Introduction to Life on Earth: Characteristics of Living Organisms and Scientific Method

CHAPTER 1: AN INTRODUCTION TO LIFE ON EARTH

What is Biology?

Biology is the science of living organisms and life processes. It seeks to understand the nature of life, its characteristics, and the processes that sustain living things.

Characteristics of Life

To be considered alive, an entity must possess all of the following characteristics:

• Complex, organized structure: Living things are highly organized, with multiple levels of complexity, from subatomic particles to the biosphere.

• Ability to acquire material and energy: Organisms obtain nutrients and energy from their environment. Energy and materials are often transformed and recycled. Heterotrophs take in food for raw materials and energy; autotrophs use sunlight (photosynthesis) and take in raw materials.

• Ability to maintain structure and regulate internal environment: This is called homeostasis, the tendency to maintain stable internal conditions.

• Response to stimuli: Organisms react to external and internal stimuli, leading to changes in their state or behavior.

• Growth: All organisms grow during their lifetime.

• Reproduction: Organisms reproduce their own kind, either sexually or asexually. Genetic information (DNA) is passed to offspring.

• Ability to evolve: Populations of organisms change over time in response to environmental changes, leading to adaptation and sometimes the formation of new species.

Levels of Biological Organization

Biological complexity is organized into hierarchical levels:

• Subatomic particles

• Atoms

• Molecules

• Organelles (not present in prokaryotes)

• Cells

• Tissues (present only in multicellular eukaryotes)

• Organs (present only in multicellular eukaryotes)

• Organ systems (present only in multicellular eukaryotes)

• Multicellular organisms

• Population

• Community

• Ecosystem

• Biosphere

Each level consists of components that interact to create something greater than the sum of the parts.

Metabolism and Energy Transformation

Metabolism refers to all chemical reactions that change raw materials and energy into forms needed for maintenance, growth, reproduction, etc.

• Heterotrophs: Obtain energy by consuming other organisms.

• Autotrophs: Obtain energy from sunlight (photosynthesis) and raw materials.

Homeostasis

Homeostasis is the ability of organisms to maintain stable internal conditions despite changes in the external environment.

• Example: Regulation of body temperature in mammals.

Response to Stimuli

Organisms detect and respond to changes in their environment. Responses can be immediate or gradual.

• Example: Plants bending toward light (phototropism).

Growth

All living organisms increase in size or number of cells during their lifetime.

Reproduction

Reproduction ensures the continuation of a species. It can be sexual or asexual.

• DNA contains genetic information, the blueprint for offspring.

Evolution

Populations of organisms change over time through adaptation and natural selection. Evolutionary changes can lead to the formation of new species.

• Adaptation: Traits that improve survival and reproduction in a given environment.

• Mutation: Changes in DNA that can accumulate over generations.

• Natural selection: Survival and reproduction of the fittest members of a population.

• If evolutionary changes do not occur fast enough to keep up with environmental changes, extinction can occur.

Classification of Living Organisms

Organisms are grouped based on evolutionary relationships. The largest groups are called domains:

Domain	Type	Examples
Bacteria	Prokaryotic	Escherichia coli
Archaea	Prokaryotic	Halobacterium
Eukarya	Eukaryotic	Plants, animals, fungi, protists

Domains are subdivided into kingdoms based on more specific characteristics.

Binomial nomenclature is the system of naming species using two names: genus and species. The genus is capitalized, and the species is lowercase. Scientific names are usually italicized or underlined.

• Example: Homo sapiens

Science and the Scientific Method

Science is a process of discovery based on observation, hypothesis formation, experimentation, and conclusion.

• Natural causality: All events have a natural cause.

• Natural causes obey natural laws.

• Natural laws do not change with time or distance.

The scientific method involves:

1. Observation: Noticing phenomena (e.g., rocks sink in water).

2. Hypothesis: Proposing explanations (e.g., things with weight sink in water).

3. Experiment: Testing hypotheses (e.g., dropping objects in water).

4. Conclusion: Determining if results support the hypothesis.

If supported, the hypothesis may become part of a scientific theory, which is an explanation of natural events based on many observations and experiments.

Key Terms and Definitions

• Biology: The study of living organisms and life processes.

• Homeostasis: Maintenance of stable internal conditions.

• Metabolism: All chemical reactions in an organism.

• Adaptation: Trait that improves survival and reproduction.

• Mutation: Change in DNA sequence.

• Natural selection: Process by which the fittest organisms survive and reproduce.

• Binomial nomenclature: Two-part scientific naming system.

• Scientific method: Systematic approach to scientific inquiry.

Important Equations

• There are no specific mathematical equations in this section, but the following is a general representation of natural selection: $\text{Survival and reproduction} \rightarrow \text{Passing of genes to next generation}$

Additional info: Some examples and definitions have been expanded for clarity and completeness.