Answer: Basically cells make up tissues, tissues make up organs, and organs make up organ systems.
Explanation:
Answer: Possession of Valves
Explanation: Veins possess valves which ensures that blood flows in only one direction. Valves helps blood to flow back to the heart against gravitational force.
Arteries don't have valves because the pressure originating from the heart is capable of causing the blood to flow in one direction.
Outputs : Oxygen
Inputs: Sunlight;Carbon dioxide;Water