As humans plants also need oxygen to breathe they only take in carbon dioxide to do photosynthesis.So they wont do photosynthesis at night and so they only need to breathe. even though their stomata are closed at night some oxygen can go inside. and this is how plants breathe when their stomata are … Enzymes change carbon dioxide to glucose.
        
                    
             
        
        
        
Skin remains red after a bad sun burn because:
inflammation causes increased blood flow.
Explanation:
When our skin is exposed to sun rays , the epidermal layer starts getting damaged. The damage to the cell caused by  sun rays triggers the  melanin secretion. Increased secretion of melanin results in darkening of the exposed region .
However, the damage and inflammation to the skin increases blood flow to the skin, this causes reddening of the skin.