General Biology I: Comprehensive Course Review Notes

What is Life and How Do We Study It?

The Scientific Method

The scientific method is a systematic approach used in biology to investigate natural phenomena. It ensures that scientific inquiry is objective and repeatable.

• Steps: Background research, question generation, hypothesis formation, predictions, observation, results, and interpretation.

• Variables: Independent variable (manipulated), dependent variable (measured), and controlled variables (kept constant).

• Data Interpretation: Understanding graphs and tables is essential for analyzing results.

Properties and Organization of Life

Living organisms share several defining properties and are organized in hierarchical levels.

• Properties: Order, response to stimuli, reproduction, adaptation, growth and development, regulation (homeostasis), and energy processing.

• Organization: Atoms & molecules → cells → tissues → organs → organ systems → organisms → populations → communities → ecosystems → biosphere.

Classification of Life

Biologists classify life using hierarchical systems and phylogenetic trees to reflect evolutionary relationships.

• Linnaean Classification: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Phylogeny: Evolutionary trees show relationships among species based on common ancestry.

The Origin and History of Life

The origin of life involves chemical evolution, and the history of life traces major evolutionary events.

• Origin of Life: Key steps include the formation of simple molecules, polymers, protocells, and the emergence of self-replicating systems.

• Evidence: Laboratory simulations (e.g., Miller-Urey experiment), fossil records, and molecular data.

• Endosymbiotic Theory: Explains the origin of mitochondria and chloroplasts in eukaryotic cells via symbiosis with prokaryotes.

Cells, Genetics, and Evolution

Cells

Cells are the basic units of life, with two main types: prokaryotic and eukaryotic.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., Bacteria, Archaea).

• Eukaryotic Cells: Have a nucleus and organelles (e.g., plants, animals, fungi, protists).

• Cell Structures: Nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, plasma membrane, etc.

Mitosis

Mitosis is the process by which somatic cells divide, producing two genetically identical daughter cells.

• Stages: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.

• Role: Growth, repair, and asexual reproduction in multicellular organisms.

Meiosis

Meiosis produces gametes (sperm and eggs) with half the chromosome number of the parent cell, enabling sexual reproduction.

• Stages: Meiosis I (separates homologous chromosomes), Meiosis II (separates sister chromatids).

• Genetic Variation: Crossing over and independent assortment increase diversity.

• Comparison: Mitosis produces identical cells; meiosis produces genetically unique cells.

Mendelian Genetics

Gregor Mendel's experiments with pea plants established the basic principles of inheritance.

• Test Cross: Determines genotype by crossing with a homozygous recessive individual.

• Monohybrid Cross: Examines inheritance of a single trait.

• Dihybrid Cross: Examines inheritance of two traits simultaneously.

• Laws: Law of Segregation, Law of Independent Assortment.

History of Evolutionary Thought

Evolutionary theory has developed over centuries, with key contributions from Lamarck, Darwin, and Wallace.

• Lamarck: Proposed inheritance of acquired traits (later disproven).

• Darwin & Wallace: Proposed natural selection as the mechanism for evolution.

• Natural Selection: Differential survival and reproduction of individuals due to differences in phenotype.

Evidence for Evolution

Multiple lines of evidence support the theory of evolution.

• Categories: Fossil record, comparative anatomy, embryology, molecular biology.

• Natural Selection vs. Evolution: Natural selection is a mechanism; evolution is the change in populations over time.

Mechanisms of Evolution

Evolution occurs through several mechanisms, each affecting genetic variation and fitness.

• Mechanisms: Natural selection, genetic drift, gene flow, mutation, non-random mating.

• Fitness: Some mechanisms increase fitness (natural selection), others may decrease it (genetic drift).

Population Genetics (Hardy-Weinberg Equilibrium)

Population genetics studies allele frequencies and how they change over time. The Hardy-Weinberg Equilibrium (HWE) provides a null model for genetic variation in populations.

• Equations:

  • $p + q = 1$

  • $p^2 + 2pq + q^2 = 1$

• Conditions for HWE: No mutations, random mating, no natural selection, large population size, no gene flow.

