Unit 7: Gaseous Exchange in Living Organisms (Biology)

# Unit 7: Gaseous Exchange in Living Organisms ## Unit 1: Gaseous Exchange in Living Organisms ### Introduction to Gaseous Exchange For aerobic respiration to occur efficiently, cells need a constant supply of oxygen and must expel carbon dioxide, a waste product of aerobic respiration. Organisms...

# Unit 7: Gaseous Exchange in Living Organisms ## Unit 1: Gaseous Exchange in Living Organisms ### Introduction to Gaseous Exchange For aerobic respiration to occur efficiently, cells need a constant supply of oxygen and must expel carbon dioxide, a waste product of aerobic respiration. Organisms take in oxygen from their environment and release carbon dioxide back into it. Different organisms have specialized organs for this process, such as lungs in humans and gills in fish. The movement of respiratory gases—oxygen into the body and carbon dioxide out across gas exchange surfaces is called gas exchange, which occurs by diffusion. Molecules move down a concentration gradient from high to low concentration. ### Key Concepts * **Cellular respiration:** A chemical process inside cells where food molecules like glucose are broken down to release energy. * **Breathing:** The physical process of moving oxygen-rich air into the lungs and expelling carbon dioxide-rich air out of them. * **Gas exchange:** The process of oxygen and carbon dioxide diffusing across a surface or membrane in opposite directions, necessary for cellular respiration and removing carbon dioxide from cells. ### Diffusion Diffusion is the movement of molecules from a region of high concentration to a region of low concentration. ### Breathing Breathing involves ventilating the lungs by moving air in and out. ### Surface Area-to-Volume Ratio As organisms grow, their surface area-to-volume ratio decreases. This ratio affects how much oxygen can be absorbed through the surface relative to the organism's volume. Small organisms have a large surface area relative to their volume, allowing sufficient gas exchange by diffusion across their body surface. Larger organisms have a smaller surface area relative to their volume and need specialized structures to facilitate gas exchange. ### Specialized Structures in Larger Organisms * Gas exchange organs: Such as gills in fish and lungs in humans, with specialized surfaces providing a large surface area. * Circulatory systems: Transport gases between the gas exchange surface and distant cells. * Flattened bodies: Increase surface area and reduce diffusion distance, as seen in planarians (flatworms). ### Requirements for Efficient Gas Exchange * Large surface area: To provide enough oxygen and remove sufficient carbon dioxide. * Thin gas exchange surface: For rapid diffusion. * Permeable and moist surface: For gas molecules to pass through in solution. * Good ventilation: To bring fresh supplies of air or water and remove carbon dioxide. * Efficient transport system: Like a good blood supply close to the gas exchange surface. * Protection: To prevent drying out and damage. A steep concentration gradient of oxygen and carbon dioxide across the gas exchange surface ensures fast, efficient diffusion. In many animals, this gradient is maintained by blood transport and ventilation. ### Gas Exchange in Different Organisms #### Unicellular Organisms Unicellular organisms are aquatic, and their cell surface membranes have a large surface area-to-volume ratio for efficient gas exchange. #### Small Multicellular Organisms Animals like earthworms, with a long, thin shape and a large surface area-to-volume ratio, use their entire outer skin for gas exchange. These animals must stay in moist environments to keep their gas exchange surfaces wet. #### Aquatic Animals Fish have specialized gas exchange organs called gills, with a structure that ensures efficient oxygen extraction from water. #### Terrestrial Animals Most terrestrial animals have internal gas exchange surfaces to reduce water loss. For example, insects like locusts have a tracheal system, and mammals like humans have lungs. #### Plants Plants have pores (stomata) in their leaves for gas exchange. The epidermis and waxy cuticle protect these surfaces and reduce water loss. Gas exchange occurs through these pores and the moist cell membranes inside the leaves. ### Gaseous Exchange in Specific Organisms #### Earthworm