BIOLOGY 3 Marks Question

• The oxygen dissociation curve is a graph obtained when the percentage saturation of haemoglobin with oxygen is plotted against the partial pressure of oxygen.
• When the first molecule of oxygen binds to haemoglobin, its affinity for the second molecule of oxygen increases.
• Hence, the formation of oxyhaemoglobin is faster which is indicated by the steep slope of the S curve.
• When the formation of oxyhaemoglobin comes to rest or when there are no haemoglobin molecules available for binding, the curve achieves a plateau phase.

As altitude increases, the oxygen level in the atmosphere decreases. Therefore, as a man goes uphill, he gets less oxygen with each breath. This causes the amount of oxygen in the blood to decline. The respiratory rate increases in response to the decrease in the oxygen content of blood. Simultaneously, the rate of heart beat increases to increase the supply of oxygen to blood.

1. Artificial respiration is provided to a person, who has stopped breathing due to smoke inhalation, drowning or electric shock.
2. No, a person cannot be brought back to life (consciousness) once he is dead.
3. Neha is an intelligent, sensible, cautious and a helpful, kind and humble girl.

In some industries, workers may inhale harmful dust. For example, workers in stone crushing plant may inhale silica dust. When there is long term exposure to such situations, lungs can develop inflammation, which leads to fibrosis and ultimately to serious damage to lungs.

1. Air filters in automobiles prevent dust from getting into the carburetor.

Explanation:
We know that the respiratory system has a very good air filter mechanism. Hairs in the inner lining of the nasal cavity; along with mucus; prevent dust particles from entering the lungs. This prevents accumulation of undesirable substances inside the lungs. The oral cavity does not have such air-filter system. When someone breathes through the mouth, he also inhales dust particles and some germs along with the air. The dust particles and germs can prove detrimental for the lungs. While germs can cause infection, dust particles can lead to blisters in the inner B lining of the lungs. Such blisters are often seen in the lungs of workers who work Stein stone quarries.

1. Inspiration is initiated by the contraction of diaphragm, which increases the volume of the thoracic chamber along the antero-posterior axis.
2. The contraction of external intercostal muscles lifts the ribs and sternum upwards and increases the volume of the thoracic cavity along the dorso-ventral axis.
3. The overall increase in the thoracic volume causes an increase in the pulmonary volume.
4. This decreases the intra-pulmonary pressure to less than that of the atmospheric pressure and hence, air from outside rushes into the lungs, i.e., inspirationis achieved.

Large number of chemoreceptors are located in the carotid bodies (lie bilaterally in the bifurcations of the common carotid arteries). Their afferent nerve fibres pass through glossopharyngeal cranial nerve and thus to dorsal respiratory area of the medulla oblongata, sizeable number of chemoreceptors are also located in the aortic bodies (which lie along the arch of aorta). Their afferent nerve fibres pass through the vagus cranial nerve and thus, to dorsal respiratory group of neurons.

Pulmonary respiration involves the following steps:

1. Breathing or pulmonary ventilation by which atmospheric air is drawn into the lungs and carbon dioxide-rich air is sent out.
2. Diffusion of the respiratory gases, oxygen and carbon dioxide across the aoveolar membrane into the blood.
3. Transport of gases in the blood.
4. Diffusion of oxygen from the blood into the tissues and carbon dioxide from the tissues into the blood.
5. Utilisation of oxygen by the cells for oxidation and release of carbon dioxide.

1. Haemoglobin is the respiratory pigment present in the erythrocytes; it transports oxygen and carbon dioxide, the respiratory gases.

Transport of oxygen:

1. Oxygen combines with the haemoglobin in a reversible manner to form oxyhaemoglobin; each haemoglobin molecule can carry a maximum of four oxygen molecules.
2. 97% of oxygen is carried as oxyhaemoglobin in the blood and every 100ml of blood can deliver about 5ml of oxygen.

Transport of carbon dioxide:

1. Carbon dioxide combines with the haemoglobin to form carbaminohaemoglobin in the erythrocytes.
2. About 20-25 percent of the carbon dioxide is transported as carbaminohaemoglobin and every 100ml of deoxygenated blood transports about 4ml of carbon dioxide.

1. The factors which affect the rate of diffusion of a gas are:

1. The thickness of the membrane.
2. The solubility of the gas.

2. Vital capacity.
3. Cigarette smoking is the major cause of emphysema.

1. Expiration occurs when the intra-pulmonary pressure is greater than the atmospheric pressure.
2. The diaphragm muscles and the intercostal muscles relax.
3. The diaphragm moves upward and the rib cage downward and inward.
4. This causes a decrease in the volume of the thoracic cavity, that results in an increased intra-pulmonary pressure.
5. So air rushes out of the lungs (expiration) into the atmosphere.

The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. The pressure within the lungs is less than the atmospheric pressure so, there is a negative pressure in the lungs with respect to atmospheric pressure. The puncture in the chest affects this pressure gradient maintained by the lungs and thus, may cause cessation of breathing.

Anatomically. thoracic chamber is an air-tight chamber. The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome-shaped diaphragm. The anatomical setup of lungs in thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung pulmonary) cavity. Such an arrangement is essential for breathing, as we cannot directly alter the pulmonary volume.