Biology MCQs

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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Page 44 of 103
Question #861
The 10% law of energy transfer in a food chain was proposed by:
A. Charles Elton
B. Eugene Odum
C. Raymond Lindeman
D. Arthur Tansley
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Correct Answer: Option C

Explanation:
The 10% law of energy transfer, which states that only about 10% of the energy from one trophic level is transferred to the next, was proposed by Raymond Lindeman in 1942. This law explains why food chains typically have only 3-4 trophic levels; there is simply not enough energy available to support higher levels.
This question belongs to: Science Biology
Question #862
Gross Primary Productivity (GPP) is defined as:
A. The total rate of photosynthesis or organic matter production by producers
B. The rate of storage of organic energy by consumers
C. The rate of decomposition by microbes
D. The rate of organic matter production after accounting for respiration
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Correct Answer: Option A

Explanation:
Gross Primary Productivity (GPP) is the total rate of photosynthesis, or the total amount of organic matter (biomass) produced by producers (plants) per unit area per unit time, including the organic matter used in respiration. Net Primary Productivity (NPP) is GPP minus the energy used by the plants for respiration (NPP = GPP - R).
This question belongs to: Science Biology
Question #863
The process by which water-soluble nutrients are washed out of decomposing organic matter into the soil is called:
A. Leaching
B. Humification
C. Fragmentation
D. Catabolism
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Correct Answer: Option A

Explanation:
Decomposition involves several steps. Leaching is the process where water-soluble inorganic nutrients (like nitrates, phosphates) are washed out of the decomposing organic matter (detritus) and move deep into the soil profile, where they may become unavailable to plants. Fragmentation is the breakdown of detritus by detritivores (like earthworms).
This question belongs to: Science Biology
Question #864
In the carbon cycle, carbon is removed from the atmosphere primarily by:
A. Photosynthesis
B. Combustion
C. Respiration
D. Decomposition
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Correct Answer: Option A

Explanation:
In the biogeochemical carbon cycle, carbon dioxide (CO2) is removed from the atmosphere primarily by autotrophs (plants, algae) through the process of photosynthesis, where it is fixed into organic compounds (glucose). Carbon is returned to the atmosphere through respiration (by plants and animals), decomposition of dead organic matter, and combustion of fossil fuels.
This question belongs to: Science Biology
Question #865
The conversion of ammonia (NH3) to nitrites (NO2-) and then to nitrates (NO3-) by bacteria is called:
A. Nitrogen fixation
B. Denitrification
C. Ammonification
D. Nitrification
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Correct Answer: Option D

Explanation:
Nitrification is a two-step process in the nitrogen cycle where ammonia is oxidized to nitrates. First, ammonia (NH3) is converted to nitrites (NO2-) by bacteria like Nitrosomonas. Then, nitrites are converted to nitrates (NO3-) by bacteria like Nitrobacter. Nitrates are the primary form of nitrogen absorbed by plants. Denitrification is the reverse process, converting nitrates back to nitrogen gas.
This question belongs to: Science Biology
Question #866
The sequence of progressive, predictable changes in the species composition of a community over time is called:
A. Ecological succession
B. Biological magnification
C. Eutrophication
D. Stratification
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Correct Answer: Option A

Explanation:
Ecological succession is the gradual and predictable process of change in the species composition of an ecological community over time. It occurs after a disturbance (secondary succession) or on a newly formed, lifeless substrate (primary succession). The final, stable community that is in near equilibrium with the environment is called the climax community. The entire sequence of communities is called a sere.
This question belongs to: Science Biology
Question #867
Which of the following is a recognized biodiversity hotspot in India?
A. Thar Desert
B. Western Ghats
C. Deccan Plateau
D. Indo-Gangetic Plains
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Correct Answer: Option B

Explanation:
Biodiversity hotspots are biogeographic regions with high levels of species richness and endemism that are under threat. The Western Ghats and Sri Lanka, along with the Himalayas, are recognized biodiversity hotspots in India. They harbor a vast array of flora and fauna, many of which are found nowhere else in the world, due to their unique geographical and climatic conditions.
This question belongs to: Science Biology
Question #868
National parks and wildlife sanctuaries are examples of which type of conservation?
A. Tissue culture
B. Cryopreservation
C. Ex-situ conservation
D. In-situ conservation
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Correct Answer: Option D

Explanation:
In-situ (on-site) conservation involves the conservation of species in their natural habitats. National parks, wildlife sanctuaries, and biosphere reserves are examples of in-situ conservation. Ex-situ (off-site) conservation involves taking endangered species out of their natural habitat and placing them in special settings like zoological parks, botanical gardens, and seed banks for conservation and breeding.
This question belongs to: Science Biology
Question #869
Zoological parks and botanical gardens are examples of:
A. In-situ conservation
B. Ecological succession
C. Ex-situ conservation
D. Biodiversity hotspots
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Correct Answer: Option C

Explanation:
Ex-situ (off-site) conservation involves protecting endangered species outside their natural habitats. Zoological parks, botanical gardens, seed banks, and cryopreservation facilities are examples of ex-situ conservation. This method allows for controlled breeding, research, and education, and can be a last resort for species whose natural habitats are severely degraded or destroyed.
This question belongs to: Science Biology
Question #870
Biological Oxygen Demand (BOD) is a measure of:
A. The amount of oxygen produced by algae
B. The total dissolved oxygen in a water body
C. The amount of oxygen required by bacteria to decompose organic matter in water
D. The amount of oxygen consumed by fish
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Correct Answer: Option C