Earthworms, living in moist habitats, diffuse gases through their thin, permeable body surface. Gland cells in their skin secrete mucus to keep the surface moist. Blood capillaries transport gases to and from body cells. #### Locust Locusts have a waterproof body surface with a tracheal system for gas exchange. Air enters through spiracles, diffuses across the moist tracheal system, and is regulated by spiracle movements. Rhythmic body movements ventilate the tracheal system. #### Bony Fish Bony fish have gills made up of gill filaments and lamellae, providing a large surface area. Water passes over the lamellae, ensuring efficient gas exchange by maintaining a concentration gradient. Blood capillaries transport gases, and the gills are protected by the operculum. Fish continuously ventilate their gills using mouth and operculum movements. #### Dicotyledonous Plant In plants, gas exchange occurs mainly through leaves via stomata, controlled by guard cells. Gases diffuse between the atmosphere and leaf cells through intercellular air spaces and the spongy mesophyll, increasing the internal surface area for gas exchange. #### Mammals Humans and other mammals have lungs with alveoli as gas exchange surfaces. Detailed study of human gas exchange will be covered in Unit 2. ### The Breathing (Ventilation) System #### Introduction You may have seen other names for the breathing system, such as the ventilation system, respiratory system, or gaseous exchange system. These terms all refer to the system you can see in Figure 7.9. #### Structure of the Breathing System ##### Nasal Cavity * The two nostrils (external openings of the nose) lead into two nasal passages that open into a nasal cavity. * The nasal cavity has bony projections called conchae that increase the surface area and help to slow down the flow of air so that it can be warmed and filtered. * There are many blood vessels in the lining of the upper part of the nasal cavity, which warm the air that is breathed in. Ciliated columnar epithelium lines the nasal cavity and the cilia, together with the hairs behind the nostrils, filter out dust and foreign particles. * Goblet cells in the epithelium secrete mucus, which moistens the air and traps dust, bacteria and foreign particles. * Mucus is also secreted by mucous glands in the lining of the nasal cavity. * The cilia move the mucus to the pharynx to be swallowed. ##### Pharynx * The pharynx or throat connects the nasal cavity with the larynx. ##### Larynx * The larynx or voice box contains the vocal cords. When we speak, air passes over the cords and sound is produced. * The epiglottis, a flap of cartilage, closes the glottis, the opening of the larynx, when food is swallowed. This prevents food from passing into the trachea, causing the person to choke. ##### Trachea * The trachea is located in front of the oesophagus. * The trachea is flexible and is held open by C-shaped rings of cartilage that are incomplete at the back of the trachea. * The incomplete rings in the trachea allow the oesophagus at the back of the trachea to expand when food is swallowed. * The trachea is lined with ciliated columnar epithelium with goblet cells that secrete mucus. * The mucus moistens the air and traps dust and bacteria. * The cilia sweep mucus with trapped foreign substances towards the pharynx to be swallowed. #### Bronchi and Bronchioles * The trachea branches into two bronchi. One bronchus goes to each lung. * The bronchi are kept open by cartilage rings. * The bronchi are lined with a ciliated epithelium that secretes mucus. * Inside the lungs, the bronchi subdivide into many smaller branches called bronchioles. * Bronchioles are lined with cuboidal epithelium that does not secrete mucus. * Bronchioles do not have cartilage rings. * The walls of the bronchioles are made of smooth muscle that can contract and relax to alter air flow. #### Lungs * The two lungs are spongy organs that fill most of the thoracic (chest) cavity. * The left lung has two lobes and the right lung has three lobes. * Within the lungs, bronchioles lead into clusters of alveoli. * The alveoli are joined by connective tissue to form the lung lobes. #### Alveoli * Alveoli or air sacs provide a large surface area for gas exchange. * The walls of the alveoli are thin and consist of a single layer of squamous epithelium. * A thin layer of tissue fluid