In the 1880s louis pasteur developed a method of weakening viruses. the weakened viruses could be injected into healthy individuals. how is this method effective in fighting viral diseases? a. the immune system develops antibodies in response to the weakened viruses b. the weakened viruses attach to unaffected viruses in the host and interrupt the viral reproductive cycle c. the rate of genetic mutation in the host is decreased due to the introduction of weakened viruses d. weakened viruses are unable to enter the host organism

A. the immune system develops antibodies in response to the weakened viruses

Ans. (A). The Immune system develops antibodies in response to the weakened viruses.

The process of developing immunity by injecting weakened or killed pathogens (vaccines) is known as vaccination. The weakened virus or pathogen acts as disease agent and activates the immune system to fight against the pathogen.

The immune system stimulates B cells to produce antibodies and memory cells against that particular pathogen. These memory cells remain in body for lifetime and encounter the pathogen in subsequent infections by producing antibodies against it.

Thus, the correct answer is option (A).

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.