Conditions necessary for the growth of microbes

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes P1.1<br /> P1. The conditions necessary for the growth of microbes<br /> Pupils store uncooked and cooked rice under different conditions to<br /> determine the conditions needed for microorganisms to grow.<br /> SAFETY NOTE: ONCE THE INVESTIGATION IS UNDERWAY, DO<br /> NOT ALLOW PUPILS TO OPEN THE TUBES. THE TUBES AND<br /> CONTENTS SHOULD BE DISPOSED OF BY AUTOCLAVING.<br /> The following results can be expected:<br /> conditions in theappearance afterappearance after<br /> KS3<br /> science and food technology<br /> Timing - 15 minutesto set up the<br /> apparatus; the tubes then need to<br /> be looked at after approximately 1<br /> and 2 weeks.<br /> Pupil activity sheet P1 accompanies<br /> this activity.<br /> Requirements<br /> • test tubes or boiling tubes<br /> uncooked rice<br /> cooked ricealone<br /> cooked rice in<br /> refrigerator<br /> cooked rice with<br /> oil<br /> tube<br /> no water, warm,air<br /> present<br /> water present,<br /> warm, air present<br /> water present,<br /> cold, air present<br /> water present,<br /> warm, layer of oil<br /> stops air reaching<br /> rice<br /> 1 week<br /> rice looks same<br /> mould starting<br /> togrow<br /> rice looks the<br /> same<br /> rice looks the<br /> same<br /> 2 weeks<br /> rice looksthe<br /> same<br /> more mould<br /> present<br /> rice looksthe<br /> same<br /> rice looksthe<br /> same<br /> • dry, uncooked rice<br /> • cooked (boiled and drained)<br /> rice<br /> • cotton wool<br /> • access to a refrigerator (not<br /> where food for consumption is<br /> stored)<br /> • marker pens or sticky labels<br /> You are advised to check the tubes periodically, and show them to the<br /> pupils when some mould has appeared in tube B. None of the other tubes<br /> should show this in the same period of time. The tubes can be left for<br /> longer if desired, in which case mould growth will occur in the other tubes<br /> except tube A. However, this may take a number of weeks.<br /> The follow up discussion should reach the conclusion that<br /> water/moisture, warm temperature and air (oxygen from the air) are<br /> needed for the growth of microorganisms. Mould growth occurs because<br /> air containing mould spores has been able to get into the tubes.<br /> The tubes and contents should be disposed of by autoclaving.<br /> <br /> THE CONDITIONS NECESSARY FOR THE GROWTH OF MICROBESpupil activity P1<br /> As soon as food is picked (harvested) or slaughtered it will begin to deteriorate as the<br /> microorganisms that cause food spoilage begin to attack.<br /> What conditions do microbes need in order to make our food go ‘off’ or ‘bad’?<br /> Carry out the following experiment to be able to answer this question.<br /> SAFETY NOTE<br /> ONCE PREPARED: DO NOT REMOVE COTTON<br /> WOOL BUNG FROM TUBES<br /> Method<br /> 1.Label four tubes A - D.<br /> 2.Place some uncooked rice in tube A.<br /> 3.Place some cooked rice in tubes B, C and D.<br /> 4.Place enough cooking oil in tube D to just cover the rice.<br /> 5.Put a cotton wool bung in each tube.<br /> 6.Put tube C in a refrigerator.<br /> 7.Leave the other tubes at room temperature.<br /> 8.Look at the tubes after 1 week and 2 weeks.<br /> Results<br /> Look for the growth of mould in the tubes. Decide what the conditions were like in<br /> each tube during the experiment. Fill in the table below:<br /> uncooked rice<br /> conditions appearance appearance<br /> in the tube after 1 week after 2 weeks<br /> cooked rice alone<br /> cooked rice<br /> in refrigerator<br /> cooked rice with oil<br /> What conditions are needed for microorganisms to grow?<br /> If mould has grown in any of the tubes, where has the mould come from?