Biology Test 353

Each haemoglobin molecule can carry a maximum of four molecules of O₂. Binding of oxygen with haemoglobin is primarily related to partial pressure of O₂. Partial pressure of CO₂, hydrogen ion concentration and temperature are the other factors which can interfere with this binding. A sigmoid curve is obtained when percentage saturation of haemoglobin with O₂ is plotted against the pO₂. This curve is called the Oxygen dissociation curve and is highly useful in studying the effect of factors like pCO₂, H₊ concentration, etc., on binding of O₂ with haemoglobin. In the alveoli, where there is high pO₂, low pCO₂, lesser H₊ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, whereas in the tissues, where low pO₂, high pCO₂, high H₊ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin.

A shift of the curve to the right indicates decreased affinity of the haemoglobin for oxygen and hence an increased tendency to give up oxygen to the tissues. A shift to the left indicates increased affinity and so an increased tendency for haemoglobin to take up and retain oxygen.

The effect of this rightward shift of the curve increases the partial pressure of oxygen in the tissues when it is most needed, such as during exercise, or hemorrhagic shock. In contrast, the curve is shifted to the left by the opposite of these conditions.

Carbon dioxide is released during respiration and respirating is a catabalic process, though respiration is also referred to as the amphibolic process. This is because, during synthesis of fatty acids, acetyl CoA is withdrawn from respiratory pathway. Also, in the synthesis of proteins, respiratory substrates get withdrawn. Hence, respiration is also involved in anabolism.

The trachea is divided into primary and secondary bronchi at the level of the 5th thoracic vertebrae, and inter into lungs. Inside the lungs, bronchi divide into numerous bronchioles, each of which terminates into an elongated saccule called the alveolar duct. This duct bears air sacks or alveoli on its surface. Alveoli provide a large surface for gaseous exchange. The number of alveoli in the human lungs has been estimated to be approximately 750 million.

Cellular respiration is a biochemical process of catabolism that involves the oxidation of glucose to CO₂ and water with the release of energy. It is an intracellular process and occurs inside the cells. In contrast, breathing is a physical process that involves simple diffusion and exchange of gases. It is an extracellular process.

The trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of 5th thoracic vertebra into a right and left primary bronchi. Each bronchus undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles. The tracheae, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings. They are lined by ciliated columnar or cuboidal epithelium.

Heterotrophic bacteria are most abundant in nature. The majority are important decomposers.

Many of them have a significant impact on human affairs.

Option (B) is the correct answer because every 100mL of oxygenated blood can deliver around 5mL of O₂ to the tissues under normal physiological conditions.

Option (C), (D) and (A) are incorrect because every 100mL of deoxygenated blood delivers approximately 4mL of CO₂ to the alveoli.

Option (C) is the correct answer because during joint diastole, blood moves freely from atrium to ventricle as atrioventricular valve remain open during joint diastole.

Option (D) is incorrect because decrease in ventricular pressure, during ventricular diastole closes semilunar valves to produce ‘dub’ heart sound.

Option (A) is incorrect because SA node generates action potential to stimulate atrial contraction.

Option (B) is incorrect because bicuspid and tricuspid valves open due to pressure exerted by blood present in atria and decrease in pressure in ventricles during ventricular diastole.

Option (d) is correct because persons with 'AB' blood group contain antigens 'A' and 'B' but lack antibodies anti-A and anti-B in plasma. So, persons with 'AB' blood group can accept blood from persons with AB as well as the other groups of blood due to lack of antibodies in their blood. Therefore, such persons are called "Universal recipients".

SA node acts as pace-maker of heart because its autoexcitable tissue have the ability to generates heart impulses at highest rate(frequency).