digestive system I with answer[1].doc

1、F.4 Biology experiment Digestion I Page 1 F.4 Biology Experiment I Name: _ Class: _ ( ) TASK 1 : 1. Perform a simple experiment to show the need for digestion of food. 2. Tie a knot at one end of a dialysis tubing. Fill the tubing with equal volumes of starch solution and glucose solution. 3. Tie th

2、e other end of the tubing and make sure the tubing does not leak. Wash the outside of the tubing with distilled water. 4. Immerse the tubing in a boiling tube of water. 5. Test the water outside the tubing immediately for starch and glucose using iodine solution and Clinstix paper respectively. Perf

3、orm the same tests after 45 minutes. Questions for discussion: 1. In the space below, draw a table to show the results of all the tests done during the experiment. ( 4 marks ) 2. Explain why it is necessary to rinse the outside of the tubing with distilled water before putting it into the boiling tu

4、be. ( 2 marks ) To remove any starch or glucose solution sticking on the surface of the dialysis tubing (1). This can prevent the contamination of water in the beaker. (1) Iodine Test Clinstix Paper Test At time 0 Brown/ yellow Pink After 45 mins Brown/ yellow Purple Starch and glucose solution star

5、ch solution F.4 Biology experiment Digestion I Page 2 3. In this experiment, the main concept is : A selectively permeable membrane only allows small molecules to pass through. (a) Which part of a cell is selectively permeable ? ( 1 mark ) The cell membrane (b) Suggest how the processes of food dige

6、stion and absorption are related to the selectively permeability of the part you have mentioned in part (a). ( 3 marks ) Large food molecules such as starch have to be digested to smaller molecules such as glucose (1), which are small enough to pass through the membrane of the cells of the small int

7、estine (1). After that, the small food molecules can through the wall of the blood vessels and enter the blood. (1) 4. Repeat the experiment by adding equal volume of starch solution and amylase solution. After 45 minutes, test the water in the boiling tube using iodine solution , Benedicts solution

8、 and clinstix paper. (a) In the space below, tabulate the results of the three tests at the end of the experiment. ( 3 marks ) (b) Referring to the results in part (a), what conclusion can be drawn ? ( 1 mark ) The water inside the tubing contains reducing sugars , but not starch and glucose. (1) (c

9、) In the space below, write a word equation to show the digestion of starch by amylase. ( 2 marks ) amylase Starch maltose (d) A living cell does not store glucose. Suggest TWO possible reasons for this finding. ( 4 marks ) Glucose is small in size (1). If glucose molecules are stored at a high conc

10、entration inside living cells, they will diffuse out and be lost. (1) When large amount of glucose dissolves in the cytoplasm, it will lower the water potential of the cell. (1) Water moves into the cells by osmosis and eventually they burst. (1) Iodine Test Clinstix Paper Test Benedicts test Brown/ yellow(-ve) Pink (-ve) Green/ brown/ orange ppt (+ve)