Lecture 1

What is Life?

Defining Life

Biologists define life by a set of characteristics that distinguish living organisms from non-living matter. All living things share certain properties that are used to identify them as alive.

• Organization: Living organisms are highly organized, composed of one or more cells.

• Metabolism: They acquire and use energy and materials from their environment to maintain life processes.

• Homeostasis: Organisms actively maintain stable internal conditions.

• Response to Stimuli: Living things sense and respond to environmental changes.

• Growth and Development: Organisms grow and develop over time, often involving complex changes.

• Reproduction: All living things reproduce, passing genetic information to offspring.

• Evolution: Populations of organisms evolve over generations through genetic changes.

Chemical Basis of Life

All organisms are composed of water, proteins, sugars, and fats, but living organisms are fundamentally different from mere chemicals due to their organization and complexity.

• Elements: Life is made primarily of elements such as carbon, hydrogen, oxygen, nitrogen, and others, which originated from stars ("star stuff" - Carl Sagan).

• Atoms and Molecules: Atoms combine to form molecules, which are organized into cells.

Cellular Organization

Cells: The Basic Unit of Life

All living things are made of cells, which are the smallest units capable of all life functions.

• Unicellular: Organisms consisting of a single cell (e.g., bacteria).

• Multicellular: Organisms composed of many cells (e.g., plants, animals).

• Compartmentalization: Cells have defined volumes and membranes that separate internal components from the external environment.

• Specialization: In multicellular organisms, cells are specialized for specific functions (e.g., tissues, organs).

Structure and Function

The structure of biological systems is closely related to their function. For example, the lungs have millions of tiny sacs (alveoli) that provide a large surface area for gas exchange.

• Example: Alveoli in lungs maximize surface area for efficient oxygen and carbon dioxide exchange.

Metabolism and Homeostasis

Metabolism

Metabolism is the sum of all chemical activities within an organism, including breaking down nutrients and building cellular components.

• Formula: $\text{Metabolism} = \text{Catabolism} + \text{Anabolism}$

Homeostasis

Homeostasis refers to the maintenance of stable internal conditions necessary for life, such as temperature and pH.

• Example: Human body temperature is regulated around 37°C.

Genetic Information and Heredity

DNA: The Genetic Program

DNA (deoxyribonucleic acid) is the molecule that stores genetic information in all living organisms.

• Genes: Units of heredity that transmit information from parent to offspring.

• DNA Alphabet: Four nucleotide bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• Information Flow: DNA sequences encode instructions for cellular functions and development.

Evolution and Scientific Theory

Evolution: The Scientific Theory

Evolution is the process by which populations of organisms change over time. It is supported by extensive scientific evidence and is considered a scientific theory.

• Key Contributors: Charles Darwin and Alfred Russel Wallace.

• Scientific Theory: A well-supported explanation based on evidence; stronger than a hypothesis.

• Natural Selection: Individuals with advantageous traits are more likely to survive and reproduce.

Comparison: Scientific Theory vs. Law

Scientific Theory	Scientific Law
Explanation of phenomena based on evidence	Describes phenomena, often mathematically
Can change with new evidence	Generally fixed and universal
Example: Theory of Evolution	Example: Law of Thermodynamics

Taxonomy and Classification

Domains of Life

Organisms are classified based on evolutionary relationships into three domains:

Domain	Characteristics
Bacteria	Prokaryotic, simple structure, no nucleus
Archaea	Prokaryotic, distinct biochemistry, often extremophiles
Eukarya	Eukaryotic, complex structure, nucleus present, includes multicellular organisms

• Taxonomic Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

• Relatedness: Organisms are grouped based on shared ancestry; closer branches indicate more recent common ancestors.

Diversity and Inclusion in Biology

Valuing All Perspectives

Biology values diversity and inclusion, recognizing that individuals of all backgrounds, beliefs, and identities contribute to the scientific community and learning environment.

• Safe Spaces: Creating environments where all students feel welcome and valued.

• Intersectionality: Understanding and respecting the multiple identities that individuals may hold.

Summary

This guide introduces the foundational concepts of biology, including the definition and characteristics of life, cellular organization, metabolism, heredity, evolution, taxonomy, and the importance of diversity in science. These principles form the basis for further study in biological sciences.