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BIOLOGY Assertion & Reason

MODEL PAPER 9 · Gujarat Board (GSEB) STD 11 Science (GSEB - English Medium). 4 questions.

Questions

Assertion & Reason

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4 questions · self-marked practice — reveal the answer and mark yourself.

MCQ 11 Mark
Assertion (A): Excessive inflation of the lungs is prevented by the Hering-Breuer reflex.
Reason (R): On overstretching of the lungs, the stretch receptors send impulses along the vagus nerve to stimulate the expiratory centre.
  • A
    Both A and R are true and R is the correct explanation of A.,
  • B
    Both A and R are true but R is not the correct explanation of A
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
(c) A is true but R is false.
Explanation: In the walls of bronchi and bronchioles stretch receptors are located and are stimulated by overstretching of the lungs. Nerve impulses are sent along the vagus nerve to inhibit the inspiratory area. The result is that expiration begins. Therefore, it is mainly a protective mechanism for preventing excessive inflation of the lungs.
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MCQ 21 Mark
Assertion (A): Proenzyme is the precursor of an enzyme.
Reason (R): Proenzyme is as active as the enzyme.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
(c) A is true but R is false.
Explanation: Proenzyme is the inactive precursor of an enzyme. Many enzymes are initially produced in the proenzyme or zymogen state. They become reactive or active enzymes only at a particular pH, in the presence of substrate or some special treatment.
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MCQ 31 Mark
Assertion (A): Oxygenation of blood promotes the release of carbon dioxide from the blood in the lungs.
Reason (R): Carbon dioxide is carried as bicarbonates in erythrocytes of blood.
  • A
    Both A and R are true and R is the correct explanation of A
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false
  • D
    A is false but R is true.
Answer
(b) Both A and R are true but R is not the correct explanation of A.
Explanation: Carbon dioxide is carried in the form of bicarbonates and carbamino haemoglobin in erythrocytes in blood. On reaching the lungs blood is oxygenated. Oxygenation of blood promotes the release of carbon dioxide from the blood in the lungs in two ways. Firstly, since oxyhaemoglobin is a stronger than deoxyhaemoglobin, therefore it donates $H ^{+}$ which joins bicarbonates $\left( HCO _3^{-}\right)$ to form carbonic acid $\left( H _2 CO _3\right)$. The latter is cleaved into water and carbon dioxide by carbonic anhydrase. Thus carbon dioxide is released from bicarbonate. Secondly, oxyhaemoglobin, can not holds as much carbon dioxide as deoxyhaemoglobin, therefore, oxygenation of hemoglobin simultaneously releases carbon dioxide from carbaminohaemoglobin.

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MCQ 41 Mark
Assertion (A): The mycelium is coenocytic in Zygomycetes.
Reason (R): The gametes are uninucleate.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A
  • C
    A is true but R is false.
  • D
    A is false but R is true.
Answer
(c) A is true but R is false.
Explanation: The mycelium is multinucleate, aseptate (i.e. coenocytic) in Zygomycetes. The gametes are commonly multinucleate and are called coenogametes.
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