Biology

1. (d) Although often attributed to Charles Darwin, the phrase “survival of the fittest” was actually coined by the philosopher Herbert Spencer in his work “Principles of Biology” (1864).

2.(a) Gregor Johann Mendel, an Austrian monk, conducted experiments on pea plants in the mid-19th century. He discovered the fundamental principles of inheritance, now known as Mendel’s Laws of Inheritance, which laid the foundation for the science of genetics. He is often referred to as the “Father of Genetics.”

3. (b) Cancer is a disease characterized by uncontrolled cell division and growth. When normal regulatory mechanisms that control cell division malfunction, cells can proliferate uncontrollably, forming tumors and interfering with the normal functioning of tissues and organs. Fever and inflammation are not direct consequences of uncontrolled cell division.

4. (b) A mutation is a sudden and permanent change in the DNA sequence of a gene or chromosome. Mutations can occur spontaneously due to errors in DNA replication, exposure to mutagens (such as radiation or certain chemicals), or through genetic recombination. Mutations can lead to variations in traits within a population and are a primary source of genetic diversity, which is essential for evolution to occur.

5. (a) Bacteria belong to the kingdom Monera, which includes unicellular prokaryotic organisms. Monera is one of the five kingdoms of life classification system, and it encompasses bacteria, archaea, and some other microorganisms. Bacteria are diverse and ubiquitous, inhabiting various environments and playing important roles in ecological processes, nutrient cycling, and human health.

6. (c) In binomial nomenclature, the system used for naming species in biology, the scientific name of an organism consists of two parts: the genus name (which is capitalized) and the species name (which is written in lowercase). For example, in Homo sapiens (the scientific name for humans), “Homo” is the genus name, and “sapiens” is the species name.

7. (b) Genetics is the branch of biology that deals with the study of genes, heredity, and genetic variation in organisms. By examining similarities and differences in traits among family members, such as facial features or physical characteristics, one can infer patterns of inheritance and genetic relationships. Therefore, genetics can explain why certain traits resemble those of specific family members.

8. (b) One of the key distinguishing features between plant and animal cells is the presence of a cell wall in plant cells and its absence in animal cells. Plant cells have a rigid cell wall composed primarily of cellulose, which provides structural support and protection to the cell. In contrast, animal cells lack a cell wall and instead have a flexible plasma membrane that surrounds the cell’s cytoplasm and organelles. Additionally, both plant and animal cells have nuclei, although the size and shape of the nucleus may vary between cell types. Vacuoles, which are membrane- bound organelles involved in storage and waste management, are typically larger and more prominent in plant cells compared to animal cells.

9. (b) Gregor Mendel is considered the father of modern genetics. His experiments with pea plants in the 19th century led to the discovery of the basic principles of heredity and inheritance.

10. (a) The kiwi is a flightless bird and a vertebrate, meaning it has a backbone. Sponges, starfish, and threadworms are invertebrates and lack a backbone,

11. (a) The electron microscope was invented by Ernst Ruska and Max Knoll in 1931. They were awarded the Nobel Prize in Physics in 1986 for their work.

12. (b) The centromere is the point where chromatids are attached in a chromosome, facilitating spindle fiber attachment and sister chromatid separation during cell division.

Nucleosomes are units of DNA packaging consisting of DNA wrapped around histone proteins.

Centrosomes are organelles in animal cells responsible for organizing microtubules during cell division.

Genes are units of heredity containing înstructions for specific traits.

13. (d) The group of the cell of similar origin, function, and structure is called tissue.

The plant tissue is of four types: Epidermal tissue, Vascular tissue, Ground tissue, and Meristematic tissue.

Human Body is made up of four types of tissue: Nervous, Muscle, Epithelial and Connective tissue.

14. (d)

15. (c) Turtle – Reptiles

Crocodile – Reptiles

Toad – Amphibia

Snake – Reptiles

16. (c) A fungal cell wall is made up of a tough and complex sugar called ‘Chitin’. Fungi are non-green, eukaryotic, hetero- trophic organisms. Most of them are saprotrophs. They feed upon decaying organic matter.

Examples: yeast, Aspergillus, Penicillium, Mushrooms.

17. (a) Metaphase: Chromosomes align at the equatorial plate, spindle fibers attach to the centromeres of each chromosome.

18. (b) Sclerenchyma is the permanent tissue  that makes a plant hard and stiff.

Collenchyma cells are those which have irregularly thick cell walls which provide support and structure.

Parenchyma are thin-walled tissues which are involved in food storage, photosynthesis, and other activities of plant life.

Aerenchyma are spongy tissues which form air channels in the leaves, stem, and roots of some plants.

19. (a) Only meristem is capable of cell division.

Meristem: This is the primary growth tissue in plants, found in the tips of roots and shoots, and responsible for increasing the plant’s length and girth. Meristematic cells are undifferentiated and have the ability to continuously divide, giving rise to other specialized tissues.

20. (a) Oparin’s theory proposes that life arose from simpler organic molecules in a “primordial soup” through a series of chemical reactions. This concept falls under the umbrella of chemical evolution, which explores how life emerged from non-living matter.

21. (b) The group of animals that are exclusively free-living marine animals is Echinodermata. Echinoderms include animals such as starfish, sea urchins, and sea cucumbers, which are found exclusively in marine environments.

22. (a) Agaricus: This is a genus of mushrooms, which are classified as fungi. Fungi are eukaryotic organisms that are typically multicellular.

23. (b) Arthropoda is the largest group of animals. An Arthropoda is an invertebrate animal that forms the phylum Arthropoda, which includes insects, arachnids, myriapods, and crustaceans. Over two-thirds of all named species on Earth are Arthropoda.

