Section B
[1 Marks]
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(A) CH₄ + O₂ → CO₂ + 2H₂O
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(B) CH₄ + 2O₂ → CO₂ + 2H₂O + Energy
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(C) CH₄ + 2O₂ → 2CO₂ + 2H₂O + Energy
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(D) CH₄ + 2O₂ → CO₂ + 2H₂O
Explanation: The correct answer is 'CH₄ + 2O₂ → CO₂ + 2H₂O + Energy'. This equation accurately represents the combustion of natural gas (methane, CH₄) with oxygen (O₂) to produce carbon dioxide (CO₂) and water (H₂O), while also indicating that energy is released during the process, which is characteristic of exothermic reactions.
[1 Marks]
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(A) Sodium
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(B) Calcium
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(C) Magnesium
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(D) Aluminium
Explanation: The sign is used to warn against corrosive chemicals that can destroy living tissues or materials upon contact. Sodium hydroxide (NaOH) is:
Highly corrosive in nature
Can cause severe chemical burns to skin and eyes
Reacts vigorously with water and organic tissues
Therefore, containers with sodium hydroxide must display this warning symbol.
[1 Marks]
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(A) 6.1 to 6.8
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(B) 6.5 to 7.3
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(C) 7.5 to 8.1
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(D) 7.0 to 7.8
Explanation: The correct option is 7.0 to 7.8 because the provided context states that our body functions within this pH range. Living organisms require a specific pH level to survive, and the context emphasizes that this range is crucial for human health.
[1 Marks]
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(A) Its reaction with iron is highly exothermic.
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(B) When it is heated with iron (III) oxide, molten iron is obtained.
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(C) Its melting point is low as compared to iron and a molten alloy of iron and aluminium is formed on heating which is used to join railway tracks.
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(D) When it is heated with iron (III) oxide, molten aluminium oxide is obtained to join railway tracks.
Explanation: The correct option is 'When it is heated with iron (III) oxide, molten iron is obtained.' This is correct because the thermit reaction involves the reduction of iron (III) oxide (Fe2O3) by aluminium (Al), which produces molten iron (Fe) and aluminium oxide (Al2O3), along with a significant amount of heat, allowing the metal to be in a molten state for effective welding.
[1 Marks]
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(A) Brass and Solder
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(B) Bronze and Brass
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(C) Solder and Bronze
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(D) Brass and Bronze
Explanation: The correct answer is 'Brass and Bronze.' Brass is an alloy of copper and zinc (Cu and Zn), while bronze is an alloy of copper and tin (Cu and Sn). This is consistent with the context that explains the compositions of these alloys.
[1 Marks]
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(A) Alveoli
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(B) Capillaries
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(C) Veins
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(D) Arteries
Explanation: The correct answer is 'Capillaries' because, according to the context, the smallest blood vessels are described as having walls that are one-cell thick. These capillaries are responsible for the exchange of materials between the blood and surrounding cells.
[1 Marks]
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(A) Apical buds formed on the tip of the plant
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(B) Vegetative buds produced in the notches of the leaf
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(C) Fruits formed on the branches of the plant
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(D) Flowers produced in the notches of the branches
Explanation: Bryophyllum produces new plants through vegetative buds that are formed in the notches along the leaf margins. When these buds fall on moist soil, they can develop into new plants, as stated in the relevant context.
[1 Marks]
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(A) Only testis
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(B) Only ovary
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(C) Ovary and testis both
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(D) All cells of the body
Explanation: The correct option is 'Ovary and testis both' because meiosis is the type of cell division that reduces the chromosome number by half, producing gametes (sperm and eggs) in both the male (testis) and female (ovary) reproductive organs. This process is essential for sexual reproduction and ensures that when fertilization occurs, the resulting offspring have the correct number of chromosomes.
[1 Marks]
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(A) 10/9
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(B) 9/8
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(C) 8/9
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(D) 9/10
Explanation: The refractive index of medium Y with respect to medium X can be calculated using the formula: n(Y relative to X) = n(Y) / n(X). Here, n(Y) = 4/3 and n(X) = 6/5. Thus, n(Y relative to X) = (4/3) / (6/5) = (4/3) * (5/6) = 20/18 = 10/9. Therefore, the correct answer is 10/9.
[1 Marks]
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(A) -15 cm
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(B) -20 cm
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(C) +15 cm
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(D) +20 cm
Explanation: To find the focal length of the concave mirror, we use the mirror formula: 1/v + 1/u = 1/f, where v = -60 cm (image distance, negative for real images) and u = -30 cm (object distance, negative as per sign convention). Substituting the values gives 1/(-60) + 1/(-30) = 1/f, simplifying leads to f = -20 cm. Thus, the focal length of the mirror is -20 cm.
