Gross Primary Production Calculation Steps:

• Identify net primary production (NPP) as energy in formation of new grass: 23,500 kJ.
• Identify autotrophic respiration as heat loss via plant respiration: 500 kJ.
• Add NPP and respiration to find gross primary production (GPP): 23,500 + 500 = 24,000 kJ.
• Confirm GPP represents total sunlight energy converted to chemical energy by photosynthesis.

Why D is correct:

• Gross primary production equals net primary production plus plant respiration, per ecological energy flow definitions.

Why the others are wrong:

• A: Matches only respiration, ignoring energy stored in new grass.
• B: No combination of values yields 1,000 kJ.
• C: Equals only NPP, excluding respiration from total photosynthetic fixation.

Final answer: D