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DIGESTION – ENZYMES AND FOOD TESTS

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DIGESTION – ENZYMES AND FOOD TESTS

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  1. Clicking here will move you to the next page DIGESTION – ENZYMES AND FOOD TESTS BUTTONS Click here; Clicking here will allow you to hear some information on the topic. Clicking here again will stop the sound. Clicking here will move you back a page. Clicking here will reveal some information Clicking here will reveal an answer Clicking here will bring you back to this page. TOPICS Jump to… …digestion and food molecules (two pages). …digestive enzymes(two pages). Jump to… Jump to… …food tests (three pages). Jump to… …practice questions (two pages). Jump to… …exam questions (two pages).

  2. DIGESTION Digestion is the break down of large insoluble molecules into small soluble molecules so they can be absorbed for use by the body cells. Click on the buttons for more information Enzymes are responsible for digesting large molecules of food such as starch. cell Digestive enzymes Digesting large molecules enzyme Small soluble molecules e.g. glucose Large insoluble molecule e.g. starch

  3. THE FOOD MOLECULES Much of the food we eat contains large insoluble molecules, for example, protein, fat andlarge carbohydrates such as starch. A molecule of carbohydrate such as starch is made up of smaller molecules called glucose A molecule of fat is made up of smaller molecules called fatty acids and glycerol. Click on the button for more information Food molecules carbohydrate protein Fats/oils (lipids) Carbohydrate Fat A molecule of protein is made up of many smaller molecules called amino acids. starch glycerol Protein Carbohydrate Fat one molecule of glucose amino acids fatty acids

  4. THE DIGESTIVE ENZYMES As much of the food we eat contains large insoluble molecules, a specific enzyme is needed to digest each one. Click on the button for more information Large insoluble food molecule Small soluble food molecule ase ase ase glucose carbohydrate e.g. starch carbohydrase Digestive enzymes protein amino acids protease e.g. amylase fat/oil glycerol +fatty acids lipase

  5. DENATURATION - revision Enzymes react best at their optimum temperature.This is the point where the rate of reaction is highest. If the temperature is greater than the optimum, the enzyme will become denatured, changing the shape of the active site. The substrate will not be able to bind to the active site and no product will be released. Click on the button for more information INCREASING THE TEMPERATURE When the enzyme has denatured it can not be returned to its original shape The active site has changed shape. The substrate cannot fit and a reaction will not occur and therfore, no product enzyme substrate Optimum temperature active site

  6. FOOD TESTS - starch A chemical test can be used to determine the presence of starch. Click on the button to start the food test iodine solution In the presence of starch,iodine solution will change colour from : squeeze result test yourself negative result positive result BROWN BLUE/BLACK - + starch solution

  7. FOOD TESTS – sugar (glucose) A chemical test can be used to determine the presence of glucose. Click on the button to start the food test In the presence of glucose,Benedict reagent will change colour from : squeeze result test yourself Benedict reagent There will be no colour change unless the temperature is higher than 95˚C. Click on the switch to boil the water negative result Positive result glucose solution BLUE BRICK RED 100˚C ON/OFF dŵr Thermostatic water bath

  8. FOOD TESTS – protein A chemical test can be used to determine the presence of protein Click on the button to start the food test In the presence of protein the biuret solution will change colour from : squeeze result test yourself Biuret solution negative result positive result BLUE VIOLET protein solution

  9. PRACTICE QUESTIONS 1 Which colour would you see with Benedict reagent if the food contains no sugar? The presence of which food group does Iodine solution test for? protein glucose fat green violet blue correct incorrect biuret blue to orange blue to violet no change white to blue Iodine starch brick red Benedict alcohol protein glucose biuret Benedict alcohol starch blue Iodine brick red blue to orange Blue to violet no change white to blue green violet fat Which colour change would you expect when biuret solution is added to protein? Which chemical tests for protein?

  10. PRACTICE QUESTION 2 products food molecule enzyme fatty acids and glycerol glucose Carbohydrate e.g. starch lipase amino acids carbohydrase / amylase glucose fat/oil protein amino acids carbohydrate e.g. starch carbohydrase / amylase protease glycerol +fatty acids fat /oil lipase protease protein

  11. PRACTICE QUESTION 3 Different food contain different proportions of food chemicals For each food, decide on the chemicals found in them. CHEMICALS GLUCOSE STARCH PROTEIN GLUCOSE STARCH PROTEIN GLUCOSE STARCH PROTEIN Which food contains the most sugar?

  12. EXAM QUESTION 1 Click on the answers to see how many marks the examiner awarded each response: WJEC Biology 2 Winter 2011 (higher) Q5 fatty acids 1 mark correct 1 mark correct 1 mark correct The enzyme is working at its fastest rate 0 marks Part (i) is not awarded a mark as the candidate has not given a valid reason for the decreased pH, (fatty acids lower the pH) 40˚C The enzyme is denatured and therefore the lipid molecule cannot be digested and there will be no fatty acids to lower the pH

  13. EXAM QUESTION 2 Try to answer this exam question. Once you have had a go, click on the to see the answer the examiner was looking for; WJEC Biology 1 Summer 2017 (higher) Q6 The amylase/enzyme has digested / broken down the starch Tube E / 2% amylase, as it contains the highest concentration/percentage amylase /enzyme 5 No starch being digested(1) because the{amylase / enzyme} has been{(heated to 100°C / boiled} (1) which {denatures/destroys} the enzyme’s active site (1) To act as a control/ to show that the {amylase / enzyme} digests starch

  14. EXAM QUESTION 3 Try to answer this exam question. Once you have had a go, click on the to see the answer the examiner was looking for; WJEC Biology 2 winter 2013 (foundation) Q3 carbohydrate/ starch To act lipase glycerol {Protein/gelatin/ jelly} {broken down/digested} (1) to amino acids (1) which are soluble/ can dissolve (1) enzyme denatured(1) active site {destroyed/ changed shape} (1) No digestion of protein / protein cannot fit / enzyme substrate complex cannot be formed (1) WJEC Biology 1 summer 2017 (foundation) Q9

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