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 87 of 103
Question #1721
Consider statements about human blood: 1. Red blood cells lack a nucleus at maturity. 2. Platelets are essential for blood clotting. 3. Plasma constitutes about 45% of blood volume. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
Mature mammalian red blood cells (erythrocytes) are enucleated to maximize space for hemoglobin. Platelets (thrombocytes) are cell fragments crucial for the blood coagulation cascade. Blood plasma, the liquid component, constitutes about 55% of total blood volume, while the formed elements (RBCs, WBCs, platelets) make up the remaining 45%. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1722
Consider statements about the human nervous system: 1. The brain is protected by the cranium. 2. The spinal cord is protected by the vertebral column. 3. Neurons are non-excitable cells. Which are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
The central nervous system comprises the brain and spinal cord, protected by the bony cranium and vertebral column, respectively, along with meninges. Neurons are highly excitable cells capable of generating and conducting action potentials in response to stimuli. Therefore, statements 1 and 2 are correct, while statement 3 is fundamentally incorrect.
This question belongs to: Science Biology
Question #1723
Consider statements about the endocrine system: 1. The pituitary gland is called the master gland. 2. The thyroid gland secretes calcitonin. 3. The adrenal medulla secretes cortisol. Which are correct?
A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option B

Explanation:
The pituitary gland is termed the master gland because it secretes hormones that regulate other endocrine glands. The thyroid gland secretes thyroxine, triiodothyronine, and calcitonin, which regulates blood calcium. The adrenal cortex secretes cortisol (a glucocorticoid), while the adrenal medulla secretes adrenaline and noradrenaline. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1724
Consider statements about human diseases: 1. Typhoid is caused by Salmonella typhi. 2. Malaria is caused by a virus. 3. Ringworm is a fungal infection. Which are correct?
A. 2 and 3 only
B. 1, 2 and 3
C. 1 and 2 only
D. 1 and 3 only
Discuss
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Correct Answer: Option D

Explanation:
Typhoid fever is a bacterial disease caused by Salmonella enterica serotype Typhi. Ringworm is a superficial fungal infection caused by dermatophytes like Microsporum and Trichophyton. Malaria is not caused by a virus; it is caused by a protozoan parasite of the genus Plasmodium. Therefore, statements 1 and 3 are correct, while 2 is false.
This question belongs to: Science Biology
Question #1725
Consider statements about human immunity: 1. Innate immunity is present from birth. 2. Vaccination provides artificial active immunity. 3. Antibodies are produced by T-lymphocytes. Which are correct?
A. 1 and 3 only
B. 2 and 3 only
C. 1, 2 and 3
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
Innate immunity is the non-specific defense mechanism present by birth, including physical barriers and phagocytes. Vaccination introduces antigens to stimulate the body's own antibody production, conferring artificial active immunity. Antibodies (immunoglobulins) are produced and secreted by B-lymphocytes (plasma cells), not T-lymphocytes, which are involved in cell-mediated immunity. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1726
Consider statements about human nutrition: 1. Carbohydrates are the primary energy source. 2. Proteins are made of fatty acids. 3. Vitamins are required in large quantities. Which are correct?
A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 3 only
D. 1 only
Discuss
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Correct Answer: Option D

Explanation:
Carbohydrates are the main and most readily available source of energy for cellular processes. Proteins are polymers of amino acids linked by peptide bonds, not fatty acids, which are components of lipids. Vitamins are micronutrients required in very small (trace) quantities for normal metabolism, unlike macronutrients. Therefore, only statement 1 is correct.
This question belongs to: Science Biology
Question #1727
Consider statements about vitamins: 1. Vitamin A is essential for vision. 2. Vitamin C is a fat-soluble vitamin. 3. Vitamin D deficiency causes rickets. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
Vitamin A (retinol) is crucial for the synthesis of rhodopsin, maintaining normal vision, especially in dim light. Vitamin D deficiency impairs calcium absorption, leading to rickets in children. Vitamin C (ascorbic acid) is a water-soluble vitamin, not fat-soluble; vitamins A, D, E, and K are fat-soluble. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1728
Consider statements about genetics: 1. DNA is double-stranded. 2. RNA contains thymine. 3. Genes are located on chromosomes. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
DNA is typically a double-stranded helical molecule carrying genetic information. Genes are specific sequences of DNA located linearly on chromosomes. RNA is generally single-stranded and contains the nitrogenous base uracil instead of thymine, which is found in DNA. Therefore, statements 1 and 3 are correct, while statement 2 is incorrect.
This question belongs to: Science Biology
Question #1729
Consider statements about Mendel's laws: 1. The Law of Segregation applies to alleles of a single gene. 2. The Law of Independent Assortment applies to genes on the same chromosome. 3. Mendel worked on pea plants. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option A