24. (c) Sclerenchyma is characterized by thick, lignified cell walls that provide strength and rigidity to plant structures like seeds, nutshells, and woody stems. The cells in sclerenchyma are dead at maturity, as the thickened cell walls prevent further growth and metabolic activity.

25. (c) A cell is the smallest unit capable of independent existence and reproduction. All living organisms, except viruses, are composed of cells.

26. (b) Stomata are tiny pores located on the underside of a leaf’s surface. They regulate the exchange of gases, including carbon dioxide (CO₂) and oxygen (O2), between the leaf and the atmosphere during photosynthesis and respiration. Carbon dioxide enters the leaf through the stomata, where it is used in photosynthesis to produce sugars and oxygen

27. (d) Pea plants, like other legumes, have a symbiotic relationship with nitrogen-fixing bacteria called rhizobia. These bacteria live in nodules on the roots of leguminous plants like peas and convert atmospheric nitrogen (N₂) into a form that the plants can use, such as ammonia (NH₂) or nitrate (NO₂). This process, known as nitrogen fixation, enriches the soil with nitrogen and makes it available to other plants in the ecosystem. Therefore, growing peas or other legumes can improve soil fertility and reduce the need for synthetic nitrogen fertilizers.

28. (a) Xylem is the plant tissue responsible for transporting water and minerals from the roots to the leaves and other parts of the plant. It consists of specialized cells called tracheids and vessel elements, which form interconnected tubes that facilitate the upward movement of water through capillary action and transpiration. This water transport system enables the leaves to receive the water necessary for photosynthesis and other metabolic processes.

29. (c) Photosynthesis requires solar radiation to convert solar energy into chemical energy, which is stored in glucose. Although a pigment (such as chlorophyll) and an atmospheric gas (carbon dioxide) are essential components, these terms are broader and include multiple elements. Hence, the most appropriate option is solar radiation.

30. (c) Crop rotation is an agricultural practice in which different crops are grown in the same area in sequential seasons or years. It helps to improve soil fertility and structure by returning nutrients to the soil and preventing the depletion of specific nutrients. Different crops have varying nutrient requirements and root structures, so rotating crops can help balance soil nutrient levels, reduce pest and disease pressure, and improve overall soil health and productivity.

31. (a) Differentiation is the process of taking up a permanent shape, size, and function to form a permanent tissue. During the process of differentiation, cells combine to form a specific tissue. The tissue acquired a specialized function as a result. The process of differentiation usually takes place during the stage of embryonic development.

32. (a) Meristematic tissue comprises undifferentiated cells and is found in plant regions where growth occurs. There are three types of meristem in plants: apical, lateral, and intercalary. Apical meristem is responsible for new cell growth at the tips of roots and shoots, forming buds in young seedlings. Lateral meristem divides to increase the stem or root girth in plants. Intercalary meristem, located at the internode base, facilitates cell division, leading to rapid growth in monocots.

33. (d) Cuscuta derives nutrition from plants as a parasite. The organism that lives on or inside other living organisms, to derive their food are called parasites. All parasitic plants have modified roots, called haustoria. Parasites may cause harm to the host. Examples of parasites: Cascuta, Loranthus, Balanophora, Sandalwood tree.

34. (b) Gibberellic acid (GA): This is a plant hormone that plays a crucial role in promoting stem elongation and overcoming genetic dwarfism in plants. When applied to dwarf plants, gibberellic acid stimulates cell division and elongation, leading to increased plant height and normal growth patterns.

35. (a) Phytohormones, also known as plant hormones, are chemical messengers produced within plants. They are synthesized by plants themselves, unlike substances used for photosynthesis or peeling, which are often external factors. Phytohormones have a profound influence on various physiological processes in plants, regulating aspects like growth, development, and response to stress.

36. (c) Vitamin K is essential for the coagulation (clotting) of blood. It plays a crucial role in the synthesis of clotting factors in the liver, which are necessary for the formation of blood clots to prevent excessive bleeding. Without an adequate supply of vitamin K, the blood’s ability to clot properly is impaired, leading to an increased risk of bleeding disorders and excessive bleeding.

37. (c) The Rhesus factor is a protein found on the surface of red blood cells and is unrelated to cholesterol. LDL and HDL are types of cholesterol, while “packaged protein coat” can be associated with lipoproteins.

38. (a) The energy obtained from food is measured in calories, which quantify the amount of energy released when food is metabolized by the body.

39. (a) Retinol is a form of vitamin A, which is essential for vision, immune function, and skin health.

40. (c) Homogenization is the process of breaking down fat globules in milk so they remain evenly distributed and do not separate.

41. (c) Zymase is an enzyme complex that catalyzes the fermentation of glucose into ethanol (ethyl alcohol) and carbon dioxide during the process of alcoholic fermentation.

42. (c) The normal range for blood sugar levels in a fasting state is typically considered to be between 70 to 100 milligrams per deciliter (mg/dL). This range may vary slightly depending on individual factors and the specific guidelines used.

43. (b) Vitamin B1 is also known as thiamin. It is an essential nutrient required for carbohydrate metabolism and proper functioning of the nervous system.

44. (b) Rancidity occurs when fats undergo oxidation due to a biochemical reaction with oxygen. This process alters the taste and smell of the food, resulting in what is commonly referred to as rancidity.

45. (d) Vitamin K plays a crucial role in blood clotting and the prevention of excessive bleeding. It activates proteins and calcium necessary for blood clotting. Vitamin K exists in three forms: K1 (Phylloquinone), K2 (Menaquinone), and K3 (Menadione).

46. (a) The arrangement for the given food chain will be:

C. Rice Plant – It produces food using solar energy.

E. Locust – Locust are primary consumers, They eat plants.

A. Frog – Frogs are secondary consumers, They eat Locust.

D. Snake – Snakes are tertiary consumers, They eat frogs.

B. Eagle – Eagles are Quaternary consumers, They eat snakes. So, the correct food chain is: ‘C – E – A – D – B’.

47. (a) To detect the presence of starch in food, an iodine solution is used. When iodine solution is added to a sample containing starch, it changes color from brown to blue-black, indicating the presence of starch.

