They probably do not move in direct tandem, because most of the CO2 stays in the body, which means a higher amount of oxygen is taken out of the air, then CO2 being reintroduced to it.
Every time you breathe in, you not only breath in O2, but also CO2, thus lowering the amount of CO2 in the room relatively to the amount of oxygen.
In other words, 1000 ppm CO2 in the air do not mean 1000 ppm O2 less, but significantly more parts of oxygen less.
... not at all. No CO2 is "stored", though it may temporarily hang out in buffers such as the blood. But they have a very limited capacity and the flow out is extremely close to the production on a very very short timescale, and on a longer timescale approaches equality.
> which means a higher amount of oxygen is taken out of the air, then CO2 being reintroduced to it.
This is true, and I was wrong in my comment, but not for that reason. Only some of the O2 used is paired with CO2 and breathed out. Some joins with hydrogen from foods and becomes water. Most foods are carbon chains, with each carbon atom having two hydrogen atoms, so this ratio can get as high as around 2:1 for low-oxygen foods like fat, but lower for carbs, which tend to have significant quantities of oxygen (which will in balance add to the O2, meaning that more of what is used up when breathed in is breathed out). (Proteins also have nitrogen which complicates things.)
Every time you breathe in, you not only breath in O2, but also CO2, thus lowering the amount of CO2 in the room relatively to the amount of oxygen.
In other words, 1000 ppm CO2 in the air do not mean 1000 ppm O2 less, but significantly more parts of oxygen less.