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DEL MUNDO COLEGIO WORLD R SCHOOL ÉCOLE

Biology IB - Cell Biology - Origins of Cells

Issue Date: 2012

Overview of Topics Covered According to International Baccalaureate (IB)

  • 1. Molecules

  • 2. Cells

  • 3. Organisms

  • 4. Ecosystems

Subtopics and Hours Allocated

  • A
      - A1.2 Nucleic Acids (2 hours)
      - A1.1 Water (1 hour)
      - A2.1 Origin of Cells (Higher Level):
        - Common ancestry has given living organisms many shared features while evolution has resulted in the rich biodiversity of life on Earth.
      - A2.2 Cell Structure
      - A2.3 Viruses (4 hours)
      - A3.1 Diversity of Organisms (3 hours)
      - A3.2 Classification and Cladistics (3 hours)
      - A4.1 Evolution and Speciation (4 hours)
      - A4.2 Conservation of Biodiversity (3 hours)

  • B
      - B1.1 Carbohydrates and Lipids (2 hours)
      - B1.2 Proteins (2 hours)
      - B2.1 Membrane & Transport (4 hours)
      - B2.2 Organelles and Compartmentalization (1 hour)
      - B2.3 Cell Specialization (3 hours)
      - B3.1 Gas Exchange
      - B3.2 Transport (2 hours)
      - B3.3 Muscle and Motility (3 hours)
      - B4.1 Adaptation to Environment
      - B4.2 Ecological Niches (3 hours)

  • C
      - C1.1 Enzymes and Metabolism (3 hours)
      - C1.2 Cell Respiration (2 hours)
      - C1.3 Photosynthesis
      - C2.1 Chemical Signalling (4 hours)
      - C2.2 Neural Signalling (3 hours)
      - C3.1 Integration of Body Systems
      - C3.2 Defence against Disease (5 hours)
      - C4.1 Populations and Communities (5 hours)
      - C4.2 Transfers of Energy and Matter (5 hours)

  • D
      - D1.1 DNA Replication (2 hours)
      - D1.2 Protein Synthesis (3 hours)
      - D1.3 Mutation and Gene Editing (3 hours)
      - D2.1 Cell and Nuclear Division
      - D2.2 Gene Expression
      - D2.3 Water Potential (3 hours)
      - D3.1 Reproduction (3 hours)
      - D3.2 Inheritance (2 hours)
      - D3.3 Homeostasis (5 hours)
      - D4.1 Natural Selection (2 hours)
      - D4.2 Stability and Change (4 hours)
      - D4.3 Climate Change (3 hours)

Core Concepts and Theories in Cell Biology

  • There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today.

  • Core Principle to Remember: Chemical Theory + Endosymbiosis + Cell Theory.

Essential Ideas and Understandings

  • Key Knowledge:
      - Cells can only be formed by division of pre-existing cells.
      - The first cells must have arisen from non-living material.
      - The origin of eukaryotic cells can be explained by the endosymbiotic theory.

Applications and Skills

  • Applications:
      - Evidence from Pasteur’s experiments illustrates that spontaneous generation of cells and organisms does not occur on Earth today.

Origins of the First Cells

  • It is theorized that if the first cells arrived on Earth from elsewhere in the universe, they must have originated from non-living materials, leading to the question of their initial formation.

Historical Perspectives on Abiogenesis

  • Anaximander (610-546 BCE): Introduced a systematic philosophical view of the world.

  • Aristotle (384-322 BCE): Conceived the concept of spontaneous generation.

  • Francesco Redi (1626–1697):   - One of the first to refute spontaneous generation (1668).

  • Louis Pasteur (1822-1895):
      - Falsification of spontaneous generation theory through controlled experimentation.   - Methodology and results of Pasteur's experiments showcased that cells arise only from pre-existing cells (Omne vivum ex vivo).

Pasteur's Experiment Overview

  • Experimental Setup:
      - Broth in flask boiled to kill pre-existing microorganisms, creating a sterile environment.
      - As the broth cooled, condensed water sealed the mouth of the flask preventing microbial entry.
      - No growth observed unless the neck was broken, allowing outside air to carry microorganisms.

  • Conclusion:
      - Supporting the law of biogenesis, emergent bacterial growth resulted from external contaminants and not spontaneous generation.

Cell Theory

  • The formulation of Cell Theory by Theodor Schwann, Matthias Schleiden, and Rudolph Virchow includes:   1. All living organisms are composed of cells, either unicellular or multicellular.
      2. The cell is the basic unit of life.
      3. Cells arise from pre-existing cells (Virchow, 1858).

The Origin of Cells and Abiogenesis

  • AbioGenesis Theory:
      - Proposes that the first living entities emerged from nonliving chemicals.

  • Key Claims of Abiogenesis:
      - Over time, non-living molecules underwent synthesis to form simpler organic molecules, which then became polymers and eventually protobionts (cell precursors).

Stages in the Origin of Life

  1. Organic Monomers: Simple organic molecules evolved from inorganic compounds.

  2. Organic Polymers: These monomers assembled into complex polymers.

  3. Protobionts: Enclosure of organic polymers in membranes resulted in the first cell precursors.

  4. True Cells: Protobionts evolved capabilities for self-replication leading to the first true cells and biological evolution.

Miller-Urey Experiment (1953)

  • Overview: Conducted by Stanley Miller and Harold Urey to simulate early Earth conditions and test chemical evolution hypotheses.

  • Methodology:
      - A closed system mimicked early Earth with inorganic materials heated and electrified to stimulate organic reactions.

  • Results: Found traces of amino acids and organic compounds confirming that inorganic chemicals can lead to organic molecules under certain conditions.

Primordial Soup Hypothesis

  • Asserts that Earth’s early atmosphere consisted of water vapor, carbon dioxide, methane, ammonia, and hydrogen gas with no free oxygen.

  • Proposed that energy sources allowed reactions forming organic compounds leading to early lifeforms.

Endosymbiotic Theory

  • The eukaryotic cell's evolution is explained through the endosymbiotic theory, suggesting that early prokaryotic cells were engulfed by ancestral cells leading to organelle formation.

  • Stages of Endosymbiosis:
      1. Ancestral prokaryotic cells developed infoldings forming membranes and eventually a nucleus.
      2. Early eukaryotes engulfed aerobic bacteria, forming mitochondria, and later consumed photosynthetic bacteria, leading to chloroplasts.

Evidence for Endosymbiotic Theory

  • Chloroplasts and mitochondria have their own DNA, reproduce independently by binary fission, and are susceptible to certain antibiotics indicating prokaryotic origins.

  • The variability in DNA and ribosome sizes supports this theory, reinforcing the understanding that eukaryotic cells evolved from prokaryotic ancestors.

Biological Evolution

  • Processes of Evolution:   - Descent from a common ancestor explains the shared chemistry and structure across organisms, while adaptation accounts for biodiversity.

  • The universality of the genetic code supports the common origins of life, with evidence showing the continuity from the earliest cells to all current organisms.

Evolutionary Tree and Timeline of Life

  • The fossil record suggests that the first cells were prokaryotic, with eukaryotic cells evolving from these early organisms.

  • A timeline from the Big Bang to the emergence of life on Earth displays major events along the evolutionary path and explains the evolution of various biological branches across time.

Conclusion

  • These theories present a comprehensive view of life’s origins and evolution connecting molecular, cellular, and organisms’ development through time, reflecting a systemic understanding of biology as an interconnected field of study.