Lesson Notes By Weeks and Term v5 - Grade 11
Human respiration and excretion – Week 5 focus
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Human respiration and excretion – Week 5 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Life Sciences
Class: Grade 11
Term: 3rd Term
Week: 5
Theme: General lesson support
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This week, we delve into the vital processes of human respiration and excretion. These two systems are fundamental to maintaining homeostasis, the stable internal environment necessary for our survival. Respiration provides the energy our cells need to function, while excretion removes metabolic waste products that could become toxic if allowed to accumulate. Understanding how these systems work, how they are regulated, and what can go wrong is crucial for maintaining good health and appreciating the complexity of the human body.
2.1 Human Respiratory System The respiratory system's primary function is gas exchange – taking in oxygen (O2) and eliminating carbon dioxide (CO2). This process is essential for cellular respiration, which produces energy (ATP) within cells.
Structure: The respiratory system consists of: Nasal cavity: Filters, warms, and moistens incoming air. Mucus traps particles, and cilia sweep them towards the throat to be swallowed.
Pharynx (Throat): A passageway for both air and food.
Larynx (Voice box): Contains vocal cords, which vibrate to produce sound.
Trachea (Windpipe): A tube reinforced with cartilage rings to prevent collapse.
Bronchi: The trachea divides into two bronchi, one for each lung.
Bronchioles: Bronchi branch into smaller and smaller tubes called bronchioles.
Alveoli: Tiny air sacs at the end of the bronchioles, where gas exchange occurs. The alveoli have thin walls and are surrounded by capillaries, which maximize diffusion.
Lungs: The main organs of respiration, containing bronchi, bronchioles, alveoli, and blood vessels.
Diaphragm: A large, dome-shaped muscle located at the base of the chest cavity. It plays a crucial role in breathing.
Mechanism of Breathing (Ventilation): Inhalation (Inspiration): The diaphragm contracts and flattens, and the rib cage moves up and out. This increases the volume of the chest cavity, decreasing the pressure inside the lungs. Air rushes into the lungs from the area of higher pressure (outside) to lower pressure (inside).
Exhalation (Expiration): The diaphragm relaxes and returns to its dome shape, and the rib cage moves down and in. This decreases the volume of the chest cavity, increasing the pressure inside the lungs. Air rushes out of the lungs from the area of higher pressure (inside) to lower pressure (outside).
Gas Exchange: Alveoli: Oxygen diffuses from the alveoli into the surrounding capillaries due to a higher concentration of oxygen in the alveoli than in the blood. Carbon dioxide diffuses from the capillaries into the alveoli due to a higher concentration of carbon dioxide in the blood than in the alveoli.
Capillaries: Oxygen binds to hemoglobin in red blood cells and is transported to the body's tissues. Carbon dioxide is transported in the blood in three forms: dissolved in plasma, bound to hemoglobin, and as bicarbonate ions.
Example: Consider someone living in a township with high levels of smoke from coal fires. The smoke contains particulate matter that irritates the airways, leading to inflammation and increased mucus production. This can reduce the efficiency of gas exchange in the alveoli, making it harder to breathe and increasing the risk of respiratory infections. 2.2 Human Excretory System The excretory system removes metabolic waste products, excess salts, and excess water from the body to maintain homeostasis. The primary organs of excretion are the kidneys.
Structure: The excretory system consists of: Kidneys: Filter blood and produce urine. They contain millions of tiny filtering units called nephrons.
Ureters: Tubes that carry urine from the kidneys to the bladder.
Bladder: A muscular sac that stores urine.
Urethra: A tube that carries urine from the bladder to the outside of the body.
Nephron Structure: Bowman's capsule: A cup-shaped structure that surrounds the glomerulus.
Glomerulus: A network of capillaries where filtration occurs.
Proximal convoluted tubule: Where reabsorption of water, glucose, amino acids, and salts occurs.
Loop of Henle: A U-shaped tube that concentrates the urine.
Distal convoluted tubule: Where further reabsorption and secretion occur.
Collecting duct: Where urine is collected and transported to the ureter.
Urine Formation: Filtration: Blood pressure forces water, salts, glucose, amino acids, and urea from the glomerulus into Bowman's capsule. Blood cells and large proteins remain in the blood.
Reabsorption: As the filtrate flows through the nephron, useful substances such as water, glucose, amino acids, and salts are reabsorbed back into the blood. This occurs primarily in the proximal convoluted tubule.
Secretion: Waste products such as urea, creatinine, and excess ions are secreted from the blood into the nephron tubule. This occurs primarily in the distal convoluted tubule.
Example: A person who drinks insufficient water, especially during hot weather in South Africa, may become dehydrated. This will cause the kidneys to conserve water by reabsorbing more water from the filtrate, resulting in more concentrated urine (darker in color) and a lower urine volume. This can strain the kidneys and increase the risk of kidney stones.
Calculations (Osmolarity): While detailed calculations are beyond the scope of this week, it is important to understand the principle. Osmolarity refers to the concentration of solutes in a solution. The kidneys regulate osmolarity by controlling the reabsorption of water and salts. A hypertonic solution has a higher solute concentration than another solution.