Introduction to Biology

Core Principles of Biology

• Cell theory states all living organisms are composed of cells
• Gene theory covers hereditary information is encoded in DNA and genes
• Evolution is a process where life evolves over time through descent with modification
• Homeostasis defines living organisms maintain a stable internal environment

Levels of Biological Organization

• Biosphere: all ecosystems on Earth
• Ecosystem: community of living organisms in conjunction with the nonliving components of their environment
• Community: populations of different species living in the same area
• Population: group of individuals of the same species living in the same area
• Organism: individual living entity
• Organ system: group of organs working together
• Organ: group of tissues working together
• Tissue: group of similar cells performing a specific function
• Cell: basic unit of life
• Organelle: structure within a cell that performs a specific function
• Molecule: group of atoms bonded together
• Atom: basic unit of matter

Chemical Basis of Life

• Matter consists of chemical elements in pure form and in combinations called compounds
• Essential elements for life include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur
• Atoms combine to form molecules through chemical bonds
• Covalent bonds involve the sharing of electrons between atoms
• Ionic bonds involve the transfer of electrons between atoms
• Hydrogen bonds are weak attraction between a hydrogen atom and an electronegative atom

Water and Life

• Water is essential for life due to its unique properties
• Cohesion: water molecules stick together
• Adhesion: water molecules stick to other surfaces
• High specific heat: water resists changes in temperature
• Evaporative cooling: water cools a surface as it evaporates
• Ice floats: water is less dense as a solid than as a liquid
• Versatile solvent: water dissolves polar and ionic substances

Biological Macromolecules

• Large organic molecules are essential to life
• Carbohydrates: sugars and polymers of sugars that serve as fuel and building material
• Lipids: fats, phospholipids, and steroids, which are hydrophobic molecules
• Proteins: polymers of amino acids that have diverse functions
• Nucleic acids: DNA and RNA, which store and transmit hereditary infromation

Cell Structure and Function

• Cells are the basic unit of life
• Prokaryotic cells lack a nucleus and other membrane-bound organelles
• Eukaryotic cells have a nucleus and other membrane-bound organelles
• Plasma membrane: outer boundary of the cell that controls what enters and exits
• Nucleus: control center of the cell that contains DNA
• Ribosomes: synthesize proteins
• Endoplasmic reticulum: network of membranes involved in protein and lipid synthesis
• Golgi apparatus: modifies and packages proteins
• Lysosomes: contain enzymes that break down cellular waste
• Mitochondria: generate energy in the form of ATP
• Chloroplasts: carry out photosynthesis in plants and algae

Membrane Transport

• Movement of substances across the cell membrane
• Passive transport does not require energy
• Diffusion: movement of molecules from an area of high concentration to an area of low concentration
• Osmosis: diffusion of water across a selectively permeable membrane
• Facilitated diffusion: movement of molecules across a membrane with the help of transport proteins
• Active transport requires energy
• Active transport enables the movement of molecules against a concentration gradient
• Endocytosis: cell takes in molecules by forming new vesicles from the plasma membrane
• Exocytosis: cell releases molecules by fusion of vesicles with the plasma membrane

Metabolism

• Sum of all chemical reactions in an organism
• Catabolism process breaks down complex molecules into simpler ones
• Anabolism builds complex molecules from simpler ones
• Enzymes speed up chemical reactions by lowering activation energy
• ATP: energy currency of the cell

Cellular Respiration

• Process of converting glucose into ATP
• Glycolysis: glucose is broken down into pyruvate
• Citric acid cycle: pyruvate is further broken down, releasing carbon dioxide, ATP and electron carriers
• Oxidative phosphorylation: electron carriers donate electrons to the electron transport chain, generating a proton gradient that drives ATP synthesis

Photosynthesis

• Process of converting light energy into chemical energy
• Light reactions: light energy is used to split water, releasing oxygen and generating ATP and NADPH
• Calvin cycle: carbon dioxide is fixed and converted into glucose using ATP and NADPH

Cell Communication

• Cells communicate with each other through various signaling molecules
• Reception: signaling molecule binds to a receptor protein
• Transduction: signal is converted into a form that can bring about a cellular response
• Response: cellular activity is altered

