問BIO 2001 CE MC Q.14 and Q.26

問BIO 2001 CE MC Q.14 and Q.26

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    1 十年前
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    Q.14

    Answer: D

    The bacteria break down food debris and produce acid which dissloves enamel and attacks dentine .As acid is formed ,the pH value of plaque decreases.

    (A)Destruction of the enamel will not produce acid and destruction of enamel is by acid produced by bacteria .

    (B)The bacteria break down food debris ,but not react with it.

    When a substance reacts with another one ,both of them change ;in this case,bacteria remain the same.

    (C) Saliva is slightly alkaline ;release of saliva should increase the pH of plaque.

    Q.26

    Answer:B

    Att the moment ,the atria are relaxing as they are not pumping blood to the ventricle,and the ventricles are contracting to push blood out of the heart.The pumping force of ventricles opens the semi-lunar valves .The tricuspid and bicuspid valves are closed to prevent the backflow of blood from ventricles to atria.

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