Introduction to Biology

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, and distribution of living organisms
• Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species
• Living organisms are open systems that survive by transforming energy and decreasing their local entropy

Main Tenets of Biology

• Cell theory: the cell is the basic unit of structure in all living things
• Gene theory: traits are inherited through genes
• Evolution: all life forms have evolved and diversified from a universal common ancestor
• Homeostasis: living organisms maintain a stable internal environment

Subdisciplines 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 of living organisms with one another and with their physical environment
• Evolution studies the processes that have led to the diversity of life on Earth
• Genetics studies heredity and variation in organisms
• Microbiology studies microorganisms, including bacteria, viruses, fungi, protozoa, and algae
• Molecular biology studies the structure and function of biological molecules
• Physiology studies the functions and mechanisms of living organisms and their parts
• Zoology studies animals, including their physiology, anatomy, behavior, genetics, ecology, evolution, and classification

Characteristics of Life

• Organization: Living things exhibit a complex organization, from atoms to molecules to organelles to cells to tissues to organs to organ systems to organisms
• Metabolism: Living organisms carry out a variety of chemical reactions, collectively known as metabolism, to obtain energy and build cellular components
• Homeostasis: Living organisms maintain a stable internal environment, despite changes in the external environment
• Growth: Living organisms increase in size and complexity over time
• Reproduction: Living organisms produce new individuals, either sexually or asexually
• Response to stimuli: Living organisms respond to changes in their environment
• Evolution: Living organisms evolve over time, adapting to their environment through natural selection

Cell Structure and Function

• Cells are the basic unit of life
• All cells share some common features:
  • Plasma membrane: an outer boundary that separates the cell from its environment
  • Cytoplasm: a jelly-like substance inside the cell that contains organelles and other cellular components
  • DNA: the genetic material that carries the instructions for building and operating the cell
  • Ribosomes: structures that synthesize proteins
• There are two main types of cells:
  • Prokaryotic cells: lack a nucleus and other membrane-bound organelles
  • Eukaryotic cells: have a nucleus and other membrane-bound organelles
• Organelles are specialized structures within eukaryotic cells that perform specific functions:
  • Nucleus: contains the cell's DNA and controls cellular activities
  • Mitochondria: generate energy for the cell through cellular respiration
  • Chloroplasts: found in plant cells, carry out photosynthesis
  • Endoplasmic reticulum: synthesizes and transports proteins and lipids
  • Golgi apparatus: processes and packages proteins and lipids
  • Lysosomes: break down waste materials and cellular debris
  • Vacuoles: store water, nutrients, and waste products

Genetics and Heredity

• Genes are the basic units of heredity and are composed of DNA
• DNA (deoxyribonucleic acid) is a molecule that carries the genetic instructions for all living organisms
• Genes are organized into chromosomes, which are located in the nucleus of eukaryotic cells
• During reproduction, genes are passed from parents to offspring
• The process of gene expression involves two main steps:
  • Transcription: the DNA sequence of a gene is copied into RNA
  • Translation: the RNA sequence is used to synthesize a protein
• Mutations are changes in the DNA sequence that can lead to variations in traits

Evolution and Natural Selection

• Evolution is the process of change in the heritable characteristics of biological populations over successive generations
• Natural selection is a mechanism of evolution in which individuals with advantageous traits are more likely to survive and reproduce, passing those traits on to their offspring
• Evidence for evolution comes from a variety of sources, including:
  • The fossil record: shows the history of life on Earth
  • Comparative anatomy: reveals similarities and differences in the anatomy of different species
  • Embryology: shows similarities in the development of different species
  • Molecular biology: compares the DNA and protein sequences of different species
• Speciation is the process by which new species arise

Ecology and the Environment

• Ecology is the study of the interactions of living organisms with one another and with their physical environment
• Ecosystems are communities of interacting organisms and their physical environment
• Populations are groups of individuals of the same species living in the same area
• Communities are groups of populations of different species living in the same area
• The environment includes all of the physical, chemical, and biological factors that affect living organisms:
  • Abiotic factors: non-living factors such as temperature, sunlight, water, and nutrients
  • Biotic factors: living factors such as other organisms, competition, predation, and symbiosis
• Energy flows through ecosystems from the sun to producers to consumers:
  • Producers: organisms that make their own food through photosynthesis (e.g., plants)
  • Consumers: organisms that eat other organisms (e.g., animals)
  • Decomposers: organisms that break down dead organisms and waste products (e.g., bacteria and fungi)
• Nutrient cycles are the pathways that nutrients take as they move through ecosystems

Biological Classification

• Taxonomy is the science of naming and classifying organisms
• The hierarchical system of classification includes:
  • Domain: Archaea, Bacteria, and Eukarya
  • Kingdom: Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria
  • Phylum: A group of classes with similar characteristics
  • Class: A group of orders with common features
  • Order: A group of families with related traits
  • Family: A group of genera sharing many characteristics
  • Genus: A group of closely related species
  • Species: A group of organisms that can interbreed and produce fertile offspring
• Binomial nomenclature is the system of naming species using two names: the genus and the species

Viruses

• Viruses are acellular entities consisting of a nucleic acid genome surrounded by a protein coat
• They are obligate intracellular parasites, meaning they can only replicate inside a host cell
• Viral replication involves attaching to a host cell, entering the cell, replicating the viral genome, synthesizing viral proteins, assembling new viral particles, and releasing the new viruses from the host cell
• Viruses can cause a wide range of diseases in plants, animals, and bacteria

Prokaryotes

• Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles
• They include bacteria and archaea
• Prokaryotic cells have a plasma membrane, cytoplasm, DNA, and ribosomes
• Many prokaryotes have a cell wall that provides support and protection
• Prokaryotes reproduce asexually through binary fission
• They play important roles in nutrient cycling, decomposition, and the production of food and medicines

Eukaryotes

• Eukaryotes are organisms whose cells have a nucleus and other membrane-bound organelles
• Eukaryotes include protists, fungi, plants, and animals
• Eukaryotic cells are more complex than prokaryotic cells
• Eukaryotes can be unicellular or multicellular
• They reproduce sexually or asexually
• Eukaryotes perform a wide range of functions in ecosystems

Plants

• Plants are multicellular eukaryotic organisms that belong to the kingdom Plantae
• They are autotrophs, meaning they produce their own food through photosynthesis
• Plants have cell walls made of cellulose
• Plants have specialized tissues and organs for photosynthesis, transport, support, and reproduction
• They play a vital role in ecosystems by producing oxygen, providing food and shelter for other organisms, and helping to regulate the climate

Animals

• Animals are multicellular eukaryotic organisms that belong to the kingdom Animalia
• They are heterotrophs, meaning they obtain their food by consuming other organisms
• Animals lack cell walls
• Animals have specialized tissues and organs for movement, sensing the environment, and processing information
• They play a diverse range of roles in ecosystems, including predators, herbivores, decomposers, and pollinators