--- title: "Interphase — AP Bio Definition & Exam Guide" description: "Interphase is the part of the cell cycle (G1, S, G2) where a cell grows and copies its DNA before dividing. Learn its stages and how AP Bio tests it." canonical: "https://fiveable.me/ap-bio/key-terms/interphase" type: "key-term" subject: "AP Biology" unit: "Unit 4" --- # Interphase — AP Bio Definition & Exam Guide ## Definition Interphase is the portion of the eukaryotic cell cycle made up of G1, S, and G2, during which a cell grows, duplicates its organelles, and replicates its DNA in preparation for mitosis (CED 4.5.A). ## What It Is Interphase is everything that happens between one [cell division](/ap-bio/key-terms/cell-division "fv-autolink") and the next. It looks quiet under a microscope, but it's the busiest stretch of the [cell cycle](/ap-bio/unit-4/homeostasis-feedback-loops/study-guide/OgMSpwCrEez0qyWtlCAC "fv-autolink"). The cell isn't resting, it's getting ready. Interphase breaks into three stages. In **G1 (first gap)**, the cell is metabolically active, growing and duplicating its [organelles](/ap-bio/key-terms/organelle "fv-autolink") and cytosolic components. In **S phase (synthesis)**, the DNA (in the form of loose chromatin) replicates, so each chromosome ends up as two identical sister chromatids joined at a centromere. In **G2 (second gap)**, the cell ramps up protein synthesis, produces a lot of ATP, and replicates its centrosomes so it's stocked with what mitosis needs. Some cells exit the cycle into **G0**, where they stop dividing. Once G2 wraps up, the cell is ready to enter mitosis. ## Why It Matters Interphase lives in **[Unit 4](/ap-bio/unit-4 "fv-autolink"): Cell Communication and Cell Cycle**, topic **4.5 Cell Cycle**. It directly supports **[AP Bio](/ap-bio "fv-autolink") 4.5.A**, which asks you to describe the events of the cell cycle, and it sets up **AP Bio 4.5.B**, since mitosis can only produce two genetically identical daughter cells if S phase already copied the DNA correctly. Think of interphase as the prep work that makes faithful chromosome transmission possible. If you can't explain what happens in G1, S, and G2, you can't explain how cells grow, repair tissue, or reproduce asexually with a complete, accurate genome. ## Connections ### [Mitosis (Unit 4)](/ap-bio/key-terms/mitosis) Interphase and [mitosis](/ap-bio/key-terms/mitosis "fv-autolink") alternate, but they aren't the same thing. Interphase copies the DNA in S phase; mitosis then physically separates those copies. No interphase, no chromatids to divide. ### Cell Cycle Checkpoints (Unit 4) [Checkpoints](/ap-bio/unit-4/cell-cycle/study-guide/4ztGMFvp0v4KAzL65pOP "fv-autolink") sit at the borders of interphase (G1/S and G2/M) to make sure the cell is big enough and the DNA is undamaged before it moves on. They're the quality-control gates that keep interphase from rushing a bad cell into division. ### Chromatin and the Centromere (Unit 4) During [S phase](/ap-bio/key-terms/s-phase "fv-autolink") DNA exists as loose chromatin, not condensed chromosomes. Replication produces two sister chromatids held together at a centromere, which is exactly the structure spindle fibers grab onto later in mitosis. ### S Phase in Meiosis (Unit 5) Meiosis also begins with an interphase that includes S phase. The DNA gets copied once, then divided twice. A 2024 free-response item asked you to describe the function of S phase before meiosis, so this isn't just a mitosis idea. ## On the AP Exam Expect interphase on multiple-choice questions that describe a cell's activities and ask you to name the stage or the whole process. One practice stem describes a eukaryotic cell doing DNA replication, organelle duplication, and protein synthesis before division and asks which term covers it (answer: interphase). Another asks what chromatin looks like during S phase. On free response, the 2024 long FRQ asked you to describe the function of S phase, so be ready to write that S phase replicates DNA to form sister chromatids. The DO here is matching events to the correct stage and explaining why S phase replication is required for the daughter cells to be genetically identical. ## Interphase vs Mitosis Interphase is preparation; mitosis is division. Interphase (G1, S, G2) grows the cell and copies the DNA. Mitosis (prophase, metaphase, anaphase, telophase) then splits the duplicated chromosomes into two nuclei. Saying "the cell divides during interphase" is wrong, division happens in mitosis and cytokinesis. ## Key Takeaways - Interphase has three stages in order: G1 (growth and organelle duplication), S (DNA replication), and G2 (protein synthesis, ATP production, and centrosome replication). - DNA is copied during S phase, producing two identical sister chromatids joined at a centromere, while still in chromatin form. - Interphase is preparation, not division; the actual splitting happens later in mitosis and cytokinesis. - A cell that stops dividing exits into G0, a non-dividing state outside the active cycle. - Both mitosis and meiosis are preceded by an interphase that includes S phase, so DNA gets copied before either kind of division. ## FAQs ### What is interphase in the cell cycle? Interphase is the stage of the cell cycle before division, made of G1, S, and G2. The cell grows, duplicates its organelles, and replicates its DNA so it's fully prepared to enter mitosis. ### Does the cell divide during interphase? No. Interphase is the prep phase where the cell grows and copies its DNA. The actual division of chromosomes happens in mitosis, and the cell physically splits during cytokinesis. ### What's the difference between interphase and mitosis? Interphase (G1, S, G2) prepares the cell and copies the DNA. Mitosis (prophase, metaphase, anaphase, telophase) separates that copied DNA into two nuclei. They alternate in the cycle, so interphase always comes first. ### What happens during S phase of interphase? S phase is when DNA replicates. Each chromosome's DNA (in chromatin form) is copied so it becomes two identical sister chromatids attached at a centromere, which is exactly what a 2024 AP Bio FRQ asked students to describe. ### What is G0 phase and how is it different from interphase? G0 is a state where a cell exits the cycle and stops dividing, like mature nerve cells. It branches off from G1 of interphase, but unlike interphase a cell in G0 isn't actively preparing to divide. ## Related Study Guides - [4.5 Cell Cycle](/ap-bio/unit-4/homeostasis-feedback-loops/study-guide/OgMSpwCrEez0qyWtlCAC) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/ap-bio/key-terms/interphase#resource","name":"Interphase — AP Bio Definition & Exam Guide","url":"https://fiveable.me/ap-bio/key-terms/interphase","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/ap-bio/key-terms/interphase#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-06-11T05:27:38.383Z","isPartOf":{"@type":"Collection","name":"AP Biology Key Terms","url":"https://fiveable.me/ap-bio/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/ap-bio/key-terms/interphase#term","name":"Interphase","description":"Interphase is the portion of the eukaryotic cell cycle made up of G1, S, and G2, during which a cell grows, duplicates its organelles, and replicates its DNA in preparation for mitosis (CED 4.5.A).","url":"https://fiveable.me/ap-bio/key-terms/interphase","inDefinedTermSet":{"@type":"DefinedTermSet","name":"AP Biology Key Terms","url":"https://fiveable.me/ap-bio/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is interphase in the cell cycle?","acceptedAnswer":{"@type":"Answer","text":"Interphase is the stage of the cell cycle before division, made of G1, S, and G2. 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