[1 Marks]
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(A) 1 and 6
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(B) 7 and 4
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(C) 7 and 6
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(D) 1 and 5
Explanation: The correct answer is 1 and 6. This is because the angle of incidence (∠i) is traditionally measured with respect to the normal from the refracting surface, matching to 1, while the angle of deviation (∠D) corresponds to the deviation of the ray as it passes through the prism, which is represented by the value 6.
[1 Marks]
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(A) 110 W
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(B) 11 W
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(C) 1100 W
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(D) 220 W
Explanation: The correct answer is 110 W. Using the formula P = VI, where V = 220 V and I = 0.5 A (500 mA), we calculate the power as P = 220 V × 0.5 A = 110 W.
[1 Marks]
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(A) Leather, Silk, Wool
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(B) DDT, Polyester, Glass
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(C) Cotton, Wood, Nylon
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(D) Leather, Glass, Plastic
Explanation: The correct option is ' DDT, Polyester, Glass' because these materials are known for their persistence in the environment and do not readily decompose. The context mentions non-biodegradable substances, which are generally materials that last a long time in the environment without breaking down, adversely affecting ecosystems.
[1 Marks]
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(A) Assertion (A) is false, but Reason (R) is true.
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(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
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(C) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
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(D) Assertion (A) is true, but Reason (R) is false.
Explanation: Assertion (A) is true because nichrome is indeed widely used in electrical heating devices due to its high resistivity, which allows it to convert electrical energy into heat efficiently. However, Reason (R) is false because while nichrome has high resistivity, its resistance actually increases with an increase in temperature, contrary to what is stated. Thus, the correct response is that Assertion (A) is true, but Reason (R) is false.
[1 Marks]
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(A) Assertion (A) is false, but Reason (R) is true.
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(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
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(C) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
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(D) Assertion (A) is true, but Reason (R) is false.
Explanation: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). Animals cannot derive energy from coal because specific enzymes required for breaking down organic food substances are absent, which supports the fact that coal cannot be digested and absorbed for energy.
Section C
[2 Marks]
Answer: The hind-brain consists of three main parts: the medulla oblongata, pons, and cerebellum. The medulla oblongata is the part of the hind-brain that controls involuntary actions such as blood pressure, salivation, and vomiting. It plays a crucial role in regulating essential autonomic functions necessary for survival.
[2 Marks]
Answer: The seed coat serves as a protective outer layer that safeguards the embryo from physical damage and pathogens. The cotyledon acts as the initial source of nutrients for the young plant during germination. The radicle, which is the embryonic root, is responsible for anchoring the plant and absorbing water and nutrients from the soil. Lastly, the plumule is the embryonic shoot that eventually develops into the stem and leaves of the plant.
[2 Marks]
Answer: The concave lens diverges a parallel beam of light that falls on it. When parallel rays pass through a concave lens, they appear to diverge from a point on the same side of the lens, known as the principal focus. The rays do not actually converge; instead, they spread apart after refraction. A ray diagram would illustrate parallel rays entering the lens and diverging from the principal focus on the same side.
[2 Marks]
Answer: To determine if the electric kettle can be used in a 3 A circuit, we first calculate the current it draws. Using the formula P = VI, we find I = P/V, which gives I = 750 W / 220 V = 3.41 A. Since 3.41 A exceeds the 3 A fuse rating, using the kettle could lead to fuse blowout. Thus, the kettle cannot be safely used in this circuit.
[2 Marks]
Answer: To culture yeast, first dissolve about 10 grams of sugar in 100 mL of water. Then, take 20 mL of this sugar solution in a test tube and add a pinch of yeast granules. Seal the test tube with a cotton plug to allow gas exchange and keep it in a warm place. After 1 to 2 hours, take a small drop of the yeast culture from the test tube, place it on a slide, and cover it with a coverslip for observation under a microscope.
[2 Marks]
Answer: (i) A ray of light passing through the principal focus of a convex lens is refracted by the lens such that it emerges parallel to the principal axis. The ray diagram shows the incident ray coming from the left, passing through the focal point (F) of the convex lens before striking the lens, and then refracting to travel parallel to the principal axis on the other side.
(ii) The point through which the incident ray passes before entering the convex lens is called the principal focus of the lens.
