IGCSE Biology Paper-5: Specimen Questions with Answers 45 - 46 of 62

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Question 45


Describe in Detail


Starch, a complex carbohydrate, is composed of 15 %-20 % amylose and 80 %-85 % amylopectin. It mainly found in rice, wheat, maize.

An experiment was done to identify the presence of starch in potato. What may be the procedure of it?



  • Test tubes
  • Test-tube stand
  • Spirit lamp
  • Dropper
  • Filter paper
  • Iodine solution
  • Distilled water

Foodstuff like potato, rice, wheat or maize grains


  • Take a few freshly cut pieces of potato in a clean test tube. Pour 10 ml distilled water into the test tube.
  • Boil the contents of the test tube for about 5 minutes.
  • Filter the contents of the test tube through a filter paper
  • Test the obtained filtrate for the presence of starch by the following method.
  • Then take 2 ml filtrate in a clean test-tube and add 2 drops of iodine solution by dropper

Observation-The color of the filtrate changes dark blue black

Result-It shows presence of starch in potato

Image Shows Test for the Presence of Starch

Question 46


Describe in Detail


Potato membrane behaves as a semi-permeable membrane through which water moves from its higher concentration to lower concentration. Such movement of water is called osmosis.

Experiment how water moves between cells in plants.


To observe how water moves between cells in plants we first require a medium-sized potato, potato peeler, knife, sugar solution, pins, Petri plate and water.


  • Use one potato, peel off its skin and keep both ends flat by cutting off thin slices with cutter.
  • From one end, carefully expose out a hole in the potato, leaving a thin layer tissue around the hole of potato.
  • Fill half of the potato cavity with sugar solution.
  • Mark the level of sugar solution inside the cavity by using a pin into the potato wall.
  • Then place the potato cup in a plate having water, such that most of the potato cup is dipped in water, but the level of water is lower than that of sugar solution
  • Keep the set-up for 2 - 3 hours and observe the level of sugar solution in the cavity.
Image Shows Slices of Potato in Petri Plate

After a few hours, we will observe that water from the Petri plate enters the potato cavity and the level of solution in the cavity rises.

Therefore, we can state that The Petri plate has higher concentration of water molecules than the potato cavity. Water moves from the Petri plate into the potato cup across the cell walls and cell membranes

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