Explanation:

• Aquaponics is a system that combines hydroponics, soil-less agriculture, and aquaculture within a closed system (not open system). 
• There are three biological components in the aquaponics process: fish, plants, and bacteria (for cycling of nutrients- ammonia to nitrate conversion). 
• Hydroponics is a method of growing plants in a water-based, nutrient-rich solution.
• Hydroponics does not use soil, instead, the root system is supported using an inert medium such as clay pellets.
• The basic premise behind hydroponics is to allow the plant’s roots to come in direct contact with the nutrient solution, while also having access to oxygen, which is essential for proper growth.

Hence only statement 3rd is correct.