All Free Biology MCQs with Answers

1491. First Actions spectrum was obtained by using__________?

• A. Algae
• B. Fungi
• C. Bacteria
• D. Spirogyra

Explanation: T.W. Engelmann obtained the first action spectrum using the filamentous green alga Spirogyra and aerobic bacteria that gathered near regions releasing the most oxygen. Students may choose algae because Spirogyra is an alga, but the question asks for the specific organism used, which was Spirogyra.

1492. The first action spectrum was obtained by___________?

• A. T.W.Englemam
• B. Malleus
• C. T.W.Inws
• D. W.Stapes

Explanation: The first action spectrum was obtained by Theodor Wilhelm Engelmann, who used algal filaments and aerobic bacteria to relate oxygen production to wavelength. Students may choose Malleus or Stapes because those names are also associated with biology, but they are bones of the middle ear, not photosynthesis researchers.

1493. Which of the following light is least absorbed by the plants?

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

Explanation: Green light is least absorbed by chlorophyll and is largely reflected, which is why most leaves look green. Students may choose orange because it is absorbed less strongly than red or blue, but green is the least-absorbed region among these choices.

1494. The percentage of light absorbed by the leaf is ___________?

• A. 20%
• B. 15%
• C. 10%
• D. 1%

Explanation: Only about 1% of the incident solar energy is ultimately captured and stored as chemical energy by photosynthesis in green plants. Students may choose 10% by confusing the amount of light absorbed by a leaf with the much smaller fraction converted into stored chemical energy.

1495. Visible light used in photosynthesis ranges from:__________?

• A. 300 - 700 nm in wavelength
• B. 350 - 750 nm in wavelength
• C. 380 - 750 nm in wavelength
• D. 390 - 790 nm in wavelength.

Explanation: The photosynthetically useful part of visible light is commonly given as approximately 380 to 750 nm, covering the wavelengths absorbed by photosynthetic pigments. Students may choose 300 to 700 nm because it resembles a broad visible-light range, but 300 nm is ultraviolet and excludes part of the useful red region.

1496. PS I has chlorophyll a molecule which absorbs maximum light of _________ nm ?

• A. 600
• B. 650
• C. 680
• D. 700

Explanation: Photosystem I has a reaction-centre chlorophyll a molecule called P700 because it absorbs maximally at about 700 nm. Students may choose 680 nm by confusing P700 with P680, the reaction centre of photosystem II.

1497. Van neil hypothesis about the production of oxygen during phosynthesis was based on the study and investigations on___________?

• A. Bacteria
• B. Algae
• C. Protenema
• D. Cyanobacteria

Explanation: Van Niel developed his hypothesis from studies of photosynthetic bacteria, especially purple and green sulfur bacteria, and proposed that oxygen comes from the electron donor rather than carbon dioxide. Students may choose cyanobacteria because they release oxygen, but Van Niel's key investigations involved non-oxygenic photosynthetic bacteria.

1498. Air contains __________ % of CO2 ?

• A. 0.02-0.03
• B. 0.03-0.04
• C. 0.04-0.05
• D. 0.05-0.06

Explanation: Atmospheric carbon dioxide is approximately 0.03% to 0.04% in the traditional textbook value used in many biology examinations. Students may choose 0.04% to 0.05% because modern atmospheric carbon dioxide is close to 0.04% and is increasing, but the submitted key follows the conventional textbook range.

1499. The point at which there is no net exchange of gases between leaves and atmosphere is known as_____________?

• A. Neutral point
• B. Compensation point
• C. Parallel point
• D. Competitive point

Explanation: At the compensation point, the rate of carbon dioxide uptake and oxygen release in photosynthesis equals the rate of respiratory gas exchange, so there is no net gas exchange with the atmosphere. Students may choose neutral point because it sounds equivalent, but compensation point is the established biological term.

1500. Net yield of H2O in Photosynthesis is__________?

• A. 1 molecule
• B. 6 molecules
• C. 3 molecules
• D. 0 molecule

Explanation: The simplified photosynthesis equation can be written as 6CO2 + 6H2O -> C6H12O6 + 6O2, so water is used rather than produced and its net yield is 0 molecule. Students may choose 6 molecules by reading the water coefficient in an alternative expanded equation without cancelling the water molecules appearing on both sides.