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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Question #21
The enzyme pepsin is secreted by which cells of the gastric glands?
A. Mucous cells
B. Parietal (oxyntic) cells
C. G cells
D. Chief (peptic) cells
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Correct Answer: Option D

Explanation:
Chief cells (peptic cells) in the gastric mucosa secrete pepsinogen, which is converted to active pepsin by HCl. Pepsin digests proteins into peptides. Parietal cells secrete HCl and intrinsic factor. Mucous cells produce mucus that protects the stomach lining. G cells secrete gastrin hormone. Pepsin functions optimally at pH 1.8-2.0. The stomach thus initiates protein digestion.
This question belongs to: Science Biology
Question #22
Which enzyme hydrolyzes starch into maltose in the human digestive system?
A. Salivary amylase
B. Trypsin
C. Pepsin
D. Lipase
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Correct Answer: Option A

Explanation:
Salivary amylase (ptyalin) is secreted by salivary glands and begins starch digestion in the mouth, hydrolyzing starch into maltose and dextrins. It works optimally at neutral to slightly alkaline pH. Pancreatic amylase continues starch digestion in the small intestine. Pepsin digests proteins, trypsin digests proteins in the intestine, and lipase digests fats. Salivary amylase action stops in the acidic stomach.
This question belongs to: Science Biology
Question #23
Bile juice is produced by the:
A. Liver
B. Gall bladder
C. Pancreas
D. Stomach
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Correct Answer: Option A

Explanation:
Bile is synthesized by hepatocytes of the liver and stored and concentrated in the gall bladder. It contains bile salts (sodium glycocholate and taurocholate) that emulsify fats, aiding lipase action. Bile also contains bile pigments (bilirubin, biliverdin) from hemoglobin breakdown. Pancreas secretes pancreatic juice with digestive enzymes. Gall bladder only stores bile, doesn't produce it.
This question belongs to: Science Biology
Question #24
The voice box or sound-producing organ in humans is the:
A. Pharynx
B. Bronchi
C. Trachea
D. Larynx
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Correct Answer: Option D

Explanation:
The larynx, also called the voice box, contains vocal cords that vibrate as air passes, producing sound. It is located at the top of the trachea. The trachea (windpipe) conducts air; pharynx is the common passage for food and air; bronchi lead to lungs. The larynx is cartilaginous, and in males, the thyroid cartilage forms the Adam's apple.
This question belongs to: Science Biology
Question #25
The respiratory pigment in human blood that transports oxygen is:
A. Hemoglobin
B. Cytochrome
C. Hemocyanin
D. Myoglobin
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Correct Answer: Option A

Explanation:
Hemoglobin is a red, iron-containing protein in red blood cells (erythrocytes) that reversibly binds oxygen to form oxyhemoglobin. Each molecule has four heme groups, each binding one O₂ molecule. Hemocyanin (copper-based) is found in some invertebrates. Myoglobin stores oxygen in muscles. Cytochromes are electron carriers in respiration. Hemoglobin also transports CO₂ as carbaminohemoglobin.
This question belongs to: Science Biology
Question #26
Which chamber of the human heart receives deoxygenated blood from the body?
A. Right ventricle
B. Right atrium
C. Left atrium
D. Left ventricle
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Correct Answer: Option B

Explanation:
The right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae. It then passes to the right ventricle, which pumps it to the lungs for oxygenation. The left atrium receives oxygenated blood from the lungs via pulmonary veins, and the left ventricle pumps it to the body. Thus, the right atrium is the receiving chamber for systemic deoxygenated blood.
This question belongs to: Science Biology
Question #27
Which of the following blood groups is considered the universal donor?
A. A positive
B. AB positive
C. B negative
D. O negative
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Correct Answer: Option D

Explanation:
O negative blood group lacks A and B antigens on RBCs and Rh antigen. Hence, it can be transfused to any person without causing agglutination, making it the universal donor. AB positive has both antigens and is the universal recipient. Blood grouping is based on ABO and Rh systems. O negative is crucial in emergency transfusions when blood type is unknown.
This question belongs to: Science Biology
Question #28
The functional unit of the kidney is the:
A. Neuron
B. Alveolus
C. Hepatocyte
D. Nephron
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Correct Answer: Option D