48. (c) Lipase enzymes are used in the stabilization of rice bran oil. Rice bran oil, known for its nutritional properties, is extracted from the outer layer of rice. Lipase helps in inactivating natural lipases that could otherwise hydrolyze the oil, leading to a rancid taste and smell.

49. (a) Waterborne diseases are caused by pathogenic microorganisms that are transmitted through contaminated water. Disinfection of water involves the killing or inactivation of these microorganisms using methods such as chlorination, ultraviolet (UV) irradiation, or filtration, thereby making the water safe for consumption.

50. (b) Viruses are microscopic infectious agents that are composed of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses also have an outer lipid envelope derived from the host cell’s membrane. The genetic material of the virus (either DNA or RNA) carries the instructions for viral replication and infection, while the protein coat protects the genetic material and helps the virus infect host cells.

51. (c) Thalassemia is a genetic disorder characterized by abnormal hemoglobin production, leading to anemia. Individuals with thalassemia have mutations in the genes responsible for producing hemoglobin proteins, which results in reduced or abnormal hemoglobin production. This genetic condition is inherited from one or both parents who carry thalassemia gene mutations. Thalassemia is not caused by lifestyle factors, infectious agents, or metabolic abnormalities but rather by genetic inheritance.

52. (b) HIV (Human Immunodeficiency Virus) is a retrovirus that infects cells of the human immune system, specifically targeting CD4+ T cells. HIV gradually weakens the immune system over time, leading to acquired immunodeficiency syndrome (AIDS), a condition characterized by the progressive failure of the immune system and increased susceptibility to opportunistic infections and certain cancers.

53. (b) Leprosy, also known as Hansen’s disease, is caused by the bacterium Mycobacterium leprae. It primarily affects the skin, peripheral nerves, upper respiratory tract, and eyes. The disease is named after Dr. Gerhard Henrik Armauer Hansen, who identified the causative bacterium in 1873.

54. (d) Louis Pasteur developed the first successful rabies vaccine in 1885. His work in microbiology and vaccination was ground breaking and saved many lives.

55. (c) The Western blot test is a laboratory method used to detect specific proteins in a sample and is commonly used to confirm the presence of HIV antibodies.

56. (b) Cirrhosis is a chronic liver disease characterized by scarring (fibrosis) and impaired liver function.

57. (d) Hepatitis B is primarily transmitted through blood and bodily fluids, not airborne transmission.

58. (d) Allergy screening tests such as RAST, ELISA, and IgE specifically measure the immune response to allergens. Hemoglobin is a measure of blood’s oxygen-carrying capacity and is not related to allergies.

59. (c) Silicosis is a lung disease caused by inhaling silica dust, typically in occupational settings like mining, construction, and manufacturing.

60. (a) Color blindness is typically a genetic condition, meaning it’s inherited and present from birth. It results from abnormalities in the genes responsible for the perception of color.

61. (a) Yellow fever is primarily transmitted to humans through the bite of infected female mosquitoes, particularly those of the Aedes aegypti species. These mosquitoes can carry the yellow fever virus and transmit it to humans when they feed on blood.

62. (d) Dehydration occurs when there is a loss of water from the body, either through inadequate intake, excessive sweating, vomiting, or diarrhea. It disrupts normal bodily functions and can lead to sérious health complications if left untreated.

63. (b) Typhoid fever is caused by the bacterium Salmonella typhi. It is transmitted through contaminated food and water and affects the gastrointestinal tract, leading to symptoms such as fever, abdominal pain, and diarrhea.

64. (a) Poliomyelitis, commonly known as polio, is caused by the poliovirus, which primarily affects the nervous system, leading to paralysis. It is transmitted through contaminated food and water.

65. (c) Chloroquine is a medication used to prevent and treat malaria, a mosquito-borne infectious disease caused by parasites of the Plasmodium species.

66. (d) Antacids are used to neutralise acidity.

67. (d) Vitamins are essential organic non- protein substances required for normal metabolic function, but they cannot be synthesized in sufficient quantities by organisms. They are classified into two categories: fat- soluble and water-soluble. Fat-soluble vitamins (A, D, E, K) are stored in the body when not in use, unlike water- soluble vitamins. Water-soluble vitamins (B, C) are easily excreted by the body if consumed in excess.

68. (a)

• Hepatitis A is caused by the Hepatitis A virus (HAV).
• It spreads through the ingestion of contaminated food or water and close contact with an infected person but does not lead to chronic liver disease.

69. (b)

• The housefly belongs to the order Diptera and genus Musca, with the scientific name Musca domestica.
• Houseflies are often considered nuisances and health hazards, but their larvae can be useful for feeding livestock and biodegradation.

70. (b) Alexander Fleming discovered penicillin. This discovery led to the introduction of antibiotics that greatly reduced the number of deaths from infection. Penicillin prevents the bacteria from synthesizing peptidoglycan, a molecule in the cell wall that provides the wall with the strength it needs to survive in the human body.

71. (b)

• It is the well-known natural-source cancer(Breast, lung, and ovarian) drug in the USA and is one of the best plant- based treatments available.
• Taxol is obtained from the bark of the Yew tree.
• The process was invented by Robert Holton of Florida State University was licensed and developed to produce taxol by Bristol Myer.

72. (a)

• The female Anopheles mosquito transmits malaria, an acute febrile illness caused by the Plasmodium parasite.
• When the mosquito bites a person, it injects the parasite into the bloodstream. Malaria is prevalent in tropical and subtropical regions around the equator.

