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 structure, function, growth, origin, evolution, and distribution of living things.

• Definition: Biology is the study of "life" and living systems.

• Scope: Includes all forms of life, from microscopic bacteria to complex multicellular organisms.

The Characteristics of Life

All living things share certain fundamental characteristics that distinguish them from non-living matter.

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

• Ability to acquire material and energy: Organisms obtain and transform energy and materials from their environment.

• Ability to maintain structure and regulate internal environment: This is known as homeostasis.

• Response to stimuli: Organisms react to changes in their environment.

• Growth: All living things grow during their lifetime.

• Reproduction: Organisms produce offspring, passing on genetic information (DNA).

• Ability to evolve: Populations of organisms change over time in response to environmental changes.

Levels of Biological Organization

The complexity of life is organized into hierarchical levels, each with components that interact to form systems greater than the sum of their parts.

• 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

• Populations

• Community

• Ecosystem

• Biosphere

Acquisition of Material and Energy

Organisms must obtain energy and raw materials to sustain life.

• Heterotrophs: Take in nutrients (food) for raw materials and energy.

• Autotrophs: Use sunlight for energy (photosynthesis) and take in raw materials.

• Metabolism: The sum of all chemical reactions that change raw material and energy into forms needed for maintenance, growth, reproduction, etc.

Homeostasis: Regulation of Internal Environment

Organisms maintain a stable internal environment despite changes in the external environment.

• Homeostasis: The tendency to maintain and regulate internal conditions.

• Examples: Regulation of body temperature, pH, water balance.

Response to Stimuli

Organisms detect and respond to internal and external stimuli.

• Responses can be rapid (e.g., movement) or slow (e.g., growth).

• Some reactions are visible, others are not.

Growth

All living organisms grow during their lifetime, increasing in size and often in complexity.

Reproduction

Living things reproduce to ensure the continuation of their species.

• Sexual reproduction: Involves the combination of genetic material from two parents.

• Asexual reproduction: Offspring arise from a single organism.

• DNA: The genetic blueprint for building offspring.

Evolution

Populations of organisms change over time in response to environmental pressures.

• Adaptation: Survival and reproduction of the fittest members of the population.

• Natural selection: The process by which advantageous traits become more common in a population.

• Mutation: Changes in DNA that can lead to evolutionary changes.

• Speciation: Formation of new species due to evolutionary adaptations.

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

Classification of Living Organisms

Organisms are grouped based on evolutionary relationships and shared characteristics.

• Domains: The largest groups, based on evolutionary relationships discerned from DNA analysis.

• Three domains: Bacteria, Archaea (both prokaryotic), and Eukarya (eukaryotic).

• Kingdoms: Domains are subdivided into kingdoms based on more specific characteristics.

• Binomial nomenclature: Scientific naming system developed by Linnaeus; uses genus and species names (e.g., Homo sapiens).

Scientific Method

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

• Principles:

  1. All events have a natural cause (natural causality).

  2. Natural laws govern natural events.

  3. Natural laws do not change with time or distance.

• Steps of the Scientific Method:

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

  2. Hypothesis: Formulating a testable explanation (e.g., things with greater weight sink in water).

  3. Experiment: Testing the hypothesis (e.g., dropping various objects in water).

  4. Conclusion: Determining if results support the hypothesis; if not, revise the hypothesis.

• Scientific theory: An explanation of natural events based on many observations and experiments.

Example of Scientific Method Application

• Observation: Rocks sink in water; metal bars sink; raybans sink when dropped.

• Hypothesis: Things with greater weight sink in water.

• Experiment: Drop various objects (e.g., 2-pound log, 10 pounds of ice, your best friend) in water.

• Conclusion: Analyze results to support or refute the hypothesis.

Additional info: The scientific method is foundational to all scientific inquiry and is used to develop scientific theories, which are robust explanations supported by extensive evidence.