What is the relationship between light and depth of the ocean

The sunlight that falls on the ocean surface in an open ocean, can penetrate up to a depth of about 200 to 300 m below the sea level.  

Depending upon the depth the sunlight can penetrate, the ocean body is divided into 3 parts. They are as follows-

(1) Euphotic zone- This zone is also known as the sunlight zone. It extends up to a depth of about 200 meter below the sea level. this layer is comprised of most of the commercial fisheries  and many other marine animals exist such as the turtles.

(2) Twilight zone- This zone is below the euphotic zone. It cover a vertical depth from 200 to 1000 meters below the sea level. The amount of light significantly decreases here due to the greater depth. The process of photosynthesis does not take place here due to the due to the absence of sunlight.

(3) Midnight (Aphotic) zone- This zone is the deepest part of the ocean where there is no sunlight and its totally dark. At the depth below 1000 meters is this zone and here very complex type of organisms are able to survive that can exist under the extreme pressure condition.

Thus, the amount of light decreases with the increasing amount of depth in the ocean.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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