5. Understanding of one’s own genus and species.