In photosynthesis, oxygen is released from: MCQ with Answer and Explanation

Question
In photosynthesis, oxygen is released from:
A. Water
B. Glucose
C. Chlorophyll
D. Carbon dioxide
Answer: Option A
Solution (By JKSSB Mock Tests)
During the light reactions of photosynthesis, photolysis of water occurs at photosystem II, splitting water into protons, electrons, and molecular oxygen. The oxygen comes from water, not CO₂. This was demonstrated by using isotopically labeled oxygen (H₂O¹⁸). Glucose is formed in the Calvin cycle. Chlorophyll absorbs light but does not provide oxygen. The overall equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O.
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Practice More Biology Questions

Question #1
Amoebiasis is caused by which protozoan?
A. Giardia lamblia
B. Trypanosoma brucei
C. Plasmodium vivax
D. Entamoeba histolytica
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Correct Answer: Option D

Explanation:
Amoebiasis, also known as amoebic dysentery, is an intestinal infection caused by the protozoan parasite Entamoeba histolytica. It is transmitted through ingestion of cysts in contaminated food or water. Symptoms include abdominal pain, diarrhea, and dysentery (bloody stools). It can also spread to the liver, causing amoebic liver abscesses.
This question belongs to: Science Biology
Question #2
Consider the following statements about the human excretory system:
1. ADH increases water reabsorption.
2. Aldosterone increases sodium reabsorption.
3. Renin converts angiotensinogen to angiotensin I.
Which of the above is/are correct?
A. 1 and 3 only
B. 1 and 2 only
C. 1, 2, and 3
D. 2 and 3 only
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Correct Answer: Option C

Explanation:
All are correct: ADH (water), aldosterone (Na⁺), renin (angiotensinogen cleavage).
This question belongs to: Science Biology
Question #3
The organ that produces the hormone renin is the:
A. Adrenal gland
B. Liver
C. Heart
D. Kidney
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Correct Answer: Option D

Explanation:
Renin is secreted by juxtaglomerular cells of the kidney in response to low blood pressure or sodium. It converts angiotensinogen to angiotensin I, initiating the RAAS. Liver produces angiotensinogen, adrenal aldosterone, heart ANP.
This question belongs to: Science Biology
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