Answer:
When the calcium level is high in the bloodstream, the thyroid gland releases calcitonin. Calcitonin slows down the activity of the osteoclasts found in bone. This decreases blood calcium levels. When calcium levels decrease, this stimulates the parathyroid gland to release parathyroid hormone.
Answer:
850 meters
Explanation:
From the base of the epipelagic zone to a depth of about 850 meters, there is still enough light for a human to see. The second zone between 200 meters and 1,000 meters is known as the "twilight zone". Some light penetrates as far as 1000 meters down into the ocean.
