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 37 of 103
Question #721
The organelle that is the site of oxidative phosphorylation is:
A. Ribosome
B. Nucleus
C. Golgi apparatus
D. Mitochondrion
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Correct Answer: Option D

Explanation:
Oxidative phosphorylation occurs on the inner mitochondrial membrane, where the electron transport chain creates a proton gradient, and ATP synthase uses this gradient to produce ATP. This is the major source of cellular energy. Nucleus stores DNA, Golgi processes proteins, ribosomes synthesize proteins.
This question belongs to: Science Biology
Question #722
The vitamin that is a coenzyme for carboxylases (e.g., pyruvate carboxylase) is:
A. Riboflavin
B. Thiamine
C. Biotin
D. Folate
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Correct Answer: Option C

Explanation:
Biotin is a coenzyme for carboxylation enzymes, including pyruvate carboxylase (gluconeogenesis) and acetyl-CoA carboxylase (fatty acid synthesis). Thiamine (B₁) is for decarboxylation, riboflavin (B₂) for redox, folate (B₉) for one-carbon transfers. Biotin is often bound to lysine in enzymes.
This question belongs to: Science Biology
Question #723
The process by which plants shed their leaves is called:
A. Senescence
B. Transpiration
C. Abscission
D. Germination
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Correct Answer: Option C

Explanation:
Abscission is the controlled shedding of leaves, flowers, or fruits, facilitated by the hormone ethylene and enzymes that degrade cell walls at the abscission zone. Senescence is the aging process leading to cell death. Transpiration is water loss, germination is seed sprouting.
This question belongs to: Science Biology
Question #724
Which of the following is considered the defining property of living organisms?
A. Reproduction
B. Metabolism
C. Movement
D. Growth
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Correct Answer: Option B

Explanation:
Metabolism is the sum of all chemical reactions occurring in a living body. It is the only feature present in all living organisms without exception. While growth and reproduction are common, they are not universal (e.g., sterile mules). Non-living things can also exhibit growth by accumulation or movement, making metabolism the true defining property.
This question belongs to: Science Biology
Question #725
Who is known as the father of Binomial Nomenclature?
A. Carolus Linnaeus
B. Robert Whittaker
C. Charles Darwin
D. Aristotle
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Correct Answer: Option A

Explanation:
Carolus Linnaeus, a Swedish botanist, is known as the father of Binomial Nomenclature. He introduced this system of naming organisms using two terms: the generic name and the specific epithet. This standardized naming system eliminated the confusion caused by local and common names across different languages and regions.
This question belongs to: Science Biology
Question #726
Which branch of biology deals with the study of animal behavior?
A. Eugenics
B. Ethology
C. Ecology
D. Entomology
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Correct Answer: Option B

Explanation:
Ethology is the branch of biology that deals with the scientific and objective study of animal behavior, usually with a focus on behavior under natural conditions. Ecology studies ecosystems, Entomology studies insects, and Eugenics deals with the improvement of human genetic traits.
This question belongs to: Science Biology
Question #727
How does growth in living organisms differ from growth in non-living things?
A. Growth occurs from inside the organism
B. Growth occurs by accumulation externally
C. Growth in living things is due to physical processes
D. Growth is reversible in living organisms
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Correct Answer: Option A

Explanation:
Growth in living organisms occurs from inside the body through cell division and synthesis of new cellular material. In contrast, non-living things grow by the accumulation of material on their surface externally. Living growth is intrinsic and irreversible, whereas non-living growth is extrinsic and can be reversed.
This question belongs to: Science Biology
Question #728
What does Taxonomy primarily deal with?
A. Study of diseases
B. Classification of organisms
C. Study of fossils
D. Study of tissues
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Correct Answer: Option B

Explanation:
Taxonomy is the branch of science concerned with the classification, identification, and naming of organisms. It involves arranging organisms into hierarchical categories based on their shared characteristics and evolutionary relationships. The study of tissues is Histology, and the study of fossils is Paleontology.
This question belongs to: Science Biology
Question #729
Which of the following defines a biological species?
A. Organisms sharing the same genetic code
B. Organisms living in the same habitat
C. Organisms that can interbreed and produce fertile offspring
D. Organisms having similar physical appearances
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Correct Answer: Option C

Explanation:
A biological species is defined as a group of potentially interbreeding natural populations that are reproductively isolated from other such groups and produce fertile offspring. Physical similarity or shared habitat does not guarantee species status, as reproductive isolation is the key criterion.
This question belongs to: Science Biology
Question #730
Response to stimuli is a defining property of living organisms. Which of the following is true about this property?
A. Plants do not respond to environmental factors
B. Response to stimuli is not seen in unicellular organisms
C. Only animals show response to stimuli
D. All living organisms from prokaryotes to complex eukaryotes can sense and respond to stimuli
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Correct Answer: Option D

Explanation:
Consciousness or the ability to sense and respond to environmental stimuli is a defining property of all living organisms. Every organism, from simple prokaryotes to complex multicellular eukaryotes, can sense environmental factors like light, temperature, and chemicals. Plants also respond to light, gravity, and touch.
This question belongs to: Science Biology
Question #731
At which level of biological organization does the living state first become evident?
A. Organ level
B. Molecular level
C. Cellular level
D. Tissue level
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Correct Answer: Option C

