One of the characteristics that define an organ is to have different layers of tissue, which fits the description that an organ must be comprised of at least two different kinds of tissue. The fact that a serous membrane contains superficial and deeper layers of epithelial and connective tissues, grants it the category of being an organ.
Alright, so the highest temperature at which water is most dense id 4 degrees Celcius, if it gets lower than that, water would start to expand. So at 5 degrees, it would just be rain.