Explanation:
Mendel's Law of Segregation states that allele pairs separate during gamete formation, applying to a single gene. His Law of Independent Assortment applies to genes located on different (non-homologous) chromosomes, not those linked on the same chromosome. Mendel conducted his pioneering genetic experiments on the garden pea, Pisum sativum. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1730
Consider statements about evolution: 1. Natural selection was proposed by Darwin. 2. Evolution always leads to perfect organisms. 3. Homologous organs indicate common ancestry. Which are correct?
A. 2 and 3 only
B. 1 and 3 only
C. 1, 2 and 3
D. 1 and 2 only
Discuss
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Correct Answer: Option B

Explanation:
Charles Darwin proposed the theory of evolution by natural selection, where organisms with favorable traits survive and reproduce. Homologous organs share a common structural plan and evolutionary origin, indicating divergent evolution from a common ancestor. Evolution does not lead to perfection; it only results in adaptation to the current environment. Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1731
Consider statements about ecology: 1. Producers form the first trophic level. 2. Energy flow in an ecosystem is unidirectional. 3. The pyramid of energy can be inverted. Which are correct?
A. 1, 2 and 3
B. 1 and 3 only
C. 2 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
Green plants (producers) always occupy the first trophic level in a food chain. Energy flow is unidirectional, moving from the sun to producers and then to consumers, never returning to the sun. Due to the 10% law of energy transfer, the pyramid of energy is always upright and can never be inverted. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1732
Consider statements about the environment: 1. The ozone layer is in the stratosphere. 2. CFCs deplete the ozone layer. 3. Global warming is caused by excess oxygen. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option B

Explanation:
The ozone layer, which absorbs harmful UV radiation, is located in the stratosphere. Chlorofluorocarbons (CFCs) release chlorine atoms in the stratosphere that catalytically destroy ozone molecules. Global warming is primarily driven by the greenhouse effect due to excess carbon dioxide and other greenhouse gases, not oxygen. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1733
Consider statements about microorganisms: 1. Bacteria are prokaryotic. 2. Fungi have chlorophyll. 3. Viruses can reproduce without a host. Which are correct?
A. 1 and 3 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 only
Discuss
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Correct Answer: Option D

Explanation:
Bacteria are unicellular prokaryotes lacking a true nucleus and membrane-bound organelles. Fungi are heterotrophic eukaryotes that lack chlorophyll and cannot perform photosynthesis. Viruses are obligate intracellular parasites that lack metabolic machinery and absolutely require a living host cell to replicate. Therefore, only statement 1 is correct.
This question belongs to: Science Biology
Question #1734
Consider statements about biotechnology: 1. Restriction enzymes cut DNA at specific sites. 2. PCR is used to amplify DNA. 3. Gel electrophoresis separates proteins by size. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 2 and 3 only
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
Restriction endonucleases act as molecular scissors, cleaving DNA at specific palindromic recognition sequences. Polymerase Chain Reaction (PCR) is a technique used to amplify specific DNA segments exponentially. Gel electrophoresis is primarily used to separate DNA or RNA fragments based on size, though it can separate proteins (SDS-PAGE), the statement implies it's exclusively or primarily for proteins in general biotech context, but 1 and 2 are definitively core facts. Let's refine: Gel electrophoresis separates charged molecules; for DNA it's by size. Statements 1 and 2 are universally correct core principles.
This question belongs to: Science Biology
Question #1735
Consider statements about animal husbandry: 1. Apiculture is the rearing of honeybees. 2. Sericulture is the rearing of silkworms. 3. Pisciculture is the rearing of poultry. Which are correct?
A. 2 and 3 only
B. 1, 2 and 3
C. 1 and 3 only
D. 1 and 2 only
Discuss
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Correct Answer: Option D