Cell Cycle

• Ordered sequence of events in the life of a cell
• Interphase: cell growth and DNA replication
• Mitotic phase: cell division
• Mitosis: division of the nucleus
• Cytokinesis: division of the cytoplasm

Genetics

• Study of heredity and variation
• Genes: units of heredity that are made up of DNA
• Chromosomes: structures that carry genes
• DNA: genetic material that carries information from one generation to the next
• RNA: involved in protein synthesis

DNA Replication

• Process of copying DNA
• DNA polymerase: enzyme that adds nucleotides to the growing DNA strand
• Semi-conservative replication: each new DNA molecule consists of one original strand and one new strand

Gene Expression

Process by which DNA directs protein synthesis

• Transcription: DNA is transcribed into RNA
• Translation: RNA is translated into protein

Mutations

• Changes in the DNA sequence
• Point mutations: changes in a single nucleotide base
• Frameshift mutations: insertions or deletions of nucleotides that alter the reading frame

Control of Gene Expression

• Regulation of gene activity to ensure proper timing and location of protein synthesis
• Transcriptional control: regulation of RNA synthesis
• Translational control: regulation of protein synthesis

Viruses

• Infectious particles consisting of nucleic acid enclosed in a protein coat
• Viruses cannot reproduce on their own and must infect a host cell

Evolution

• Change in the genetic makeup of a population over time
• Natural selection: process by which individuals with certain heritable traits survive and reproduce at a higher rate than others
• Adaptation: inherited characteristic that enhances an organism's survival and reproduction

Evidence of Evolution

• Fossil record: provides evidence of extinct species and the sequence of evolutionary change
• Comparative anatomy: similarities in the anatomy of different species reflect common ancestry
• Comparative embryology: similarities in the development of different species reflect common ancestry
• Molecular biology: similarities in the DNA and proteins of different species reflect common ancestry

Mechanisms of Evolution

• Mutation: provides raw material for evolutionary change
• Gene flow: transfer of genes between populations
• Genetic drift: random changes in allele frequencies
• Natural selection: differential survival and reproduction based on heritable traits

Speciation

• Process by which new species arise
• Allopatric speciation: geographic separation leads to the evolution of reproductive isolation
• Sympatric speciation: reproductive isolation evolves within the same geographic area

Classification of Life

• Taxonomy: science of classifying organisms
• Bacteria: prokaryotic organisms
• Archaea: prokaryotic organisms that are distinct from bacteria
• Eukarya: eukaryotic organisms
• Protista: diverse group of mostly unicellular eukaryotes
• Fungi: eukaryotic organisms that obtain nutrients by absorption
• Plantae: eukaryotic organisms that carry out photosynthesis
• Animalia: eukaryotic organisms that obtain nutrients by ingestion

Ecology

• Study of interactions between organisms and their environment
• Population ecology: study of factors that affect population size and density
• Community ecology: study of interactions between different species in a community
• Ecosystem ecology: study of interactions between living organisms and the nonliving components of their environment

Population Growth

• Exponential growth: population increases rapidly under ideal conditions
• Logistic growth: population growth slows as it approaches carrying capacity
• Carrying capacity: maximum population size that an environment can support

Community Interactions

• Competition: organisms compete for resources
• Predation: one organism eats another
• Symbiosis: close relationship between two species
• Mutualism: both species benefit
• Commensalism: one species benefits and the other is not affected
• Parasitism: one species benefits and the other is harmed

Ecosystems

• Consist of living organisms and the nonliving components of their environment
• Energy flow: energy flows through ecosystems from producers to consumers
• Nutrient cycling: nutrients cycle within ecosystems
• Producers: autotrophs that produce their own food through photosynthesis or chemosynthesis
• Consumers: heterotrophs that obtain energy by eating other organisms
• Decomposers: break down dead organisms and waste products

Conservation Biology

• Study of the conservation of biodiversity
• Habitat loss: destruction or fragmentation of habitats
• Invasive species: non-native species that can harm native species
• Pollution: introduction of harmful substances into the environment
• Climate change: changes in the Earth's climate that can have significant impacts on ecosystems