73. (c)

• The Aedes mosquito is a carrier of the dengue virus, which causes dengue fever. Symptoms include high fever, headache, vomiting, muscle and joint pains, and a . characteristic skin rash.
• The disease typically manifests three to fourteen days after infection and lasts for about two to seven days.

74. (c) UVA causes your skin to wrinkle, tan and/or burn. Too much exposure leads to skin cancer. UVB can damage the outermost layers of your skin. It can cause sun spots, tanning, sunburns and blistering, which can lead to skin cancer.

75. (c) Warts are caused by the human papillomavirus (HPV). This virus infects the top layer of the skin, causing an excess production of keratin, which results in the formation of the rough, hard texture characteristic of warts.

76. (c) The average gestation period for a human fetus, from conception to birth, is approximately 280 days or 40 weeks. However, it can vary slightly from individual to individual.

77. (c) Endosperm serves as nutritive tissue for groutting embryo. Endosperm is a tissue found around the embryo in angiosperm seeds, supplying it with nutrients like starch and protein.

• The ovary, a part of the female reproductive system, generates female gametes and transforms into fruit post-fertilization. Ovules, located within the ovary, mature into female reproductive cells and evolve into seeds upon fertilization.
• When sperm fertilizes an egg, the resulting entity is known as a zygote.

78. (c) The urethra is a tube that carries urine from the Urinary bladder. In females, urethra contains only urine, while in males, it contains both urine and sperms.

79. (b) The testis serves as the primary male sex organ. Situated in the scrotum, the testis houses seminiferous tubules where sperm production occurs. Sertoli cells within the seminiferous tubules nourish male germ cells. Leydig cells in the testis produce male hormones, including androgens.

80. (a) The egg is carried from the ovary to the womb through the oviduct, also known as the fallopian tube.

81. (c) Motile: means capable of movement.

Germ cell: is a reproductive cell that carries half the genetic information and fuses with another germ cell during fertilization to create a new organism.

Isogamete: is a gamete that is similar in size, shape, and behavior to the gamete with which it fuses. They are not motile in most cases.

Female gamete: is called an ovum or egg cell and is not motile.

Male gamete: is called a sperm or spermatozoon and is the motile germ cell responsible for reaching and fertilizing the egg.

82. (d) Genes: These are the fundamental units of heredity, located on chromosomes in the nucleus of a cell. They are composed of DNA (deoxyribonucleic acid) and contain the instructions that determine an organism’s traits and characteristics.

83. (a) Reproduction allows species to continue existing by creating new generations. Without it, populations would dwindle and eventually disappear. Circulation, digestion, and respiration are all important bodily functions, but they don’t directly contribute to maintaining a species’ population size.

84. (a) The part of the human reproductive system that helps the embryo get its nutrition from the mother’s blood is the placenta. The placenta is a temporary organ that forms inside the uterus during pregnancy. It connects the developing baby (fetus) to the mother’s uterine wall and serves several important functions.

85. (c) The embryo develops in the uterus. The utreus, fallopian tubes, and cervix are all part of the female reproductive system, but they play different roles in reproduction.

86. (d) Testes are located in the scrotum, outside the abdominal cavity, to maintain a lower temperature necessary for spermatogenesis. The scrotum ensures a temperature about 2-2.5°C lower than the normal internal body temperature.

87. (c) The cornea is the part of the human eye that acts as a protective barrier and helps focus light.

88. (b) The iris works with the rest of your eye to help you see. Specifically, it controls how much light enters your eye. Muscles in your iris adjust your pupil automatically based on changes in lighting.

89. (b) The iris, the colored part of the eye, controls the size of the pupil and the amount of light that enters the eye. In bright light, the iris contracts to make the pupil smaller and reduce the amount of light that enters the eye. This is called the pupillary light response.

90. (b) The vestibular system detects head movements and sends information to the brain to help maintain balance, while the part of the inner ear responsible for hearing is the cochlea.

91. (c) Photoreceptor cells are specialized cells that convert light into signals that the brain can use to create a visual image. The retina is a layer of cells in the eye that contains photoreceptors and glial cells.

92. (a) The optic nerve is comprised of millions of nerve fibers that send visual messages to your brain to help you see. You have an optic nerve at the back of each eye that connects directly to your brain.

93. (c) The pinna is the visible part of the outer ear, made of cartilage covered by skin. It acts like a reverse megaphone to funnel sound waves into the ear canal.

94. (a) The eardrum is a thin, semi-transparent, oval-shaped membrane that’s about 1 cm in diameter. When sound waves hit the eardrum, it vibrates, and these vibrations are then passed on to the tiny bones in the middle ear. These bones are called the ossicles, and are commonly referred to as the “hammer” (malleus), “anvil” (incus), and “stirrup” (stapes).

95. (a) The cochlea is filled with a fluid that moves in response to the vibrations from the oval window. As the fluid moves, 25,000 nerve endings are set into motion. These nerve endings transform the vibrations into electrical impulses that then travel along the eighth cranial nerve (auditory nerve) to the brain.

96. (d) The receptors responsible for transduction of odor molecules are found in the olfactory mucosa. This portion of nasal mucosa is 1 to 2 cm² in size and is located in the roof of the nasal cavity on the inferior surface of the cribriform plate and along the nasal septum and medial wall of the superior turbinate.

97. (d) Cones are photoreceptor cells in the retina of the eye that are responsible for color vision. Cones are sensitive to different wavelengths of light and allow the brain to perceive colors. Rods, on the other hand, are responsible for vision in low-light conditions but do not perceive color.

98. (d) Receptors are specialized structures composed of protein, which respond to light, heat or external stimulus and transmit the signal to the sensory nerve. 

Gustatory receptors are the receptors for detecting taste.

99. (c) The sensation of sound persists in the human brain for about 0.1 sec. This is also known as the persistence of hearing.

