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.
Another option is to do a double session on one of those lifting days if time permits. Maybe you get up 30 minutes early and go outside for some hill sprints, or hop on the Air Assault bike before work, then hit the gym on your way home, later that day. There are plenty of ways to get it in.