Q.Compare: Photosynthesis and Respiration.

Step 1. Compare direction and purpose. Photosynthesis is an anabolic, energy-STORING process: it reduces CO2 to glucose (an energy-rich compound) using light energy trapped by chlorophyll. Respiration is a catabolic, energy-RELEASING process: it oxidises glucose back down to CO2 and water, releasing the energy that was stored in it, and trapping a large share of that released energy in ATP.

Step 2. Compare gas exchange. Photosynthesis takes in CO2 and releases O2. Respiration takes in O2 (in its aerobic form) and releases CO2 - the exact reverse gas exchange.

Step 3. Compare site and cell type. Photosynthesis occurs only in chloroplast-containing (green) cells. Respiration occurs in the cytoplasm and mitochondria of every living cell, green or not.

Step 4. Compare timing/light dependence. Photosynthesis's light reactions need light and effectively stop in the dark (though its 'dark reaction' itself is only light-independent, not light-opposed). Respiration is continuous, going on in every living cell at all times, in light or darkness alike. …

Comparing photosynthesis and respiration across direction (build vs break down), gas exchange, s …

• Describing only the gas-exchange difference (CO2 in/O2 out vs O2 in/CO2 out) without also covering the energy direction (storing vs releasing) and site differences. …