Introduction to Biology

• Biology is the scientific study of life, examining the structure, function, growth, origin, evolution, and distribution of living organisms.
• It recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the mechanism that drives the formation of new species.
• Living organisms share key characteristics including organization, metabolism, responsiveness, homeostasis, growth, reproduction, and adaptation.

Branches of Biology

• Biochemistry explores the chemical processes within and related to living organisms.
• Botany is the scientific study of plants.
• Cell biology studies the structure and function of cells.
• Ecology examines the interactions of organisms with each other and their environment.
• Evolutionary biology studies the evolutionary processes that have produced the diversity of life on Earth.
• Genetics studies heredity and variation in organisms.
• Microbiology studies microorganisms, including bacteria, viruses, fungi, and protozoa.
• Molecular biology studies the structure and function of biological macromolecules, such as proteins and nucleic acids.
• Zoology is the study of animals.

Basic Biological Concepts

• Cell theory posits that the cell is the fundamental unit of life, all living organisms are composed of cells, and all cells arise from pre-existing cells.
• Gene theory states that traits are inherited through genes, which are specific regions of DNA that encode for proteins or RNA molecules.
• Homeostasis is the ability of an organism to maintain a stable internal environment despite changes in external conditions.
• Evolution is the change in the heritable characteristics of biological populations over successive generations.

Chemical Basis of Life

• Water is essential for life due to its properties as a solvent, its high heat capacity, and its role in many biochemical reactions.
• Carbon is the primary element in organic molecules due to its ability to form stable covalent bonds with other carbon atoms and a variety of other elements.
• Carbohydrates are organic compounds consisting of carbon, hydrogen, and oxygen atoms, generally with a hydrogen-oxygen atom ratio of 2:1; major source of energy for the body.
• Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, and others; the main biological functions of lipids include storing energy, signaling, and acting as structural components of cell membranes.
• Proteins are macromolecules composed of amino acids, and they perform a wide variety of functions, including catalysis, transport, and structural support.
• Nucleic acids (DNA and RNA) are polymers of nucleotides that store and transmit genetic information.

Cell Structure and Function

• Prokaryotic cells lack a nucleus and other membrane-bound organelles; Bacteria and Archaea.
• Eukaryotic cells have a nucleus and other membrane-bound organelles; protists, fungi, plants, and animals.
• The plasma membrane is a selectively permeable barrier that controls the movement of substances into and out of the cell made of a phospholipid bilayer.
• The nucleus contains the cell's genetic material (DNA) and controls the cell's activities.
• Ribosomes are responsible for protein synthesis.
• The endoplasmic reticulum (ER) is involved in protein and lipid synthesis.
• The Golgi apparatus processes and packages proteins and lipids.
• Mitochondria are the powerhouses of the cell and generate ATP through cellular respiration.
• Lysosomes contain enzymes that break down cellular waste and debris.
• Chloroplasts (in plant cells) are the sites of photosynthesis.

Metabolism

• Metabolism is the sum of all chemical reactions that occur within an organism.
• Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.
• Cellular respiration is the process by which cells break down glucose to produce ATP.
• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose.

Genetics

• DNA (deoxyribonucleic acid) is the molecule that carries genetic information.
• Genes are specific sequences of DNA that encode for proteins or RNA molecules.
• Chromosomes are structures within the cell that contain DNA.
• DNA replication is the process by which DNA is copied.
• Transcription is the process by which RNA is synthesized from a DNA template.
• Translation is the process by which proteins are synthesized from an RNA template.
• Mutations are changes in the DNA sequence that can lead to genetic variation.

Evolution

• Natural selection is the process by which organisms with traits that are better suited to their environment survive and reproduce more successfully than organisms with less suited traits.
• Adaptation is a trait that enhances an organism's survival and reproduction in a particular environment.
• Species are groups of organisms that can interbreed and produce fertile offspring.
• Speciation is the process by which new species arise from existing species.
• Evidence for evolution includes fossil records, comparative anatomy, embryology, and molecular biology.

Ecology

• Populations are groups of individuals of the same species living in the same area.
• Communities are groups of interacting populations of different species living in the same area.
• Ecosystems are communities of organisms and their physical environment.
• The biosphere is the sum of all ecosystems on Earth.
• Energy flow in ecosystems: energy flows from the sun to producers (plants), which are then consumed by consumers (animals).
• Nutrient cycling in ecosystems: nutrients are recycled between living organisms and the physical environment.
• Biomes are large geographic areas characterized by distinct climate conditions, animal populations, and plant species.