A free, self-paced textbook in 7 chapters. Read a chapter, then drill it with the 53 companion flashcards using spaced repetition.
Biology is the scientific study of life and living organisms, a discipline that examines everything from the smallest cellular structures to the vast interactions among species acr...
The cell is the basic structural and functional unit of all living organisms, often called the building block of life. The cell theory formalizes this idea with three core claims:...
Life depends on four main types of biological macromolecules, each built from smaller subunits and serving distinct roles. Carbohydrates provide quick energy and structural support...
Living organisms must continually capture, store, and release energy to maintain their activities. Photosynthesis is the process by which plants, algae, and some bacteria convert l...
Cells reproduce themselves through division, and the type of division depends on the cell's role. Mitosis is the process by which a single cell divides to produce two genetically i...
The instructions for building and maintaining an organism are encoded in deoxyribonucleic acid, or DNA, a double-helix molecule that stores genetic information in sequences of four...
Life on Earth has changed dramatically over billions of years, and the theory of evolution by natural selection, first proposed by Charles Darwin in On the Origin of Species, expla...