Lecture 1: Introduction to Biology

Overview of Biology

• Diversity in Biology: Different universities focus on various aspects of biology.
  • Ecosystem studies
  • Memorization of phyla
  • Organism physiology
• MIT's Perspective: A specific point of view for teaching 7.012 focuses on the organization of life.

Levels of Organization in Life

1. Biosphere

   • Definition: All the ecosystems on Earth functioning as a whole.
   • Diversity: ~10^6 eukaryotic species, many microbial species.
   • Note: This level will not be emphasized in the course.

2. Ecosystem

   • Definition: Interacting communities of organisms (e.g., forests).
   • Components include trees, animals, fungi, etc.

3. Organism

   • Definition: An individual in a species.
   • Focus on physiology and integration of systems within an organism.
   • Example: Human as an organism.

4. Organ

   • Definition: A group of tissues organized to carry out a function.
   • Example: Eye in humans, composed of various tissues.

5. Tissue

   • Definition: Homogeneous groups of cells.
   • Example: Retina in the eye.

6. Cell

   • Definition: Basic unit of life, bounded by a membrane.
   • Example: Photoreceptor cell in the retina.

7. Organelle

   • Definition: Distinct components within a cell.
   • Example: Mitochondria, producing ATP.

8. Molecule

   • Definition: Various types of biological molecules (e.g., DNA, sugars).
   • Example: ATP.

Focus of the Course

• Emphasis on the molecular and cellular levels of organization.
• Aim to identify universal principles across all life forms.
• Understanding commonalities, such as the genetic code and regulatory systems, is prioritized.

Important Dates in the History of Life

• 4.0 billion years ago: Earth cooled; no life existed.
• 3.7 billion years ago: Evidence of the first life (prokaryotic organisms).
  • Early life led to significant atmospheric changes (oxygen).
• 1.5 billion years ago: Emergence of eukaryotic cells through prokaryotic symbiosis.
• 0.5 billion years ago: Multicellular organisms with body plans evolved.
  • Multicellularity led to rapid diversification of body forms.
• 0.005 billion years ago: Appearance of humans.
• 0.00000015 billion years ago: Founding of MIT.

Types of Cells

• Prokaryotic Cells: Primitive cells without a true nucleus.

  • Example: Bacteria.
  • Size: 1 to 2 microns.

• Eukaryotic Cells: Cells with true nuclei and various organelles.

  • Include all animals, plants, and fungi.
  • Size: 10 to 40 microns (1,000 to 60,000 times larger than prokaryotic cells).