Introduction to Biology

Biology: "If it squirms… it’s biology; if it stinks… it’s chemistry; if it doesn’t work… it’s physics; if you can’t understand it… it’s mathematics."

Organization: Living things are organized as cells.
Response to Stimuli: Organisms can respond to environmental changes.
Regulation of Internal Processes: Homeostasis is maintained to regulate internal functions.
Energy Utilization: Organisms use energy to grow.
Metabolism: All living things carry out metabolic processes.
Development: Organisms develop, change, and mature within their lifetime.
Adaptation: Over generations, organisms adapt to their environments.
Reproduction: All forms of life can reproduce.
Genetics and Heredity: Life relies on genetic information to pass traits to offspring.

Hydrogen (H): Smallest and most abundant element in the universe.
Oxygen (O): Exists primarily in the diatomic form (O₂).
Carbon (C): Found in various forms, such as charcoal, graphite, and diamond.
Sulfur (S): Notable for its smell; used in various compounds.
Phosphorus (P): Important in biological molecules, particularly DNA and ATP.
Nitrogen (N): Essential for all living organisms, but certain forms can be toxic.
Potassium (K): Highly reactive; contributes to cellular functions.

The Earth exists in the Solar System's habitable zone where liquid water is possible.
Comparison with other planets:
- Venus: Too hot (+420°C, 95% CO₂ atmosphere).
- Earth: Just right (+15°C, 0.03% CO₂).
- Mars: Too cold (-50°C, mostly CO₂).

Supernatural Creation: Not testable in scientific contexts.
Organic Materials from Comets: Testable hypothesis suggesting meteorites contributed to life's essential elements.
Spontaneous Abiotic Origin: Life emerging spontaneously from non-organic molecules.

Steps to Life's Origin:
1. Abiotic synthesis of small organic molecules.
2. Bonding of these molecules into macromolecules.
3. Packaging macromolecules into protobionts.
4. Origin of self-replicating molecules (possibly RNA).

Building block for life: These molecules may form the foundation of biological complexity such as amino acids, DNA, RNA, and proteins.

Conducted to test the abiotic synthesis of organic molecules.
Conditions mimicked early Earth:
- Water vapor, electrodes for discharging sparks, heated water, reducing atmosphere with gases such as H₂O, N₂, NH₃, CO₂, CO, CH₄, and H₂.
- Resulted in condensation of liquid with complex organic molecules, including amino acids.

Spontaneous Formations:
- Mixed phospholipids could spontaneously form vesicles (microspheres) that are compartmentalized.

Defined as aggregates of abiotically produced molecules enclosed by membranes.
Capable of simple replication and metabolism; maintain an internal chemical environment.

Oldest fossils identified as stromatolites (3.5 billion years old), created by layers of bacteria.
Prokaryotes dominated Earth from 3.5 to 2.1 billion years ago.

Early photosynthetic prokaryotes produced atmospheric oxygen (O₂), leading to the formation of oxidized minerals.
The photosynthesis process reacted with dissolved iron, leading to banded iron formations (2.7 billion years ago).

Took place approximately 2.7 to 2.2 billion years ago.
Resulted in significant changes to Earth's atmosphere, where oxidation became a challenge but also an opportunity for new energy exploitation.

Evidence suggests that the oldest eukaryotic cell fossils date back to 2.1 billion years.
Theory of Endosymbiosis states that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by larger host cells.

Life on Earth most likely originated from non-living materials approximately 3.5 billion years ago. Self-replicating molecules, potentially RNA, may have developed in early environments.
Development of membranes was crucial for allowing these self-replicating molecules to undergo replication and metabolism, thereby leading to the definition of life as we understand it.