Search Previous Year Questions

The correct answer is Development of reproductive organs and secondary sexual characteristics.

Key Points

• Sexual maturation, commonly referred to as puberty, is the developmental stage where a child transitions into an adult capable of sexual reproduction.
• This process is triggered by the hypothalamus, which releases Gonadotropin-Releasing Hormone (GnRH), stimulating the pituitary gland to produce Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).
• The primary sexual characteristics involve the physical maturation of the gonads (testes in males and ovaries in females) and the growth of reproductive tracts, including the uterus, vagina, and penis.
• The development of secondary sexual characteristics includes physiological changes not directly related to the reproductive system, such as mammary gland development in females and the growth of facial hair and laryngeal enlargement (voice deepening) in males.
• Sexual maturation also marks the functional onset of gametogenesis, which is the biological process of producing spermatozoa in males and oocytes in females.

 Additional Information

• Hormonal Influence:
• Testosterone: An androgenic steroid produced by Leydig cells that drives spermatogenesis and increases bone density and muscle mass.
• Estrogen: Primarily estradiol, it regulates the menstrual cycle and promotes the deposition of adipose tissue in the hips and breasts.
• Significant Milestones:
• Menarche: The first occurrence of menstruation, typically occurring between ages 10 and 15, signifying the maturity of the uterine lining.
• Spermarche: The initiation of sperm production, often detected through the presence of sperm in nocturnal emissions.
• Biological Significance:
• Unlike general physical growth, which involves somatic cell division (mitosis), sexual maturation involves specialized germ cell maturation and specific endocrine signaling.
• The process concludes with the epiphyseal closure of bones, which eventually stops further increase in height.

The correct answer is 20 Hz to 20,000 Hz.

Key Points

• The audible range of sound for human beings is generally considered to be between 20 Hz and 20,000 Hz (or 20 kHz).
• Frequency is defined as the number of sound wave cycles per second, and it is measured in the SI unit Hertz (Hz).
• The human ear is most sensitive to the frequency range between 2,000 Hz and 5,000 Hz, which is the range where most human speech occurs.
• Sound waves are longitudinal mechanical waves that require a medium to travel; the human ear detects these pressure variations through the tympanic membrane and cochlea.
• The ability to hear high-frequency sounds often declines with age, a medical condition known as Presbycusis, which typically limits the upper range to around 12,000 Hz to 15,000 Hz in older adults.

 Additional Information

• Infrasonic Sound (Infrasound):
• These are longitudinal waves with frequencies lower than 20 Hz.
• Natural sources include earthquakes, volcanic eruptions, and lightning.
• Animals like elephants, hippopotamuses, and whales use infrasound for long-distance communication.
• Ultrasonic Sound (Ultrasound):
• These are sound waves with frequencies higher than 20,000 Hz.
• Bats, dolphins, and porpoises utilize ultrasound for echolocation and navigation in the dark or underwater.
• In medical science, it is used for Echocardiography and Ultrasonography to visualize internal organs.
• Industrial applications include SONAR (Sound Navigation and Ranging) for measuring ocean depth and detecting submerged objects.

The correct answer is To and fro motion of an object.

Key Points

• Vibration is defined as the rapid to and fro or back and forth movement of an object about its central or mean position.
• Sound is produced when an object vibrates; these vibrations cause the surrounding air molecules to fluctuate, creating pressure waves that travel through a medium.
• In Physics, this type of movement is a form of oscillatory motion. When the frequency of these oscillations falls within the range of 20 Hz to 20,000 Hz, it becomes audible to the human ear as sound.
• Common examples include the vibration of stretched strings in a guitar, the membrane of a drum, or the vocal cords in the human larynx during speech.
• The intensity and pitch of the sound produced are directly influenced by the nature and speed of this rapid motion.

 Additional Information

• Characteristics of Vibration:
• Frequency: This is the number of vibrations per second. Higher frequency results in a higher pitch, measured in Hertz (Hz).
• Amplitude: The maximum displacement from the equilibrium position. A larger amplitude results in a louder sound.
• Time Period: The time taken to complete one full vibration or oscillation.
• Propagation of Sound:
• Sound is a longitudinal mechanical wave, meaning it requires a material medium (solid, liquid, or gas) to propagate.
• It travels fastest in solids due to the close proximity of atoms and slowest in gases. Sound cannot travel through a vacuum.

The correct answer is 18 N.

Key Points

• The weight of an object is defined as the gravitational force with which a celestial body attracts that object toward its center.
• The acceleration due to gravity on the surface of the Moon is significantly lower than that on Earth, measuring approximately 1.62 m/s², which is about 1/6^th of Earth's 9.8 m/s².
• The mathematical relationship between the weight of a body on the Earth and its weight on the Moon is expressed as: Weight on Moon = (1 ÷ 6) × Weight on Earth.
• To determine the weight on Earth when the Moon weight is known, the formula is rearranged as: Weight on Earth = 6 × Weight on Moon.
• Substituting the given value of 3 N into the equation: Weight on Earth = 6 × 3 N = 18 N.

