Foundations of General Biology: Life, Cells, Genetics, and Classification

Learning Objectives

• Describe the levels of biological organization in their proper order.

• Describe how the flow of energy through organisms and matter cycles within it.

• Explain the three domains of life.

• Describe the Linnaean classification system.

• Explain the scientific method and how science operates in media.

Characteristics of Life

Defining Life

Life is an emergent, replicating system that evolves by natural selection. Living organisms share several key characteristics:

• Cellular Organization: All living things are composed of one or more cells, which are the basic units of life. Cells may be prokaryotic (no nucleus) or eukaryotic (with nucleus).

• Ordered Structure: Living organisms have highly organized structures, such as cellular and subcellular organization.

• Energy Use: Organisms require energy to maintain order. For example, plants use photosynthesis to convert solar energy into chemical energy.

• Growth and Development: Life undergoes growth, which is controlled by DNA regulation of gene expression.

• Response to Environment: Organisms respond to stimuli, regulating homeostasis and adapting to changes.

• Reproduction: Life reproduces, passing on genetic material to offspring, either sexually or asexually.

• Evolution: Populations of organisms evolve over time through natural selection, adapting to their environment.

Viruses: Viruses are not considered living because they cannot reproduce or carry out metabolism independently. They consist of DNA or RNA surrounded by a protein coat and require host cells to replicate.

The Hierarchy of Life

Levels of Biological Organization

Life is organized into a hierarchy, from smallest to largest:

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Each level reveals emergent properties not present at lower levels. For example, tissues are made of cells, but have functions that individual cells do not.

Cell Types: Prokaryotes vs. Eukaryotes

Comparison of Cell Types

Feature	Prokaryotes	Eukaryotes
Nucleus	No nucleus	Has nucleus
Organelles	No membrane-bound organelles	Has membrane-bound organelles
Genetic Material	Single circular DNA molecule	Linear chromosomes
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Genetic Information: Transmission and Expression

Transmission of Genetic Information

Genetic information is stored in DNA (deoxyribonucleic acid). Transmission occurs via:

• Mitosis: DNA is replicated and passed down to each cell, ensuring genetic continuity in somatic cells.

• Meiosis: DNA is passed down to future generations, with genetic material coming from each parent, resulting in genetic diversity in gametes.

Expression of Genetic Information

Genes are heritable units of DNA that encode for proteins. The process of gene expression involves:

• Transcription: Messenger RNA (mRNA) is made from DNA.

• Translation: Proteins are synthesized based on the mRNA code.

• Gene Regulation: Controls when and how much protein is produced.

Gene expression encompasses DNA replication, transcription, and translation.

Energy Transfer in Living Systems

Energy Flow

Life requires the transfer of energy. Plants capture energy from sunlight via photosynthesis, converting it to chemical energy. This energy is transferred through food chains and food webs, and is lost as heat in ecosystems.

• Producers (autotrophs) → Consumers (heterotrophs) → Decomposers

Energy and matter cycle through ecosystems, supporting life at all levels.

Evolution: Change Over Time

Definition and Mechanism

Evolution is the process of biological change in which species accumulate differences from their ancestors. It is driven by natural selection, genetic drift, mutation, and gene flow.

• Natural Selection: Individuals with traits better suited to their environment are more likely to survive and reproduce.

• Adaptation: Traits that enhance survival and reproduction become more common in a population over time.

Linnaean Classification System

Taxonomic Hierarchy

Organisms are grouped based on similarities in morphology, DNA sequence, and biological name. The Linnaean system uses the following ranks:

Rank	Example
Domain	Eukarya
Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Primates
Family	Hominidae
Genus	Homo
Species	Homo sapiens

Mnemonic: "King Philip Came Over For Good Soup" helps remember the order.

The Scientific Process

Steps of the Scientific Method

Science is a systematic way of learning about the natural world. The scientific method involves:

1. Make an observation

2. Form a question

3. Form a testable hypothesis ("If... then...")

4. Conduct an experiment

5. Collect data and observations

6. Report results

• A hypothesis cannot be proven, only supported by evidence.

• Correlation: When factor A changes, so does condition B.

Additional info:

• Emergent properties: New characteristics appear at each level of biological organization.

• Homeostasis: The maintenance of stable internal conditions.

• Domains of life: Bacteria, Archaea, Eukarya.

• Radioactive isotopes: Unstable isotopes that release particles and energy; used in dating and medical imaging.