(a) An aquarium is an artificial system which is also incomplete due to absence of producers, food chains and decomposers. There is no recycling and self-cleaning. However, a pond or a lake is a self-sustained, natural and complete ecosystem where there is perfect recycling of nutrients.
(b) Due to the release of CFCs in the environment, the ozone layer is getting depleted at higher levels of the atmosphere.
Skin Cancer: exposure to UV rays from the sun can lead to increased risk for developing of several types of skin cancers. Malignant melanoma, basal and squamous cell carcinoma are the most common cancers caused by exposure to UV rays.
