The equation you must be able to write
6CO₂ + 6H₂O → (light energy, chlorophyll) → C₆H₁₂O₆ + 6O₂
In words: carbon dioxide and water, using light energy captured by chlorophyll, become glucose and oxygen. Write the condition above the arrow, not beside it — examiners look for that.
Where each ingredient comes from
Carbon dioxide enters through the stomata on the underside of the leaf. Water travels up from the roots through the xylem. Light is absorbed by chlorophyll inside the chloroplasts, which are concentrated in the palisade layer near the top of the leaf where light is strongest.
The two stages
Light-dependent stage: light splits water molecules, releasing oxygen as a by-product and storing energy in ATP and NADPH. This happens in the thylakoid membranes.
Light-independent stage (Calvin cycle): the stored energy is used to fix carbon dioxide into glucose, in the stroma. It does not need light directly, but it stops quickly without the products of the first stage.
Limiting factors
The rate of photosynthesis is capped by whichever factor is in shortest supply: light intensity, carbon dioxide concentration, or temperature. Graph questions almost always show a line rising and then flattening — the flat part means some other factor has become limiting.
Temperature behaves differently from the other two: above roughly 40 °C the rate falls, because the enzymes involved denature.
Common exam traps
Plants respire all the time, including in daylight — photosynthesis does not replace respiration. Oxygen comes from water, not from carbon dioxide. And chlorophyll is not used up; it absorbs light and is not a reactant in the equation.