Page 9 - 59. P6BST Answer key (old1)
P. 9

UNIT 4 : Revision 1
                 SECTION A

                 1       (3)      Since substance X can increase the amount of carbon dioxide in the water, it changes the
                                  amount of carbon dioxide in the water when different amounts of it are added to the water.
                                  Therefore, the independent variable is the amount of carbon dioxide in the water.

                 2       (3)      •   Water + Carbon dioxide → Food + Oxygen
                                  •   As oxygen occupies more air spaces, it pushes the water downwards.

                 3       (4)      There is no starch formed at the part of the leaf exposed to substance X. This shows
                                  that  substance  X  removes  carbon  dioxide  and  this  part  of  the  leaf  cannot  carry  out
                 4       (2)      •   The stem of a plant has water-carrying tubes to transport water within the plant.
                                  •   It also help to support the leaves to trap maximum amount of sunlight.
                 5       (4)      •   Water in the soil is absorbed by the roots and is transported to the leaf by the water-
                                   carrying tubes.
                                  •   Sugar made in the leaf is transported out of the leaf to the other parts of the plant by the
                                   food-carrying tubes.
                                  •   The exchange of carbon dioxide and oxygen takes place through the stomata of the leaf.
                                   Carbon dioxide enters the leaves while oxygen is released into the air.

                 SECTION B
                 1    (a)   Q. The amount of oxygen produced by the water plant was the greatest when the colour of light Q
                            shone on it. This shows that the water plant carried out the photosynthesis the fastest.
                      (b)   In a brightly-lit room, light from the surroundings can also affect the rate of photosynthesis in the
                            water plant. Therefore, by carrying out the experiment in a dark room, Siti can ensure a fair test.

                 2    (a)   Water
                      (b)   This ensures that there is enough time for the plant to carry out photosynthesis to form starch.
                      (c)   Yes. Carbon dioxide was able to flow to leaf Y through the holes of the bag. Water could also reach
                            leaf Y because the water-carrying tubes were not removed at part Q. Sunlight could also reach
                            leaf Y as clear plastic bag is transparent. Therefore, it had carbon dioxide, sunlight and water to
                            carry out photosynthesis.

                      (d)   He should conduct the experiment on more leaves of the same plant.

                 3    (a)   (i)   carbon dioxide

                            (ii)  water                                                                      Unit 4 | Revision 1
                            (iii)  food / sugar / glucose
                            (iv)  oxygen

                      (b)   P. When the number of tracing paper increased, the amount of light could pass through them
                            became lesser, so the rate of photosynthesis decreased. As a result, the amount of gas collected
                            decreased when the number of tracing paper increased.

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