Introduction to Biomolecular Science: The Science of Life (BMS 102, Section 02R)

Fundamentals of Life

The Science of Life

This topic introduces the foundational concepts that define living organisms and distinguishes them from non-living matter. Understanding these characteristics is essential for studying biology and the unity of life.

• Living Things Fight Against Entropy: - Entropy is the degree of disorder or randomness in a system. According to the second law of thermodynamics, entropy always increases in isolated systems. - Physical and chemical processes tend to move toward lower potential energy and increased disorder. - Living organisms maintain order and organization, actively resisting entropy through metabolic processes. Equation: $\Delta S_{universe} > 0$ (where $S$ is entropy; living systems maintain local order at the expense of increased entropy elsewhere)

• Organization: - Living things maintain a high degree of organization compared to non-living things. - All organisms are composed of membrane-bound cells. - Cells may be further organized into tissues, organs, organ systems, and higher levels such as organisms, populations, communities, ecosystems, biospheres. - Organization requires energy and is maintained by metabolic processes.

• Metabolism: - All organisms acquire and use energy (e.g., sunlight, ATP) and materials to build structure and perform work. - Metabolism refers to the sum of all chemical reactions that occur within an organism. - Key metabolic activities include movement, responsiveness, and homeostasis. Equation: $\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

• Movement: - Living organisms can move, either internally (e.g., transport of molecules) or externally (e.g., locomotion).

• Responsiveness: - Organisms respond to stimuli in their environment, which is essential for survival.

• Homeostasis: - Maintenance of constant internal conditions despite changes in the external environment. - Examples include regulation of body temperature, pH, and water balance.

• Reproduction: - All living organisms are capable of reproduction prior to their demise, ensuring the perpetuation of life. - Reproduction can be sexual or asexual.

• Development: - Organisms develop from small and simple forms to larger and more complex forms. - Includes processes such as healing, aging, and dying.

• Genes and Heredity: - Information for reproduction and development is encoded by genes. - All organisms possess hereditary information in the form of DNA. - Genes replicate faithfully but can mutate, leading to genetic variation. - Genes are passed on to the next generation. Equation: $\text{DNA} \xrightarrow{\text{Replication}} \text{DNA}$

• Diversity and Evolution: - Life is diverse, and evolution is the process by which populations change over time. - Descent with modification means that living things change over generations, leading to adaptation to their environment. - Natural selection acts on heritable variation, resulting in changes in population characteristics. Example: Artificial selection in domesticated species (e.g., selecting kernels with high protein content over generations).

Scientific Method

Understanding Science

Science is a systematic method for understanding the natural world, based on certain foundational assumptions and a logical process of inquiry.

• Assumptions of Science:

  • Causality: Events occur due to natural causes.

  • Uniformity: The laws of nature are constant throughout time and space.

  • Common Perception: All humans perceive natural events in fundamentally the same way, allowing for reliable observations.

• The Scientific Method:

  1. Question: Based on observations.

  2. Hypothesis: A reasonable explanation for the observation.

  3. Prediction: "If my guess is right, and if I do X, then Y will happen."

  4. Experiment: Collect data to test the prediction.

  5. Results: Data will support or refute the hypothesis.

  6. Conclusion: Draw conclusions based on the results.

  Example: If a car won't start on a cold morning, one might hypothesize that the battery is dead, predict that replacing the battery will allow the car to start, and then test this prediction.

Major Theories in Biology

Cell Theory

The cell theory is a central, unifying idea in biology, stating that the cell is the fundamental structural unit in all living organisms.

• All organisms are made of cells.

• Cells arise from pre-existing cells.

• Cells are highly organized compartments:

  • Bounded by a plasma membrane.

  • Contain concentrated chemicals in an aqueous solution.

• Types of Cells:

  • Eukaryotic cells: Have a membrane-bound nucleus.

  • Prokaryotic cells: Do not have a membrane-bound nucleus.

• Pasteur's Experiment: Demonstrated that cells arise from other cells, not by spontaneous generation.

Theory of Evolution by Natural Selection

Evolution explains the diversity of life and how populations change over time through natural selection.

• Species are related by common ancestry.

• Natural selection requires:

  • Variation in heritable characteristics (mutations are necessary).

  • Certain traits help individuals reproduce more successfully in a given environment.

  • These traits become more common in the population over time.

• Artificial Selection: Humans select which individuals reproduce, leading to changes in population characteristics over generations.

Classification of Life

Taxonomy

Taxonomy is the science of classifying living organisms. The system established by Carolus Linnaeus in 1735 is still in use today.

• Hierarchical Classification:

  • Domain

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

• Example (Human Classification):

  • Domain: Eukarya

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Primates

  • Family: Hominidae

  • Genus: Homo

  • Species: sapiens

Table: Comparison of Eukaryotic and Prokaryotic Cells

Feature	Eukaryotic Cells	Prokaryotic Cells
Nucleus	Present (membrane-bound)	Absent
Membrane-bound Organelles	Present	Absent
Examples	Animals, plants, fungi, protists	Bacteria, archaea

Additional info: Academic context and definitions have been expanded for clarity and completeness.