Question

Bone marrow is absent in
A. Reptiles
B. Amphibians
C. Aves
D. Mammals

Answer 1

Hint: Bone marrow is found within the spongy portions of bones. It is a semi-solid tissue. The process of hematopoiesis (a process of production of blood cells) takes place in the bone marrow.

Complete answer: Bone marrow is the site of the production of new blood cells. This process is called haematopoiesis. Bone marrow is composed of marrow adipose tissue, haematopoietic cells, and supportive stromal cells. Kingdom Animalia is one of the three kingdoms and it is further divided into different classes. They are Vermes, Insecta, Amphibia, Aves, and Mammals.
-Reptiles cold-blooded, with four-legged or tetrapod animals. Bone marrow is found within the bones of the reptiles and also in the ribs of snakes.
-The ectothermic tetrapod vertebrates that require water or a moist environment to survive are known as amphibians. Amphibians are the first phylogenetic group to exhibit the presence of hematopoietic bone marrow.
-Warm-blooded vertebrates that belong to the class of aves are known as birds. They are characterized by the presence of feathers. The mode of locomotion of most of the aves is flying except the ostrich. Aves do not possess the bone marrow.
-Groups of animals that are characterized by the presence of mammary glands in females are placed in the Mammalia group. This characteristic of mammals makes them different from birds and reptiles. Bone marrow is present in all animals which belong to the group mammals.
Therefore, bone marrow is absent in Aves.
So, option C is the correct option.

Note: In human beings, bone marrow can be found in the ribs, sternum, vertebrae, and bones of the pelvis. It constitutes about 5% of the total body mass of a healthy person. The bones of birds are hollow with an air cavity and fully ossified. Such bones are called pneumatic bones. All birds have adapted pneumatic bones for the purpose of flying.