Cellular Respiration Crossword Puzzle

Print a criss-cross vocabulary crossword on cellular respiration, one set for each stage from glycolysis to the electron transport chain.

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Cellular Respiration Crossword

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Answer key: Cellular Respiration Crossword

1YO2GURT3P4FRRE5WATERORD6GTMI7GLUCOSE8KREBSYNNNCT9MITOCHONDRIAULTS10OXYGENICSOLIN11HEATS

Across 1 YOGURT · 5 WATER · 7 GLUCOSE · 8 KREBS · 9 MITOCHONDRIA · 10 OXYGEN · 11 HEAT

Down 2 GRADIENT · 3 PROTON · 4 FERMENTATION · 6 GLYCOLYSIS · 9 MUSCLE

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Inputs, Outputs and Energy 29

  • Adenosine The A in ATP
  • ADP What is left when ATP gives up its third phosphate group
  • Aerobic Word for respiration in which O2 takes up the electrons at the end
  • Carbon dioxide CO2, the waste gas that respiration gives off
  • Catabolism Set of pathways that break molecules into smaller units, releasing energy
  • Combustion Burning; respiration is technically this, but slow and controlled
  • Currency ATP is often called the molecular unit of this, as if cells paid with it
  • Equation C6H12O6 + 6 O2 gives 6 CO2 + 6 H2O + energy, for example
  • Eukaryotic Kind of cell, like yours, that runs the later stages in a special organelle
  • Exergonic Word, like exothermic, for a reaction with a negative ΔG
  • Fifty Kilograms of ATP that an average adult makes and breaks down in a day
  • Fuel What sugar is to a cell, as gasoline is to a car
  • Glucose Also called dextrose or grape sugar; a cell breaks it down for ATP
  • Heat What brown fat gives off instead of making ATP
  • Metabolism Word, from the Greek for change, for the chemistry of life
  • Mitochondria Organelles that descend from once free-living microbes; they make most ATP
  • Nutrients Sugar, amino acids and fatty acids: what cells commonly use in respiration
  • Oxidation What happens to NADH when it hands its electrons to the chain
  • Oxygen Gas written O2; six molecules are used for each C6H12O6
  • Photosynthesis Process of algae and green leaves that stores the energy which respiration later releases
  • Plants Green living things that respire as well as photosynthesize
  • Powerhouse Nickname for the organelle that makes most of the ATP: the ___ of the cell
  • Prokaryotic Kind of cell, such as a bacterium, that runs the later stages in its cytoplasm
  • Reactant C6H12O6 is one in respiration; so is O2
  • Redox Kind of reaction that makes up several steps of respiration: electrons change hands
  • Reduction Fate of O2 at the end of the chain, where it becomes H2O
  • Thirty-eight ATP per C6H12O6 that textbooks often state; current estimates are 29 to 30
  • Triphosphate The TP in ATP: three phosphate groups
  • Water H2O; six molecules are made for each C6H12O6 broken down

Glycolysis 19

  • Aldolase Enzyme that cleaves the sugar molecule
  • Ancient Word for this pathway: it is so widespread that it is thought very old
  • Committed Word for the step, run by the enzyme PFK-1, after which the sugar must go on
  • Cytosol Watery cell fluid in which stage one happens
  • Embden Gustav ___, the first of three names on the EMP pathway of sugar breakdown
  • Fructose ___ 1,6-bisphosphate: the sugar that breaks into two three-carbon pieces
  • Glycolysis Stage that every living organism shares, O2 or no O2
  • Hexokinase Enzyme that adds a phosphate to a six-carbon sugar
  • Hexose Kind of sugar with as many carbons as an insect has legs
  • Kinase Kind of enzyme that transfers phosphate groups
  • Meyerhof Otto ___, the M of the EMP pathway and a 1922 prizewinner
  • Pay-off Phase of the first stage that makes ATP and 2 NADH
  • Phosphorylation Addition of a phosphate group to a molecule
  • Preparatory Word for the opening phase, which uses up 2 ATP
  • Pyruvate End of stage one: C6H12O6 has become two of these
  • Red ___ blood cells carry O2 but use none of it, making their ATP without it
  • Splitting Glyco- means sugar; -lysis means this
  • Substrate ___-level: word for ATP made directly in the first stage and in the citric acid cycle
  • Ten Number of enzyme-driven reactions in the first stage

