Unit 4 origin of life and taxonomy
Summary: Origin of Life and Taxonomy
This content provides a comprehensive overview of the origin of life theories, characteristics of life,
cell theory, evolutionary concepts, and the modern taxonomy classification system. It explores
molecular biology fundamentals, historical scientific experiments, and the classification hierarchy
from domains down to species.
Origin of Life
● DNA is Universal:
All known living organisms share the same genetic code structure, primarily using DNA for
genetic information storage. Some viruses use RNA but similarly encode genetic information.
The universality of DNA suggests that all life forms share common ancestors.
● Theories Explaining Life’s Origin:
Various hypotheses attempt to explain the formation of biomolecules and the emergence of
simple cells, including:
● Lightning theory
● Community Clay theory
● Deep Sea Vents hypothesis
● Ice World model
● RNA World hypothesis
● Panspermia (life originating from outer space)
● Spontaneous Generation:
An outdated hypothesis proposing life arose from non-living matter. It was disproved by
scientists such as Francesco Redi and Louis Pasteur through experiments involving flies,
demonstrating that life arises from existing life.
● Miller-Urey Experiment:
Not detailed here but referenced as a foundational experiment simulating early Earth
conditions to test organic molecule formation.
Characteristics of Life
, Unit 4 origin of life and taxonomy
Life is defined by several essential criteria, commonly remembered with the acronym D R C R O M A
G:
Characteristic Description
DNA/Genetic Material Contains hereditary information
Respond to Stimuli Reacts to internal or external changes
Cells (at least one) Basic unit of life
Reproduction Ability to produce offspring
Obtain and Use Energy Metabolism: chemical reactions sustaining life
Maintain Homeostasis Regulation of internal environment
Adaptation and Evolution Changes in traits and species over time
Growth and Development Increase in size and complexity
● Definitions:
● Stimuli: Internal or external factors triggering responses.
● Metabolism: All chemical reactions in an organism.
● Homeostasis: Maintaining stable internal conditions.
● Adaptation: Traits that enhance survival.
● Evolution: Species change over generations.
Cell Theory
● All living organisms consist of cells.
● Cells are the fundamental unit of life.
● New cells arise only from existing cells.
● A complete cell must have a cell membrane, cytoplasm, and DNA.
Endosymbiotic Theory
● Proposes that some organelles (chloroplasts and mitochondria) originated from free-living
prokaryotic cells that entered into a symbiotic relationship with ancestral eukaryotic cells.
● Evidence supporting this includes:
● These organelles possess their own DNA.
● Their membranes resemble those of bacteria.
Summary: Origin of Life and Taxonomy
This content provides a comprehensive overview of the origin of life theories, characteristics of life,
cell theory, evolutionary concepts, and the modern taxonomy classification system. It explores
molecular biology fundamentals, historical scientific experiments, and the classification hierarchy
from domains down to species.
Origin of Life
● DNA is Universal:
All known living organisms share the same genetic code structure, primarily using DNA for
genetic information storage. Some viruses use RNA but similarly encode genetic information.
The universality of DNA suggests that all life forms share common ancestors.
● Theories Explaining Life’s Origin:
Various hypotheses attempt to explain the formation of biomolecules and the emergence of
simple cells, including:
● Lightning theory
● Community Clay theory
● Deep Sea Vents hypothesis
● Ice World model
● RNA World hypothesis
● Panspermia (life originating from outer space)
● Spontaneous Generation:
An outdated hypothesis proposing life arose from non-living matter. It was disproved by
scientists such as Francesco Redi and Louis Pasteur through experiments involving flies,
demonstrating that life arises from existing life.
● Miller-Urey Experiment:
Not detailed here but referenced as a foundational experiment simulating early Earth
conditions to test organic molecule formation.
Characteristics of Life
, Unit 4 origin of life and taxonomy
Life is defined by several essential criteria, commonly remembered with the acronym D R C R O M A
G:
Characteristic Description
DNA/Genetic Material Contains hereditary information
Respond to Stimuli Reacts to internal or external changes
Cells (at least one) Basic unit of life
Reproduction Ability to produce offspring
Obtain and Use Energy Metabolism: chemical reactions sustaining life
Maintain Homeostasis Regulation of internal environment
Adaptation and Evolution Changes in traits and species over time
Growth and Development Increase in size and complexity
● Definitions:
● Stimuli: Internal or external factors triggering responses.
● Metabolism: All chemical reactions in an organism.
● Homeostasis: Maintaining stable internal conditions.
● Adaptation: Traits that enhance survival.
● Evolution: Species change over generations.
Cell Theory
● All living organisms consist of cells.
● Cells are the fundamental unit of life.
● New cells arise only from existing cells.
● A complete cell must have a cell membrane, cytoplasm, and DNA.
Endosymbiotic Theory
● Proposes that some organelles (chloroplasts and mitochondria) originated from free-living
prokaryotic cells that entered into a symbiotic relationship with ancestral eukaryotic cells.
● Evidence supporting this includes:
● These organelles possess their own DNA.
● Their membranes resemble those of bacteria.