lines the inside surface of the alveolus, keeping the surface moist and preventing the cells from drying out. * Each alveolus is surrounded by a network of blood capillaries. * The walls of these capillaries are thin and consist of a single layer of cells. * Efficient diffusion of oxygen and carbon dioxide occurs across the walls of the alveoli to and from the blood in the capillaries. * Surfactant, a substance that lowers the surface tension of the moist film lining the alveoli, prevents their collapse. #### Ventilation of the Lungs * To maintain a good supply of oxygen required for aerobic respiration, 'fresh' air rich in oxygen must constantly be brought into the lungs from the environment. * Air rich in carbon dioxide ('stale' air) needs to be removed from the lungs to the environment. * The replacement of stale air with fresh air in the lungs is called ventilation of the lungs. * In order to ventilate our lungs, we breathe air into and out of our bodies. * The process of breathing draws oxygen-rich air into the lungs and pushes carbon dioxide-rich air out of the lungs. * Put your hands on your chest. Breathe in deeply. What happens to your rib cage? Then breathe out. What happens to your rib cage now? You should notice that your chest expands when you breathe in and reduces in size when you breathe out. * Breathing in (inspiration or inhalation) and breathing out (expiration or exhalation) * Occurs due to changes in the volume of the thoracic cavity. * The ribs, intercostal muscles and diaphragm all play a role in breathing. ### Exchange and Transport of Gases #### Gaseous exchange in the alveoli * Blood flowing into the capillaries around the alveoli comes from the body tissues. * The blood is deoxygenated since it contains a low concentration of oxygen and a high concentration of carbon dioxide. * The air breathed into the alveoli contains a higher concentration of oxygen. * Because of this concentration gradient, diffusion of oxygen occurs from the higher concentration of oxygen in the air in the alveoli to a lower concentration of oxygen in the blood capillaries. * Oxygen dissolves in the moisture lining each alveolus and diffuses through the thin wall of the alveolus and the thin wall of the capillary into the blood. * The blood becomes oxygenated since it is now rich in oxygen. * The oxygenated blood leaves the lungs and passes through the heart to the tissues of the body. #### Deoxygenated blood in the capillaries around the alveoli contains a high concentration of carbon dioxide * a waste product from cellular respiration. * The air in the alveoli has a lower concentration of carbon dioxide. Because of this concentration gradient, carbon dioxide diffuses from the blood into the air in the alveoli to be exhaled from the lungs. #### Transport of Oxygen * A small amount of oxygen dissolves in the blood plasma and is transported in this way. * Most of the oxygen that diffuses from the air in the alveoli into the blood enters the red blood cells. * In the red blood cells, oxygen combines with a substance called haemoglobin to form oxyhaemoglobin.  * It is mainly in the form of oxyhaemoglobin that oxygen is transported in the blood to the tissues of the body. #### Gaseous exchange in the tissues * All cells of body tissues have a network of blood capillaries between them. * When blood reaches the tissues, oxyhaemoglobin releases its oxygen. * The blood arriving at the cells from the lungs has a high concentration of oxygen. * The cells have a lower concentration of oxygen since they use oxygen for respiration. * The oxygen diffuses from the blood into the body cells. * Respiring cells produce carbon dioxide. * Carbon dioxide diffuses from a higher concentration in the cells into the blood in the capillaries, where it is at a lower concentration. * Carbon dioxide is transported in the blood to the alveoli of the lungs. #### Transport of Carbon Dioxide * Carbon dioxide is transported in the blood in three different ways. * Some of the carbon dioxide dissolves in the blood plasma. * Some of it binds to haemoglobin in the red blood cells. * Most of the carbon dioxide is carried as bicarbonate ions in the plasma. * When the blood reaches the lungs, carbon dioxide is released and diffuses from the blood into the air in the alveoli. ### Gaseous Exchange: A Detailed Overview 1. **Introduction to Gaseous Exchange** * Gaseous exchange is essential for life. It’s the process by which organisms obtain oxygen for cellular respiration and expel carbon dioxide, a by-product of energy production. In all aerobic organisms, this process primarily occurs through diffusion, allowing gases to move naturally across respiratory surfaces from high to low concentration. 