Chapter 1: The Study of Life – Foundations of General Biology

Characteristics of Life

Defining Features of Living Organisms

All living things share a set of fundamental characteristics that distinguish them from non-living matter. These features are essential for the maintenance, growth, and reproduction of life.

• Order: Living organisms exhibit complex but ordered organization.

• Energy Processing: Organisms obtain and use energy (e.g., consuming food) to power activities and chemical reactions.

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

• Evolutionary Adaptation: Populations evolve over generations through adaptations that enhance survival and reproduction.

• Response to the Environment: Organisms detect and respond to environmental stimuli.

• Regulation: Internal mechanisms regulate an organism’s internal environment (e.g., thermal regulation in mammals).

• Reproduction: Organisms produce offspring, passing on genetic material to the next generation.

Important Terminology

Key Concepts in Scientific Inquiry

• Hypothesis: A testable statement that explains a specific observation. Example: "If plants receive more sunlight, then they will grow faster."

• Theory: A broad explanation for a general phenomenon, supported by a large body of evidence. Example: The theory of evolution by natural selection.

• Experiment: A controlled procedure to test a hypothesis, often involving manipulation of variables and observation of outcomes.

• Prediction: A statement about what will happen if a hypothesis is correct (often in "if...then..." format).

Additional info: A null hypothesis predicts no effect or difference, serving as a baseline for comparison.

Types of Theories

Major Biological Theories

• Cell Theory: All living organisms are composed of cells.

• Theory of Evolution by Natural Selection: Explains the origin of species and adaptation through differential survival and reproduction.

• Chromosome Theory of Inheritance: Describes how genetic information is transmitted from one generation to the next via chromosomes.

Life is Cellular and Replicates through Cell Division

Discovery and Implications of Cell Theory

• Robert Hooke (1665) observed small compartments in cork, naming them "cells." Anton van Leeuwenhoek later observed single-celled organisms ("animalcules").

• All organisms are made up of cells, and all cells arise from preexisting cells (cell division).

• Pasteur’s experiment disproved spontaneous generation, showing that cells do not arise from non-living matter.

Example: Pasteur’s swan-neck flask experiment demonstrated that sterilized broth remained free of cells unless exposed to preexisting cells from the air.

Life Replicates through Cell Division

Principles of Cellular Reproduction

• Cells must replicate for life to persist.

• All cells in multicellular organisms originate from preexisting cells and are connected by a common lineage.

• Early life likely arose from non-living molecules via chemical evolution.

The Expression and Transmission of Genetic Information

Genetic Material and Its Role in Life

• DNA (Deoxyribonucleic Acid): The molecule that stores genetic information in all living cells.

• Double Helix: DNA consists of two strands made up of four types of nucleotides: A, T, C, G.

• Genes: Segments of DNA that encode instructions for building proteins and regulating cellular processes.

• DNA is copied (replicated) with high accuracy, but mutations can occur, leading to genetic variation.

• Mutations in DNA sequence can result in changes in proteins, affecting an organism’s traits and potentially leading to evolution.

Additional info: Heritable variations in DNA are the basis for evolution by natural selection.

Information and Required Energy

• Cells require energy to carry out chemical reactions and maintain organization.

• Organisms acquire energy in various ways, such as consuming food or photosynthesis.

The Central Dogma

Flow of Genetic Information

• The central dogma describes the flow of information from DNA to RNA to protein.

• DNA is transcribed into RNA, which is then translated into proteins.

$\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$

Life Evolves

Evolution and Natural Selection

• Darwin and Wallace proposed that species are related by common ancestry and change over time.

• Evolution is defined as a change in the characteristics of a population over time.

• Population: A group of individuals of the same species living in the same area at the same time.

• Descent with modification: Species change and diversify from common ancestors.

Natural Selection

Mechanism of Evolution

• Natural selection explains how evolution occurs.

• Two conditions for natural selection:

  • Individuals in a population vary in heritable traits.

  • Some traits help individuals survive and reproduce more than others (increase fitness).

• Natural selection acts on individuals, but evolution affects populations.

• Speciation: The formation of new species from existing populations.

Finches on Galapagos Island

Example of Natural Selection in Action

• Finches with small, soft seeds available due to increased rainfall had higher fitness if they had small, pointed beaks.

• Beak shape and size are adaptations that increase fitness in specific environments.

Tree of Life

Classification and Phylogeny

• The Tree of Life represents genealogical relationships among species, tracing back to common ancestors.

• Three major domains of life:

  • Bacteria

  • Archaea

  • Eukarya

• Phylogeny: The evolutionary history and relationships among species.

• Phylogenetic Tree: Diagram showing evolutionary relationships; branches that share recent ancestors represent closely related species.

Taxonomy

Classification of Organisms

• Taxonomy is the science of naming and classifying organisms.

• Major taxonomic ranks:

  • Domain: Largest group (Bacteria, Archaea, Eukarya)

  • Phylum: Major lineage within a domain

  • Genus: Group of closely related species

  • Species: Individuals that regularly breed together and are distinct from other groups

Characteristics of a Good Experimental Design

Principles for Reliable Scientific Experiments

• Use of a control group for comparison.

• Experimental conditions must be constant across groups.

• Repeating tests ensures reproducibility.

• Sample size should be sufficiently large to ensure statistical validity.

• Independent and dependent variables must be clearly defined.

• Confounding variables should be controlled or standardized (e.g., temperature, light, age, health, weather).