100. (d) Warm-blooded animals, such as birds and mammals, maintain a constant body temperature regardless of the environmental temperature.

101. (c) The ability of the eye to focus on both near and distant objects by adjusting its focal length is known as accommodation. This is achieved by the eye muscles adjusting the lens to change its shape and focal length.

102. (a) According to scientist G.S. Carter there are three stages in respiration-
(i) External Respiration (Ventilation): Gaseous exchange between environment and lungs.
(ii) Internal Respiration:
(A) Gaseous exchange between lungs and blood.
(B) Gaseous exchange between blood and tissue fluid.
(iii) Cellular Respiration: Oxidation of organic compounds in cell in which energy is released.

103. (c) The diaphragm is a thin dome-shaped muscle which separates the thoracic cavity (lungs and heart) from the abdominal cavity (intestines, stomach, liver, etc.). It is involved in respiration, drawing downward in the chest on inhalation, and pushing upward in exhalation.

104. (c) The lung on your right side is divided into three lobes: the superior, the middle and the inferior. It’s shorter than your left lung, but also wider than your left lung.

105. (a) The alveoli are the structural and functional units of the respiratory system. There are around 300 million alveoli in an adult human amounting to approximates 80 square meters of surface area for the gaseous exchange.

106. (c) The terminal end of the soft palate is known as the uvula which is bent towards the pharyngeal cavity. During the swallowing of food, the uvula lifts up and covers the internal nares, and thereby it prevents the entry of food into the nasal passage.

107. (c) The exchange of gases, specifically oxygen (O2) and carbon dioxide (CO₂), occurs in the alveoli of the lungs. Alveoli are tiny air sacs located at the ends of bronchioles where oxygen from the inhaled air diffuses across the thin alveolar walls into the bloodstream, while carbon dioxide from the blood diffuses into the alveoli to be exhaled out of the body during exhalation.

108. (b) Oxygen makes up approximately 21% of Earth’s atmosphere by volume. This concentration of oxygen is essential for supporting aerobic respiration in living organisms, including humans, animals, and plants. Oxygen is produced primarily through photosynthesis by green plants and algae, which convert carbon dioxide and water into glucose and oxygen in the presence of sunlight.

109. (d) During human respiration, oxygen is taken in, and carbon dioxide is released as a waste product of cellular metabolism. Carbon dioxide is expelled from the body during exhalation.

110. (b)

• Planarians are a type of flatworm known for their remarkable regenerative abilities. They are also hermaphrodites, meaning they have both male and female reproductive organs.
• Snails are simultaneous hermaphrodites, meaning they possess both male and female reproductive organs at the same time. While they can potentially fertilize each other, they might not always self-fertilize. Ascaris and Nereis are not known to change sex during their lifespan.

111. (c)

• Air pollution is responsible for causing various respiratory diseases, such as chronic obstructive pulmonary disease (COPD), asthma, and lung cancer.
• Air pollutants, which include a variety of harmful chemicals and particulates, affect the respiratory system and can lead to serious health issues.

112. (c) Aerobic respiration is a process that occurs when oxygen is present and releases energy from food by breaking down organic compounds like glucose. It’s the most common type of respiration in plants and animals.

113. (d) When the terminal phosphate linkage in ATP is hydrolyzed using water, it releases approximately 30.5 kJ/mol of energy. This energy is crucial for various cellular processes such as muscle contraction and biosynthesis.

114. (d) Oxygen is used by living organisms during cellular respiration to produce energy from food, making it crucial for all aerobic life forms.

115. (b) The respiratory pigment in the human body is hemoglobin, found in red blood cells. Hemoglobin carries oxygen from the lungs to body tissues and helps transport carbon dioxide from the tissues to the lungs for exhalation.

116. (a)

• Respiration in plants converts glucose into energy using oxygen, producing carbon dioxide as a waste product.
• During photosynthesis, plants absorb carbon dioxide and release oxygen.
• Transpiration is the process of water loss through the stomata, not involving carbon dioxide production.

117. (c) The epiglottis is the structure that prevents food from entering the windpipe during swallowing in mammals.

118. (a) The pharynx, also known as the throat, is a muscular tube in the neck that serves both the respiratory and digestive systems. It receives air from the nasal cavity and air, food, and water from the oral cavity. At the bottom of the pharynx, two pipes split off, one for air and one for food.

119. (a) Enamel is the hardest substance in the human body, even stronger than bones. It’s a highly mineralized, white to off-white tissue that covers the crown of the tooth.

120. (d) Parietal cells (also known as oxyntic cells), are the stomach epithelial cells that secrete gastric acid (HCl) and intrinsic factor.

121. (c) The two sets of teeth in humans are known as primary or milk teeth which are 20 in numbers and permanent or adult teeth which are 32 in numbers. There are about 20 teeth in humans which regrow twice to form the permanent set of teeth.

122. (d) Incisors are the flat, sharp-edged teeth at the front of the mouth, used for cutting and biting into food. Canines are the pointed, cone-shaped teeth next to the incisors, used for tearing and shredding food.

123. (c) Saliva contains an enzyme called amylase, which helps break down complex carbohydrates (such as starch) into simpler sugars (such as glucose and maltose) during the process of digestion. When you chew bread, the amylase in saliva starts to break down the starch molecules into sugars, which can give the bread a slightly sweet taste.

124. (c) An endoscope is a medical instrument used to view the inside of the digestive tract.

125. (d)

• Rabbit: As a strict herbivore, rabbits have a particularly long intestine, often 10-12 times their body length, to efficiently extract nutrients from their plant-based diet.
• Dog: While also containing some plant material in their diet, dogs are predominantly carnivores and have a shorter intestine compared to rabbits, typically around 6-8 times their body length.
• Tiger and Fox: Similar to dogs, both tigers and foxes are carnivores or omnivores with a shorter intestine length compared to a herbivore like a rabbit.

