An aphotic zone is a zone where light can be received from the sun (or other sources of light).
For example in the ocean, it will be the zone that begins a 200m deep and goes to the bottom of the sea.
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Answer:
They are stimulated by an antigen.
Explanation:
Natural killer cells are cytotoxic cells that help our body in innate immune response. These are an critical and important component of the innate immune system of our body. These natural killer cells provide a rapid response towards the virus infected cells. These cells have capability to detect MHC that are present on the infected cells. Natural killer cells do not require activation for killing those cells which are missing MHC I. Due to this feature, they are named as the Natural killer cells. These cells can directly induce the death of tumor cells and play an important role in immunosurveillance.
It is not necessary that the eukaryotic cell contain vacuole. Newly form cells donot have vacuole. So the option with vacuole are all wrong and the right option is c. Because cell membrane, E. R, ribosomes and nucleus are always present in the living eukaryotic cell