Explanation:
Apiculture is the maintenance of honeybee hives for honey and wax production. Sericulture involves rearing silkworms (Bombyx mori) for silk production. Pisciculture is the breeding and rearing of fish (fish farming), whereas poultry farming is the rearing of birds like chickens for meat and eggs. Therefore, statements 1 and 2 are correct, while 3 is false.
This question belongs to: Science Biology
Question #1736
Consider statements about scientists: 1. Robert Hooke discovered the cell. 2. Louis Pasteur disproved spontaneous generation. 3. Alexander Fleming discovered the structure of DNA. Which are correct?
A. 2 and 3 only
B. 1 and 3 only
C. 1 and 2 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option C

Explanation:
Robert Hooke first observed and coined the term 'cell' in 1665 using cork tissue. Louis Pasteur definitively disproved the theory of spontaneous generation using his swan-neck flask experiment. Alexander Fleming discovered the antibiotic penicillin, not the structure of DNA; that was elucidated by Watson and Crick. Thus, statements 1 and 2 are correct.
This question belongs to: Science Biology
Question #1737
Consider statements about plant reproduction: 1. Pollination is the transfer of pollen to the stigma. 2. Double fertilization is unique to gymnosperms. 3. Seeds develop from ovules. Which are correct?
A. 1 and 2 only
B. 1, 2 and 3
C. 1 and 3 only
D. 2 and 3 only
Discuss
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Correct Answer: Option C

Explanation:
Pollination is the mechanism of transferring pollen grains from the anther to the stigma of a flower. After fertilization, the ovule develops into a seed and the ovary into a fruit. Double fertilization, involving syngamy and triple fusion, is a unique characteristic of angiosperms, not gymnosperms. Therefore, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1738
Consider statements about human excretion: 1. The kidneys regulate blood pressure. 2. Ammonia is the primary nitrogenous waste in humans. 3. The nephron filters blood in the glomerulus. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1, 2 and 3
D. 1 and 3 only
Discuss
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Correct Answer: Option D

Explanation:
The kidneys regulate blood pressure via the renin-angiotensin-aldosterone system and by controlling fluid volume. The nephron's glomerulus filters blood plasma into Bowman's capsule. Humans are ureotelic, meaning the primary nitrogenous waste excreted is urea, not ammonia (which is highly toxic and excreted by aquatic animals). Thus, statements 1 and 3 are correct.
This question belongs to: Science Biology
Question #1739
Consider statements about cell organelles: 1. Chloroplasts are found in all plant cells. 2. Vacuoles are larger in plant cells than animal cells. 3. Centrioles are present in higher plant cells. Which are correct?
A. 1 and 2 only
B. 2 only
C. 1 and 3 only
D. 1, 2 and 3
Discuss
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Correct Answer: Option B

Explanation:
Chloroplasts are present only in the green, photosynthetic parts of plants, not in root cells or non-green tissues. Plant cells typically have a single, large central vacuole occupying most of the volume, whereas animal cells have small, temporary vacuoles. Centrioles are absent in higher plants (angiosperms and gymnosperms) but present in animal cells and some lower plants. Only statement 2 is correct.
This question belongs to: Science Biology
Question #1740
Consider statements about human skeleton: 1. The human skull has 22 bones. 2. The femur is the longest bone. 3. Ribs are attached to the sternum directly or indirectly. Which are correct?
A. 1, 2 and 3
B. 2 and 3 only
C. 1 and 2 only
D. 1 and 3 only
Discuss
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Correct Answer: Option A

Explanation:
The human skull consists of 22 bones (8 cranial and 14 facial). The femur (thigh bone) is the longest and strongest bone in the human body. Humans have 12 pairs of ribs; the first 7 are true ribs (direct attachment), next 3 are false ribs (indirect), and last 2 are floating. All statements are anatomically correct.
This question belongs to: Science Biology

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