Introduction to Biology: Exploring Life and Scientific Principles

Biology: Exploring Life

1.1 What is Life?

Biology is the scientific study of life. To understand what constitutes life, biologists identify several key properties that all living things share.

• Order: Highly ordered structure that typifies life.

• Reproduction: The ability of organisms to reproduce their own kind.

• Growth and Development: Consistent growth and development controlled by inherited DNA.

• Energy Processing: Use of chemical energy to power an organism’s activities and chemical reactions.

• Regulation: Ability to control an organism’s internal environment within limits that sustain life (homeostasis).

• Response to the Environment: Ability to respond to environmental stimuli.

• Evolutionary Adaptation: Adaptations evolve over many generations, as individuals with traits best suited to their environments have greater reproductive success and pass their traits to offspring.

Homeostasis is the maintenance of a stable internal environment. It involves:

• Metabolism: Life-sustaining chemical reactions, including:

  • Catabolism: Breakdown of molecules to obtain energy.

  • Anabolism: Synthesis of all compounds needed by the cells.

Living vs. Non-living

Living things differ from non-living things in several fundamental ways:

• Order: Living things have organized structures, such as proteins.

• Reproduction: Living things can reproduce, non-living things cannot.

• Living things grow, utilize energy, respond to stimuli, maintain homeostasis, and adapt.

• Non-living things do not exhibit these characteristics.

1.2 Biologists Arrange the Diversity of Life into Three Domains

Diversity is a hallmark of life. Biologists have identified about 1.8 million species, with estimates ranging up to 100 million or more. Taxonomy is the branch of biology that names species and classifies them into a hierarchy of broader groups: genus, family, order, class, phylum, and kingdom.

Life is classified into three domains:

• Bacteria: Prokaryotic, most diverse and widespread, peptidoglycan cell walls, some cause disease (e.g., Escherichia coli, Staphylococcus aureus).

• Archaea: Prokaryotic, often live in extreme environments (e.g., halophiles, thermophiles, methanogens), lack peptidoglycan in cell walls.

• Eukarya: Eukaryotic cells, include protists, fungi, plants, and animals.

Domain	Cell Type	Examples	Key Features
Bacteria	Prokaryotic	E. coli, S. aureus	Peptidoglycan cell wall, diverse habitats
Archaea	Prokaryotic	Halophiles, thermophiles	Extreme environments, unique membrane lipids
Eukarya	Eukaryotic	Plants, animals, fungi, protists	Membrane-bound organelles, multicellularity common

Kingdoms within Eukarya:

• Protists: Mostly single-celled, diverse (e.g., amoeba, paramecium, algae).

• Fungi: Mushrooms (multicellular), yeast (single-celled), decomposers, cell wall of chitin.

• Plantae: Multicellular, photosynthetic, cell wall of cellulose.

• Animalia: Multicellular, no cell wall, mobile.

All domains have cells with:

• Plasma membrane

• DNA

• Cytoplasm

• Ribosomes

1.3 Life’s Hierarchy of Organization: New Properties Emerge at Each Level

Biological organization unfolds as follows:

• Biosphere: All environments on Earth that support life.

• Ecosystem: All organisms in a particular area and their physical environment.

• Community: All organisms living in a particular ecosystem.

• Population: All individuals of a species in a specific area.

• Organism: An individual living thing.

• Organ System: Several organs that cooperate in a specific function.

• Organ: Structure composed of tissues.

• Tissue: Group of similar cells performing a specific function.

• Cell: Fundamental unit of life.

• Organelle: Membrane-enclosed structure within a cell.

• Molecule: Cluster of atoms held together by chemical bonds.

Emergent properties are new properties that arise at each step upward in the hierarchy of life, due to the arrangement and interactions among component parts.

1.4 What is Science?

Science is a way of knowing about the world based on inquiry and evidence. Scientists:

• Make observations

• Form hypotheses (proposed explanations for observations)

• Test hypotheses

• Utilize data

• Form theories (broader in scope than hypotheses, supported by a large body of evidence)

Types of Data:

• Qualitative: Descriptive

• Quantitative: Numerical measurements

Types of Reasoning:

• Inductive reasoning: Makes generalizations based on a large number of specific observations.

• Deductive reasoning: Flows from general premises to specific results.

1.5 Hypotheses Can Be Tested Using Controlled Experiments

In controlled experiments, researchers manipulate one component in a system and observe the effects. Key terms:

• Independent variable: The factor that is changed or manipulated.

• Dependent variable: The factor that is measured or observed.

• Control group: The group that does not receive the experimental treatment.

• Experimental group: The group that receives the treatment.

Experiments should differ by only one factor to ensure valid results.

1.6 Hypotheses Can Be Tested Using Observational Data

• Scientists can test hypotheses about evolutionary relationships using physical similarities and DNA sequences.

• Recent studies use DNA to clarify relationships among species.

1.7 The Process of Science is Repetitive, Nonlinear, and Collaborative

Science involves exploration, analysis, feedback, and societal benefits. It is a collaborative and iterative process.

1.8 Biology, Technology, and Society are Connected in Important Ways

• Science seeks to understand natural phenomena.

• Technology applies scientific knowledge for specific purposes.

• Both are interdependent; advances in one often benefit the other.

Five Unifying Themes in Biology

• Evolution

• Information

• Structure and function

• Energy and matter

• Interactions

1.11 Theme: Life Depends on the Flow of Information

All cells have DNA, the chemical substance of genes. Genes are units of inheritance that transmit information from parents to offspring, grouped into chromosomes, and control cell activities.

• DNA is composed of four kinds of building blocks (nucleotides) forming a double helix.

• The sequence of nucleotides encodes genetic information.

1.12 Theme: Structure and Function are Related

The structure of biological molecules and organisms is closely related to their function. For example, hemoglobin’s structure enables it to transport oxygen in blood.

1.13 Theme: Life Depends on the Transfer and Transformation of Energy and Matter

Living organisms interact with their environment, exchanging energy and matter. In most ecosystems:

• Producers (autotrophs): Make their own food (e.g., plants via photosynthesis).

• Consumers (heterotrophs): Eat plants and other animals.

• Decomposers (saprobes): Recycle nutrients by breaking down dead organisms.

Heterotrophs can be further classified as:

• Herbivores: Eat only plants.

• Carnivores: Eat only animals.

• Omnivores: Eat both plants and animals.

• Detritivores: Consume dead plant/animal material.

1.14 Theme: Life Depends on Interactions Within and Between Systems

Biological systems are complex and involve interactions at many levels. Systems biology is an approach to understanding the larger picture by putting together the pieces of how parts interact within a biological system.