Explanation:
The living state and all vital functions first become evident at the cellular level. While macromolecules are present in both living and non-living systems, it is the organized interaction of these molecules within a cell that manifests life. Cells are the fundamental structural and functional units of life.
This question belongs to: Science Biology
Question #732
What does ICZN stand for in biological nomenclature?
A. International Commission on Zoological Nomenclature
B. Indian Commission for Zoological Names
C. International Code for Zoological Nomenclature
D. Indian Code of Zoological Nomenclature
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Correct Answer: Option A

Explanation:
ICZN stands for the International Commission on Zoological Nomenclature. It is the organization that establishes and maintains the International Code of Zoological Nomenclature, which provides the universal rules for naming animals to ensure stability and universality in scientific names.
This question belongs to: Science Biology
Question #733
Who proposed the Cell Theory?
A. Louis Pasteur and Gregor Mendel
B. Matthias Schleiden and Theodor Schwann
C. Rudolf Virchow and Robert Brown
D. Robert Hooke and Antonie van Leeuwenhoek
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Correct Answer: Option B

Explanation:
The Cell Theory was proposed by Matthias Schleiden (1838) and Theodor Schwann (1839). Schleiden concluded that all plants are composed of cells, while Schwann extended this to animals, stating that all living organisms are composed of cells and their products. Rudolf Virchow later added that all cells arise from pre-existing cells.
This question belongs to: Science Biology
Question #734
What is the size of ribosomes found in prokaryotic cells?
A. 60S
B. 50S
C. 80S
D. 70S
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Correct Answer: Option D

Explanation:
Prokaryotic cells contain 70S ribosomes, which are composed of a 50S large subunit and a 30S small subunit. The 'S' stands for Svedberg units, a measure of sedimentation rate. Eukaryotic cytoplasm contains 80S ribosomes, though their mitochondria and chloroplasts contain 70S ribosomes.
This question belongs to: Science Biology
Question #735
The plant cell wall is primarily composed of which of the following?
A. Cellulose, Hemicellulose, and Pectin
B. Silica and Calcium
C. Proteins and Lipids
D. Chitin and Peptidoglycan
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Correct Answer: Option A

Explanation:
The plant cell wall is primarily made up of cellulose, hemicellulose, pectins, and proteins. Cellulose provides the main structural framework, while hemicellulose and pectins help in cross-linking and providing flexibility. Chitin is found in fungal cell walls, and peptidoglycan is found in bacterial cell walls.
This question belongs to: Science Biology
Question #736
Which organelle is known as the 'powerhouse of the cell' and is semi-autonomous?
A. Chloroplast
B. Golgi apparatus
C. Endoplasmic reticulum
D. Mitochondria
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Correct Answer: Option D

Explanation:
Mitochondria are known as the powerhouse of the cell because they are the site of aerobic respiration and ATP production. They are semi-autonomous because they possess their own circular DNA, RNA, and 70S ribosomes, allowing them to synthesize some of their own proteins and replicate independently of the nucleus.
This question belongs to: Science Biology
Question #737
In a chloroplast, the flattened membranous sacs arranged in stacks are called?
A. Grana
B. Matrix
C. Thylakoids
D. Stroma
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Correct Answer: Option A

Explanation:
In a chloroplast, the thylakoids are flattened membranous sacs that are arranged in stacks like coins, which are called grana (singular: granum). The stroma is the fluid-filled matrix surrounding the thylakoids. The thylakoid membranes contain the pigments necessary for the light reactions of photosynthesis.
This question belongs to: Science Biology
Question #738
Which of the following is the primary function of the Smooth Endoplasmic Reticulum (SER)?
A. ATP production
B. Protein synthesis
C. Lipid synthesis and detoxification
D. Protein modification
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Correct Answer: Option C

Explanation:
The Smooth Endoplasmic Reticulum (SER) lacks ribosomes on its surface and is primarily involved in the synthesis of lipids, including sterols and phospholipids. In liver cells, SER also plays a crucial role in the detoxification of poisons and drugs. Rough ER, which has ribosomes, is responsible for protein synthesis.
This question belongs to: Science Biology
Question #739
The Golgi apparatus is primarily involved in which of the following processes?
A. Photosynthesis
B. Cellular respiration
C. Packaging and secretion of materials
D. Intracellular digestion
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Correct Answer: Option C

Explanation:
The Golgi apparatus consists of flat, disc-shaped cisternae and is primarily involved in the packaging, modification, and secretion of materials (proteins and lipids) synthesized in the ER. It has a cis face (forming face) near the ER and a trans face (maturing face) directed towards the plasma membrane.
This question belongs to: Science Biology
Question #740
Which of the following cytoskeletal elements is composed of tubulin and is involved in cell division?
A. Microtubules
B. Intermediate filaments
C. Collagen fibers
D. Microfilaments
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Correct Answer: Option A

Explanation:
Microtubules are hollow, tube-like structures made of the protein tubulin. They are a major component of the cytoskeleton and play a crucial role in maintaining cell shape, intracellular transport, and cell division by forming the mitotic spindle that separates chromosomes during mitosis and meiosis.
This question belongs to: Science Biology

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