Answer:
Naturally: only during daylight hours
Artificially: all 24 hours (under perfect circumstances)
Explanation:
Photosynthesis can only occur when a plant receives energy from a light source. Naturally, the light source would be the sun which is only around for a certain amount of hours. If the plant is under an artificial light source, like a lamp, then photosynthesis can occur at all hours of the day.
If all humans had the same DNA, and one person got the cold, everyone would die at some point. The more diversity there is the more chance of surviving an outbreak or natural disaster or something. Think of the flu. there are HUNDREDS of strains out there. some are resistant to our medicines and others aren't.
