Home / Learn / Biology / Nitrogen cycle gameTool #L156 (formerly #1275)

Nitrogen cycle game: follow a nitrogen atom through air, bacteria, plants, animals and decay

Move one nitrogen atom round the nitrogen cycle by picking the right process at each step: fixation, nitrification, uptake by plants, feeding, death, decay and denitrification. Reach the goal in the fewest steps, or name the lit-up arrow. A Class 11 level adds the bacteria, enzymes and chemical forms.

Keep it one tap away for everyday use.

Bookmark Nitrogen cycle game?

Press Ctrl + D now. Your browser opens its own bookmark box, where you choose the name and folder.

  1. Get a goal
  2. Pick process
  3. Round cycle
  4. Practise
Nothing is uploadedWorks offline once open

The nitrogen cycle

    The processes

      Try this

      • Take an atom from the air into an animal in as few steps as you can. Three is the least.
      • Find two different ways for nitrogen to leave the air. Which one needs no living thing?
      • Waterlogged fields lose nitrogen. Which arrow is that, and which bacteria do it?
      • Why do farmers grow peas or beans between cereal crops? Look at arrow 1.

      A teaching model: the real cycle has more side paths (for example ammonia escaping to the air, and nitrate washing into rivers).

      Check yourself

      Fresh questions every time. Type the number of your answer. Nothing is saved.

      What it does

      Every protein and every strand of DNA in your body contains nitrogen. The air is nearly four-fifths nitrogen gas (N₂), but plants and animals cannot use N₂ directly. Nitrogen reaches them, and returns to the air, through a cycle of processes, most of them carried out by bacteria.

      This page draws the cycle as six stores, the air, plants, animals, dead matter and wastes, soil ammonium and soil nitrate, joined by eleven numbered arrows. There are two games:

      • Follow an atom: your nitrogen atom (the red N) starts in one store, and you are given a goal (a green dashed box), or asked to take it all the way round and back. Press the process that moves it. If you pick one that does not start where the atom is, the page says where that process does start and which ones you can use. At the end it tells you whether you used the fewest steps.
      • Name the arrow: one arrow lights up; choose its name from four.

      The Class 8–9 level describes each process in plain words; the Class 11 level adds the bacteria (Rhizobium, Nitrosomonas, Nitrobacter, Pseudomonas), the enzyme nitrogenase and the chemical forms NH₄⁺, NO₂⁻ and NO₃⁻. It fits the Class 9 Science chapter on the Earth as a system of energy, matter and life, the Class 8 chapters on microorganisms and crop production, and nitrogen metabolism in Class 11 Biology.

      Carbon moves round a similar loop in the carbon cycle sandbox; nitrogen passes up the food chains in the food web builder, and plants build their proteins with energy captured in the photosynthesis lab.

      How to use it

      1. Read the challenge above the picture.
      2. Press a process button. The atom moves along the arrow, which lights up, and the step is added to your path.
      3. New challenge gives a fresh start and goal.
      4. Switch to Name the arrow for a naming quiz; your score for this visit is shown with each answer.
      5. The list under the picture explains every process at the level you chose.

      A worked example

      The first challenge is: atom in the air, goal animals. Press Lightning and the atom drops into soil nitrate; press Uptake of nitrate and it is in a plant; press Feeding and it reaches an animal. That took 3 steps, which the page confirms is the fewest. Another 3-step route is fixation, uptake of ammonium, feeding.

      Going back takes longer: from an animal to the air needs 4 steps (death and excretion, decay, nitrification, denitrification), because only denitrification returns nitrogen to the air.

      Tips

      • Only two kinds of arrow leave the air in nature: fixation by bacteria and lightning. People add a third, the fertiliser factory (dashed arrow).
      • Only one arrow returns nitrogen to the air: denitrification, which happens where soil has little oxygen.
      • Legumes (peas, beans, gram) carry nitrogen-fixing bacteria in their root nodules, which is why farmers grow them to enrich the soil.

      Check yourself

      Four fresh questions: three ask you to choose the process that fits a description (type the number of your choice), and one asks the fewest processes between two stores. Nothing is saved.

      FAQ

      Is this the whole nitrogen cycle? No: it is a teaching model. The real cycle also has ammonia escaping from soil and dung to the air, nitrate washing into rivers, and nitrogen locked in rocks.

      Why can’t we breathe in nitrogen and use it? The two atoms in N₂ are held by a very strong triple bond. Only the enzyme nitrogenase, lightning, or a factory at high temperature and pressure can break it.

      Is this from the NCERT book? It covers the same topic with fibub’s own words and pictures. fibub is not part of NCERT.

      Where the numbers come from

      • Standard school biology of the nitrogen cycle: fixation by Rhizobium (root nodules, nitrogenase, leghaemoglobin), Azotobacter and cyanobacteria, lightning, the Haber process, nitrification by Nitrosomonas and Nitrobacter, assimilation, ammonification and denitrification by Pseudomonas and Thiobacillus. Written for fibub in its own words.
      • The fewest-steps answers come from a breadth-first search of the cycle's arrows, checked by hand for every pair of stores (for example air to animals: fixation, uptake of ammonium, feeding = 3).

      Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

      Last updated 2026-11-09.

      Change log for Nitrogen cycle game

      1. Add #1275 Nitrogen cycle game Details on GitHub

      Every change to fibub

      Related tools

      Photosynthesis lab #L56 Move a lamp, add carbon dioxide and warm the water around a pondweed, then watch and count the oxygen bubbles. See which factor is limiting the rate, and graphs of rate against light at several carbon dioxide levels (Blackman's law). Food web builder #L63 Explore a forest or pond food web drawn by trophic level. Tap to add or remove who eats whom, remove a species and see who dies out or increases, count the food chains, and read the energy pyramid with the 10 % rule. Carbon cycle sandbox #L152 Five carbon stores, the air, plants and soil, the surface ocean, the deep ocean and fossil fuels, joined by flows you can see. Choose how much fuel to burn and forest to clear or plant, run the years to 2100 and watch the CO₂ in the air rise or fall, and where each year's carbon goes. Osmosis lab #L55 Drop a potato piece, a raisin, an onion cell or a red blood cell into sugar or salt water and watch water move in or out. See plasmolysis, a % mass change graph, water potential at Class 11 level, a virtual practical and quick questions. Cell explorer #L57 Tap the parts of a plant cell, an animal cell and a bacterium to see what each one does, zoom in, compare the three cells in a table and work out how much the drawing is magnified. Class 9 and Class 11 levels, with quick questions. Mendel's pea garden #L58 Cross tall and short pea plants, or round yellow and wrinkled green seeds, and grow 20, 100 or 1000 random children. Compare the counts with 3 : 1 and 9 : 3 : 3 : 1, see the Punnett square, and at Class 12 level add incomplete dominance, codominance (ABO) and a chi-square check.