The Krebs Cycle 22

  • Acetyl ___-CoA: the two-carbon unit that enters the citric acid cycle
  • Citrate Six-carbon molecule made in the first step of the cycle that is named after it
  • Citrus Kind of fruit in which citric acid occurs naturally
  • Coenzyme ___ A: the helper molecule that delivers a two-carbon group to the cycle
  • Decarboxylation Reaction that removes a carboxyl group and releases CO2
  • Dehydrogenase Kind of enzyme that oxidizes one molecule by reducing an electron taker such as NAD+
  • Eight Number of steps in the citric acid cycle
  • FAD Carrier that takes up 2 electrons and 2 H+ to become FADH2
  • Fumarate Cycle molecule whose acid, with a fruit-like taste, is also a food additive
  • GTP High-energy molecule, one for each trip round the cycle, that can go on to make ATP
  • Isocitrate Cycle molecule whose acid is a structural isomer of citric acid
  • Ketoglutarate Alpha-___: cycle molecule with 5 carbons, one fewer than the molecule before it
  • Krebs Hans ___, whose name is on the citric acid cycle
  • Lemon Fruit, like the lime, in which citric acid can reach 8% of the dry weight
  • Malate Cycle molecule whose acid is named from the Latin for apple
  • Matrix Enzyme-rich space inside both membranes of the ATP-making organelle, where its DNA is kept
  • Nobel Prize awarded in 1953 to the cycle's discoverer
  • Oxaloacetate Four-carbon molecule that begins the cycle and is formed again at its end
  • Succinate Cycle molecule whose acid is named from the Latin for amber
  • Tricarboxylic The T in TCA cycle, another name for the citric acid cycle
  • Twice How often the cycle must run to finish off one C6H12O6
  • Vitamin Pantothenate, or B5, is one; the body needs it to build CoA

Electron Transport Chain 19

  • Acceptor O2 is the final electron ___ of the chain
  • Chemiosmosis Flow of H+ back across the membrane through the ATP-making enzyme
  • Cristae Wrinkles that give the membrane of the chain its characteristic shape
  • Cytochrome ___ c: small heme protein that hands electrons on near the end of the chain
  • Gradient Build-up of H+ on one side of a membrane, which drives the making of ATP
  • Hibernating Word for mammals, asleep through winter, that rely on brown fat
  • Intermembrane Word for the narrow space between the two mitochondrial membranes
  • Leaky Word for the mitochondrial membrane that lets a few H+ slip back
  • Machine The ATP-making enzyme is a molecular one
  • Mitchell Peter ___, who proposed the chemiosmotic hypothesis in 1961
  • Motor The ATP-making enzyme has a rotating one
  • Newborn Very young mammal, which relies on brown fat
  • Potential Chemiosmotic ___: the stored energy of the H+ build-up
  • Proton H+, the particle pushed across a membrane to build a store of energy
  • Pump To push H+ across a membrane, using energy released by electrons
  • Synthase ATP ___: the enzyme at the end of the chain that makes ATP
  • Thermogenin Uncoupling protein of brown fat: a channel that lets H+ back through
  • Transport Electron ___ chain: the last stage, where the most ATP is made
  • Ubiquinone Also called Q: a fat-loving part of the chain, made by the human body

