Properties and Organization of Life

Characteristics of Living Organisms

Living organisms share several key properties that distinguish them from non-living matter. Understanding these properties is fundamental to biology.

• Order: Organisms exhibit a complex, organized structure.

• Energy Utilization: Living things take in energy and use it to perform work.

• Response to Environment: Organisms can respond to environmental stimuli.

• Reproduction: Living things have the ability to reproduce and pass on genetic information.

• Homeostasis: Organisms maintain a stable internal environment.

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

Example: Humans maintain a constant body temperature (homeostasis) and reproduce sexually.

Levels of Biological Organization

Life is organized in a hierarchical fashion, from the simplest to the most complex levels.

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

Example: The human heart is an organ composed of muscle tissue, which is made up of cells.

Cells: The Basic Unit of Life

Cells are the fundamental units of life. All living things are composed of cells, which can be classified as prokaryotic or eukaryotic.

• Prokaryotic Cells: Lack a nucleus and most organelles; examples include bacteria and archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles; examples include plants, animals, fungi, and protists.

Example: Escherichia coli is a prokaryotic bacterium, while human cells are eukaryotic.

Classification of Life

Domains and Kingdoms

Organisms are classified into three domains and several kingdoms based on cellular structure and genetic relationships.

• Domains: Bacteria, Archaea, Eukarya

• Kingdoms within Eukarya: Protista, Fungi, Plantae, Animalia

Example: Fungi and plants are kingdoms within the domain Eukarya.

Prokaryotes vs. Eukaryotes

Prokaryotes include organisms in the domains Bacteria and Archaea. Eukaryotes include all organisms in the domain Eukarya.

• Bacteria: Single-celled, lack a nucleus, have cell walls made of peptidoglycan.

• Archaea: Single-celled, lack a nucleus, have unique membrane lipids, often live in extreme environments.

• Eukarya: Cells with a nucleus and organelles; includes animals, plants, fungi, and protists.

Example: Streptococcus (Bacteria), Halobacterium (Archaea), Homo sapiens (Eukarya).

Kingdom Fungi

Fungi are eukaryotic organisms that obtain food by decomposing dead organisms and absorbing nutrients.

• Characteristics: Multicellular (except yeasts), cell walls made of chitin, heterotrophic by absorption.

• Role: Decomposers in ecosystems.

Example: Mushrooms and molds are fungi.

Genetics and Molecular Biology

DNA Structure and Function

DNA (deoxyribonucleic acid) is the molecule that carries genetic information in all living organisms.

• DNA Composition: Made up of nucleotides, each consisting of a sugar, phosphate, and nitrogenous base.

• Genetic Code: The sequence of nucleotides determines the genetic instructions.

Example: Human DNA contains genes that code for proteins.

Ecology and Energy Flow

Producers, Consumers, and Decomposers

Organisms in ecosystems are classified by how they obtain energy.

• Producers: Autotrophs (e.g., plants, algae) that produce food via photosynthesis.

• Consumers: Heterotrophs that eat other organisms.

• Decomposers: Break down dead organisms and recycle nutrients (e.g., fungi, bacteria).

Example: Plants are producers, cows are consumers, and mushrooms are decomposers.

Energy Flow in Ecosystems

Energy flows through ecosystems in a one-way stream, from producers to consumers to decomposers.

• Energy enters as sunlight, is converted by producers, and passed through food chains.

• Each energy transfer is inefficient; some energy is lost as heat.

Equation:

Evolution and Natural Selection

Darwin's Theory of Natural Selection

Natural selection is the process by which organisms with advantageous traits survive and reproduce more successfully.

• Variation: Individuals in a population vary in traits.

• Inheritance: Traits are heritable.

• Differential Survival: Some traits confer advantages in survival and reproduction.

• Adaptation: Over time, advantageous traits become more common.

Example: Antibiotic resistance in bacteria is an example of natural selection.

Evolutionary Adaptations

Adaptations are inherited traits that enhance an organism's ability to survive and reproduce in a particular environment.

• Structural Adaptations: Physical features (e.g., beak shape in birds).

• Behavioral Adaptations: Actions that aid survival (e.g., migration).

Example: Camouflage in insects helps them avoid predators.

The Scientific Method

Steps in Scientific Inquiry

The scientific method is a systematic approach to investigating natural phenomena.

• Observation: Gathering information about phenomena.

• Question: Asking about causes or explanations.

• Hypothesis: A testable, falsifiable explanation.

• Experiment: Testing the hypothesis under controlled conditions.

• Analysis: Interpreting data and drawing conclusions.

• Peer Review: Sharing results for validation.

Example: Testing whether fertilizer increases plant growth by comparing treated and untreated plants.

Hypotheses, Theories, and Laws

Scientific explanations are classified by their scope and evidence.

• Hypothesis: A testable statement about a phenomenon.

• Theory: A broad, well-supported explanation (e.g., theory of evolution).

• Law: A statement describing consistent natural phenomena (e.g., law of gravity).

Example: "All vertebrates have backbones" is a hypothesis that can be tested.

Controlled Experiments

Controlled experiments compare an experimental group to a control group to isolate the effect of a variable.

• Control Group: The group not exposed to the experimental variable.

• Experimental Group: The group exposed to the variable.

• Variable: The factor being tested.

Example: Testing a new drug by comparing treated patients to untreated controls.

Table: Domains and Kingdoms of Life

Table: Levels of Biological Organization

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