126. (c) Chemical energy stored in the bonds of complex food molecules (carbohydrates, proteins, fats) is broken down during digestion. This breakdown process releases chemical energy in a form that the body can readily use, such as Adenosine Triphosphate (ATP). ATP is the primary energy currency in cells and fuels various cellular processes.

127. (c) The small intestine absorbs most of the nutrients in your food, and your circulatory system passes them on to other parts of your body to store or use. Special cells help absorbed nutrients cross the intestinal lining into your bloodstream.

128. (c) The breakdown of carbohydrates, proteins and facts occurs in the duodenum region of the small intestine. Small intestine is distinguishable into three regions:
‘U’ shaped duodenum
A long coiled middle portion jejunum.
A highly coiled ileum.

129. (c) The liver produces bile juice, which is stored in the gallbladder. Bile contains bilirubin, biliverdin, bile salts, and cholesterol and helps emulsify fats for digestion. The liver is the largest gland in the human body, located on the right side of the stomach.

130. (c)

• A layer of mucus protects the inner lining of the stomach from the highly acidic environment.
• Gastric mucus is secreted by epithelial and glandular cells in the stomach wall, forming a barrier that shields the stomach lining from digestive acids and. enzymes, preventing damage and ulcers.

131. (b)

• Adipose tissue is the fat-storing tissue in our body. It stores energy in the form of fat, cushions internal organs, and insulates the body.
• There are three types of adipose tissue: white, brown, and beige, each serving different functions in energy regulation and storage.

132. (a) Bile salts break up large fat globules into smaller ones, increasing the surface area for lipase to act on and speeding up fat digestion. This emulsification aids in the absorption of lipids and fat-soluble vitamins (A, D, E and K).

133. (d) The lining of the small intestinal mucosa is very highly specialized for maximizing digestion and absorption of nutrients. The lining is highly folded to form microscopic finger-like projections called villi which increase the surface area to help with absorption.

134. (d) The rumen is a large chamber in the stomachs of ruminants, like cows, where food is stored and partially digested. It is critical for the process of cud formation, which involves the partial breakdown of food that the animal regurgitates and chews again.

135. (b) Bile juice, produced by the liver and stored in the gallbladder, neutralizes the acidic chyme from the stomach when it enters the small intestine. Bile contains bile acids, which help in emulsifying fats, making them easier to digest. This neutralization process is essential for creating an alkaline environment suitable for the digestive enzymes in the small intestine to function effectively.

136. (b) Lymph carries nutrients, hormones, and absorbs fats from the intestinal villi. Lymph is a clear fluid present in the lymphatic system. It contains specialized lymphocytes that control the immune responses of the body.

137. (b) Platelets
Also known as thrombocytes, these are cytoplasmic fragments that help blood clot and prevent excessive bleeding. Platelets lack a nucleus and are derived from the megakaryocytes of the bone marrow or lung.

138. (b) Blood clotting
Platelets are cell fragments that circulate in the blood until they are activated to form a clot. When a blood vessel is damaged, platelets travel to the injury site, stick to the lining of the vessel, and form a clot to stop bleeding.

139. (c) Platelets are cell fragments that clump together to stop bleeding at the site of an injury. They attach to the injured blood vessel, change shape, and secrete chemical messengers to form a clot.

140. (a) Red blood cell antigens determine your blood group. The antigens expressed on the red blood cell determine an individual’s blood group. The main two blood groups are called ABO (with blood types A, B, AB, and O) and Rh (with Rh D-positive or Rh D-negative blood types).

141. (d) Group O can donate red blood cells to anybody. It’s the universal donor. Group AB can donate to other AB’s but can receive from all others. Group B can donate red blood cells to B’s and AB’s.

142. (a) The Rh factor is a protein found on the surface of red blood cells that is inherited from biological parents. If the blood cells have the Rh protein, the blood type is positive, and if they do not, the blood type is negative. The Rh D antigen is the most important of the more than 20 Rh antigens.

143. (b) An antibody is a protein component of the immune system that circulates in the blood, recognizes foreign substances like bacteria and viruses, and neutralizes them.

144. (d) Plasma makes up about 55% of the total blood volume in the body. The remaining 45% is made up of red blood cells, white blood cells, and platelets.

145. (c) Red blood cells, or red blood corpuscles, lack a nucleus in mammals. This absence of a nucleus allows them to have more space to carry hemoglobin, the oxygen-carrying protein, and increases their flexibility, enabling them to pass through narrow blood vessels.

146. (b) The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. It branches into the left and right pulmonary arteries, which deliver blood to the respective lungs. In contrast, the pulmonary vein carries oxygenated blood from the lungs back to the left atrium of the heart. The aorta carries oxygenated blood from the left ventricle of the heart to the rest of the body, and the renal artery carries oxygenated blood to the kidneys.

147. (c) An average adult human body contains about 5 liters of blood, which circulates throughout the body to supply oxygen and nutrients and remove waste products.

148. (b) An echocardiogram provides a detailed image of the heart’s structure and function, making it more appropriate for assessing heart function compared to an electrocardiogram.

149. (a) Platelets release prothrombin, which is converted to thrombin during the clotting process, leading to the formation of fibrin and blood clots.

150. (b) Anemia is a condition characterized by a deficiency of red blood cells (RBCs) or hemoglobin, which impairs the blood’s ability to carry oxygen to tissues. It’s often caused by a lack of iron or certain vitamins essential for RBC production.

151. (c) Blood group AB is known as the universal recipient because individuals with this blood type can receive blood from any other blood group without experiencing an immune reaction. This is because they have both A and B antigens on their red blood cells.

