Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Explain the mechanisms of gas exchange in the lungs.
• Describe the structures and functions of the urinary system.
• Explain the kidney's role in osmoregulation and the action of ADH.
• Understand the importance of keeping these systems healthy.

Lesson summary

This week, we delve deeper into the vital processes of human respiration and excretion. These systems are crucial for maintaining homeostasis – the stable internal environment necessary for our cells to function correctly. Understanding these processes is essential for maintaining your own health and well-being, as malfunctions can lead to serious diseases common in South Africa, like respiratory infections and kidney problems. The air quality in some areas of South Africa is poor, impacting respiratory health. Similarly, access to clean water, which is vital for kidney function, is a challenge in some regions.

Lesson notes

2. 1. Human Respiration (Deep Dive) 2.1.

1. Ventilation: This is the process of breathing – moving air into and out of the lungs.

It involves two phases: Inhalation (Inspiration): The diaphragm (a muscle below the lungs) contracts and flattens, increasing the volume of the thoracic cavity (chest cavity). The rib muscles (intercostal muscles) also contract, pulling the ribs upwards and outwards. This increases the thoracic volume and lowers the air pressure inside the lungs relative to atmospheric pressure. Air then rushes into the lungs down the pressure gradient. Think of it like sucking through a straw - you create a lower pressure inside the straw!

Exhalation (Expiration): The diaphragm and intercostal muscles relax. The thoracic cavity volume decreases, increasing the air pressure inside the lungs relative to atmospheric pressure. Air rushes out of the lungs. This is usually a passive process, but during forceful exhalation (e.g., during exercise or coughing), abdominal muscles can contract to further decrease the thoracic volume. 2.1.

2. Gas Exchange: This involves the exchange of oxygen (O 2 ) and carbon dioxide (CO 2 ) between the air in the lungs and the blood, and between the blood and the body tissues. External Respiration (Pulmonary Gas Exchange): Occurs in the alveoli (tiny air sacs in the lungs). The alveoli have very thin walls surrounded by capillaries (tiny blood vessels). The air in the alveoli has a higher concentration of O 2 and a lower concentration of CO 2 than the blood in the capillaries. Due to diffusion, O 2 moves from the alveoli into the blood, and CO 2 moves from the blood into the alveoli. The blood then becomes oxygenated. This is where the haemoglobin in red blood cells plays a vital role, binding to the oxygen to transport it. Internal Respiration (Tissue Gas Exchange): Occurs between the blood in the capillaries and the body tissues. The blood has a higher concentration of O 2 and a lower concentration of CO 2 than the tissue cells. Due to diffusion, O 2 moves from the blood into the tissues, and CO 2 moves from the tissues into the blood. The blood then becomes deoxygenated and carries the CO 2 back to the lungs. 2.1.

3. The Importance of Surface Area: The alveoli provide a huge surface area for gas exchange (estimated to be around 70 square meters!). This large surface area allows for efficient diffusion of gases. Emphysema, a respiratory disease, damages the alveoli, reducing the surface area and making breathing difficult. This is often linked to smoking. 2.1.

4. Worked

Example: Imagine a learner, Thando, living in a polluted area near a coal power plant. The air quality is poor, leading to frequent coughing and shortness of breath. Explain how the pollutants in the air affect his respiratory system.

Explanation: Pollutants like particulate matter and sulfur dioxide irritate the lining of the respiratory tract, causing inflammation and increased mucus production. This narrows the airways, making it harder to breathe. Long-term exposure can damage the alveoli and lead to chronic respiratory diseases like asthma or bronchitis. Thando's coughing is a reflex to try and clear the irritants from his airways. 2.

2. Human Excretion (Deep Dive) 2.2.

1. The Urinary System: The primary excretory system in humans, responsible for removing metabolic waste products from the blood and regulating fluid balance.

It consists of: Kidneys: Two bean-shaped organs that filter the blood and produce urine.

Ureters: Two tubes that carry urine from the kidneys to the bladder.

Urinary Bladder: A sac that stores urine.

Urethra: A tube that carries urine from the bladder out of the body. 2.2.

2. The Kidney: The functional unit of the kidney is the nephron. Each kidney contains millions of nephrons. The nephron filters blood in two main stages: Filtration: Occurs in the glomerulus (a network of capillaries) surrounded by Bowman's capsule. High blood pressure forces water, salts, glucose, amino acids, and urea from the blood into Bowman's capsule, forming glomerular filtrate. Blood cells and large proteins are too big to be filtered.

Reabsorption: As the glomerular filtrate flows through the renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct), useful substances like glucose, amino acids, water, and some salts are reabsorbed back into the blood. This occurs via active transport (requires energy) and osmosis.

Secretion: Some substances, like excess hydrogen ions and certain drugs, are actively secreted from the blood into the renal tubule. 2.2.

3. Urine Formation: The remaining fluid in the renal tubule, now containing primarily water, urea, and excess salts, becomes urine. Urine is collected in the collecting ducts and flows into the renal pelvis, then into the ureters, and finally to the bladder. 2.2.

4. Osmoregulation and ADH: Osmoregulation is the regulation of water and salt balance in the body. The kidneys play a crucial role in osmoregulation.