Explanation:
The nephron is the structural and functional unit of the kidney, responsible for filtration, reabsorption, and secretion to form urine. Each kidney has about 1 million nephrons. A nephron consists of the Bowman's capsule, glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. Neurons are units of nervous system, alveoli of lungs, hepatocytes of liver.
This question belongs to: Science Biology
Question #29
Which part of the nephron is primarily involved in the reabsorption of glucose and amino acids?
A. Loop of Henle
B. Collecting duct
C. Distal convoluted tubule
D. Proximal convoluted tubule
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Correct Answer: Option D

Explanation:
The proximal convoluted tubule (PCT) reabsorbs about 70-80% of electrolytes and water, and almost 100% of glucose, amino acids, and vitamins back into the blood via active transport and facilitated diffusion. The loop of Henle concentrates urine, the DCT reabsorbs sodium and water under hormonal control, and the collecting duct reabsorbs water (ADH-dependent). PCT cells have microvilli for increased surface area.
This question belongs to: Science Biology
Question #30
The reflex action is controlled by the:
A. Spinal cord
B. Cerebrum
C. Cerebellum
D. Medulla oblongata
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Correct Answer: Option A

Explanation:
Reflex actions are rapid, involuntary responses to stimuli, primarily coordinated by the spinal cord without immediate brain involvement. The reflex arc includes receptor, sensory neuron, interneuron (in spinal cord), motor neuron, and effector. The brain is later informed. Examples: withdrawal of hand on touching a hot object. The medulla controls autonomic functions like breathing. The cerebrum handles conscious thought, cerebellum coordination.
This question belongs to: Science Biology
Question #31
Which part of the human brain is responsible for maintaining posture and balance?
A. Thalamus
B. Cerebrum
C. Cerebellum
D. Hypothalamus
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Correct Answer: Option C

Explanation:
The cerebellum, located at the back of the brain below the cerebrum, coordinates voluntary movements, maintains posture, balance, and muscle tone. Damage leads to unsteady gait and tremors. The cerebrum controls thinking, memory, and voluntary actions. Thalamus relays sensory impulses, hypothalamus regulates body temperature, hunger, and endocrine functions. Cerebellum is often called the 'little brain'.
This question belongs to: Science Biology
Question #32
Which endocrine gland is known as the 'master gland'?
A. Pituitary
B. Adrenal
C. Pancreas
D. Thyroid
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Correct Answer: Option A

Explanation:
The pituitary gland, located at the base of the brain, controls other endocrine glands through its hormones (e.g., TSH, ACTH, FSH, LH). Hence, it is called the master gland. The hypothalamus regulates the pituitary via releasing and inhibiting hormones. Thyroid secretes thyroxine, adrenal secretes adrenaline, pancreas (endocrine part) secretes insulin and glucagon. The pituitary has two lobes: anterior and posterior.
This question belongs to: Science Biology
Question #33
In the female reproductive system, fertilization normally occurs in the:
A. Uterus
B. Ovary
C. Fallopian tube (oviduct)
D. Cervix
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Correct Answer: Option C

Explanation:
The fallopian tube (oviduct) is the site of fertilization where sperm meets the ovum. The fertilized zygote then travels to the uterus for implantation. Ovary releases the ovum. The uterus is the site of implantation and fetal development. Cervix is the lower narrow portion of the uterus. The ampulla of the fallopian tube is the most common fertilization site.
This question belongs to: Science Biology
Question #34
Which of the following is a bacterial disease?
A. AIDS
B. Influenza
C. Typhoid
D. Malaria
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Correct Answer: Option C

