Grade 12 – Breathing and Exchange of Gases – Key Concepts in Biology

1. How is the respiratory system structured and what are its main functions?

The respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli. Its main functions include the exchange of gases (oxygen and carbon dioxide) between the body and the environment, regulation of blood pH through the elimination of carbon dioxide, and the production of speech sounds.

The structure of the respiratory system is designed to facilitate gas exchange. The nose acts as an entrance for air, where it is moistened, warmed, and filtered by the nasal hairs and mucus. The air then passes through the pharynx, larynx, and trachea, which are supported by cartilage rings to prevent collapse.

The trachea branches into two bronchi, which further divide into bronchioles. The bronchioles end in tiny air sacs called alveoli, where gas exchange occurs. The walls of the alveoli are thin and surrounded by capillaries, allowing for the diffusion of gases.

2. Explain the process of ventilation and the mechanism of breathing.

Ventilation refers to the movement of air in and out of the lungs. It involves two phases: inspiration and expiration.

During inspiration, the diaphragm contracts and moves downwards, while the external intercostal muscles contract, elevating the ribcage. This increases the volume of the thoracic cavity, causing a decrease in pressure. As a result, air rushes into the lungs to equalize the pressure.

Expiration, on the other hand, is a passive process. The diaphragm and external intercostal muscles relax, causing the ribcage to move downwards and inwards. This decreases the volume of the thoracic cavity, leading to an increase in pressure. The increased pressure forces air out of the lungs.

The mechanism of breathing is regulated by the respiratory centers located in the medulla oblongata and pons of the brain. These centers receive sensory information from chemoreceptors, which detect changes in the levels of oxygen, carbon dioxide, and pH in the blood. Based on this information, the respiratory centers adjust the rate and depth of breathing to maintain homeostasis.

3. Describe the process of gas exchange in the alveoli.

Gas exchange in the alveoli occurs through the process of diffusion. Oxygen from the inhaled air moves from the alveoli into the capillaries surrounding them, while carbon dioxide moves from the capillaries into the alveoli.

The thin walls of the alveoli and capillaries allow for efficient diffusion. The concentration gradient between the alveoli and capillaries drives the movement of gases. Oxygen diffuses from an area of higher concentration in the alveoli to an area of lower concentration in the capillaries, where it binds to hemoglobin in red blood cells.

Simultaneously, carbon dioxide diffuses from an area of higher concentration in the capillaries to an area of lower concentration in the alveoli. It is then exhaled out of the body.

4. How does the respiratory system regulate the pH of the blood?

The respiratory system plays a crucial role in maintaining the pH of the blood through the elimination of carbon dioxide. Carbon dioxide is a waste product of cellular respiration and forms carbonic acid when dissolved in water. This carbonic acid can lower the pH of the blood, making it more acidic.

To regulate blood pH, the respiratory system increases or decreases the rate and depth of breathing. When the blood becomes too acidic, the respiratory centers in the brain stimulate an increase in breathing rate and depth. This causes more carbon dioxide to be exhaled, reducing the concentration of carbonic acid and restoring the blood pH to normal.

Conversely, when the blood becomes too alkaline, the respiratory centers decrease the breathing rate and depth, allowing carbon dioxide to accumulate in the blood. This leads to the formation of carbonic acid, which lowers the pH back to normal.

5. How does the respiratory system adapt to high altitudes?

At high altitudes, the partial pressure of oxygen decreases, making it harder for the body to obtain sufficient oxygen. The respiratory system undergoes several adaptations to cope with this challenge.

One of the primary adaptations is an increase in the production of red blood cells. This is triggered by the hormone erythropoietin, which is released by the kidneys in response to low oxygen levels. The increased number of red blood cells allows for a higher oxygen-carrying capacity in the blood.

Additionally, the respiratory rate and depth increase to enhance oxygen uptake. The body also undergoes structural changes, such as the development of a larger lung volume and increased capillarization in the lungs, to optimize gas exchange.

These adaptations help individuals acclimatize to high altitudes and ensure that sufficient oxygen is delivered to the tissues, preventing hypoxia.

