ACT Science Photosynthesis and Respiration: Track Energy and Matter Flow

Photosynthesis: Plants use sunlight to convert CO₂ and H₂O into glucose and O₂. Energy stored in glucose. Formula: 6CO₂+6H₂O+light → C₆H₁₂O₆+6O₂. Respiration: Organisms break down glucose to release energy (ATP), producing CO₂ and H₂O. Formula: C₆H₁₂O₆+6O₂ → 6CO₂+6H₂O+energy. Notice: Photosynthesis is respiration in reverse. One stores energy; one releases it. Questions ask you to predict energy flow in food chains. Producers (plants) capture sunlight. Consumers eat producers (or other consumers) and release stored energy. Energy decreases at each level (not all food is consumed; some is used for living).

Example energy flow: Sun → Plant (photosynthesis stores energy) → Herbivore (eats plant, respires) → Carnivore (eats herbivore, respires). Energy decreases with each step.

Mistake 1: Forgetting that respiration releases energy; photosynthesis stores it. Mistake 2: Assuming all energy transfers to the next level. Only about 10% of energy is passed to the next consumer; the rest is lost to heat and living processes. Mistake 3: Confusing matter flow with energy flow. Matter (atoms) cycles: CO₂ → plant → animal → respiration → CO₂. Energy flows one way: sun → organisms → heat. Track matter cycling separately from energy flow.

During practice, draw energy pyramids and matter cycles. This visual representation clarifies both concepts.

Scenario 1: Sunlight hits a plant. Photosynthesis stores energy in glucose. A cow eats the plant. Respiration releases about 10% of energy (rest is lost). Lion eats the cow. Again, about 10% energy transfer. Energy decreases through each level. Scenario 2: Plant photosynthesizes: takes in CO₂, releases O₂. Animal respires: takes in O₂, releases CO₂. Cycle continues. Scenario 3: A plant is eaten by 100 herbivores. Each herbivore gets 1% of plant's energy. Carnivore eats all 100 herbivores and gets about 10% of total energy available. Energy decreases dramatically with each transfer. For each scenario, predict energy flow and matter cycling.

Find three ACT Science passages with photosynthesis/respiration questions. Predict energy and matter flow. By the third passage, flow prediction will be systematic.

Photosynthesis and respiration questions appear on some ACT Science sections. They test understanding of energy and matter in ecosystems. Students who predict energy and matter flow accurately pick up 1 point because the logic is consistent and generalizable.

On your next practice test, draw energy pyramids and matter cycles for every ecosystem described. By test day, energy and matter flow should guide your ecology answers.