152. (b) Voluntary actions: These are actions that are consciously initiated and controlled by an individual’s will. They involve the deliberate movement of muscles.

• Beating of heart: This is an involuntary action, meaning it happens automatically and is not under our conscious control. The heart muscle has its own pacemaker cells that regulate its rhythm, and we cannot directly influence its beat through our will.

153. (c)

• WBCS (White Blood Cells): These are responsible for fighting infections.
• Blood platelets: These are involved in blood clotting, not transporting materials.
• RBCs (Red Blood Cells): Their primary function is to transport oxygen throughout the body.
• Plasma: This is the liquid portion of blood and acts as the main carrier of various substances, including nutrients (food), waste products (CO₂ and nitrogenous waste), hormones, and antibodies.

154. (a)

• The embryo gets nutrition from the mother’s blood with the help of a special tissue called the placenta.
• Uterus: While the uterus is the organ that houses the developing embryo, it doesn’t directly provide nutrients.
• Fallopian tube: This is the tube where fertilization typically occurs, and it plays no role in nourishing the embryo after implantation.
• Cervix: The cervix is the lower part of the uterus that connects to the vagina. It plays a role in menstruation and childbirth but not in nourishing the embryo.

155. (b) Red Blood Cells (RBCs) are the components of blood responsible for oxygen transportation. They contain hemoglobin, a protein that binds to oxygen in the lungs and carries it to tissues throughout the body. This oxygen is crucial for cellular respiration and energy production. Therefore, RBCs play a vital role in the oxygenation of tissues and organs in the body.

156. (d) O negative blood is known as the universal blood type and is called “the giver of all” because it can be safely given to anyone. This is because O negative red blood cells have the lowest risk of causing serious reactions in most people who receive them.

157. (c) Anuria is a condition where there is no urine production or less than 100 milliliters of urine is produced in a day.

158. (a) Diuresis is a condition in which the excretory volume of urine increases. It occurs when the kidneys filter too much bodily fluid, which leads to increased urine production and more frequent urination.

159. (b) The kidneys remove urea from the bloodstream through glomerular filtration, and the renal vein carries the purified blood away from the kidneys. This results in the renal vein having the lowest concentration of urea in the body.

160. (c) Tadpoles are aquatic organisms that excrete nitrogenous waste in the form of ammonia. Ammonia is a toxic byproduct of protein metabolism, but tadpoles can excrete it into their environment because they are surrounded by water. The process of excreting ammonia is called ammonotelism.

161. (b) Hematuria: The medical term for the presence of blood in urine. I

162. (a) When a person eats protein, the body breaks it down into amino acids. The body uses most of the amino acids, but converts the excess into ammonia. The liver then converts the ammonia into urea, which is transported to the kidneys and excreted in urine. This process is called the urea cycle

163. (b) The ornithine cycle is a series of biochemical reactions that occur in the liver and convert excess amino acids and ammonia into urea. Urea is a nitrogenous waste that’s less toxic than ammonia and is excreted in the urine of ureotelic organisms, like humans and amphibians.

164. (b) In mammals, the urinary bladder opens into the urethra, the last part of the excretory system.

165. (b) When proteins are broken down in the body, they are first split into amino acids, which are then further processed to produce ammonia, which is then converted into urea in the liver through a process called the urea cycle.

166. (d) Aquatic animals excrete ammonia because it’s highly soluble in water and there’s more water available to dilute it. Ammonia is a toxic compound that can cause harmful effects if it remains in an animal for a long time.

167. (b) The main nitrogenous waste product in ureotelic animals is urea.

168. (c) The excretory product of mammals is urea. Urea is the primary nitrogenous waste in mammals.

169. (b) Uremia
A dangerous medical condition that occurs when the kidneys are unable to filter waste products out of the blood. The term “uremia” literally means “urine in the blood”.

170. (d) The heart sends around 1 Litre blood to the kidneys every minute, which is processed by the glomerulus to form around 125 ml filtrate. Thus, it can be calculated to 180 litres of filtrate in 24 hours.

171. (b) Growth hormone (GH) is the hormone that regulates growth, cell reproduction, and regeneration. GH is a peptide hormone that stimulates growth in almost all tissues and organs of the body. It also helps maintain normal body structure in adults and plays a role in metabolism.

172. (a) Oxytocin is the hormone that regulates uterine contractions during childbirth and influences social bonding and emotional behaviors.

173. (c) The pineal gland is the gland that secretes melatonin, a hormone that regulates sleep and wake cycles.

174. (d) Thyroid hormones, which include thyroxine (T4) and triiodothyronine (T3), play a crucial role in regulating metabolism, heart rate, and body temperature.

175. (c) The salivary glands are exocrine glands that are part of the digestive system. They produce saliva through a system of ducts, and are located in the mouth, tongue, palate, lips, and cheeks. Humans have three major paired salivary glands, the parotid, submandibular, and sublingual glands, as well as hundreds of minor salivary glands.

176. (b) The liver is not a gland; it’s the largest internal organ in the human body and plays a vital role in metabolism, detoxification, and various other functions. Glands are organs or tissues that secrete substances for use elsewhere in the body.

177. (d) The thyroid gland, situated in the neck, is an essential endocrine gland. It produces two hormones: thyroxine and triiodothyronine, which influence the central nervous system, cardiovascular system, and skeleton. Thyroxine is initially inactive, and it is converted into the active form, triiodothyronine, by the liver and kidneys. Iodine and selenium are vital micronutrients necessary for the synthesis of thyroid hormones.

178. (c) The liver is not classified as an endocrine gland in humans.

• Endocrine glands are part of the endocrine system and produce hormones that are released directly into the bloodstream. The pituitary gland secretes the growth hormone in humans.
• The adrenal gland, situated near the kidneys, regulates emotions and responses to crisis situations.
• The pineal gland, located in the brain, releases melatonin into the bloodstream and controls the circadian rhythm in humans.

