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 cells 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 share key characteristics including organization, metabolism, homeostasis, growth, reproduction, and response to stimuli.

Branches of Biology

• Biochemistry studies the chemical processes within and relating to living organisms.
• Botany is the scientific study of plants.
• Cell biology studies the structure, function, and behavior of cells.
• Ecology studies the interactions of organisms with each other and their environment.
• Evolutionary biology studies the evolutionary processes that 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 molecular basis of biological activity between biomolecules in a cell.
• Zoology is the scientific study of animals.

Key Concepts in Biology

• Cell theory states that all living organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
• Gene theory states that traits are inherited through genes, which are specific locations on chromosomes.
• Homeostasis refers to the ability of an organism to maintain a stable internal environment.
• Evolution is the change in the heritable characteristics of biological populations over successive generations. Genes are the unit of heredity upon which evolution acts.
• Heredity is the passing of traits from parents to offspring, and variation refers to the differences among individuals within a population.

Chemical Basis of Life

• Water is essential for life due to its properties as a solvent, its high heat capacity, and its role in chemical reactions.
• Carbon is the primary element in organic molecules due to its ability to form stable bonds with many other carbon atoms and other elements like hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
• Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms that serve as a primary source of energy for living organisms. Examples are sugars, starches, and cellulose.
• Lipids are hydrophobic molecules composed mainly of carbon and hydrogen atoms. They include fats, oils, phospholipids, and steroids, and they play roles in energy storage, insulation, and cell membrane structure.
• Nucleic acids are composed of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base; there are two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
• Proteins are complex molecules made up of amino acids. They perform a wide variety of functions in living organisms, including catalyzing biochemical reactions (enzymes), transporting molecules, providing structural support, and regulating gene expression.

Cell Structure and Function

• Prokaryotic cells lack a nucleus and other membrane-bound organelles and include bacteria and archaea.
• Eukaryotic cells possess a nucleus and other membrane-bound organelles, such as mitochondria and endoplasmic reticulum and are found in protists, fungi, plants, and animals.
• The plasma membrane is a selectively permeable barrier that encloses the cell and regulates the movement of substances in and out.
• The nucleus contains the cell's genetic material (DNA) and controls cell activities.
• Ribosomes are responsible for protein synthesis.
• The endoplasmic reticulum (ER) is involved in protein and lipid synthesis and transport.
• The Golgi apparatus modifies, sorts, and packages proteins and lipids.
• Mitochondria are responsible for cellular respiration and ATP production.
• Lysosomes contain enzymes that break down cellular waste and debris.
• The cytoskeleton provides structural support and facilitates cell movement.

Energy and Metabolism

• Metabolism is the sum of all chemical reactions that occur within a living organism.
• Anabolism refers to the building up of complex molecules from simpler ones, requiring energy input.
• Catabolism refers to the breaking down of complex molecules into simpler ones, releasing energy.
• Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.
• ATP (adenosine triphosphate) serves as the primary energy currency of the cell, providing energy for various cellular processes.
• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose.
• Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP.

Genetics

• Genes are the basic units of heredity and are composed of DNA.
• Chromosomes are structures within the cell nucleus that contain DNA.
• DNA replication is the process by which DNA is copied, ensuring genetic information is passed on during cell division.
• 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 altered protein function and phenotypic variation.
• Mendelian genetics describes the principles of inheritance, including segregation and independent assortment.

Evolution

• Natural selection is the process by which individuals with certain heritable traits survive and reproduce at a higher rate than others, leading to the adaptation of populations to their environment.
• Genetic drift is the random change in the frequency of alleles in a population, particularly significant in small populations.
• Gene flow is the transfer of genetic material from one population to another.
• Mutation introduces new genetic variation into populations.
• Speciation is the process by which new species arise from existing ones, often involving reproductive isolation.
• Evidence for evolution comes from various sources, including the fossil record, comparative anatomy, embryology, and molecular biology.

Ecology

• Populations are groups of individuals of the same species living in the same area.
• Communities are assemblages of different populations of species interacting with each other.
• Ecosystems consist of communities of organisms interacting with their physical environment.
• Biomes are large-scale ecosystems characterized by specific climate conditions and dominant plant communities.
• The biosphere encompasses all of Earth's ecosystems.
• Trophic levels describe the position of organisms in a food chain or food web, including producers, consumers, and decomposers.
• Energy flow describes how energy is transferred between trophic levels in an ecosystem.
• Nutrient cycling describes how essential nutrients are recycled within ecosystems.
• Biodiversity refers to the variety of life at all levels of biological organization, including genetic diversity, species diversity, and ecosystem diversity.