The outer covering of diatom is made of-

The outer covering of diatom is made of
a) Magnesium
b) Silica
c) Hydrocarbons
d) None
Correct Answer - B
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 transport 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
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