Fermentation and Life Without Oxygen 21

  • Anaerobic Word for a way of making ATP that needs no O2
  • Archaea Microbes that, like bacteria, can respire without O2
  • Buchner Eduard ___, who showed that living cells are not needed to ferment sugar
  • Cori ___ cycle: the liver turns the waste of hard-working cells back into C6H12O6
  • Dough Bread mix that rises as its sugars are fermented
  • Ethanol Two-carbon product, besides CO2, when a baking fungus ferments sugar
  • Facultative Word for a microbe that can switch to fermenting when O2 is absent
  • Fermentation Without O2, this process makes only 2 ATP for each C6H12O6
  • Fifteen With O2, a cell's ATP yield is up to this many times what it is without
  • Kimchi Napa cabbage and Korean radish are its main ingredients
  • Lactate Lactic acid in solution, by its other name
  • Methanogen Microbe that gives off methane as it makes its ATP
  • Muscle Kind of animal cell in which lactic acid can be made when O2 runs short
  • Nitrate NO3-, which some microbes use in place of O2 to take up electrons
  • Obligate ___ anaerobe: microbe killed by the normal level of O2 in air
  • Pasteur Louis ___, who in 1876 described life without air
  • Sauerkraut Shredded cabbage with a long shelf life, thanks to bacteria and their acid
  • Sourdough Leavening agent, kept as a starter, that gives bread a tang of acid
  • Sulfate SO4 ion; with it some microbes respire where no O2 is to be had
  • Yeast Fungus that, given O2, will switch from fermenting to respiring
  • Yogurt Spoonable dairy food made with the help of fermenting bacteria

How this list was compiled: Clues written for this site for high school biology, in five sets: inputs, outputs and energy, glycolysis, the Krebs cycle, the electron transport chain, and fermentation. Stages, molecules and figures were checked against the English Wikipedia articles Cellular respiration, Glycolysis, Citric acid cycle and Electron transport chain and linked articles (CC BY-SA 4.0) in October 2026. ATP, NADH and FADH2 are clue words, never answers. Licence: own work

How it works

This printable cellular respiration crossword puzzle fits Letter or A4, answer key included. The first puzzle has 12 basic words, among them Glucose, Oxygen, Mitochondria, Glycolysis, Krebs and Fermentation. Where a word is an answer, other clues use its formula: O2, CO2, H2O, C6H12O6.

Read the full guide

One set for each stage

Glycolysis has Hexokinase, Aldolase, Fructose and Kinase. The Krebs Cycle has Acetyl, Oxaloacetate, Succinate and Malate. Electron Transport Chain has Chemiosmosis, Ubiquinone, Cytochrome and Thermogenin. Inputs, Outputs and Energy has Catabolism, Redox, Oxidation and Reduction. Fermentation and Life Without Oxygen has Ethanol, Sauerkraut, Obligate and Facultative.

Figures a class can check

Number answers come from the stages: Ten for the reactions of glycolysis, Eight for the steps of the Krebs cycle, Twice for the trips round the cycle that one glucose needs, and Thirty-eight, the ATP total textbooks often state, where current estimates are 29 to 30.

  • Print one stage set the day after its lesson, and Cellular Respiration Basics before the unit test.

Questions and answers

What grade is the cellular respiration crossword puzzle for?

Cellular Respiration Basics suits grades 8 to 10, with answers such as Glucose, Oxygen, Yeast and Muscle. The five stage sets use the vocabulary of high school and first-year college biology, such as Oxaloacetate and Chemiosmosis. These bands are our judgment, not a published standard.

Does the cellular respiration crossword puzzle have an answer key?

Yes. The key prints last, on a sheet of its own, with the grid filled in and the answers listed by clue number. It is free, with no sign-up.

What are the three stages of cellular respiration?

Glycolysis in the cytosol, the Krebs cycle in the mitochondrial matrix, and the electron transport chain on the inner mitochondrial membrane, where most of the ATP is made. Each stage has a clue set of its own.

What is the equation for cellular respiration?

C6H12O6 + 6 O2 gives 6 CO2 + 6 H2O + energy: one glucose and six oxygen molecules become six carbon dioxide and six water molecules. Glucose, Oxygen, Water and Carbon dioxide are all answers.

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