Question

How deep is the photic or euphotic zone from the upper surface of the sea?
(a) 10 metres
(b) 100 metres
(c) 200 metres
(d) 500 metres

Answer 1

Hint: Photic word similar to photosynthesis, which means photic zone is that region of the sea which receives appropriate sunlight. The photic zone is the surface part of the ocean where many phytoplankton and small mammals were found.

Complete answer:
The light zone of the ocean is divided into three parts starting from surface to depth of the ocean. These zones are the Euphotic zone, the Disphotic zone, and Aphotic Zone.
- Euphotic zone- Euphotic zone is the top zone nearest to the surface of the ocean, also called a sunlight zone. This zone receives the maximum amount of sunlight. Phytoplankton and many amphibians depend on sunlight for survival that's why they are found in this zone. This zone is 200m deep from the surface of the ocean.

Additional Information: -Disphotic zone- Disphotic zone lies at the middle layer and receives less amount of sunlight, also known as the twilight zone. This zone is not suitable for photosynthesis that's why phytoplankton are rarely present in this zone. The water of this zone is more clear as compared to the euphotic zone. This zone lies 800m deep in the ocean.
- Aphotic zone- Aphotic zone lies deep down in the ocean and receives no sunlight, also known as the midnight zone. Phytoplanktons are almost absent, only carnivorous aquatic animals are present here. The water present at this is totally clear. This zone lies 1000m deep. This zone is also called a dark zone and water present in this zone is colder than the surface water.
Most of the algae are found in the euphotic zone which helps in the production of oxygen by photosynthesis. This oxygen is taken by the bottom-dwelling animal for their survival.
Aphotic zone further divided into four zone names as mesopelagic zone, bathyal zone, abyssal zone, hadal zone. From top to bottom in these zones darkness increases with a decrease in temperature, and hardly any aquatic animal is found in the total dark zone because it is impossible for them to catch their prey. Oxygen supply is also very less in the bottom zone, that's why only that organism is found which can survive with minimum oxygen uptake.
So, the correct answer is ‘200m’.

Note: Nowadays, the euphotic zone gets covered by plastic waste, oil, and many other garbages or chemicals, which leads to the transfer of less amount of sunlight in that zone, and the production of oxygen by algae also decreases. Because of this reason many aquatic animals get extinct.