The circulatory system or vascular system is an organ system that helps in the transport of the blood from and to the heart. The blood transport also takes oxygen, nutrients, hormones, and other components from the heart to the various part of the brain with the help of the arteries and carry waste such as carbon dioxide to the heart in veins.
The oxygenated blood enters in the left atrium and moves to the left ventricle to the aorta and starts its journey to the body whereas deoxygenated blood enters in the right upper chamber or right atrium of the heart and pump to the right lower chamber and to the lungs to carry the oxygen again. This process is a continuous process.
My guess would be H₂O/ water, since osmosis is a form of passive transport and I can't see the model the question references. Gases like O₂/ oxygen, CO₂/ carbon dioxide, and simple sugars like glucose can also pass through a cell membrane with passive transport though.