• Deviations: Indicate evolution is occurring.

Ecology

Ecological Interactions

Ecology is the study of interactions between organisms and their environments.

• Types of Interactions: Competition, predation, mutualism, commensalism, parasitism, amensalism, facilitation.

• Climate Change: Alters species distributions, ecosystem function, and biodiversity.

Form and Function: Microorganisms, Plants, and Animals

Microorganisms

Viruses

• Living or Non-living? Viruses lack cellular structure and metabolism but can reproduce inside host cells.

• Reproduction: Attach to host, inject genetic material, hijack host machinery to produce new viruses.

Bacteria

• Genetic Diversity: Rapid reproduction, mutation, horizontal gene transfer (transformation, transduction, conjugation).

• Roles: Decomposers, nitrogen fixation, pathogens, symbionts.

Archaea

• Similarities to Bacteria: Prokaryotic cell structure.

• Differences: Unique membrane lipids, gene expression machinery more similar to eukaryotes.

• Roles: Extremophiles, methanogens, some are beneficial or harmful.

Protists

• Importance: Primary producers, decomposers, pathogens.

• Classification: Highly diverse; grouped by mode of nutrition, movement, and life cycle.

Fungi

• Importance: Decomposers, symbionts (mycorrhizae), pathogens.

• Major Groups: Chytrids, zygomycetes, glomeromycetes, ascomycetes, basidiomycetes.

• Roles: Food production, antibiotics, plant diseases.

Plant Biology

Plant Form and Function

• Anatomical Features: Roots, stems, leaves, vascular tissues (xylem, phloem), reproductive organs.

• Carbohydrate Production: Photosynthesis in chloroplasts converts CO2 and H2O into glucose and O2.

Plant Nutrition and Transport

• Autotrophic: Plants produce their own food via photosynthesis.

• Nutrients Needed: Macronutrients (N, P, K, etc.), micronutrients (Fe, Zn, etc.).

• Uptake: Roots absorb water and minerals; symbiotic relationships with bacteria and fungi aid nutrient acquisition.

Plant Evolution

• Adaptations for Land: Cuticle, stomata, vascular tissue, seeds, flowers.

• Transport: Xylem moves water/minerals; phloem transports sugars.

Animal Biology

Homeostasis

• Definition: Maintenance of a stable internal environment.

• Negative Feedback: Counteracts changes (e.g., body temperature regulation).

• Positive Feedback: Amplifies changes (e.g., blood clotting, childbirth).

Thermoregulation and Osmoregulation

• Thermoregulation: Endotherms (regulate body temp internally), ectotherms (depend on environment).

• Homeotherms: Maintain constant body temp; poikilotherms: body temp varies.

• Osmoregulation: Regulation of water and solute balance; animals may be hyperosmotic or hyposmotic to their environment.

Respiration

• Gas Exchange: Occurs across specialized surfaces (gills, lungs, skin).

• Comparative Respiration: Fish (gills), amphibians (skin/lungs), birds (air sacs), mammals (lungs).

• Efficiency: Countercurrent exchange in fish gills is highly efficient.

• Control: Breathing in humans is regulated by the brainstem in response to CO2 levels.

Circulation

• Open vs. Closed Systems: Open systems (hemolymph bathes organs directly); closed systems (blood confined to vessels).

• Double Circulation: Separates pulmonary and systemic circuits, increasing efficiency (seen in mammals and birds).

• Cardiac Cycle: Sequence of contraction (systole) and relaxation (diastole) of the heart chambers.

Mechanism	Effect on Genetic Variation	Effect on Fitness
Natural Selection	Can increase or decrease	Usually increases
Genetic Drift	Decreases	Can decrease
Gene Flow	Increases	Variable
Mutation	Increases	Usually neutral or deleterious
Non-random Mating	Variable	Variable

*Additional info: Some explanations and examples have been expanded for clarity and completeness beyond the original slides, following standard introductory biology textbooks.*