Describe photorespiration.

(N/A) Photorespiration is a process of respiration that occurs in the presence of light within the chloroplasts.
To understand photorespiration, one must consider the first step of the Calvin cycle:
In this reaction, $RuBP$ combines with $CO_2$ to form $2$ molecules of $3-PGA$, a reaction catalyzed by the enzyme $RuBisCO$.
$RuBP + CO_2 \xrightarrow{RuBisCO} 2 \times 3-PGA$
$RuBisCO$ (Ribulose bisphosphate carboxylase-oxygenase) is the most abundant enzyme in the world.
Characteristic: Its active site can bind to both $CO_2$ and $O_2$.
Specialty: $RuBisCO$ has a much greater affinity for $CO_2$ than for $O_2$.
Mechanism: The relative concentration of $O_2$ and $CO_2$ determines which molecule binds to the enzyme.
In $C_3$ plants, some $O_2$ binds to $RuBisCO$ instead of $CO_2$, which decreases the efficiency of $CO_2$ fixation.
In this pathway, $RuBP$ binds with $O_2$ to form one molecule of phosphoglycerate $(3C)$ and one molecule of phosphoglycolate $(2C)$. This pathway is known as photorespiration.
$5C-RuBP + O_2 \xrightarrow{\text{Photorespiration}} 1 \times \text{phosphoglycerate} (3C) + 1 \times \text{phosphoglycolate} (2C)$
In the photorespiratory pathway, there is no synthesis of sugars or $ATP$.
Instead, it results in the release of $CO_2$ and the consumption of $ATP$.
Furthermore, there is no synthesis of $ATP$ or $NADPH$ in this pathway.
Therefore, photorespiration is considered a wasteful process.