Problem 127 - Objective Biology for NEET

Question

The blood leaving the lungs has all its haemoglobin oxygenated and gives up oxygen to the tissues because (a) The tissue can absorb \(\mathrm{O}_{2}\) from oxyhaemoglobin. (b) \(\mathrm{O}_{2}\) concentration in tissues is lower and \(\mathrm{CO}_{2}\) concentration is higher as compared to lungs. (c) \(\mathrm{O}_{2}\) concentration in tissues is higher and \(\mathrm{CO}_{2}\) concentration is lower as compared to lungs. (d) Oxyhaemoglobin undergoes reduction.

Step-by-Step Solution

Answer

The correct answer is (b). O2 concentration in tissues is lower and CO2 concentration is higher as compared to lungs. This is because oxygen moves from areas of higher concentration to areas of lower concentration, which in this case are the body's tissues.

Step 1: Understand the Mechanism

Haemoglobin is a protein in red blood cells that carries oxygen from the lungs to all parts of the body. Understanding this, it can be inferred that oxygen would be released from haemoglobin in the presence of tissues that need oxygen.

Step 2: Analyzing the Statements

The next step is to analyze each statement separately:\n(a) While it is true that tissues can absorb O2 from oxyhaemoglobin, this statement does not explain why oxyhaemoglobin gives up oxygen to the tissues. Therefore, this is not the correct answer.\n(b) This makes logical sense because where there is a high concentration of CO2, there is usually a low concentration of O2. Haemoglobin would release oxygen where it is needed most, i.e., where the O2 concentration is low. This seems like a possible answer.\n (c) This statement contradicts the basic principles of diffusion - substances move from areas of higher concentration to areas of lower concentration, not the other way around. Therefore, this is incorrect.\n(d) If oxyhaemoglobin undergoes reduction, it would gain electrons and not lose any oxygen. Hence, this option is not correct.

Step 3: Choosing the Correct Answer

From the given alternatives, it is clear that option (b) is the correct answer as it supports the basic principles of diffusion and depicts the physiological necessity of tissues to absorb oxygen.

Key Concepts

Haemoglobin Function

Haemoglobin, often abbreviated as Hb, is an essential protein found in red blood cells. It is primarily responsible for transporting oxygen from the lungs to all tissues in the body. This protein has a distinctive structure that includes four subunits, each of which can bind to an oxygen molecule. Binding occurs as haemoglobin picks up oxygen molecules in the lungs, forming a compound called oxyhaemoglobin.

The design of haemoglobin allows it to effectively carry oxygen through the bloodstream. The process is reversible, enabling haemoglobin to release oxygen where it is needed. This flexibility is vital because it ensures that tissues receive an adequate oxygen supply for cellular activities. In regions where oxygen is scarce and carbon dioxide levels are high, haemoglobin's ability to 'sense' and respond to these changes becomes crucial.

Key roles of haemoglobin include:

• Transporting oxygen from lungs to tissues.
• Assisting in carbon dioxide transport from tissues back to the lungs.
• Helping maintain the acid-base balance in the blood.

Oxyhaemoglobin

Oxyhaemoglobin is the product formed when haemoglobin binds with oxygen in the lungs. This binding is a critical step in the oxygen transport process. The formation of oxyhaemoglobin facilitates the efficient transportation of oxygen throughout the circulatory system.

Upon reaching tissues that require oxygen, the oxyhaemoglobin releases its bound oxygen. This release occurs due to a combination of environmental factors, such as the local concentration of carbon dioxide and the lower partial pressure of oxygen in tissues. These factors signal that the tissue is in need and trigger the dissociation of oxygen from haemoglobin.

Essential characteristics of oxyhaemoglobin:

• It has a high affinity for oxygen at the lungs, where oxygen levels are high.
• Its affinity decreases in tissues, where it needs to release oxygen.
• It plays a key role in oxygen delivery from lungs to various parts of the body.

Diffusion Principles

Diffusion is a fundamental principle that explains how gases like oxygen and carbon dioxide move in the body. Diffusion occurs when molecules move from an area of higher concentration to an area of lower concentration. This process is passive and requires no energy input from the body.

In the context of oxygen transport, diffusion is crucial at multiple stages:

• Oxygen diffuses from the alveoli in the lungs into blood vessels, where it binds with haemoglobin to form oxyhaemoglobin.
• In tissues, oxygen diffuses from the blood, where its concentration is higher, into cells, where its concentration is lower.

This natural diffusion mechanism ensures that oxygen is delivered to where it is most needed and highlights the elegance of the body's ability to self-regulate through basic physical principles.

Physiology of Respiration

The physiology of respiration encompasses all the processes involved in getting oxygen into the body and removing carbon dioxide. It involves two main components: pulmonary ventilation (breathing) and gas exchange.

Breathing allows the intake of oxygen-rich air into the lungs and the expulsion of carbon dioxide-rich air. Inside the lungs, oxygen is transferred to the blood via alveoli, tiny sacs where gas exchange occurs. Here, carbon dioxide, a metabolic waste product from the body's cells, diffuses from the blood back into the lungs to be exhaled.

Gas exchange reflects a perfect orchestration:

• Oxygen from inhaled air binds to haemoglobin in red blood cells in the lungs.
• Haemoglobin releases oxygen where it's needed, in response to factors such as pH, temperature, and carbon dioxide levels.
• Carbon dioxide is transported back to the lungs either dissolved in plasma, bound to haemoglobin, or as bicarbonate ions.

These processes ensure that cells receive oxygen for metabolism and that waste products like carbon dioxide are efficiently removed from the body.