CO[itex]_{2}[/itex] is one of the basic inputs for plant growth, along with water, nutrients & energy (sunlight). The output (of photosynthesis) is glucose and O[itex]_{2}[/itex]. Plants convert the glucose into various molecules (e.g. starch, cellulose, lignin, pectin) for anatomical structures (leaves, stems, roots) and an important part of its physiology (biochemistry). Plants do respire; deriving energy from stored molecules (e.g. glucose) and releasing CO[itex]_{2}[/itex] & energy, to accomplish physiological functions (e.g. transport of nutrients, cell division, hormonal regulation).
We may deduce intuitively that more CO[itex]_{2}[/itex] is taken up by plants during photosynthesis than there is released during respiration.
That is why forests and the ocean's algae are often referred to as Carbon sinks. To show this directly we would need to write the biochemical equations (for photosynthesis and respiration) as a function of time and mass of living plant tissue.