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IGCSE BIOLOGY CHAPTER 9: RESPIRATION 9.1 RESPIRATION RELEASES ENERGY FROM FOODRespiration is the chemical reactions that break down glucose in living cells to release energy.

9.2 AEROBIC RESPIRATION INVOLVES OXYGENAerobic respiration is the release of energy from glucose by combining it with oxygen. Word equation for aerobic respiration: Glucose + Oxygen Carbon + Water dioxideChemical equation for aerobic respiration: C6H12O6 + 6O2 6CO2 + 6H2O

9.3 ANAEROBIC RESPIRATION DOES NOT INVOLVE OXYGENAnaerobic respiration is the release of energy from glucose in the absence of oxygen.Yeast can respire anaerobically. It breaks down glucose to ethanol and carbon dioxide. This process is called fermentation.Word equation for fermentation: Glucose Ethanol + Carbon dioxide

9.3 ANAEROBIC RESPIRATION DOES NOT INVOLVE OXYGENChemical equation for fermentation: C6H12O6 2C2H5OH + 2CO2Muscle cells can respire anaerobically too. They make lactic acid only. Word equation for anerobic respiration in muscles: Glucose Lactic acid9.3 ANAEROBIC RESPIRATION DOES NOT INVOLVE OXYGENChemical equation for anaerobic respiration in muscles: C6H12O6 2C3H6O3

9.4 YEAST IS USED FOR BAKING AND BREWING

9.4 YEAST IS USED FOR BAKING AND BREWINGAerobic respiration Anaerobic respirationUses oxygenDoes not use oxygenNo ethanol or lactic acid madeEthanol (in yeasts and plants) or lactic acid (in animals) is madeLarge amount of energy released from each molecule of glucoseSmall amount of energy released from each molecule of glucoseCarbon dioxide madeCarbon dioxide is made by yeasts and plants but not by animals9.5 GAS EXCHANGE OCCURS AT SPECIAL SURFACES9.6 THE STRUCTURE OF THE BREATHING SYSTEMEach lung is filled with many tiny air sacs called alveoli. From the alveoli, oxygen diffuses into the blood. The lungs are supplied with air through the windpipe or trachea. 9.6 THE STRUCTURE OF THE BREATHING SYSTEM

The human respiratory system 9.7 AIR FLOWS TO THE LUNGSPathway of air flow: 9.7 AIR FLOWS TO THE LUNGSThe nose and mouthIt is better to breathe through the nose because the nose allows air to be moist and filtered before it enters the lungs.Inside the nose are thin bones called turbinal bones which are covered with a thin layer of cells.

9.7 AIR FLOWS TO THE LUNGSTypes of cells in the turbinal bones: (i) Goblet cells - Secretes mucus which traps bacteria and dust and also moistens the air in the nose (ii) Ciliated cells - Sweep the mucus which trapped bacteria and dust to the back of the throat 9.7 AIR FLOWS TO THE LUNGS

Goblet cells and ciliated cells 9.7 AIR FLOWS TO THE LUNGSThe tracheaFrom the nose or mouth, the air then passes into the windpipe or trachea. At the top of the trachea is a piece of cartilage called the epiglottis. The epiglottis prevents food from going down the trachea when you swallow. The trachea has rings of cartilage around it which keep it open. 9.7 AIR FLOWS TO THE LUNGSThe bronchiThe trachea braches into two bronchi. One bronchus goes to each lung and then branches out into smaller tubes called bronchioles.

9.7 AIR FLOWS TO THE LUNGSThe alveoliAt the end of each bronchiole are many tiny alveoli. This is where gas exchange takes place.

9.8 ALVEOLAR WALLS ARE THE SURFACE FOR GAS EXCHANGE

Alveoli 9.8 ALVEOLAR WALLS ARE THE SURFACE FOR GAS EXCHANGEThe walls of the alveoli are the gas exchange surface.Tiny capillaries are wrapped around the outside of the alveoli. Oxygen diffuses across the walls of the alveoli into the blood. Carbon dioxide diffuses the other way.

9.8 ALVEOLAR WALLS ARE THE SURFACE FOR GAS EXCHANGE

Cross section of the lungGas exchange in an alveolus9.9 MUSCLES CAUSE BREATHING MOVEMENTS To make air move in and out of the lungs, you must keep changing the volume of your thorax. To inhale, the volume of the thorax must be increased. To exhale, the volume of the thorax must be decreased. There are two sets of muscles which help you to breathe which are the intercostal muscles and the diaphragm.9.9 MUSCLES CAUSE BREATHING MOVEMENTS

The rib cage 9.10 BREATHING IN IS CALLED INSPIRATIONMechanism of inspiration:

9.10 BREATHING OUT IS CALLED EXPIRATIONMechanism of expiration:

9.12 INTERNAL INTERCOSTAL MUSCLES CAN FORCE AIR OUTTo exhale, the external intercostal muscles and diaphragm relax. When coughing, you breathe out more forcefully. The internal intercostal muscles contract strongly, making the rib cage drop even further. The muscles of the abdomen wall also contract, squeezing extra air out of the thorax. 9.13 EXERCISE CAN CREATE AN OXYGEN DEBT9.15 PLANTS RESPIRE AND PHOTOSYNTHESISEGreen plants photosynthesise. Word equation for photosynthesis: Carbon + Water Glucose + Oxygen dioxide Chemical equation for photosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2 When plants need energy, it releases it from the glucose by respiration.

Sunlight ChlorophyllSunlight Chlorophyll9.15 PLANTS RESPIRE AND PHOTOSYNTHESISE

How the energy in sunlight is changed to useful energy in a plant 9.16 PLANTS, LIKE ANIMALS, NEED ENERGYPlants do not need so much energy as animals. They are not so active, partly because they do not have to move to find their food. However, plant cells need energy for growth, reproduction, for transporting food material between cells.

9.17 THE BALANCE BETWEEN PHOTOSYNTHESIS AND RESPIRATION9.17 THE BALANCE BETWEEN PHOTOSYNTHESIS AND RESPIRATION

Photosynthesis and respiration in plants 9.18 PLANTS GET OXYGEN BY DIFFUSION