6. Explain the role of surfactant in the respiratory system.

Surfactant is a substance produced by the type II alveolar cells in the lungs. It is a mixture of lipids and proteins that reduces the surface tension within the alveoli.

Without surfactant, the surface tension within the alveoli would be very high. This would cause the alveoli to collapse during expiration, making it difficult for them to inflate again during inspiration.

Surfactant lowers the surface tension by disrupting the cohesive forces between water molecules lining the alveoli. This reduces the work of breathing and prevents the collapse of the alveoli, ensuring efficient gas exchange.

7. What is the role of the medulla oblongata in regulating breathing?

The medulla oblongata is a part of the brainstem that contains the respiratory centers responsible for regulating breathing. It plays a crucial role in controlling the rate and depth of breathing to maintain homeostasis.

The medulla oblongata contains two main respiratory centers: the dorsal respiratory group (DRG) and the ventral respiratory group (VRG). The DRG primarily controls the basic rhythm of breathing, while the VRG is responsible for modifying the rhythm during certain conditions, such as exercise or speaking.

These respiratory centers receive sensory information from chemoreceptors, located in the carotid and aortic bodies, which detect changes in oxygen, carbon dioxide, and pH levels in the blood. Based on this information, the medulla oblongata adjusts the rate and depth of breathing by sending signals to the respiratory muscles, such as the diaphragm and intercostal muscles.

8. How does smoking affect the respiratory system?

Smoking has numerous detrimental effects on the respiratory system. It damages the airways, reduces lung function, and increases the risk of developing respiratory diseases.

When smoke is inhaled, it irritates and inflames the lining of the airways. This leads to the production of excess mucus, which can clog the airways and impair airflow. The smoke also paralyzes the cilia, tiny hair-like structures that help in clearing mucus and foreign particles from the airways, further compromising their function.

Smoking causes chronic bronchitis, characterized by a persistent cough and excessive mucus production. It also damages the alveoli, leading to emphysema, a condition where the walls of the alveoli become weakened and lose their elasticity. This impairs gas exchange and reduces lung function.

Furthermore, smoking increases the risk of developing lung cancer, as it introduces numerous carcinogens into the respiratory system. It also increases the risk of other respiratory conditions, such as pneumonia and chronic obstructive pulmonary disease (COPD).

9. Discuss the role of the respiratory system in vocalization and speech production.

The respiratory system plays a crucial role in vocalization and speech production. It provides the necessary airflow and pressure for the vocal cords to vibrate and produce sound.

During speech, air from the lungs passes through the larynx, where the vocal cords are located. The vocal cords are stretched across the larynx and vibrate when air passes through them. The pitch and volume of the sound produced depend on the tension and position of the vocal cords.

The muscles of the respiratory system, including the diaphragm and intercostal muscles, control the airflow and pressure needed for speech. They adjust the rate and depth of breathing to provide the appropriate amount of air for vocalization.

Additionally, the articulatory organs, such as the tongue, lips, and teeth, shape the sounds produced by modifying the airflow from the lungs. This allows for the formation of different speech sounds and the ability to communicate effectively.

10. How does exercise affect the respiratory system?

Exercise has several effects on the respiratory system, enabling the body to meet the increased oxygen demand during physical activity.

During exercise, the respiratory rate and depth increase to enhance oxygen uptake and carbon dioxide removal. This is regulated by the respiratory centers in the medulla oblongata, which respond to the increased metabolic activity and carbon dioxide levels in the blood.

The increased breathing rate and depth result in a higher tidal volume (amount of air inhaled and exhaled with each breath) and minute ventilation (total volume of air moved in and out of the lungs per minute). This allows for a greater oxygen uptake and efficient removal of carbon dioxide.

Exercise also improves lung function by increasing lung capacity and efficiency. Regular physical activity strengthens the respiratory muscles, such as the diaphragm and intercostal muscles, improving their ability to expand the thoracic cavity and increase lung volume.

Furthermore, exercise promotes the development of a more extensive capillary network in the lungs, enhancing gas exchange. This results in improved oxygen delivery to the muscles and tissues, allowing for enhanced performance during physical activity.