Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of the respiratory system.
• Explain the mechanics of breathing (ventilation).
• Explain gas exchange in the lungs.
• Define excretion and differentiate it from egestion.
• Identify the main excretory organs.

Lesson summary

The human body is a complex machine that requires energy to function. This energy comes from the food we eat, but the process of releasing that energy isn't a simple one. Respiration is the process where glucose (sugar) is broken down in cells to release energy. This week, we'll focus on the mechanics of external respiration - how we get oxygen into our lungs and carbon dioxide out. Simultaneously, our bodies produce waste products that need to be eliminated. Excretion is the process of removing these metabolic wastes from the body.

Lesson notes

2. 1.

The Respiratory System: Structure and Function The respiratory system is responsible for gas exchange – taking in oxygen (O₂) and releasing carbon dioxide (CO₂). This is external respiration. Cellular respiration, happening inside cells, uses the oxygen delivered by the respiratory system.

Let's look at the main components: Nasal Cavity: Air enters through the nose or mouth. The nasal cavity filters, warms, and moistens the air. Hairs and mucus trap dust and other particles. This is vital in a country like South Africa where air pollution (from industrial areas or burning) can be a significant problem. Think about how your nose feels stuffy and runny when you have a cold – that's your body trying to trap and expel irritants.* Pharynx (Throat): A passageway for both air and food.

Larynx (Voice Box): Contains the vocal cords, which vibrate to produce sound. The epiglottis, a flap of tissue, prevents food from entering the trachea.

Trachea (Windpipe): A tube reinforced with C-shaped rings of cartilage to prevent it from collapsing. The cartilage keeps the airway open, allowing for consistent breathing.

Bronchi: The trachea divides into two bronchi, one leading to each lung. Like the trachea, they are also supported by cartilage rings.

Bronchioles: Within the lungs, the bronchi branch into smaller and smaller tubes called bronchioles. These do not have cartilage.

Alveoli: Tiny air sacs at the end of the bronchioles where gas exchange occurs. They are surrounded by a network of capillaries (tiny blood vessels). Imagine bunches of grapes – each grape is an alveolus!*. Their structure – thin walls and a huge surface area – is perfectly adapted for efficient gas exchange. The large surface area maximizes the amount of oxygen that can be absorbed into the bloodstream.

Lungs: The main organs of respiration, containing the bronchi, bronchioles, and alveoli.

Pleura: Two layers of membrane surrounding the lungs, separated by a fluid-filled space. This fluid reduces friction during breathing.

Diaphragm: A large, dome-shaped muscle located at the bottom of the chest cavity. It plays a crucial role in breathing.

Intercostal Muscles: Muscles located between the ribs that also play a crucial role in breathing. 2.

2. Ventilation: The Mechanics of Breathing Ventilation refers to the process of moving air in and out of the lungs.

It involves two phases: inspiration (inhalation) and expiration (exhalation).

Inspiration (Inhalation): The diaphragm contracts and moves downwards, increasing the volume of the chest cavity. The external intercostal muscles contract, lifting the ribs upwards and outwards, further increasing the chest cavity volume. As the volume of the chest cavity increases, the pressure inside the lungs decreases (becomes lower than atmospheric pressure). This is Boyle's Law (P₁V₁ = P₂V₂). Air rushes into the lungs from the atmosphere to equalize the pressure.

Expiration (Exhalation): The diaphragm relaxes and moves upwards, decreasing the volume of the chest cavity. The external intercostal muscles relax, allowing the ribs to move downwards and inwards, further decreasing the chest cavity volume. As the volume of the chest cavity decreases, the pressure inside the lungs increases (becomes higher than atmospheric pressure). Air rushes out of the lungs into the atmosphere to equalize the pressure. Think about blowing up a balloon. You have to use your muscles to increase the volume of the balloon so the air can rush in. Breathing is similar – your muscles change the volume of your chest cavity. 2.

3. Gas Exchange in the Alveoli Gas exchange occurs in the alveoli. The air in the alveoli is separated from the blood in the capillaries by very thin walls (only one cell thick). This allows for efficient diffusion of gases. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

Oxygen: The concentration of oxygen is higher in the alveoli than in the blood in the capillaries.

Therefore, oxygen diffuses from the alveoli into the blood. The oxygen binds to haemoglobin in red blood cells and is transported to the rest of the body.

Carbon Dioxide: The concentration of carbon dioxide is higher in the blood in the capillaries than in the alveoli.

Therefore, carbon dioxide diffuses from the blood into the alveoli to be exhaled. The alveoli are like tiny trading posts where oxygen and carbon dioxide are exchanged between the air and the blood. 2.4 Excretion: Waste Removal Excretion is the removal of metabolic waste products from the body. Metabolic wastes are substances produced by the body's chemical processes (metabolism). It is not the same as egestion, which is the removal of undigested food from the digestive system (faeces).

Key Excretory Organs: Lungs: Remove carbon dioxide (a waste product of cellular respiration) and some water vapour.

Skin: Removes water, salts (like sodium chloride), and small amounts of urea in sweat.