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Zoology Question 60 – AP-EAMCET 2025

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Assertion (A): Gastric juice plays an important role in absorption of vitamin B12. Reason (R): Gastric juice contains Castle's intrinsic factor. Identify the correct option from the following

Recall the various components of gastric juice and their functions in digestion and absorption.

Step 1: Analyze Assertion (A)✦ Active

The assertion states that gastric juice plays an important role in the absorption of vitamin B12. Gastric juice is secreted by the stomach lining. Vitamin B12 (cobalamin) is essential for red blood cell formation and neurological function. Its absorption is indeed a complex process that begins in the stomach.

💡 Teacher's Secret Hint

Remember that most nutrient absorption occurs in the small intestine, but vitamin B12 has a special requirement involving the stomach.

Step 2: Analyze Reason (R)○ Expand

The reason states that gastric juice contains Castle's intrinsic factor. Intrinsic factor is a glycoprotein secreted by the parietal cells (oxyntic cells) of the stomach. It is crucial for the absorption of vitamin B12.

💡 Teacher's Secret Hint

Parietal cells are also responsible for secreting hydrochloric acid (HCl) in the stomach.

Step 3: Evaluate Truthfulness of A and R○ Expand

From the analysis in Step 1, Assertion (A) is true because gastric juice, through its intrinsic factor, is vital for B12 absorption. From the analysis in Step 2, Reason (R) is also true because gastric juice does contain Castle's intrinsic factor.

Step 4: Determine if R is the Correct Explanation for A○ Expand

Intrinsic factor, secreted in the gastric juice, binds to vitamin B12 in the stomach and small intestine. This complex then travels to the ileum, where it is absorbed. Without intrinsic factor, vitamin B12 cannot be absorbed, leading to conditions like pernicious anemia. Therefore, the presence of Castle's intrinsic factor in gastric juice (R) directly explains why gastric juice is important for vitamin B12 absorption (A).

💡 Teacher's Secret Hint

A good way to check if R explains A is to read them together: 'Assertion (A) because Reason (R)'. If it makes logical sense, R is likely the correct explanation.

Step 5: Select the Correct Option○ Expand

Since both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), the correct option is 1.

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