Which scientist is credited with the discovery of the cell nucleus? MCQ with Answer and Explanation

Explanation:
Diatomaceous earth is a siliceous, sedimentary rock formed from the fossilized remains of diatoms. Diatoms have unique, highly resistant cell walls called frustules, made of hydrated silicon dioxide (silica). Over millions of years, these frustules accumulate on ocean and lake floors, forming diatomaceous earth, which has numerous industrial applications due to its abrasive and porous nature.

Explanation:
Down syndrome (trisomy 21) is an autosomal aneuploidy caused by nondisjunction resulting in three copies of chromosome 21. It is characterized by intellectual disability, flat facial profile, protruding tongue, and simian crease. Turner's syndrome is monosomy X (45, X). Klinefelter's is 47, XXY. Phenylketonuria is an inborn error of metabolism (autosomal recessive) due to deficiency of phenylalanine hydroxylase.

Explanation:
Porifera (sponges) are characterized by the presence of a complex water canal system (canal system) used for food gathering, respiratory exchange, and waste removal. Water enters through numerous small pores called ostia and exits through a large opening called the osculum. They are mostly marine and asymmetrical.