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

• Describe gaseous exchange in the lungs.
• Explain aerobic and anaerobic cellular respiration.
• Describe the structure of the kidney and nephron.
• Explain the process of urine formation.
• Describe the liver's role in excretion.

Lesson summary

This week we delve into the vital processes of respiration and excretion in the human body. These processes are fundamental to life, ensuring our cells receive the energy they need and that waste products are efficiently removed. Understanding these systems is crucial for maintaining good health and appreciating the intricate workings of our bodies. Consider, for example, the high prevalence of respiratory illnesses like asthma and TB in South Africa, or the impact of kidney disease on communities. Understanding respiration and excretion helps us to better understand the causes, treatments, and prevention strategies for these conditions.

Lesson notes

2.1 Human Respiration 2.1.1 Gaseous Exchange in the Lungs (Alveoli): Respiration, in this context, refers to external respiration – the exchange of gases between the lungs and the blood. This process occurs in the alveoli, tiny air sacs in the lungs, surrounded by a dense network of capillaries. The key principle here is diffusion, the movement of molecules from an area of high concentration to an area of low concentration.

Oxygen: Alveolar air has a high concentration (or partial pressure) of oxygen (pO2), while the blood in the capillaries has a low pO2 (because cells have used up the oxygen).

Therefore, oxygen diffuses from the alveoli into the blood, binding to haemoglobin in red blood cells.

Carbon Dioxide: Conversely, blood arriving at the alveoli from body tissues has a high concentration (or partial pressure) of carbon dioxide (pCO2), a waste product of cellular respiration. The alveolar air has a low pCO

2. Thus, carbon dioxide diffuses from the blood into the alveoli to be exhaled. The large surface area of the alveoli, their thin walls (single-celled epithelium), and the rich capillary network maximise the efficiency of gaseous exchange.

Example: Imagine a classroom (alveolus) full of learners (oxygen molecules). A few learners move to the empty seats in the auditorium (blood capillaries) until both areas have an even distribution. Then, learners who finished their exams (CO2) from the auditorium are ushered to the empty spaces of the classroom until an even distribution occurs. The teacher is the blood, bringing and collecting learners (gases). 2.1.2 Cellular Respiration: Cellular respiration is the process by which cells break down glucose (sugar) to release energy in the form of ATP (adenosine triphosphate).

There are two main types: Aerobic Respiration: This occurs in the presence of oxygen.

The chemical equation is: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP) Glucose + Oxygen → Carbon Dioxide + Water + Energy This process takes place in the mitochondria and is far more efficient at producing ATP than anaerobic respiration.

Example: Think of a braai using a gas cylinder. The gas (glucose) is burned (oxidized) with oxygen to produce heat (energy).

Anaerobic Respiration: This occurs in the absence of oxygen. In humans, this is primarily lactic acid fermentation. C6H12O6 → 2C3H6O3 + Energy (ATP) Glucose → Lactic Acid + Energy Anaerobic respiration produces much less ATP than aerobic respiration and results in the build-up of lactic acid, which can cause muscle fatigue.

Example: Consider a sprinter running a 100m race. They are using energy faster than their lungs can supply oxygen, leading to anaerobic respiration and the burning sensation caused by lactic acid buildup. 2.1.3 Differences in Aerobic and Anaerobic Respiration | Feature | Aerobic Respiration | Anaerobic Respiration (Lactic Acid Fermentation) | |-------------------|------------------------------------------------------|-------------------------------------------------------| | Oxygen Required | Yes | No | | ATP Production | High (approx. 36-38 ATP molecules per glucose) | Low (approx. 2 ATP molecules per glucose) | | End Products | Carbon dioxide, Water | Lactic Acid | | Location | Cytoplasm and Mitochondria | Cytoplasm | | Duration | Can be sustained for long periods | Short periods (until lactic acid build-up becomes limiting)| 2.2 Human Excretion 2.2.1 The Kidneys and Nephron Structure: Excretion is the removal of metabolic waste products from the body. The kidneys are the primary organs of excretion in humans. They filter the blood and produce urine. Each kidney contains millions of microscopic filtering units called nephrons.

A nephron consists of: Bowman's Capsule: A cup-shaped structure that surrounds the glomerulus.

Glomerulus: A network of capillaries where filtration occurs.

Proximal Convoluted Tubule (PCT): A highly coiled tubule where reabsorption of essential substances begins.

Loop of Henle: A U-shaped loop responsible for concentrating urine. It has a descending and ascending limb.

Distal Convoluted Tubule (DCT): Another coiled tubule where further reabsorption and secretion occur.

Collecting Duct: A duct that collects urine from several nephrons and transports it to the renal pelvis.

Example: The kidney acts like a water filtration plant. The nephron is like an individual filter within the plant, removing impurities (waste products) from the water (blood) and returning the clean water (filtered blood) to the system. 2.2.2 Urine Formation (Filtration, Reabsorption, and Secretion): Urine formation involves three main processes: Filtration: Occurs in the glomerulus. Blood pressure forces water, salts, glucose, amino acids, and urea (a nitrogenous waste product) from the blood into the Bowman's capsule, forming the glomerular filtrate. Large molecules like proteins and blood cells remain in the blood.

Example: Imagine pouring a mixture of sand, sugar, and water through a coffee filter.