Aerobic respiration

The most heavily penalised error on this topic. Glucose and oxygen belong on the left; carbon dioxide and water on the right. If glucose has ended up on the right you have written photosynthesis. Both equations use the same four substances, so recalling the shape is not enough — anchor the direction: you breathe in oxygen and out $\text{CO}_2$.

Energy cannot be created. Respiration releases chemical energy that was already stored in the glucose, so the cell can use it. "Respiration produces energy", "makes energy" and "creates energy" are all refused, and "the organism gains energy" is too vague to credit. The safe mark-scheme form is: energy is released from glucose.

Breathing (ventilation) is the mechanical movement of air in and out of the lungs, driven by the diaphragm and intercostal muscles. Aerobic respiration is the chemical process inside cells. Breathing delivers the oxygen; respiration is what uses it. Examiners advise qualifying the word as "aerobic" or "cell/tissue" respiration wherever both could be meant.

Every organism that needs oxygen respires aerobically — plants, fungi, bacteria and protists as much as animals. Plants do it in every cell, including roots and stems that never see light. Writing that a plant photosynthesises "instead of" respiring loses the mark: it does both, and it is respiration that supplies the energy its cells actually use.

Plants respire continuously, day and night. In a lit leaf cell both processes run at once in different organelles — photosynthesis in the chloroplasts, respiration in the mitochondria. A lit plant appears to take in $\text{CO}_2$ only because photosynthesis outpaces respiration, not because respiration has switched off.