All Free Biology MCQs with Answers

1471. In which of the following component of the body, lactic acid fermentation takes place?

• A. Brain
• B. Heart
• C. Liver
• D. Muscles

Explanation: Lactic acid fermentation occurs in muscle cells when oxygen supply is insufficient, allowing glycolysis to continue by regenerating NAD+. The likely alternative is the heart, because it also uses respiration, but cardiac muscle normally depends mainly on aerobic respiration and does not commonly accumulate lactic acid.

1472. The most important photosynthetic pigment is ___________?

• A. Chlorophyll a
• B. Chlorophyll b
• C. Xanthophyll
• D. Carotenes

Explanation: Chlorophyll a is the primary photosynthetic pigment because it is present in the reaction centres and directly converts light energy into chemical energy. Students often choose chlorophyll b because it also absorbs light, but chlorophyll b is an accessory pigment that transfers absorbed energy to chlorophyll a.

1473. The chlorophyll molecule is embedded in the core of thylakoid membrane which acts as___________?

• A. Hydrophilic
• B. Hydrophobic
• C. Both of these
• D. None of these

Explanation: The core of the thylakoid membrane is made largely of nonpolar lipid tails, so it is hydrophobic and can accommodate the nonpolar regions of chlorophyll and other membrane proteins. The likely mistake is choosing both hydrophilic and hydrophobic by considering the whole membrane, but the question specifically asks about its core.

1474. In alcoholic fermentation Pyruvic acid is broken down into?

• A. Acetaldehyde
• B. Methyl alcohol
• C. Ethyl alcohol
• D. Lactic acid

Explanation: In alcoholic fermentation, pyruvic acid first loses carbon dioxide to form acetaldehyde, which is then reduced to ethyl alcohol. The likely distractor is lactic acid, because it is also produced from pyruvate, but that occurs in lactic acid fermentation rather than alcoholic fermentation.

1475. Deficiency of ___________ causes yellowing in plants?

• A. Magnesium
• B. Iron
• C. Chlorine
• D. Oxygen

Explanation: Magnesium is part of the chlorophyll molecule, so its deficiency reduces chlorophyll formation and produces yellowing, called chlorosis, especially in older leaves. Iron deficiency can also cause chlorosis, so option b may be chosen, but magnesium is the mineral directly present at the centre of chlorophyll.

1476. Complete breakdown of glucose molecule takes place in which of the following?

• A. Alcoholic fermentation
• B. Lactic acid fermentation
• C. Aerobic respiration
• D. All of these

Explanation: Aerobic respiration completely oxidizes glucose to carbon dioxide and water through glycolysis, the Krebs cycle and the electron transport chain. The likely mistake is choosing alcoholic or lactic acid fermentation because both begin with glucose breakdown, but fermentation stops before complete oxidation and leaves energy-rich end products.

1477. Xanthophylls are _________ pigments

• A. Yellow
• B. Red
• C. Orange
• D. Green

Explanation: Xanthophylls are accessory carotenoid pigments that appear yellow and help absorb wavelengths that chlorophyll does not absorb efficiently. Carotenes may be confused with them because both are carotenoids, but carotenes are generally orange rather than yellow.

1478. Chlorophylls are found embedded in the __________ membranes?

• A. Stroma
• B. Grana
• C. Thylakoid
• D. Intergrana

Explanation: Chlorophyll molecules are embedded in thylakoid membranes, where they form photosystems and absorb light for the light-dependent reactions. The likely alternative is grana, but grana are stacks of thylakoids, not the membranes themselves.

1479. The dense fluid filled region in the chloroplast is____________?

• A. Grana
• B. Stroma
• C. Thylakoid
• D. None of these

Explanation: The stroma is the dense, enzyme-containing fluid region surrounding the thylakoids inside a chloroplast, and it is the site of the Calvin cycle. Students may choose grana because they are another major chloroplast structure, but grana are stacks of membranes rather than a fluid-filled region.

1480. Photosystem II has molecules which absorbs maximum light of___________?

• A. 680 nm
• B. 100 m
• C. 700 nm
• D. 670 nm

Explanation: Photosystem II has a reaction-centre chlorophyll called P680 because it absorbs maximally at about 680 nm. The likely alternative is 700 nm, which identifies the reaction centre of Photosystem I, not Photosystem II.