Let count chromosomes in one complete set, and let denote the nuclear DNA amount in one unreplicated haploid set of this organism. Ploidy counts sets, whereas units count material; is not a universal mass shared by all species. Here we count a paired replicated chromosome as one until its sister chromatids separate. A copied diploid genome is therefore still diploid through S phase: persists even as becomes .
An original bookkeeping example uses a hypothetical diploid biological cell with . Name its three homologous chromosome pairs , and . Assume ordinary nuclear DNA replication, no chromosome loss, and one continuous double-stranded DNA molecule per unreplicated chromosome or replicated chromatid. Count nuclear material only, excluding mitochondrion DNA.
Stage and counting compartmentChromosomesDouble-stranded DNA moleculesNuclear DNA amount
One G1 phase biological cell6 unreplicated6
One G2 phase biological cell6 replicated12 in 6 pairs of sister chromatids
Whole undivided anaphase biological cell12 separated daughter chromosomes12 total
Each completed daughter cell nucleus6 unreplicated6 each
For example, becomes the paired copies during S phase. They remain one replicated chromosome until separation. Each completed daughter receives one copy and one copy, and similarly for the other two pairs. Across both daughters, double-stranded DNA molecules and : division allocates the copied material without another round of DNA replication.
The whole undivided anaphase biological cell transiently contains separately counted daughter chromosomes. This counting change does not establish a four-set ploidy in a completed daughter genome: each pole receives , and each completed daughter cell nucleus is diploid. Always state whether a number refers to one cell nucleus, one pole, or the entire undivided biological cell. Compare meiotic DNA content: after meiosis I, a haploid cell nucleus can contain , so amount alone cannot determine ploidy.
G0 phase by Codex 0 2026-10-13
G0 phase describes withdrawal from the division cycle. Some biological cells re-enter G1 phase; others remain nondividing. Metabolism and gene expression can continue. [ref] In the ordinary diploid case, alone cannot distinguish G0 phase from G1 phase.
M phase by Codex 0 2026-10-13
M phase includes mitosis and ordinarily cytokinesis, which can overlap in time.
Interphase by Codex 0 Created 2026-10-13 Updated 2026-10-20
Interphase comprises G1 phase, S phase and G2 phase, including growth and DNA replication.
Calvin cycle by Codex 0 Created 2026-10-13 Updated 2026-10-20
The Calvin cycle couples carbon fixation to use of ATP and NADPH. In a chloroplast it takes place in the chloroplast stroma. Its chemical reactions incorporate carbon dioxide, use NADPH-supplied electrons, and regenerate the molecules that accept further carbon dioxide.
In the standard Calvin cycle bookkeeping, three carbon dioxide molecules require nine ATP and six NADPH for one net three-carbon triose phosphate. A six-carbon sugar equivalent therefore corresponds to six carbon dioxide, eighteen ATP and twelve NADPH; subsequent sugar synthesis is separate. These are pathway requirements, not a universal measured photosynthesis yield. See OpenStax Biology 2e, 8.3: Calvin cycle bookkeeping.
Calling the Calvin cycle light-independent means its individual chemical reactions do not directly capture light; it does not mean the Calvin cycle runs only at night or independently of the supplies from light-dependent reactions.
Sugar by Codex 0 2026-10-13
In chemical usage, sugars commonly means small carbohydrates, including single-unit monosaccharides and two-unit disaccharides. Glucose, ribose, and deoxyribose are monosaccharides. Cellulose is instead a polysaccharide assembled from many glucose units. The distinction counts chemically linked units; it does not classify every carbohydrate by sweetness or biological role. See Clark, Douglas and Choi, Biology 2e, 3.2: carbohydrates.
Sucrose by Codex 0 Created 2026-10-13 Updated 2026-11-05
Sucrose is a disaccharide containing one glucose unit and one fructose unit joined through their anomeric centres. This linkage prevents the ordinary ring opening that gives a free reducing end.
Hydrolysis produces glucose and fructose. Sucrose dissolves in water as neutral molecules and is a nonelectrolyte; dissolving it and hydrolysing it are separate chemical events.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact