Add organelles to grow, but every one burns energy and a bigger cell costs more to run: keep the ATP flowing or starve.
Your cell starts with one mitochondrion, one ribosome, 20 ATP (its energy), 30 nutrients and full health. Spend ATP to build organelles: mitochondria turn nutrients into ATP, chloroplasts make ATP from light, lysosomes digest food into nutrients, ribosomes make proteins, membrane patches blunt virus damage, and nucleoli add ATP storage and slow self-repair. Every organelle also costs ATP every second just to keep running.
Every organelle makes the cell bigger, and a bigger cell pays more: each organelle's build cost and upkeep are multiplied by 1 + (organelles ÷ 80), so at 40 organelles everything costs 1.5 times as much. Nutrients can only come in through the membrane, whose area grows more slowly than the cell, so past a certain size extra lysosomes stop helping. If ATP runs out, every missing unit of ATP costs 2 health.
Viruses attack from the 25-second mark onward, each one tougher than the last. While a virus is inside, every ribosome makes 0.9 proteins a second, each costing 1.5 ATP. A slider splits them between antiviral proteins, which destroy the virus, and repair proteins, which heal 0.5 health each. Survive 3 minutes to win.
At the start your mitochondrion makes 4 ATP a second while the two organelles cost about 1.13 to run, so you gain 2.87 ATP a second. The mitochondrion needs 1.2 nutrients a second but only 1 diffuses in, so the starting pool of 30 slowly drains; once it is empty the mitochondrion runs at five-sixths power and you gain 2.21.
Building a second mitochondrion straight away (12 ATP) backfires: once the pool is empty both share the same 1 nutrient a second, so they still make only 3.33 ATP between them while upkeep rises, and your gain falls to 1.67. Build a lysosome (10 ATP) as well and nutrients rise to 2.1 a second: the two mitochondria make 7 ATP, upkeep is 2.1, and you gain 4.9 ATP a second.
Cell Sprawl turns a cell into an energy budget: every part has to pay its way, and bigger is not automatically better.
Every organelle runs on ATP, the molecule cells use to carry energy. Two of them were once independent: the theory that mitochondria and chloroplasts descend from free-living bacteria swallowed by another cell was outlined by Konstantin Mereschkowski in 1905 and revived with evidence by Lynn Margulis in 1967 (symbiogenesis).
Cells stay small because a small cell has a lot of surface for its volume, which helps it take in nutrients across its membrane; as a cell grows, its volume rises faster than its surface (surface-area-to-volume ratio). Cell Sprawl's size limit is that rule.
The game simplifies the rest. Real infected cells do not make antibodies, which come from plasma cells of the immune system; instead they release interferons that protect their neighbours, first described by Alick Isaacs and Jean Lindenmann in London in 1957 (interferon). The real nucleolus builds ribosome parts rather than storing energy, and chloroplasts are found mostly in plant and algal cells, not alongside every other organelle in the game.
Cell Sprawl is an original PlayPendium game. It started from one question: what does it cost a cell to run each of its parts? Runs last up to three minutes, need no install or account, and the Daily is the same for everyone.