2. **Key Concepts** * **Cellular Respiration:** The biochemical reactions within cells that convert glucose and oxygen into ATP (energy), water, and carbon dioxide. * **Breathing:** The physical act of inhaling and exhaling air, facilitating gas movement into and out of the lungs or other respiratory structures. * **Gas Exchange:** The actual exchange of oxygen and carbon dioxide across cell membranes or respiratory surfaces, necessary for cellular respiration. 3. **Role of Diffusion in Gaseous Exchange** * Diffusion is the primary method for gases to move across cell membranes: * **Concentration Gradient:** Oxygen diffuses into cells or blood where it is less concentrated, and carbon dioxide exits cells where it is more concentrated. * **Conditions Favoring Diffusion:** * **High Surface Area** enhances gas passage. * **Moist Membranes** allow gases to dissolve for easier diffusion. * **Thin Walls** reduce the distance gases travel. * **Blood Supply** in animals transports gases quickly to maintain the concentration gradient. 4. **Surface Area-to-Volume Ratio** * The surface area-to-volume ratio is a key factor in efficient gas exchange: * **Small Organisms:** Their high surface area relative to volume enables direct gas exchange through body surfaces. * **Large Organisms:** Their smaller surface area-to-volume ratio requires specialized structures (lungs, gills) with large surface areas for adequate gas exchange. 5. **Adaptations for Gas Exchange in Different Organisms** * Different organisms have evolved specialized structures and methods for gas exchange, optimized for their environment and size: * **Unicellular Organisms** (e.g., Amoeba) * Use direct diffusion across their cell membrane due to small size and high surface area-to-volume ratio. * **Small Multicellular Organisms** (e.g., Earthworm) * Use their moist skin for gas exchange; oxygen diffuses into their bloodstream while carbon dioxide diffuses out. * **Aquatic Animals** (e.g., Fish) * Use gills with lamellae for high surface area. Water flows over gills in one direction, while blood flows in the opposite direction (countercurrent exchange), maximizing oxygen uptake. * **Terrestrial Insects** (e.g., Locust) * Use a tracheal system with spiracles and branching tubes (tracheae) that carry air directly to cells without blood transport. * **Plants** (e.g., Dicotyledonous Plants) * Exchange gases mainly through stomata on leaf surfaces. Stomata allow carbon dioxide in for photosynthesis and release oxygen and water vapor. * **Mammals** (e.g., Humans) * Have lungs with millions of alveoli, providing a large surface area. Oxygen diffuses from alveoli into capillaries, while carbon dioxide diffuses out, to be expelled upon exhalation. 6. **Regulation of Breathing and Homeostasis** * The body maintains stable oxygen and carbon dioxide levels through breathing regulation, controlled by the medulla oblongata in the brain: * **CO2 Sensitivity:** The medulla senses carbon dioxide levels in the blood and adjusts the breathing rate accordingly. * **Adaptations to Exercise and Altitude:** * **Exercise** increases breathing rate to meet muscle oxygen needs. * **High Altitude** causes increased red blood cell production and breathing rate to cope with lower oxygen levels. 7. **Measurement of Lung Capacity** * A spirometer measures lung capacity, providing insights into respiratory health: * **Tidal Volume:** Normal air volume per breath (about 0.5 liters in humans). * **Vital Capacity:** The maximum air volume exhaled after a full inhalation (around 4.5 liters in men) ### Gaseous Exchange and Respiratory Health 1. **Residual Volume in the Lungs** * **Definition:** The volume of air that remains in the lungs after a full exhalation, called the residual volume. * **Location:** Air remains in alveoli and air passages like the bronchi and trachea, held open by cartilage rings to maintain lung structure. 