Photosynthesis versus respiration: the one table that ends the confusion

Students lose marks on this pair every year, not because either process is hard, but because they are taught weeks apart and never put side by side. Put them side by side and the confusion goes.

Photosynthesis builds. It takes carbon dioxide and water, uses light energy, and makes glucose and oxygen. It happens in chloroplasts, only in green parts of a plant, and only in light.

Respiration breaks down. It takes glucose and oxygen and releases carbon dioxide, water and energy. It happens in mitochondria, in every living cell of every organism, all the time, day and night.

Now the table, in your own hand:

Inputs: photosynthesis takes CO2 and water; respiration takes glucose and oxygen. Outputs: photosynthesis gives glucose and oxygen; respiration gives CO2, water and energy. Energy: photosynthesis stores it; respiration releases it. Where: chloroplast versus mitochondrion. Who: green plants only, versus every living thing including plants. When: light only, versus always.

Notice the outputs of one are the inputs of the other. That is not a coincidence, it is the point: the two processes are the carbon cycle at the scale of one leaf.

The three traps in exam questions:

First, 'plants respire'. Yes, they do, all the time, including in daylight. In bright light photosynthesis is faster than respiration so the plant is a net producer of oxygen; at night only respiration runs. A question about a plant in a dark cupboard is a respiration question.

Second, the word equation direction. Write the arrow the right way and label which process it is. Half the marks are for the labels.

Third, 'energy' is not an input to respiration. Glucose contains the energy; respiration releases it. Writing 'energy + glucose + oxygen' on the left side loses the mark.

The full chapter notes for Class 10 Science, with the diagrams, are in my SEE Science upload. This post is the two pages of it that matter most.