However these get mixed in the ventricle while being pumped to the body organs. In higher reptiles, birds and mammals heart is four chambered and the oxygenated and deoxygenated blood are completely separated. Thus the oxygenated and deoxygenated blood are stored separately. The oxygenated blood from lungs is collected in the left auricle and deoxygenated blood from rest of the body in the right auricle. There are two auricles and one ventricle. In amphibians and lower reptiles, the heart is three chambered. The auricles receive blood from the entire body and ventricle pumps it to the gills. Homology in structure of heart- The heart is two chambered in fishes, with one auricle and one ventricle. Thus, homology in structural organisation provides a convincing evidence for the concept of descent with modification.
The existence of homology in the structural plan of limbs of vertebrates can be explained on the basis that all of them have evolved from common ancestors. However they have the same pentadactyl pattern, with almost the same skeletal elements or bones (humerus, radius-ulna,Ĭarpals, metacarpals and phalanges), muscles, nerves and blood vessels arranged on the same pattern. The functions of the fore limbs of these animals are completely different and they also differ in their external appearance. The forelimbs of whale is modified for swimming, the fore limbs of birds and bats are modified for flying, horse for running and man for grasping. Homology of fore limbs- Consider forelimbs of whale (flippers), bat (wings), bird (wings), horse and man. They have different appearance, perform different functions but have common origin and same basic pattern.This phenomenon of similarity between organs of different animals having common origin is called Homology. Structures that are embryologically similar, but have different functions, are called homologous structures. This process has occurred resulting in more than a million species from one common ancestor and is described as "descent with modification". to maintain life all living organisms use energy to synthesise new compounds for growth.Īll these similarities indicate that organisms have evolved from one common ancestor.all living organisms obtain matter and energy from their surroundings.The macromolecules forming the protoplasm is also similar in all cells.Different types of cells also have same basic structure with same organelles.all organisms are made up of one or more cells.Similarities can be seen in structural organisation.
This indicates that all living organisms have evolved from a common ancestor. Despite the diversity in organisms, all living beings exhibit basic unity in both structure and life processes.
According to the theory of evolution, all present day organisms have evolved from simple forms that existed in the past.
0 kommentar(er)