Explanation:
Biological Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen required by aerobic microorganisms (mainly bacteria) to decompose the organic matter present in a given volume of water sample at a specific temperature over a specific time (usually 5 days at 20°C). High BOD indicates high levels of organic pollution, which depletes oxygen for aquatic life.
This question belongs to: Science Biology
Question #871
Eutrophication in a water body leads to:
A. Increased biodiversity
B. Decreased nutrient levels
C. Algal blooms and hypoxia
D. Increased oxygen levels
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Correct Answer: Option C

Explanation:
Eutrophication is the excessive enrichment of water bodies with nutrients (primarily nitrates and phosphates from fertilizers and sewage). This leads to rapid growth of algae, known as an algal bloom. When the algae die, their decomposition by bacteria consumes large amounts of dissolved oxygen, leading to hypoxia (low oxygen levels) or anoxia, causing the death of fish and other aquatic organisms.
This question belongs to: Science Biology
Question #872
Ozone layer depletion in the stratosphere is primarily caused by:
A. Chlorofluorocarbons (CFCs)
B. Carbon dioxide
C. Sulfur dioxide
D. Methane
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Correct Answer: Option A

Explanation:
The ozone layer in the stratosphere protects Earth from harmful ultraviolet (UV) radiation. Its depletion is primarily caused by Chlorofluorocarbons (CFCs), which were widely used in refrigerants, aerosols, and solvents. UV radiation breaks down CFCs, releasing chlorine atoms that catalytically destroy ozone molecules. The Montreal Protocol (1987) was an international treaty to phase out the production of CFCs.
This question belongs to: Science Biology
Question #873
The cell wall of bacteria is primarily composed of:
A. Chitin
B. Peptidoglycan (Murein)
C. Cellulose
D. Silica
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Correct Answer: Option B

Explanation:
The bacterial cell wall is a rigid structure that provides shape and protection. It is primarily composed of peptidoglycan (also known as murein), a polymer consisting of sugars and amino acids. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane. Cellulose is in plant walls, and chitin is in fungal walls.
This question belongs to: Science Biology
Question #874
The most common method of reproduction in bacteria is:
A. Spore formation
B. Fragmentation
C. Budding
D. Binary fission
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Correct Answer: Option D

Explanation:
Binary fission is the primary and most common method of asexual reproduction in bacteria. In this process, the bacterial cell replicates its DNA and then divides into two identical daughter cells. Under optimal conditions, some bacteria can divide every 20 minutes. Bacteria can also exchange genetic material through processes like conjugation, transformation, and transduction.
This question belongs to: Science Biology
Question #875
A virus particle (virion) consists of genetic material enclosed in a protein coat called:
A. Cell wall
B. Plasmid
C. Capsid
D. Envelope
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Correct Answer: Option C

Explanation:
A virus is an obligate intracellular parasite. The basic structure of a virus particle, or virion, consists of genetic material (either DNA or RNA, but never both) enclosed in a protective protein coat called a capsid, made of subunits called capsomeres. Some viruses also have an outer lipid envelope derived from the host cell membrane.
This question belongs to: Science Biology
Question #876
Fungi primarily reproduce asexually by the formation of:
A. Gems
B. Buds only
C. Spores
D. Seeds
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Correct Answer: Option C

Explanation:
Fungi reproduce asexually primarily through the formation of spores, which are produced in large numbers in specialized structures like sporangia (in Rhizopus) or conidiophores (in Aspergillus). These spores are highly resistant and can be dispersed by wind, water, or animals. Some fungi, like yeast, also reproduce asexually by budding.
This question belongs to: Science Biology
Question #877
The primary photosynthetic pigment found in all algae is:
A. Phycocyanin
B. Chlorophyll b
C. Chlorophyll a
D. Fucoxanthin
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Correct Answer: Option C

Explanation:
Chlorophyll a is the primary photosynthetic pigment found in all algae and is essential for the light reactions of photosynthesis. Different groups of algae also contain other accessory pigments like chlorophyll b, c, phycobilins (phycocyanin, phycoerythrin), and carotenoids (fucoxanthin), which give them their characteristic colors (green, red, brown) and help in capturing light energy.
This question belongs to: Science Biology
Question #878
Amoeba moves and captures food using temporary extensions of its cell body called:
A. Tentacles
B. Pseudopodia
C. Flagella
D. Cilia
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Correct Answer: Option B

Explanation:
Amoeba, a protozoan, moves and captures food using temporary, foot-like extensions of its cytoplasm called pseudopodia (false feet). This type of movement is called amoeboid movement and is driven by the assembly and disassembly of microfilaments (actin) in the cytoskeleton. Cilia and flagella are hair-like structures used by other protozoans like Paramecium and Euglena.
This question belongs to: Science Biology
Question #879
The conversion of milk to curd is primarily caused by which microorganism?
A. Saccharomyces cerevisiae
B. Lactobacillus
C. Aspergillus niger
D. Penicillium notatum
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Correct Answer: Option B

Explanation:
The conversion of milk to curd (yogurt) is a fermentation process primarily caused by lactic acid bacteria (LAB), such as Lactobacillus. These bacteria ferment the lactose (milk sugar) into lactic acid. The lactic acid lowers the pH, causing the milk protein (casein) to coagulate and solidify, forming curd. It also improves the nutritional value by producing Vitamin B12.
This question belongs to: Science Biology
Question #880
The microorganism responsible for the leavening of bread dough is:
A. Lactobacillus
B. Saccharomyces cerevisiae (Yeast)
C. Propionibacterium
D. Aspergillus
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Correct Answer: Option B

Explanation:
The leavening (rising) of bread dough is caused by the anaerobic respiration (fermentation) of the yeast Saccharomyces cerevisiae (baker's yeast). The yeast ferments the sugars in the dough, producing carbon dioxide (CO2) gas and ethanol. The CO2 gas gets trapped in the dough, causing it to expand and rise, giving bread its light and fluffy texture.
This question belongs to: Science Biology

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