Higher: limiting factors and oxygen debt

The idea

Light intensity is inversely proportional to the square of distance from the light source: doubling the distance cuts the intensity to a quarter. Growers use limiting factor graphs to decide how much heat, light and carbon dioxide are worth paying for. After exercise, an oxygen debt remains: extra oxygen is needed to react with the lactic acid, which the blood carries to the liver to convert back to glucose.

1. Use light intensity ∝ 1 ÷ distance².
2. Read which factor limits each part of a graph.
3. Explain where lactic acid goes after exercise.

Watch out Doubling the distance does not halve the light intensity: it cuts it to a quarter.