The four important characteristics of respiratory surface are:
1. Thin walls
2. Moisture
3. Large surface area
4. Blood supply
Respiratory system or respiratory tract is divided into upper and lower tract. Upper respiratory tract includes nose and its cavities, sinuses, pharynx and the part of the larynx. Lower respiratory tract consists of the trachea, bronchi, bronchioles and the alveoli.
Alveoli are the ends of the respiratory tract the smallest units in it. Alveoli are small folded air sacs that are branching off from alveolar ducts and providing an extremely large surface area for the gas exchange. Gas exchange occurs thanks to small blood vessels – capillaries that surround alveoli and it occurs via the process of diffusion.
So, respiratory surface is thin membrane also known as the blood–air barrier that consists of the alveolar epithelial cells, their basement membranes and the endothelial cells of the alveolar capillaries.
Answer:
A) histone coding genes
Explanation:
Histones are the proteins involved in the packing of DNA in eukaryotes. They are positively charged proteins and are not found in bacteria. To analyze the evolutionary relationship in a gene between eukaryotes and bacteria, one must choose the gene present in both of them. The tRNA, rRNA and hexokinase encoding genes are common to both bacteria and eukaryotes. Therefore, one of these genes may be chosen for the study. However, histone encoding genes are not present in the genomes of bacteria. Therefore, the study of the histone encoding gene would not be useful for the mentioned purpose.
I recall that Professor Kwang had observed amoebas that had cannibalized bacteria cells. The bacteria were slaughtering the amoebas, but somehow some survived. This particular group of amoebas contained bacteria that thrived inside it. Hence the name, endosymbiosis. However, this lucky group and it's offspring could not survive without bacteria.
