All Free Biology MCQs with Answers

1281. The productivity of aquatic ecosystem is basically determined by light and____________?

• A. CO2
• B. O2
• C. Water
• D. Nutrients

Explanation: Aquatic ecosystem productivity depends strongly on available light for photosynthesis and on nutrients such as nitrates and phosphates needed for algal and plant growth. Students may choose CO2 because it is a photosynthetic raw material, but nutrient availability is usually the major limiting factor after light penetration is considered.

1282. Ecosystem not found in Pakistan is_____________?

• A. Tropical rain forest
• B. Temperate deciduous forest
• C. Grassland
• D. Tundra

Explanation: Pakistan contains grasslands, temperate deciduous forests and cold high-altitude regions that may be classified as tundra, but it does not have a true tropical rainforest ecosystem. Students may choose tundra because of the country's northern mountains, but alpine tundra does occur at very high elevations.

1283. Which of the following is most constant abiotic component of ecosystem___________?

• A. Air
• B. Water
• C. Land
• D. Gravity

Explanation: Gravity is a highly constant abiotic factor because its strength does not vary substantially across the ordinary habitats of an ecosystem and it continuously influences water movement and organismal support. Students may choose water because it is essential to life, but its amount and availability can change greatly between habitats.

1284. According to cohesion-tension theory, tension is created by__________________?

• A. Hydrogen bonding
• B. Transpiration
• C. Adhesion
• D. Root prerssure

Explanation: Transpiration creates negative pressure in the leaf and pulls the continuous water column upward through xylem under the cohesion-tension theory. Hydrogen bonding provides cohesion between water molecules, but it does not by itself create the tension, so a student may choose a by confusing cohesion with the force-generating process.

1285. ______________ of earth surface is covered with water?

• A. 10%
• B. 30%
• C. 75%
• D. 90%

Explanation: Approximately 71% of Earth's surface is covered by water, and this is conventionally rounded to about 75% in many biology texts. The 90% option greatly overestimates the coverage and may be chosen by confusing Earth's water-rich appearance with its actual surface proportion.

1286. Oxygen accounts for __________ percent of totals human body mass?

• A. 65%
• B. 18%
• C. 10%
• D. 3%

Explanation: Oxygen is the most abundant element in the human body by mass, contributing about 65%, largely because it is present in body water and organic molecules. Students may choose 18% because carbon contributes roughly that proportion of body mass, but the question asks for oxygen.

1287. Percentage of water in brain cells is_______?

• A. 20%
• B. 65%
• C. 85%
• D. 89%

Explanation: Brain tissue contains a high proportion of water, commonly given in introductory biology as about 85%, because water forms the medium for cellular reactions and transport. Students may choose 65%, a value associated with the approximate water content of the whole human body rather than brain cells.

1288. All of the following are elements that plants need in very small amounts except___________?

• A. Iron
• B. Hydrogen
• C. Chlorine
• D. Copper

Explanation: Hydrogen is a macronutrient because plants require it in relatively large amounts, mainly as part of water and organic compounds. Iron, chlorine, and copper are micronutrients needed only in small quantities. The likely mistake is choosing iron, because it is important for chlorophyll formation, but importance does not mean that it is required in a large amount.

1289. Removal or degradation of environmental pollutants or toxic materials by living organisms is called__________?

• A. Integrated disease management
• B. Hydroponic culture technique
• C. Pasteurization
• D. Bioremediation

Explanation: Bioremediation uses living organisms, especially microorganisms or plants, to break down, remove, or detoxify environmental pollutants. Hydroponics is a method of growing plants without soil, so it is the likely alternative for students who focus on plants rather than pollutant removal. The other options concern disease management or food treatment.

1290. Vaccine was first developed by_______________?

• A. Louis Pasture
• B. Edward Jenner
• C. Jaber Ibn Hayan
• D. Aristotle

Explanation: Edward Jenner developed the first successful vaccine by using cowpox material to provide protection against smallpox. Students may choose Louis Pasteur because he later developed important vaccines, including vaccines against rabies and anthrax, but Jenner came first.