The outer covering of diatom is made of ?

Ans. is 'b' i.e., Silicon The extracellular coat of diatoms has silica. Diatoms are unicellular algae, suspended in water. They have silicaceous cell wall (i.e. cell wall contains silica) which resist acid digestion and putrefaction. Only live body with a circulation can transpo diatoms form lung to brain, bone marrow, muscles etc. So, presence of diatoms in brain and bone marrow indicates death due to drowning. For detection of diatoms, bone marrow of long bones, e.g. femur, tibia, humerus or sternum is highly suitable and reliable. As diatoms resist acid digestion, to extract them acid digestion techinique is used. Diatoms test is negative in dead bodies thrown in water and in dry drowning. However, diatoms test is invalid, if deceased had drunk this water before submersion or species of diatoms do not match with specimen from the site of drowning