JWSS Biology Chapter 7 Respiration in Humans

Sec 3 G3 Science (Biology) Chapter 7 Notes Prepared by Ms Pui LX JURONG WEST SECONDARY SCHOOL SECONDARY THREE – SCIENCE BIOLOGY Chapter 7: RESPIRATION IN HUMAN Learning Outcomes: Candidates should be able to: (a) identify the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries and state their functions in human gaseous exchange (b) explain how the structure of an alveolus is suited for its function of gaseous exchange (c) state the major toxic components of tobacco smoke – nicotine, tar and carbon monoxide , and describe their effects on health (d) define aerobic respiration in human cells as the release of energy by the breakdown of glucose in the presence of oxygen and state the word equation (e) define anaerobic respiration in human cells as the release of energy by the breakdown of glucose in the absence of oxygen and state the word equation (f) explain why cells respire anaerobically during vigorous exercise resulting in an oxygen debt that is removed by rapid, deep breathing after exercise (a) identify the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries and state their functions in human gaseous exchange VIDEO: Play video and you will fill in the labels with the helping words given. Bronchiole Bronchus Alveolus Larynx Trachea nasal cavity Larynx pharynx Trachea bronchiole alveolus bronchus diaphragm

Sec 3 G3 Science (Biology) Chapter 7 Notes 2 The Respiratory Pathway THE NOSE o Dust and foreign particles (e.g. bacteria in the air) are trapped by the hairs in the nostrils as well as the mucus on the mucus membrane. o As air passes through the nasal passages, it is warmed and moistened. o Harmful chemicals may be detected by the sensory cells in the mucous membrane. TRACHEA AND BRONCHI o Epithelium lining the trachea and bronchi consists of two types of cells o Ciliated cells ▪ Have hair-like structures called cilia on their surfaces. ▪ Cilia traps dust and dirt particles, and micro-organisms and sweep it up towards the back of the throat and out of the nostrils o Gland cells ▪ secrete mucus to trap dust and microorganisms (virus and bacteria) in the air. nasal cavity pharynx larynx trachea bronchus bronchiole alveolus

Sec 3 G3 Science (Biology) Chapter 7 Notes 3 • Trachea divides into two bronchi (plural) that branch repeatedly to give rise to bronchioles. (b) explain how the structure of an alveolus is suited for its function of gaseous exchange ALVEOLI / ALVEOLUS 1. Trachea divides into two bronchi. Each bronchus branches out repeatedly into numerous bronchioles, which end with a cluster of alveoli. 2. Site of gaseous exchange → Gaseous exchange occurs by diffusion, oxygen diffuses from alveolus and into the RBC, carbon dioxide diffuses from plasma and into the alveolus.

Sec 3 G3 Science (Biology) Chapter 7 Notes 4 3. Thousands of alveoli are found in the lungs to provide a very large surface area for gaseous exchange. Adaptations and Functions of an alveolus (Image from https://d2gne97vdumgn3.cloudfront.net/api/file/vRDE0vKRrukm2LWPdfQX) Structure Function One-cell thick alveolar wall Shorter distance for diffusion of gases, faster diffusion of gases Thin film of moisture in the alveolus Allows oxygen to dissolve and diffuse across the alveolar walls easily Many blood capillaries surrounding the alveoli A constant blood flow maintains the steep concentration gradient of gases, ensuring faster diffusion. Numerous alveoli in the lungs (**do not use this point if question is asking for the adaptation of an alveolus) Provide a large surface area for gaseous exchange QUESTION: WE BREATHE IN OXYGEN. True or False? False. We breathe in AIR, which contains 20.95% oxygen

Sec 3 G3 Science (Biology) Chapter 7 Notes 5 Gaseous exchange (diffusion) 1. Blood entering lungs (and hence capillaries which surround the alveoli) have: o low concentration of oxygen and o high concentration of carbon dioxide. 2. Oxygen dissolves into the thin film of moisture and then diffuses into the capillaries. 3. Oxygen combines with haemoglobin in the RBCs, forming oxyhaemoglobin. 4. When blood passes through oxygen -poor tissues, oxyhaemoglobin releases oxygen which diffuses through capillary walls to reach tissue cells. 5. Blood entering lungs (and hence capillaries which surround the alveoli) have: o high concentration of carbon dioxide. 6. Carbon dioxide diffuses from the blood capillary into the alveolus. QUESTION: Carbon dioxide is transported in the blood. Via blood plasma or RBC? 1 2 3 5 6

Sec 3 G3 Science (Biology) Chapter 7 Notes 6 Gaseous exchange Cells ⇄ tissue fluid ⇄ blood in blood capillaries Inspired VS Expired air Do you think inspired air (air you inhale) is the same as expired air (air you exhale)? Component Inspired air Expired air INVESTIGATION What about temperature? Place your hand near your nostrils and feel the air you exhale. Is it warmer or cooler than inspired air? Oxygen ~ 21% ~ 16.4% Carbon dioxide ~ 0.03% ~ 4% Nitrogen ~ 78% ~ 78% Water vapour Variable (rarely saturated) Saturated

Sec 3 G3 Science (Biology) Chapter 7 Notes 7 (d) define aerobic respiration in human cells as the release of energy by the breakdown of glucose in the presence of oxygen and state the word equation (e) define anaerobic respiration in human cells as the release of energy by the breakdown of glucose in the absence of oxygen and state the word equation (f) explain why cells respire anaerobically during vigorous exercise resulting in an oxygen debt that is removed by rapid, deep breathing after exercise RESPIRATION IS NOT BREATHING • Tissue Respiration (chemical process) o oxidation of organic food substances(glucose) with the release of energy, • Gaseous Exchange (physical process) o process of the transfer of oxygen from the surrounding to the cells and carbon dioxide from cells back to surrounding. What is respiration? • Respiration supplies energy for muscle contraction, germination and cell division. • There are two types of respiration: Aerobic Respiration (with oxygen) Anaerobic Respiration (without oxygen) 1. Aerobic respiration • Aerobic respiration is the breakdown of glucose in the presence of oxygen with the release of large amount of energy. • Carbon dioxide and water are released as by-products. • It takes place in the mitochondria (organelle in cells). • Occurs in all body cells. Not in syllabus In syllabus

Sec 3 G3 Science (Biology) Chapter 7 Notes 8 • Write the word equation for aerobic respiration: 2. Anaerobic respiration • Anaerobic respiration is the breakdown of food substances glucose with the release of a comparatively small amount of energy in the absence of oxygen. • Lactic acid is released as by-products. (Lactic acid causes muscle soreness.) • It takes place in the cytoplasm. • Occurs in the muscle cells in humans. It also happens in other cells. • Write the word equation for anaerobic respiration: *NOTE! There is no carbon dioxide produced! No water produced! TRY YOURSELF! List five distinguishing features between aerobic and anaerobic respiration. Aerobic respiration Anaerobic respiration • Oxygen is required • Large amount of energy is released • Carbon dioxide and water are produced • Takes place in the mitochondrion • Oxygen not required • Small amount of energy is released • Lactic acid is produced in humans • Takes place in the cytoplasm of muscle cells Glucose + oxygen → carbon dioxide + water+ large amount of energy Glucose → lactic acid + small amount of energy

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