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Biology

Free Biology study guide: 9 units with summaries, key ideas, flashcards and 99 practice questions with step-by-step solutions.

Lines up with: AP Biology; CLEP Biology; state end-of-course exams.

Units

1. UNIT 01

   Chemistry of life

   Living things are built from a few elements arranged into four big families of molecules. Water's polarity makes life's chemistry possible.
2. UNIT 02

   Cell structure and function

   Cells are the basic unit of life. Organelles divide the work, and the membrane controls what goes in and out.
3. UNIT 03

   Cellular energetics

   Cells capture and release energy through enzyme-driven pathways. Photosynthesis stores energy in sugar, and respiration releases it as ATP.
4. UNIT 04

   Cell communication and cell cycle

   Cells talk to each other with chemical signals, and they divide in a tightly controlled cycle. When control breaks down, cancer can result.
5. UNIT 05

   Heredity

   Meiosis makes gametes with half the chromosomes, and the way alleles separate explains how traits are inherited.
6. UNIT 06

   Gene expression and regulation

   DNA stores instructions, RNA carries them, and ribosomes build proteins. Cells control which genes are expressed, and mutations change the instructions.
7. UNIT 07

   Natural selection

   Populations change over time because individuals with helpful heritable traits leave more offspring. Many lines of evidence support evolution.
8. UNIT 08

   Ecology

   Ecology studies how organisms interact with each other and their environment. Energy flows through ecosystems while matter cycles.
9. UNIT 09

   Human body systems and health

   Organ systems work together to keep the body in balance, and the immune system defends it against disease.