B11_and_12__Autosaved_.pptxasperIGCSESYLLABUSGUIDE

igcse suubject guide chapter 11 and 12

1. B11 Gas exchange in humans

2. We can see from the syllabus content that this chapter is divided into two main cores RESPIRARTION & BREATHING (Gas Exchange) Firstly we need to understand the difference between respiration and breathing RESPIRATION BREATHING The chemical reactions in cells that breakdown nutrient molecules and release energy for metabolism T he physical process of getting oxygen into the lungs and carbon dioxide out of the lungs. Oxygen brought in by breathing is used to breakdown Glucose inside cells to generate energy which is then used by the cell to function. It allows for  gas exchange  to take place so that oxygen can be absorbed from the lungs into the blood and carbon dioxide is removed from the blood and breathed out from the lungs. Takes place in all body cells Takes place in and out of lungs Does not involve any muscles Involves chest muscles

3. Energy for all LIFE processes come from the food we eat. The food is digested, absorbed into blood stream and carried to cells The main nutrients-GLUCOSE which contains a lot of chemical energy. In order to make use of this energy, cells breakdown(CATABOLIC) these glucose molecules to release energy/heat in a series of metabolic reaction- This is RESPIRATION Like all metabolic reactions, respiration involves use of certain enzymes PRIOR KNOWLWDGE CHAP 2- THE CHEMICALS OF LIFE- CARBOHYDRATES What kind of atoms do carbohydrates contain and in what ratio? What are mono di and poly saccharides ? How much energy does one gram of carbohydrate release? In what forms do animals and plants store and transport glucose? What are tests to check presence of carbohydrates?

4. RESPIRATION Define respiration. The chemical reactions in cells that breakdown nutrient molecules and release energy for metabolism State the process of respiration. Oxygen brought in by breathing is used to breakdown Glucose inside all cells to generate energy in the form of ATP which is then used by the cell to carry out all their functions. The waste products of respiration like carbondioixe is carried by blood to the lungs, diffused into alveoli and exhaled out What is the purpose of respiration? To release energy

5. WHAT IS THE ENERGY RELEASED BY REPIRATION USED FOR? 1. Contracting muscles so we can move parts of the body 2. Making protein molecules by linking amino acids 3. Cell division so that we can grow and repair tissues 4. Active transport of substances against concentration gradient 5. Transmitting nerve implses from one part of the body to another 6. Producing heat inside body to keep body temperature constant despite environment

6. There are two methods of releasing energy from glucose. With the use of oxygen – AEROBIC RESPIRATION Without the use of oxygen – ANAEROBIC RESPIRATION The chemical reactions in cells that breakdown nutrient molecules and release energy for metabolism

7. AEROBIC RESPIRATION This type of respiration uses oxygen to release energy from glucose present in our cells. This takes place inside mitochondria Glucose + Oxygen    Carbon dioxide + Water + Energy C 6 H 12 O 6  + 6O 2         6CO 2  + 6H 2 O +ENERGY (ATP) In aerobic respiration glucose is brken down completely

8. ANAEROBIC RESPIRATION Sometimes there is not enough oxygen around for animals and plants to respire, but they still need energy to survive.  Instead they carry out respiration in the absence of oxygen to produce the energy they require this is called anaerobic respiration. This process generally takes place in cytoplasm of the cell Anaerobic respiration has different end products in plants and animals. :

9. In Plants The oxygen supply to plants can also run out, this happens for example if the soil gets waterlogged. In this case they have to obtain their energy via anaerobic respiration. Below is the word and chemical equation for anaerobic respiration in plants Glucose           Ethanol + Carbon dioxide + Energy (ATP) C 6 H 12 O 6   2C 2 H 5 OH + 2CO 2  + Energy (ATP) When the above reaction occurs in yeast cells it is referred to as  fermentation.  Fermentation is the process used for baking bread and brewing alcohol.

10. 1 packet active dry yeast 1 tablespoon sugar 1 tablespoon salt 2 cups lukewarm water (not over 110°F) 5 cups flour

11. In animals Our muscles need oxygen and glucose to respire aerobically and produce the energy they require, these are carried to the muscle via the blood.  However if we were to carry out vigorous exercise our heart and lungs would not be able to get sufficient oxygen to our muscles in order for them to respire. In this case muscles carry out anaerobic respiration. The word and chemical equation for anaerobic respiration in is: Glucose         Lactic acid + Energy C 6 H 12 O 6 2C 3 H 6 O 3  + ENERGY 120 kJ/mol As you can see anaerobic respiration is not as efficient as aerobic and only a small amount of energy is released.  This is because glucose can only be partially broken down(incomplete oxidation).  As well as this inefficiency a poisonous chemical, lactic acid is also produced, if this builds up in the body it stops the muscles from working and causes a cramp.  To rid the body of lactic acid oxygen is needed, we end up with an OXYGEN DEBT!

