Introduction to Biology

• Biology is the scientific study of life.

Core Principles of Biology

• Cell theory: all living organisms are composed of cells.
• Gene theory: traits are inherited through genes.
• Evolution: all life forms have evolved over time from a common ancestor.
• Homeostasis: Living organisms maintain stable internal conditions.
• Thermodynamics: life depends on the flow and transformation of energy.

Branches of Biology

• Biochemistry: studies the chemical processes within and relating to living organisms.
• Botany: studies plants, including their physiology, structure, genetics, ecology, distribution, classification, and economic importance.
• Cell biology: studies the structure, function, and behavior of cells.
• Ecology: studies the interactions between organisms and their environment.
• Evolutionary biology: studies the evolutionary processes that have produced the diversity of life on Earth.
• Genetics: studies genes, heredity, and variation in living organisms.
• Microbiology: studies microorganisms, including bacteria, viruses, fungi, and protozoa.
• Molecular biology: studies the molecular basis of biological activity, including the interactions between DNA, RNA, and proteins.
• Physiology: studies the functions and mechanisms of living organisms and their parts.
• Zoology: studies animals, including their physiology, structure, genetics, ecology, behavior, classification, and distribution.

The Cell

• The cell is the basic structural and functional unit of all known living organisms.
• Cell structures include:
  • Plasma membrane: outer boundary of the cell that controls the movement of substances in and out.
  • Cytoplasm: gel-like substance within the cell that contains organelles.
  • Nucleus: control center of the cell that contains DNA.
  • Ribosomes: site of protein synthesis.
  • Mitochondria: site of cellular respiration, producing ATP.
  • Endoplasmic reticulum (ER): network of membranes involved in protein and lipid synthesis.
  • Golgi apparatus: modifies, sorts, and packages proteins and lipids.
  • Lysosomes: contain enzymes for breaking down cellular waste.

Cell Types

• Prokaryotic cells: lack a nucleus and other membrane-bound organelles (e.g., bacteria and archaea).
• Eukaryotic cells: contain a nucleus and other membrane-bound organelles (e.g., protists, fungi, plants, and animals).

Genetics

• Genetics is the study of heredity and variation in living organisms.
• Genes are the basic units of heredity, composed of DNA.
• DNA (deoxyribonucleic acid): molecule that carries the genetic instructions for all known living organisms.
• Chromosomes: structures within the nucleus that contain DNA.
• Genotype: genetic makeup of an organism.
• Phenotype: observable characteristics of an organism.
• Alleles: different versions of a gene.
• Dominant allele: allele that masks the effect of a recessive allele.
• Recessive allele: allele whose effect is masked by a dominant allele.
• Homozygous: having two identical alleles for a particular gene.
• Heterozygous: having two different alleles for a particular gene.

Mendelian Genetics

• Gregor Mendel's laws of inheritance:
  • Law of segregation: each individual has two alleles for each trait, and these alleles separate during gamete formation.
  • Law of independent assortment: alleles for different traits are inherited independently of each other.
  • Law of dominance: in a heterozygote, one allele may mask the effect of another allele.

Mutations

• Changes in the DNA sequence that can lead to new traits.
• Mutations can be spontaneous or caused by environmental factors.

Evolution

• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• Natural selection: process by which organisms with traits that are better suited to their environment survive and reproduce more successfully than organisms without those traits.
• Adaptation: a trait that enhances an organism's survival and reproduction in its environment.

Mechanisms of Evolution

• Mutation: introduces new genetic variation into a population.
• Gene flow: movement of genes between populations.
• Genetic drift: random changes in allele frequencies within a population.
• Natural selection: differential survival and reproduction of individuals with different traits.

Evidence for Evolution

• Fossil record: shows the history of life on Earth and the transitions between different groups of organisms.
• Comparative anatomy: similarities in the anatomy of different organisms reflect their common ancestry.
• Embryology: similarities in the development of different organisms reflect their common ancestry.
• Molecular biology: similarities in the DNA and protein sequences of different organisms reflect their common ancestry.
• Biogeography: distribution of organisms on Earth reflects their evolutionary history.

Ecology

• Ecology is the study of the interactions between organisms and their environment.
• Ecosystem: community of living organisms and their physical environment.
• Population: group of individuals of the same species living in the same area.
• Community: group of interacting populations of different species living in the same area.
• Biosphere: the part of Earth where life exists.

Ecological Roles/Functions

• Producers: autotrophs that produce their own food through photosynthesis or chemosynthesis.
• Consumers: heterotrophs that obtain their food by eating other organisms.
• Decomposers: heterotrophs that break down dead organic matter.

Food Webs

• Energy flows through an ecosystem through food chains and food webs.
• Each level in a food chain or food web is called a trophic level.
• Energy is lost at each trophic level due to heat and metabolism.

Biomes

• Major types of ecosystems characterized by climate, vegetation, and animal life.
• Examples of biomes include:
  • Tundra
  • Taiga
  • Temperate deciduous forest
  • Grassland
  • Desert
  • Tropical rainforest

Biochemistry

• Biochemistry is the study of the chemical processes within and relating to living organisms.
• Key biomolecules include:
  • Carbohydrates: provide energy and structural support.
  • Lipids: store energy, form cell membranes, and act as hormones.
  • Proteins: perform a wide variety of functions, including catalyzing reactions, transporting molecules, and providing structural support.
  • Nucleic acids: store and transmit genetic information.

Enzymes

• Proteins that catalyze biochemical reactions.
• Enzymes are highly specific for their substrates.
• Enzyme activity is affected by temperature, pH, and the presence of inhibitors and activators.

Metabolism

• The sum of all chemical reactions that occur within a living organism.
• Anabolism: building up of complex molecules from simpler ones.
• Catabolism: breaking down of complex molecules into simpler ones.

Taxonomy

• Taxonomy is the science of classifying and naming organisms.

Taxonomic Hierarchy

• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Three Domains of Life

• Bacteria: prokaryotic organisms.
• Archaea: prokaryotic organisms that are distinct from bacteria.
• Eukarya: eukaryotic organisms, including protists, fungi, plants, and animals.