The answer is D. the curculitory system transports hormons.
When you smoke a cigarette, the components; e.g. nicotine and carbon monoxide enter the lungs and are absorbed into the bloodstream. They are carried by the Red Blood Cells to the blood-brain barrier, here, nicotine binds to nicotinic acetylcholine receptors (nAChRs), resulting to a cascade that results to release of dopamine (good-feeling neurotransmitter).
It has been found that the rainforests are accountable for about one-third, that is, 28 percent of the oxygen of the Earth, however, the majority of the oxygen, that is, about 70 percent in the atmosphere is generated by the marine plants. The left-over two percent of the oxygen comes from other sources.
The majority of the oxygen comes from the tiny plants in the ocean known as phytoplankton, which lives near the surface of the water and drifts with the currents. Similarly to plants, they perform the process of photosynthesis, that is, they utilize carbon dioxide and sunlight to prepare food, oxygen is the by-product of photosynthesis.
However, the concentration of the dissolved oxygen, which the water can hold relies on the salinity and temperature of the water. The cold water can withhold more oxygen in comparison to warm water and fresh water can hold more oxygen in comparison to salt water. So, the warmer and saltier the water is, the less will be the oxygen dissolved in it.
