Energy in cells: photosynthesis and cellular respiration

The two processes run in opposite directions. Each one makes what the other needs. Start with the big picture, then open the step-by-step animations or test yourself in the Label Labs.

Light energy Glucose + O₂ CO₂ + H₂O Products of one are reactants of the other Chloroplast Photosynthesis · open activities → Mitochondrion Cellular respiration · open activities → ATP energy for cell work heat

Photosynthesis6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

Cellular respirationC₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP

Your level

Applies to every animation and Label Lab. You can still change it inside each one.

Photosynthesis

Light energy stored as glucose, in the chloroplast

Animations

Watch each stage step by step, or see it all at once.

Label Lab

Drag labels onto diagrams against the clock.

Cellular respiration

Glucose broken down to make ATP, in the cytoplasm and mitochondrion

Animations

Follow one glucose from glycolysis to the electron transport chain.

Label Lab

Drag labels onto diagrams and an electron micrograph.

How they compare

	Photosynthesis	Cellular respiration
Where	Chloroplast	Cytoplasm, then mitochondrion
Which organisms	Plants, algae and some bacteria	Nearly all living things, plants included
Reactants	CO₂ + H₂O, using light energy	Glucose + O₂
Products	Glucose + O₂	CO₂ + H₂O + ATP (and heat)
Energy change	Light energy → chemical energy in glucose	Chemical energy in glucose → ATP
Stages	Light-dependent reactions, Calvin cycle	Glycolysis, link reaction, Krebs cycle, electron transport chain
Electron carrier	NADPH	NADH and FADH₂
H⁺ gradient builds in	Thylakoid space	Intermembrane space
Final electron acceptor	NADP⁺	O₂

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