Who am I? I am the base of food chain

I occupy the top of the pyramid. I stand at the end of every food chain. Who am I?

Who am I? I am an oxide capable of showing properties for both acids and bases.

Who am I? I am a salt of potassium hydroxide and nitric .acid.

Who am I? I am gamete that has a tail and travel to fuse with female gamete

Who am I? I am a compound of calcium and can be used for disinfecting drinking water as well as for decolourisation.

Who am I? I am formed by the fusion of male and female gametes

Who am I? I am a product of gypsum and am·used to making chalks and fire proof materials.

Who am I? I am called antichlor and am used to remove excess chlorine from clothes when treated with bleaching powder.

Who am I?I depend on plants for food.

I am a part of brain. I am the site of mental abilities and memory. Who am I ?