12. MARKSCHEME a).continuation of fast heart rate to transport lactic acid in the blood from the muscles to the liver (b).continuation of deeper and faster breathing to supply oxygen breakdown of lactic acid (c). Breakdown of lactic acid takes place in the liver

13. OXYGEN DEBT While running the muscles are using a lot of energy and for this a lot oxygen is needed. You breathe faster and deeper to get more oxygen into your blood But eventually a limit is reached and but heart and lungs cannot supply any more oxygen But extra energy is yet needed which is provided by anaerobic respiration. Glucose         Lactic acid + Energy When you stop running you have quite a lot of lactic acid in your muscles which must be broken down to glucose with the help of oxygen in the liver So even after you finish running you need to continue to breathe deeper and faster to provide oxygen for the breakdown of lactic acid While you were running you built up an oxygen debt- you borrowed some extra energy without paying for it with oxygen (anaerobic) Now you need oxygen to breakdown lactic acid and are paying off the debt by breathing deeper and faster to get oxygen https://www.youtube.com/watch?v=6XT_Ivl_J1g

14. Location Mitochondria Cytoplasm

15. How can we test for respiration? To test aerobic respiration it is best to test for CO2,O2 and heat/energy as Giving out water is not a good test as the apparatus may be wet giving out water Using up glucose by measuring change in weight is not reliable as change in mass may be due to evaporation as well Experiments Activity 11.1- Heat 11.2 Oxygen 11.3- Co2

16. All gas exchange surfaces have features in common These features allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time They include: Large surface area  to allow faster diffusion of gases across the surface Thin walls  to ensure diffusion distances remain short Good ventilation with air  so that diffusion gradients can be maintained Good blood supply  to maintain a high concentration gradient so diffusion occurs faster

17. THINKING QUESTION’ Investigating the Differences in Inspired & Expired Air When we breathe in, the air is drawn through boiling tube A When we breathe out, the air is blown into boiling tube B Lime water  is  clear  but becomes  cloudy  (or milky) when carbon dioxide is bubbled through it. Which test tube remains clear and which is milky? What does this tell us about inspired and expired air?

18. Investigating the Effects of Physical Activity on Breathing Exercise increases the  frequency and depth of breathing This can be investigated by  counting the breaths taken during one minute at rest  and  measuring average chest expansion over 5 breaths  using a tape measure held around the chest Exercise for a set time (at least 3 minutes) Immediately after exercising,  count the breaths taken in one minute and measure the average chest expansion over 5 breaths Following exercise, the  number of breaths per minute will have increased  and the  chest expansion will also have increased

19. Frequency and depth of breathing  increase when exercising This is because muscles are working harder and aerobically respiring more and they  need more oxygen to be delivered to them  (and carbon dioxide removed) to keep up with the energy demand If they cannot meet the energy demand they will also  respire anaerobically , producing  lactic acid After exercise has finished, the lactic acid that has built up in muscles needs to be  removed  as it  lowers the pH of cells  and can  denature enzymes  catalysing cell reactions It can only be removed by combining it with oxygen - this is known as  ‘repaying the oxygen debt’ This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal -  the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid

20. Mechanism for increasing breathing during exercise The  rate of respiration  increases in muscle cells when exercising heavily This CO 2  diffuses out of the cells into the  blood plasma CO 2  in solution causes a slight drop in pH so the blood becomes slightly more acidic The blood flows around the circulatory system and passes to the brain where the increased carbon dioxide levels are detected by  chemoreceptors  in the brain The chemoreceptors are located in the  medulla oblongata  of the brain Chemoreceptors are cells that detect chemical changes in the body-blood gas levels, as well as changes in pH The brain sends nerve impulses to the diaphragm and the intercostal muscles to  increase the   rate and depth of muscle contraction The  rate of inspiration increases , along with the the   volume of air  moved in and out with each breath The result is  greater absorption of oxygen  and  removal rate of carbon dioxide This supports the  increased rate of respiration  in the exercising muscle cells