Explanation:
Typhoid is caused by the bacterium Salmonella typhi, transmitted through contaminated food and water. Influenza (flu) is a viral disease, malaria is protozoan (Plasmodium), AIDS is viral (HIV). Common bacterial diseases include cholera, tuberculosis, diphtheria, tetanus. Typhoid fever is characterized by prolonged fever, headache, and rose spots on the skin. Widal test is used for diagnosis.
This question belongs to: Science Biology
Question #35
Edward Jenner is associated with the discovery of the vaccine for:
A. Polio
B. Tuberculosis
C. Smallpox
D. Rabies
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Correct Answer: Option C

Explanation:
Edward Jenner, in 1796, observed that milkmaids who had cowpox were immune to smallpox. He used material from cowpox lesions to inoculate a boy, who later proved immune to smallpox. This was the first successful vaccine. Rabies vaccine was developed by Louis Pasteur, polio vaccine by Jonas Salk, TB vaccine (BCG) by Calmette and Guérin. Smallpox has been eradicated globally.
This question belongs to: Science Biology
Question #36
Which of the following is an auto-immune disease?
A. Tetanus
B. Typhoid
C. Rheumatoid arthritis
D. Malaria
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Correct Answer: Option C

Explanation:
Rheumatoid arthritis is an autoimmune disease where the immune system attacks the synovial membranes of joints, causing inflammation and joint damage. Tetanus is bacterial (Clostridium tetani), typhoid is bacterial (Salmonella typhi), malaria is protozoan (Plasmodium). Autoimmune diseases result from failure of self-recognition by immune cells. Other examples: type 1 diabetes, multiple sclerosis, lupus.
This question belongs to: Science Biology
Question #37
Which vitamin is also known as ascorbic acid?
A. Vitamin A
B. Vitamin B₁
C. Vitamin D
D. Vitamin C
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Correct Answer: Option D

Explanation:
Vitamin C, chemically ascorbic acid, is a water-soluble vitamin essential for collagen synthesis, wound healing, iron absorption, and antioxidant function. Its deficiency causes scurvy (bleeding gums, weakness). Vitamin A is retinol, B₁ is thiamine, D is calciferol. Vitamin C is abundant in citrus fruits, guava, amla. It is heat-labile and easily destroyed by cooking.
This question belongs to: Science Biology
Question #38
Deficiency of vitamin D in children leads to:
A. Beri-beri
B. Pellagra
C. Rickets
D. Scurvy
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Correct Answer: Option C

Explanation:
Rickets is characterized by defective mineralization of bones, leading to bowed legs, soft skull, and skeletal deformities due to vitamin D deficiency in children. In adults, deficiency causes osteomalacia. Scurvy is vitamin C deficiency, pellagra is niacin deficiency, beri-beri is thiamine deficiency. Vitamin D (calciferol) promotes calcium and phosphorus absorption from the gut. Sunlight exposure helps synthesize vitamin D in skin.
This question belongs to: Science Biology
Question #39
Which of the following is a fat-soluble vitamin?
A. Vitamin K
B. Vitamin B₆
C. Vitamin B₁₂
D. Vitamin C
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Correct Answer: Option A

Explanation:
Vitamins A, D, E, and K are fat-soluble, stored in body fats and liver. Vitamin K is essential for blood clotting (synthesis of prothrombin). Vitamin B complex and vitamin C are water-soluble, excreted in urine and not stored extensively. Fat-soluble vitamins require dietary fat for absorption. Excess of fat-soluble vitamins can cause toxicity (hypervitaminosis).
This question belongs to: Science Biology
Question #40
The genetic material of the human immunodeficiency virus (HIV) is:
A. Double-stranded DNA
B. Double-stranded RNA
C. Single-stranded DNA
D. Single-stranded RNA
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Correct Answer: Option D

Explanation:
HIV is a retrovirus with two copies of single-stranded RNA as its genome. It uses reverse transcriptase to convert RNA into DNA upon infection. Double-stranded DNA is typical of many organisms. Single-stranded DNA viruses exist (e.g., parvovirus). Double-stranded RNA viruses include rotavirus. The viral RNA genome enables integration into host DNA via a DNA intermediate.
This question belongs to: Science Biology

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