Doctors have had luck transplanting hearts and lungs. but science has not been very successful in growing hearts and lungs. why? a) they contain nerves and scientists cannot grow nerve cells. b) they are complex organs made of many types of cells and tissues. c) even if researchers build a heart or lung, there is no guarantee that a person's body will accept it. d) human hearts and lungs are not like any other animal organs so there is not source for cells and tissues.

Ans. (B). They are complex organs made of many types of cells and tissues.

Organ culture involves development of tissues or organs, in vitro (outside the body), to restore, maintain, or improve damaged organs or tissues. Many organs and tissues are successfully grown by engineered tissues, such as skin and cartilage.

However, heart, lungs, and other complex organs have not been very successfully grown as these organs are made up of different types of tissues and cells. For examples, heart is made up of cardiac muscle tissue, skeletal tissues, and smooth muscle tissue.

It is quite tough to assemble different types of cells and tissues to make organs fully functional or reproducible.

Thus, the correct answer is option (B).

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.

answer: c

explanation: