Biology Mock Tests

Which of the following is the primary function of Red Blood Cells (RBCs)?

Which of the following vitamin is produced in the human body by the action of sunlight on the skin?

Which of the following diseases is caused by the bite of an infected female Anopheles mosquito?

The organ responsible for producing urea in the human body is:

Which of the following is the powerhouse of the cell?

Which of the following is the smallest bone in the human body?

The following passage is an excerpt from a textbook on biology. DNA replication is the process by which a cell makes an exact copy of its DNA before cell division. This process is essential for the transmission of genetic information from one generation of cells to the next. DNA replication occurs during the S (synthesis) phase of the cell cycle. The process begins when the enzyme helicase unwinds and separates the two strands of the DNA double helix at a location called the origin of replication, forming a replication fork. Single-strand binding proteins stabilize the separated strands, preventing them from reannealing. The enzyme topoisomerase relieves the tension created by the unwinding by cutting and resealing the DNA backbone ahead of the replication fork. DNA polymerase, the main enzyme responsible for building new DNA strands, can only add nucleotides to the 3' end of an existing strand, meaning it synthesizes DNA only in the 5' to 3' direction. This creates an asymmetry: the leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together by the enzyme DNA ligase. RNA primase synthesizes short RNA primers that provide the starting point for DNA polymerase. The result is two identical DNA molecules, each consisting of one original (parental) strand and one newly synthesized strand — a process known as semi-conservative replication, as demonstrated by Meselson and Stahl in 1958. According to the passage, why is the lagging strand synthesized discontinuously?

Which vitamin is produced in the human body when skin is exposed to sunlight?