Introduction to Biology

• Biology is the scientific study of life.
• It encompasses 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 engine that propels the creation and extinction of species.
• Living organisms interact with their environment, maintaining stable internal conditions.

Core Principles

• Cell theory: All living organisms are composed of one or more cells; the cell is the basic unit of structure and function in organisms; all cells arise from pre-existing cells.
• Gene theory: Traits are inherited through genes (specific sequences of nucleotides on a DNA molecule). Genes encode proteins or RNA molecules that determine traits of an organism.
• Evolution: Changes in the heritable characteristics of biological populations over successive generations; evolutionary processes give rise to biodiversity at every level of biological organization.
• Homeostasis: An organism's ability to maintain a stable internal environment despite external changes.
• Thermodynamics: All living organisms obtain and transform energy to maintain themselves.

Branches of Biology

• Biochemistry: The study of chemical processes within and relating to living organisms, focusing on the structure and function of biomolecules (proteins, carbohydrates, lipids, and nucleic acids).
• Molecular Biology: The study of the molecular basis of biological activity, including interactions between DNA, RNA, and proteins and their regulation.
• Cell Biology: The study of the structure, function, and behavior of cells, including cell division, cell signaling, and cell death.
• Genetics: The study of heredity and variation in organisms; includes the study of genes, chromosomes, and genomes.
• Microbiology: The study of microorganisms, including bacteria, archaea, viruses, fungi, and protists.
• Botany: The study of plants, including their structure, function, growth, evolution, and classification.
• Zoology: The study of animals, including their structure, function, behavior, evolution, and classification.
• Ecology: The study of the interactions between organisms and their environment.
• Evolution: The study of the evolutionary processes that have shaped the diversity of life on Earth.
• Anatomy: The study of the structure of organisms.
• Physiology: The study of the function of organisms.

Chemical Basis of Life

• All living organisms are composed of matter, which is made up of elements.
• Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur are the most abundant elements in living organisms.
• Atoms combine to form molecules, which can be small organic molecules (e.g., sugars, amino acids, nucleotides, lipids) or large macromolecules (e.g., proteins, carbohydrates, nucleic acids).
• Water is essential for life because of its properties as a solvent, its high heat capacity, and its role in many biochemical reactions.

Cell Structure and Function

• Cells are the basic unit of life and are surrounded by a plasma membrane.
• Prokaryotic cells (bacteria and archaea) lack a nucleus and other membrane-bound organelles.
• Eukaryotic cells (protists, fungi, plants, and animals) have a nucleus and other membrane-bound organelles like mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
• The nucleus contains the cell's DNA, organized into chromosomes.
• Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration.
• The endoplasmic reticulum is involved in protein synthesis and lipid metabolism.
• The Golgi apparatus processes and packages proteins.
• Lysosomes contain enzymes that break down cellular waste products and debris.

Energy and Metabolism

• Metabolism is the sum of all chemical reactions in a living organism.
• Catabolism is the breakdown of complex molecules into simpler ones, releasing energy.
• Anabolism is the synthesis of complex molecules from simpler ones, requiring energy.
• Enzymes are biological catalysts that speed up chemical reactions.
• ATP (adenosine triphosphate) is the primary energy currency of the cell.
• 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 organisms break down glucose to generate ATP.

Genetics

• DNA (deoxyribonucleic acid) is the molecule that carries genetic information.
• DNA is a double helix composed of two complementary strands of nucleotides.
• Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).
• RNA (ribonucleic acid) is similar to DNA but contains a different sugar (ribose) and the base uracil instead of thymine.
• Genes are specific sequences of nucleotides on a DNA molecule that encode proteins or RNA molecules.
• The genome is the complete set of genes in an organism.
• DNA replication is the process by which DNA is copied.
• Transcription is the process by which RNA is synthesized from DNA.
• Translation is the process by which proteins are synthesized from RNA.
• Mutations are changes in the DNA sequence that can lead to altered protein function or gene expression.

Evolution and Diversity

• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• Natural selection is the process by which individuals with certain traits are more likely to survive and reproduce than individuals with other traits.
• Adaptation is the process by which populations become better suited to their environment through natural selection.
• Speciation is the process by which new species arise.
• Phylogeny is the evolutionary history of a group of organisms.
• The tree of life is a branching diagram that represents the evolutionary relationships among all living organisms.
• Biodiversity is the variety of life on Earth at all its levels, from genes to ecosystems.

Ecology and Environment

• Ecology is the study of the interactions between organisms and their environment.
• Populations are groups of individuals of the same species living in the same area.
• Communities are groups of different populations living in the same area.
• Ecosystems are communities of organisms interacting with their physical environment.
• The biosphere is the sum of all ecosystems on Earth.
• Biomes are large geographic areas characterized by specific climate conditions and plant communities.
• Trophic levels are the different feeding levels in an ecosystem, such as producers, consumers, and decomposers.
• Food webs are complex networks of feeding relationships among organisms in an ecosystem.
• Nutrient cycles are the movement of essential elements, such as carbon, nitrogen, and phosphorus, through ecosystems.
• Human activities, such as deforestation, pollution, and climate change, are having a significant impact on the environment.