Introduction to Biology

Biology encompasses a broad range of topics and is often divided into specialized fields, each focusing on a specific aspect of life.
All living organisms share key characteristics, including organization, metabolism, responsiveness, homeostasis, growth, reproduction, and adaptation.
The cell is the basic unit of life, providing structure and carrying out life functions.
Genes, composed of DNA, are the units of heredity and provide the instructions for building and operating a living organism.
Evolution is the process of change in the heritable characteristics of biological populations over successive generations.

Living organisms are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
Water is essential for life due to its properties as a solvent, its high heat capacity, and its role in many biochemical reactions.
Carbohydrates, lipids, proteins, and nucleic acids are the major classes of organic molecules found in living organisms.
Carbohydrates provide energy and structural support.
Lipids include fats, oils, and steroids, serving roles in energy storage, insulation, and cell membrane structure.
Proteins perform a wide variety of functions, including catalyzing reactions, transporting molecules, and providing structural support.
Nucleic acids (DNA and RNA) store and transmit genetic information.

Cells are classified as either prokaryotic (lacking a nucleus) or eukaryotic (containing a nucleus).
Prokaryotic cells, found in bacteria and archaea, are simpler in structure and lack membrane-bound organelles.
Eukaryotic cells, found in protists, fungi, plants, and animals, are more complex and contain various organelles.
The plasma membrane surrounds all cells and regulates the movement of substances in and out.
The nucleus contains the cell's DNA and controls cellular activities.
Ribosomes are responsible for protein synthesis.
The endoplasmic reticulum (ER) is involved in protein and lipid synthesis.
The Golgi apparatus modifies, sorts, and packages proteins and lipids.
Mitochondria are the powerhouses of the cell, producing ATP through cellular respiration.
Chloroplasts (in plant cells) carry out photosynthesis.
Lysosomes contain enzymes for breaking down cellular waste and debris.

Metabolism is the sum of all chemical reactions that occur within a living organism.
Enzymes are biological catalysts that speed up chemical reactions.
Cellular respiration is the process by which cells break down glucose to produce ATP (adenosine triphosphate), the main 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.
ATP powers cellular work by coupling exergonic (energy-releasing) reactions with endergonic (energy-requiring) reactions.

Genes are segments of DNA that code for specific traits or functions.
DNA is a double-stranded helix composed of nucleotides.
Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).
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 RNA.
Mutations are changes in the DNA sequence that can result in altered protein function.
Mendelian genetics describes the inheritance of traits based on the work of Gregor Mendel.
Genotype refers to the genetic makeup of an organism, while phenotype refers to its observable traits.
Natural selection is a mechanism of evolution in which organisms with advantageous traits are more likely to survive and reproduce.

Evolution is the change in the heritable characteristics of biological populations over successive generations.
Natural selection, genetic drift, mutation, and gene flow are the main mechanisms of evolution.
Adaptation is the process by which organisms become better suited to their environment through evolution.
Speciation is the process by which new species arise.
Biodiversity refers to the variety of life on Earth, including genetic diversity, species diversity, and ecosystem diversity.
Taxonomy is the science of classifying and naming organisms.

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 assemblages of different populations that live together in the same area.
Ecosystems consist of communities and their physical environment.
Biomes are large geographic areas characterized by specific climate conditions and plant and animal communities.
Food chains and food webs describe the flow of energy and nutrients through an ecosystem.
Trophic levels represent the different feeding positions in a food chain or food web.
Nutrient cycles (e.g., carbon cycle, nitrogen cycle) describe the movement of essential elements through an ecosystem.

Plants are multicellular, eukaryotic organisms that belong to the kingdom Plantae.
Plant cells contain chloroplasts, which carry out photosynthesis.
Plant tissues include epidermis, ground tissue, and vascular tissue.
Vascular tissue consists of xylem (which transports water and minerals) and phloem (which transports sugars).
Plant organs include roots, stems, leaves, flowers, fruits, and seeds.
Roots anchor the plant and absorb water and nutrients from the soil.
Stems provide support and transport substances between the roots and leaves.
Leaves are the primary sites of photosynthesis.
Flowers are involved in sexual reproduction.
Fruits develop from flowers and contain seeds.
Seeds contain the plant embryo and provide nourishment for germination.

Animals are multicellular, eukaryotic organisms that belong to the kingdom Animalia.
Animals are heterotrophic, meaning they obtain nutrients by consuming other organisms.
Animal tissues include epithelial tissue, connective tissue, muscle tissue, and nervous tissue.
Organ systems work together to perform specific functions in the body.
The digestive system breaks down food and absorbs nutrients.
The respiratory system exchanges gases (oxygen and carbon dioxide).
The circulatory system transports blood, nutrients, and gases throughout the body.
The excretory system removes waste products from the body.
The nervous system coordinates and controls bodily functions through electrical and chemical signals.
The endocrine system produces hormones that regulate various bodily functions.
The immune system protects the body from pathogens and disease.
The reproductive system is responsible for sexual reproduction.