Unit 1 – Life Starts Small: What is Life? (General Biology Study Notes)

Unit 1 – Life Starts Small

Module 1 pt. I: What is Life?

This module introduces the foundational concepts of biology by exploring the defining characteristics of life, the chemical basis of living organisms, and the central role of evolution in explaining biological diversity and unity.

Defining Life

Characteristics of Living Organisms

Biologists use several criteria to distinguish living things from non-living matter. These characteristics are shared by all known life forms:

• Order: Living things exhibit complex organization, from molecules to cells to tissues and organs.

• Growth and Development: Organisms increase in size and complexity, following specific instructions encoded in their DNA.

• Energy Processing: Life requires energy, which is obtained and transformed through metabolic processes (e.g., photosynthesis, cellular respiration).

• Response to the Environment: Organisms detect and respond to stimuli in their surroundings.

• Evolutionary Adaptation: Populations of organisms change over generations through adaptations that enhance survival and reproduction.

• Regulation: Living things maintain stable internal conditions (homeostasis) despite changes in their environment.

• Reproduction: Life forms produce new individuals, passing genetic information to offspring.

Example: A sunflower grows toward sunlight (response to environment), uses photosynthesis to make food (energy processing), and produces seeds (reproduction).

Levels of Biological Organization

Emergence of Life Properties

The properties of life emerge at specific levels of biological organization, starting from the smallest units:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere

• Cells are the smallest unit that can carry out all life processes.

Additional info: The concept of "emergent properties" refers to new characteristics that arise at each level of organization due to the interactions of components.

Origin and Composition of Life

Formation of Earth and Elements of Life

Life on Earth began approximately 4.6 billion years ago. The universe's formation involved the conversion of subatomic particles into atoms, which then fused to form elements essential for life.

• Major Elements in Living Organisms: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg)

• Trace Elements: Required in very small amounts (e.g., Chromium, Cobalt, Copper, Iron, Manganese, Molybdenum, Selenium, Vanadium, Zinc)

Element	Symbol
Oxygen	O
Carbon	C
Hydrogen	H
Nitrogen	N
Calcium	Ca
Phosphorus	P
Potassium	K
Sulfur	S
Sodium	Na
Chlorine	Cl
Magnesium	Mg

Additional info: These elements form the molecules that make up cells and tissues, such as water, proteins, lipids, carbohydrates, and nucleic acids.

Unity and Diversity of Life

Genetic Basis and Evolution

All living organisms share a common genetic code based on DNA, which serves as the unit of inheritance. The diversity of life arises from variations in DNA sequences.

• DNA: Deoxyribonucleic acid, the molecule that stores genetic information.

• Genes: Segments of DNA that code for specific traits.

• Chromosomes: Structures that organize and carry genes.

• Inheritance: Transmission of genetic information from parents to offspring.

• Variation: Differences in DNA sequences lead to diversity among organisms.

Example: The genetic differences between species, such as humans and chimpanzees, account for their distinct traits.

Evolution: The Central Principle of Biology

Natural Selection and Adaptation

Evolution explains both the unity and diversity of life. Charles Darwin's theory of natural selection describes how populations change over time:

• Descent with Modification: Species evolve from common ancestors, accumulating changes over generations.

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

• Variation: Populations contain individuals with different traits, many of which are heritable.

• Overproduction: More offspring are produced than can survive, leading to competition.

• Adaptation: Traits that enhance survival become more common in the population.

Example: The evolution of beak depth in Galápagos finches during drought conditions, where birds with deeper beaks survived better and passed on their traits.

The Scientific Process

Generating Biological Knowledge

Science advances through a systematic process of inquiry and experimentation:

• Observation: Gathering data about the natural world.

• Hypothesis: A testable statement used to build explanations.

• Experimentation: Testing hypotheses through controlled experiments.

• Theory: A well-substantiated explanation supported by a large body of evidence.

• Predictive Reasoning: Using existing knowledge to make predictions that can be tested.

Example: Scientists measured beak depth in finches before and after a drought to test hypotheses about natural selection.

Additional info: Scientific theories differ from everyday usage; in science, a theory is a comprehensive explanation, not a mere guess.

Summary Table: Defining Features of Life

Feature	Description
Order	Complex organization of living systems
Growth & Development	Increase in size and complexity, guided by DNA
Energy Processing	Acquisition and use of energy for metabolism
Response to Environment	Ability to sense and react to stimuli
Evolutionary Adaptation	Change in populations over time to enhance survival
Regulation	Maintenance of stable internal conditions
Reproduction	Production of new individuals

Key Equations and Concepts

Genetic Inheritance

The transmission of genetic information can be represented as:

$\text{Offspring Genotype} = \text{Combination of Parental Alleles}$

Natural Selection

The change in frequency of a trait in a population over time:

$\Delta p = s \cdot p \cdot (1 - p)$

Where $\Delta p$ is the change in allele frequency, $s$ is the selection coefficient, and $p$ is the initial allele frequency.