All Free Biology MCQs with Answers

1501. About __________ % of photosynthesis is carried by terrestrial plants, while rest occurs in ocean, lakes, and ponds?

• A. 10%
• B. 20%
• C. 30%
• D. 40%

Explanation: About 10% of total photosynthesis is attributed to terrestrial plants, whereas aquatic plants, algae, and other aquatic photosynthetic organisms perform most of it. Students may choose 20% by focusing on the large land area covered by vegetation and ignoring the extensive photosynthetic activity in aquatic ecosystems.

1502. Of the following which one is not an energy releasing process?

• A. Glycolysis
• B. Respiration
• C. Photosynthesis
• D. Kreb's cycle

Explanation: Photosynthesis is an energy-storing process because light energy is converted into chemical energy in glucose, whereas glycolysis, respiration, and the Krebs cycle release usable energy from organic molecules. Students may choose glycolysis because it is only the first stage of respiration, but it still produces ATP and reduced electron carriers.

1503. Carotenoids perform protective function in_____________?

• A. Animals
• B. Plants
• C. Both of these
• D. None of these

Explanation: Carotenoids protect photosynthetic tissues by dissipating excess light energy and preventing photooxidative damage to chlorophyll; in animals, dietary carotenoids can also act as antioxidant protective compounds. Students may choose plants only because the photosynthetic protective role is emphasized in biology texts, but the broader protective function occurs in both plants and animals.

1504. The organisms able to use sunlight directly as a source of energy are_____________?

• A. Plants
• B. Animals
• C. Omnivores
• D. Fungi

Explanation: Plants use chlorophyll to convert sunlight into chemical energy during photosynthesis, making them primary producers. Students may choose omnivores because they obtain energy through food, but animals cannot use sunlight directly as their main energy source.

1505. Quantitative study of energy relationships in biological systems obeys.

• A. Bioenergetics
• B. Laws of thermodynamics
• C. Laws of thermo chemistry
• D. Laws of chemical energetic

Explanation: Bioenergetics studies energy transformations in living systems, and these transformations follow the first and second laws of thermodynamics. Students may choose the laws of thermochemistry because both subjects involve energy, but thermodynamics provides the general laws governing biological energy changes.

1506. Which of the following is a compensation point:

• A. Leaves respire and utilize O2 and release CO2.
• B. Photosynthesis and respiration occur at same rate. So there is not net exchange of gases between atmosphere and plants.
• C. Rate of photosynthesis increases, so do the O2 production, with a net release of oxygen coupled with the uptake of CO2.
• D. Rate of respiration becomes more than rate of photosynthesis.

Explanation: The compensation point occurs when photosynthesis and respiration proceed at equal rates, so the oxygen taken up and released, and the carbon dioxide released and fixed, balance each other. Students may choose option d by considering only respiration, but that describes a point where the plant has a net release of carbon dioxide.

1507. At which times there is no net gaseous exchange between leaves and the atmosphere.

• A. Day time.
• B. Night time.
• C. Dawn & Dusk.
• D. Mid night.

Explanation: At dawn and dusk, light intensity is near the compensation point, so photosynthetic carbon dioxide uptake balances respiratory carbon dioxide release. Students may choose night time because photosynthesis stops then, but respiration continues alone at night and causes a net gaseous exchange.

1508. Photosynthesis is process in which ________ compounds of carbon (CO2) and hydrogen (H2O) are reduced to carbohydrate like (glucose) using light energy.

• A. Organic
• B. Energy rich
• C. Energy poor
• D. Reduced

Explanation: Carbon dioxide and water are inorganic and energy-poor compounds; photosynthesis uses light energy to reduce them into the energy-rich organic carbohydrate glucose. Students may choose organic compounds because glucose is organic, but the question refers to the starting compounds, CO2 and H2O.

1509. Which of the following is a chemical link between catabolism and anabolism?

• A. AMP
• B. ADP
• C. ATP
• D. All of these

Explanation: ATP links catabolism and anabolism because energy released during catabolic reactions is stored in ATP and then supplied by ATP hydrolysis for anabolic reactions. Students may choose ADP because it is produced when ATP is used, but ADP is mainly the lower-energy product rather than the principal energy-transfer link.

1510. What percentage of light reaching the earth is used in photosynthesis?

• A. 25%
• B. 10%
• C. 5%
• D. 1%

Explanation: Only about 1% of the sunlight reaching Earth is captured by green plants and converted into chemical energy through photosynthesis. Most incoming light is reflected, transmitted or absorbed without being stored as plant biomass. Students may choose c because 5% sounds plausible, but the standard ecological estimate is approximately 1%.