Properties of Life and Classification of Organisms
Introduction to the Properties of Life
I. The Properties of Life
A. Fundamental Properties of Life – Figure 1.4
Cellular Organization
All living things (organisms) are made of one or more cells.
Organisms can be classified based on their cellular structure:
Unicellular: Organisms made of one cell.
Multicellular: Organisms made of more than one cell.
The Cell Theory states: a. Living organisms are made of one or more cells. b. New cells are formed by the division of preexisting cells.
This division is often followed by the fusion of cells (fertilization).
All cells are surrounded by a plasma membrane, a barrier that controls the entry and exit of substances.
Energy and Metabolism
Living organisms import matter for building structures (growth or repair) and as a source of energy (metabolism).
Details of Metabolism:
Metabolism encompasses all chemical reactions within an organism and the energy transformations.
It includes:
Anabolic Processes: Consume energy to create complex molecules from simpler ones.
Example: Photosynthesis - Uses energy from sunlight to convert CO2 and H2O into glucose.
Catabolic Processes: Release energy by breaking down complex molecules.
Example: Cellular Respiration - Harvests energy from glucose breakdown to perform cellular work.
Response to Environmental Changes
Living organisms exhibit sensitivity and can respond to environmental stimuli.
Human senses exemplify this response mechanism.
Regulation and Homeostasis
Organisms possess regulatory mechanisms to control internal processes (regulation) and to maintain a stable internal environment (homeostasis).
Homeostasis: Keeps internal conditions stable (e.g., body temperature, water/solute balance, nutrient levels, oxygen, waste management), even amidst external changes.
Homeostasis necessitates careful control and coordination of organ systems using information from the nervous and endocrine systems.
Growth and Development
Growth: Involves the production of more or larger cells.
Development: Refers to systematic, gene-directed changes as organisms grow and mature.
Reproduction
Reproduction requires cell division to produce offspring that resemble their parents, influenced by the transfer of parental genes.
Genes, which are made of DNA, store the needed information for cell structure and function.
Prior to division, DNA is copied to ensure each new cell has a complete genetic blueprint.
The concept of heredity pertains to the transmission of traits from parents to offspring.
Biological Evolution
Organisms exist in groups known as populations that can evolve over generations in response to environmental changes.
This process is termed biological evolution through natural selection.
B. The Levels of Organization of Life – Figure 1.3
Living organisms display a highly organized structure, which can be examined at multiple levels.
Levels of Organization:
Subatomic Particles: Protons, neutrons, electrons (constitute atoms).
Atoms: The basic unit of matter.
Molecules: Composed of atoms joined by chemical bonds.
Macromolecules: Large molecules formed from smaller subunits.
Organelles: Assemblies of macromolecules functioning in cells (details in Chapter 4).
Cells: Basic unit of life, surrounded by the plasma membrane and containing organelles in a cytosol solution.
Tissues: Groups of cells working together for a specific function.
Organs: Composed of groups of tissues executing particular tasks.
Organ Systems: Combinations of organs functioning together.
Organisms: Formation of all organ systems yielding complex multicellular entities.
Population: A group of the same species residing in a particular area.
Species: All populations of a particular organism that can interbreed and produce viable and fertile offspring.
Community: All populations of different species cohabitating in an area.
Ecosystem: The interaction of communities with their non-living environment.
Biosphere: The entirety of ecosystems across the Earth.
These levels can also be grouped into three overarching categories:
Cellular Level: Subatomic particles → Atoms → Molecules → Organelles → Cells.
Organismal Level: Tissues → Organs → Organ Systems → Organisms.
Populational Level: Populations → Species → Communities → Ecosystems.
The course will predominantly focus on the cellular and species levels.
C. Emergent Properties
As one ascends organizational levels, new properties emerge that are absent in simpler systems.
Example: A television can display images and produce sound, yet the individual components cannot perform these functions alone.
The property of life emerges from the intricate organization of simpler matter into more complex forms.
Studying life is challenging due to this complexity; isolating components may lead to the disappearance of the very properties of interest.
Experimental biology often employs reductionism to investigate simpler particles, but it is crucial to remember that the arrangement of these components permits the emergence of even more complex processes.
D. Organisms as Open Systems
Organisms are considered open systems because they exchange matter and energy with their environment.
In contrast, a closed system does not engage in such exchanges and is primarily hypothetical in nature.
II. Life is Diverse, Yet Unified
A. General
Diversity encompasses the multitude of life forms, while unity pertains to commonalities among these forms (e.g., shared life properties and genetic material like DNA).
Biological evolution serves as a prime illustration of this unity.
Students should grasp the implications of Figures 1.5, 1.6, and 1.7 mentioned in lectures, and understand the differences between vertical evolution and horizontal gene transfer.
B. The Classification of Life
The system of classifying organisms is termed taxonomy.
General overview: All organisms comprise cells, which can be categorized into two primary types:
Prokaryotic Cells: Simplistic and ancient; includes two domains:
Domain Bacteria: Unicellular prokaryotes residing in various environments.
Domain Archaea: Unicellular prokaryotes adapted for extreme environments (e.g., hot springs).
Eukaryotic Cells: More complex organisms, inclusive of the domain Eukarya, which are presumed to have evolved from prokaryotes.
Specifics about domains:
Domain Bacteria: Mostly unicellular, found in diverse habitats.
Example: Escherichia coli, a bacterium demonstrating adaptability.
Domain Archaea: Unicellular prokaryotes thriving in extreme conditions.
Example: Methanosarcina mazei, an archaean.
Domain Eukarya: Comprises unicellular and multicellular forms with specialized internal functions categorized into:
Kingdom Plantae: Multicellular organisms capable of photosynthesis.
Kingdom Fungi: Organisms with cell walls that absorb organic material without photosynthesis.
Kingdom Animalia: Multicellular organisms that require ingestion of food.
C. Figures Related to Taxonomy:
Each kingdom under the domain Eukarya showcases variations in structure and function:
Protists: Unicellular/small multicellular, diverse feeding practices (e.g., Paramecium, a protozoan).
Plants: Include algae, flowering plants, and exhibit photosynthesis (e.g., Passiflora).
Fungi: Includes molds and mushrooms, with a focus on decomposing organic material.
Animals: Diverse forms, all requiring food ingestion (e.g., Vulpes, a red fox).
Taxonomic Grouping and Classification Tables
Detailed tables outline various classifications including their approximate species counts and evolutionary timelines.
Notable classifications:
Domain Eukarya shows a divergence at about 2,000 million years ago with over 5 million modern species.
Kingdom Animalia appeared around 600 million years ago with over 1 million species.
Kingdom Plantae and its evolution also imply significant diversification.
Specifying organisms requires full binomial nomenclature (e.g., Homo sapiens for humans) to avoid ambiguity in classification.