Section D
[3 Marks]
Answer: Sodium (Na) has an atomic number of 11, so it has 1 electron in its outermost shell. The electron-dot structure for sodium is represented as Na•. Oxygen (O), with an atomic number of 8, has 6 electrons in its outer shell, shown as ••O••. When sodium reacts with oxygen, sodium donates its one electron to oxygen, forming Na⁺ (the cation) and O²⁻ (the anion). The resulting compound is sodium oxide (Na₂O), where two sodium ions combine with one oxide ion to achieve stability.
[3 Marks]
Answer: A hormone is a chemical messenger produced by glands in the endocrine system, which travels through the bloodstream to target distant organs for regulation of various physiological processes. Hormones must be secreted in precise quantities for optimal functioning; this is managed by feedback mechanisms. For instance, when blood sugar levels rise, pancreatic cells detect this increase and secrete insulin, helping to lower blood sugar levels. As blood sugar falls, insulin secretion decreases, demonstrating the negative feedback loop that maintains homeostasis.
[3 Marks]
Answer: In this scenario, the man with attached earlobes has the genotype 'aa' (homozygous recessive) while the woman with free earlobes has the genotype 'Aa' (heterozygous). The gene for free earlobes (A) is dominant over attached earlobes (a). When they have children, there are two possible allele combinations from the parents: 'Aa' (free earlobes) and 'aa' (attached earlobes). Since there is a 50% chance for each, the offspring will have a 50% ratio of free to attached earlobes.
[3 Marks]
Answer: The nature of the image formed by the convex lens in this case is virtual and erect since the object distance is less than the focal length of the lens. For a convex lens, if the object is within the focal length, the image will form on the same side as the object. The position of the image can be calculated using the lens formula 1/f = 1/v - 1/u. Given u = -6 cm, we find that v = -12 cm. Therefore, the image is virtual and located at 12 cm from the lens. To find the focal length, we use 1/f = 1/v + 1/u, which yields f = 4 cm.
[3 Marks]
Answer: The essential function of ozone in the upper atmosphere is to protect the Earth from harmful ultraviolet (UV) radiation emitted by the Sun. This UV radiation can cause serious health issues such as skin cancer and cataracts, as well as harming various organisms and ecosystems. Ozone is formed in the upper atmosphere through a process where UV light splits oxygen molecules (O2) into individual oxygen atoms (O). These free oxygen atoms then react with other oxygen molecules to form ozone (O3). The main group of chemicals responsible for the depletion of the ozone layer are chlorofluorocarbons (CFCs), which are used in industrial applications such as refrigeration, aerosol sprays, and foam production. CFCs break down ozone molecules and significantly reduce the ozone concentration in the atmosphere.
Section E
[5 Marks]
Answer: The length of the small intestine in animals varies, adapting to their diet. Herbivores, like cows, consume fibrous plant material. Their longer small intestines allow for extended digestion and fermentation of cellulose, which is challenging to break down. In contrast, carnivores, such as tigers, eat meat that is easier to digest, resulting in shorter small intestines due to less required transit time. \nThe pancreas plays a crucial role in digestion by secreting enzymes like lipase for fats and trypsin for proteins, while bile, produced by the liver and stored in the gallbladder, aids in the emulsification of fats. \nFinally, the small intestine's design includes villi and microvilli that increase the surface area, enhancing nutrient absorption. This specialized structure ensures effective uptake of amino acids, sugars, and fatty acids, which are vital for the body’s metabolism.
[5 Marks]
Answer: The rings of cartilage in the throat, also known as tracheal rings, play a crucial role in maintaining the structure of the airway. They prevent the trachea from collapsing, thereby ensuring that air can freely flow to and from the lungs. During inhalation, the ribs and diaphragm work together to facilitate breathing; when the diaphragm contracts, it moves downward, and the ribs elevate, expanding the chest cavity. This creates a negative pressure that draws air into the lungs. Muscle cramps during heavy exercise occur due to an imbalance of electrolytes and dehydration, resulting in involuntary muscle contractions. High-intensity activity depletes energy stores and leads to the accumulation of lactic acid, which can trigger cramps. Proper hydration and stretching are key to preventing such cramps.
[5 Marks]
Answer: A solenoid is a coil consisting of many circular turns of insulated copper wire, tightly wound in a cylindrical shape. When electric current is passed through it, it creates a magnetic field similar to that of a bar magnet, with one end acting as a north pole and the other as a south pole. The magnetic field lines inside the solenoid are parallel and equidistant, indicating a uniform magnetic field. To create an electromagnet, insert a soft iron rod inside the solenoid. When current flows, the rod becomes magnetized, turning it into a magnet, which can be switched on and off by controlling the electric current.
