2.2.24 (HL)—Secondary productivity

Consumers gain secondary production from ingested organic matter. Gross secondary productivity, or assimilated food, equals ingestion minus faecal waste; net secondary productivity is the biomass retained for growth and reproduction after respiratory losses.

Use GSP = I − F and NSP = GSP − R, keeping area and time units when the values are rates. Faeces remain undigested and unabsorbed, whereas respiration uses assimilated material and releases energy mainly as heat.

A caterpillar ingests 100 kJ, loses 60 kJ in faeces and respires 30 kJ. GSP = 100 − 60 = 40 kJ assimilated; NSP = 40 − 30 = 10 kJ retained as new consumer biomass.

Do not call all ingested food productivity. State whether the question asks for assimilation/gross secondary productivity or net new biomass, show each subtraction, and include the given units.

Food ingested is not automatically growth; assimilation and retention must be separated from waste and respiration.