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.
This is energy your muscles would have normally used for weight lifting. So, when you go to lift weights in this state, your body will utilize protein for energy instead, and the protein it will use is from your muscles. So in essence, you're defeating the purpose of weight lifting by doing it after cardio. So, if you must do them on the same day, you should do cardio after weights. For maximum benifit, have a small fast uptake protein/carb supplement between the weights and cardio and wait a few minutes before starting - it would be a good time to do some deep stretches.