2. **Effects of Physical Activity on Breathing** * **Breathing Changes with Exercise:** * **Rate of Breathing:** Increases with physical activity. * **Heart Rate:** Also increases to pump oxygen-rich blood faster. * **Depth of Breathing:** Becomes deeper to supply more oxygen. * **Reason for Increased Breathing:** * Body cells, especially muscle cells, demand more oxygen for energy production during exercise. * Increased oxygen intake speeds up respiration rate. * **Oxygen Debt:** * After intense exercise, oxygen is needed to break down lactic acid (from anaerobic respiration), known as oxygen debt. 3. **Effects of Altitude on Gaseous Exchange** * **Lower Atmospheric Pressure:** At high altitudes, reduced atmospheric pressure makes air less dense, reducing oxygen availability for gas exchange. * **Short-Term Body Response:** * Breathing and heart rate increase to adapt to lower oxygen levels. * **Long-Term Acclimatization:** * Over time, the body adjusts, or acclimatizes, by enhancing its oxygen uptake efficiency. 4. **Common Respiratory Diseases** * **Tuberculosis (TB)** * **Cause:** The bacterium Mycobacterium tuberculosis, which spreads through airborne droplets. * **Symptoms:** Often affects the lungs, but can also affect other organs if the immune system is weakened. * **Types:** * **Latent TB:** No symptoms and not contagious. * **Active TB:** Symptoms are present, and the disease can spread. * **Diagnosis:** * Microscopic examination of sputum. * Chest X-ray for lung abnormalities. * Skin test for immune response to TB bacteria. * **Prevention in South Africa:** BCG vaccination for newborns. * **Asthma** * **Mechanism:** Inflammation and swelling of air passages during attacks. * **Triggers:** Exercise, pollutants, allergens like dust or pollen. * **Symptoms:** Wheezing, coughing, chest tightness, and shortness of breath. * **Hay Fever** * **Cause:** Allergic reaction to allergens (e.g., pollen). * **Symptoms:** Itchy eyes, runny nose, and sneezing. * **Treatment:** Antihistamines to reduce allergic response. * **Bronchitis** * **Types:** * **Acute Bronchitis:** Short-term inflammation, often from infection. * **Chronic Bronchitis:** Long-term condition with excessive mucus, typically from smoking or pollution. * **Symptoms:** Persistent cough, shortness of breath, chest discomfort. * **Prevention:** Avoid smoking and air pollutants; chronic bronchitis has no cure. * **Emphysema** * **Cause:** Breakdown of alveolar walls, decreasing surface area for gas exchange. * **Symptoms:** Shortness of breath; difficulty exhaling. * **Prevention:** Avoid smoking, as it is a primary risk factor. * **Lung Cancer** * **Cause:** Uncontrolled cell growth in lung tissues, often from carcinogens in cigarette smoke. * **Symptoms:** Persistent cough, coughing blood, chest pain. * **Diagnosis:** X-rays or CT scans; treatments may include surgery, chemotherapy, or radiation. * **Risk:** Smoking causes about 90% of lung cancers. 5. **Effects of Smoking on Health** * **Nicotine** * **Effect:** Addictive, increases heart rate, narrows arteries, raises blood pressure. * **Health Risks:** Increased risk of heart attack. * **Tar** * **Effect:** Carcinogenic and accumulates in lungs. * **Health Impact:** Can lead to lung cancer, damages cilia, causes smoker’s cough, and contributes to conditions like emphysema and bronchitis. * **Carbon Monoxide** * **Effect:** Poisonous gas that reduces hemoglobin’s oxygen-carrying capacity. * **Health Impact:** Increases heart rate, risks of heart attack, and can affect fetal development during pregnancy. 6. **Second-Hand Smoke (Passive Smoking)** * **Risks:** Non-smokers exposed to smoke can develop similar diseases. * **Children:** Especially vulnerable to respiratory issues like asthma and bronchitis from second-hand smoke. 7. **Smoking Legislation in South Africa** * **Purpose:** To protect non-smokers, especially youth, and encourage quitting. * **Measures:** * Advertising bans, health warnings on packaging, restrictions on smoking in public and workplaces, and increased tobacco tax. 8. **Artificial Respiration** * **Purpose:** To maintain breathing in an individual who has stopped breathing. * **Method:** Most commonly mouth-to-mouth resuscitation. * **Steps for Mouth-to-Mouth Resuscitation:** 1. Place the person on their back; tilt the head and lift the chin to open air passages. 2. Seal your lips over theirs and gently breathe out into their mouth. 3. Repeat every five seconds until the person resumes breathing or help arrives.