179. (b) The function of growth hormones depends on various factors such as the concentration of hormones, the type of tissue, and the stage of development. In some cases, growth hormones promote cell division, elongation, and differentiation, leading to growth and development. However, in other situations, they may inhibit growth by regulating specific processes or signaling pathways. Therefore, the role of growth hormones can vary and is not always strictly promotional or inhibitory.

180. (b) Auxin is a hormone found in plants, not in animals. The function of Auxins is to prevents the separation of leaves, destroys the straws, saves the crops from falling, controls the growth of the plants.

181. (d) Diencephalon: Pineal and pituitary glands emerge from this part. The thalamus and hypothalamus are part of this.

• Thalamus: These are two circular structures, which work to detect cold, heat and pain.
• Hypothalamus: it controls the hormones secreted by endocrine glands. It controls hunger, thirst, anger, love, hatred, blood pressure, happiness etc.

182. (b) Hypothalamus: it controls the hormones secreted by endocrine glands. It controls hunger, thirst, anger, love, hatred, blood pressure, happiness etc.

183. (d) Medulla Oblongata: Positioned at the base of the brainstem, the medulla oblongata serves as a vital center for various involuntary functions like breathing, heart rate regulation, blood pressure control, and reflex actions such as coughing, sneezing, and swallowing. It also acts as a bridge between the spinal cord and higher brain regions, facilitating communication between the body and the brain.

184. (b) Pons: Positioned above the medulla, the pons are involved in relaying signals between the cerebrum and the cerebellum. It contributes to various autonomic functions, including sleep regulation, respiratory control, and some aspects of facial movements. Additionally, it contains nuclei that aid in controlling certain reflexes and coordinating voluntary motor movements.

185. (c) Cerebellum: Located at the back of the brain beneath the occipital lobes, the cerebellum is crucial for motor coordination, balance, posture, and precise movement control. It receives sensory information related to body position and coordinates muscle movements to ensure smooth, coordinated, and accurate motor functions. It also plays a role in some cognitive functions, contributing to attention, language, and emotional regulation.

186. (b) The outer layer of the brain that processes sensory information from the five senses. The cerebral cortex is divided into two hemispheres, each with frontal, parietal, occipital, and temporal lobes. The cerebral cortex is the part of the brain that primarily manages the sensory processing of touch, taste, and smell.

187. (b) Mammary glands are a defining characteristic of mammals. These glands produce milk to nourish the young offspring, a process known as lactation. While not all mammals give birth to live young (some lay eggs), and not all mammals have hair (e.g., whales), the presence of mammary glands is universal among mammals.

188. (d) Fore-brain is the main thinking part of the human brain. Fore-brain comprises of Cerebrum, Thalamus and Hypothalamus. The cerebrum controls all the voluntary activities like thinking, learning, reasoning, etc.

• Hind-brain comprises of Pons, Cerebellum and Medulla oblongata, The Medulla contains centres of respiration, cardiovascular reflexes, etc.
• Cerebellum maintains orientation, posture and equilibrium of the body.
• Mid-brain comprises of four lobes called corpora quadrigemina.

189. (c) The Involuntary actions like blood pressure, salivation and vomiting are controlled by the Medulla.

• Medulla oblongata, also called the medulla, is the lowest part of the brain and the lowest portion of the brainstem.
• The Medulla oblongata or simply medulla is a long stem-like structure which makes up part of the brain.

190. (b)

• Dendrites are the parts of neurons that receive information from other neurons.
• They collect signals and transmit them to the cell body.
• The axon then transmits these signals away from the cell body as electrical impulses.
• Neurotransmitters are released into the synapse, allowing communication between neurons.

191. (a) The gluteus maximus is the largest muscle in the human body.

192. (a) The papillary muscles of the heart are pillar-like muscles seen within the cavity of the ventricles, attached to their walls. They have an integral role in proper cardiac valvular function.

193. (b) The contraction of the shortest duration is in the eyelids:
Orbicularis oculi: The muscle that closes the eyelid contracts in less than 0.01 second.
Eyelid myokymia: A common condition that causes repeated movement of the orbicularis muscle in the eyelid. It can last for seconds, minutes, hours, or even weeks.
Eye muscles: The external muscles of the eye are considered the fastest contracting muscles in the body because of the constant blinking required to keep the eyes moist.

194. (b) The total number of muscles found in the human body is 639, which makes up about 40-50 percent of the body weight of a human.

195. (c) During pregnancy, the uterine muscles significantly expand, making them the longest smooth muscles in the body.

196. (a) The human spinal column, or vertebral column, consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into the sacrum), and 4 coccygeal (fused into the соссух).

197 (c) Vertebrae are the bones that make up the spinal column, which houses and protects the spinal cord.

198. (c)

• Tendon: This is a fibrous connective tissue composed mainly of collagen fibers, which appear white under the microscope. These fibers are strong and flexible, allowing tendons to connect muscles to bones and help them move.
• Cartilage: While containing some collagen fibers, cartilage also has other components like proteoglycans and elastin.
• Bone: While containing collagen, its primary component is calcium phosphate, which gives it its characteristic hardness. Ligament: Similar to tendons, ligaments also contain collagen fibers. However, ligaments connect bones to other bones.

199. (a) Connective tissue is a broad category of tissues that provide support, structure, and connection to other tissues and organs in the body. Bones are a type of specialized connective tissue that is incredibly strong and rigid due to the presence of calcium phosphate.

200 (a)

• An adult human body has 206 bones.
• These bones include those of the skull, spine, ribs, arms, and legs. Bones provide structure, protect organs, anchor muscles, and store calcium.
• The femur is the longest bone, and the stapes in the ear is the smallest.