During photosynthesis, light energy is used to produce ATP molecules which are then used to construct sugar molecules from carbon dioxide and hydrogen obtained from water. Chloroplasts have two outer membranes and several stacks of small disc-shaped membranes called thylakoids (also spelled thylacoids) inside.
Scheduling a week off will give your body time to do this and will also help you return to your workout stronger and ready to challenge your body once again. Many endurance athletes end their season with a week off and many weightlifters will take a week off from their program every four to eight weeks.
Too few rest days and you can end up overtraining and compromising your progress. Too many rest days and your progress can also be compromised. As a general rule, I recommend taking 1-2 days off each week from all activity, spacing those days over the week.