 Additional Information

• Distinction between Mass and Weight:
• Mass: It is the measure of the quantity of matter contained in a body. It is a scalar quantity and its value remains constant regardless of the location in the universe. The SI unit of mass is the kilogram (kg).
• Weight: It is a vector quantity that depends on the local gravitational acceleration (g). The weight is calculated using the formula W = m × g, where m is mass. The SI unit of weight is the Newton (N).
• Gravitational Variance: Because the Moon has a smaller mass and radius compared to Earth, its gravitational pull is weaker. Consequently, while an astronaut's mass remains the same on the Moon, their weight decreases to 1/6^th of their weight on Earth.

The correct answer is The product of their masses increases.

Key Points

• According to Newton's Law of Universal Gravitation, every point mass attracts every other point mass in the universe with a force that is directly proportional to the product of their masses. Mathematically, this is expressed as F = G(m1 × m2) / r², where F represents the gravitational force.
• Since the force is proportional to the product of m1 and m2, any increase in the magnitude of either mass or their product will lead to a proportional increase in the gravitational attraction between them.
• The Universal Gravitational Constant (G) remains the same regardless of the environment or the masses involved, meaning the force depends strictly on the mass values and the spatial separation.
• Gravity is an attractive force that acts along the line joining the centers of the two masses, and it is the primary force responsible for the orbital motion of planets and celestial bodies.

 Additional Information

• Distance (Inverse Square Law):
• The gravitational force is inversely proportional to the square of the distance (r²) between the centers of the masses.
• If the distance increases, the force decreases significantly; for example, doubling the distance reduces the force to one-fourth of its original value.
• Medium Independence:
• Gravitational force is independent of the intervening medium. Whether two masses are kept in water, air, or a vacuum, the gravitational force between them remains unchanged as G is a universal constant.
• Universal Gravitational Constant (G):
• The value of G is approximately 6.674 × 10⁻¹¹ Nm²/kg², which indicates that gravity is a relatively weak force unless at least one of the masses involved is planetary in scale.

The correct answer is Water.

Key Points

• The Law of Constant Proportions, also known as Proust's Law, states that a chemical compound always contains the same elements combined together in the same fixed proportion by mass.
• Water (H₂O) is a pure chemical compound formed by the chemical combination of hydrogen and oxygen.
• In any sample of pure water, the mass ratio of hydrogen to oxygen is always 1:8. This is calculated using the atomic masses: Hydrogen (approx. 1 unit) and Oxygen (approx. 16 units). Since there are two hydrogen atoms, the ratio is 2:16, which simplifies to 1:8.
• This ratio remains constant regardless of whether the water is sourced from rain, wells, oceans, or is synthesized in a laboratory environment.
• The law was first proposed by the French chemist Joseph Proust in 1799, providing a foundational principle for stoichiometry and Dalton's Atomic Theory.

 Additional Information

• Distinction from Mixtures:
• Soil: It is a heterogeneous mixture whose composition varies widely based on geology, climate, and biological activity. It does not have a fixed chemical formula or constant proportions.
• Brass: This is an alloy, classified as a solid solution or mixture of copper and zinc. The percentage of zinc can vary (typically 5% to 45%) to alter the mechanical properties of the metal.
• Air: It is a homogeneous mixture of gases (mostly nitrogen and oxygen). While its composition is relatively stable in the lower atmosphere, it is not chemically bonded and can vary with altitude, humidity, and pollution levels.
• Compounds vs. Mixtures:
• In a compound like water, the constituents lose their individual properties and are bound in definite proportions.
• In mixtures (like air, soil, and brass), the constituents retain their properties and can be present in variable proportions.

The correct answer is Parenchyma.

Key Points

• Parenchyma is the most common and versatile simple permanent tissue found in plants, characterized by living cells with thin cellulosic cell walls and large central vacuoles.
• These cells are typically isodiametric, meaning they have equal expansion in all directions, though they can also be oval, round, or polygonal in shape with intercellular spaces.
• The primary function of this tissue is storage of food reserves like starch, fats, and proteins, and it serves as the site for major metabolic functions including photosynthesis and secretion.
• In leaves, specialized parenchyma called chlorenchyma contains chloroplasts to perform carbon fixation, while in aquatic plants, aerenchyma provides buoyancy through large air cavities.
• Being totipotent, parenchyma cells retain the ability to divide even at maturity, which is crucial for wound healing, regeneration, and the formation of adventitious roots.

 Additional Information

• Sclerenchyma:
• Consists of dead cells at maturity with extremely thick, lignified secondary walls.
• Divided into fibers and sclereids, its main purpose is to provide mechanical strength and structural rigidity to mature plant parts like the xylem and seed coats.
• Collenchyma:
• Composed of living cells that exhibit uneven thickening of cell walls, particularly at the corners, due to the deposition of cellulose, hemicellulose, and pectin.
• Provides mechanical support and flexibility to young, growing organs such as petioles and stems, allowing them to bend without breaking.
• Epidermis:
• The outermost protective layer of the plant body, usually one cell thick and covered by a waxy cuticle.
• Functions as a barrier against pathogens and excessive transpiration while facilitating gas exchange through specialized structures called stomata.

The correct answer is Gain of hydrogen or loss of oxygen.

Key Points

• In the classical framework of chemistry, reduction is defined as a process involving the addition of hydrogen or any other electropositive element to a chemical species.
• Alternatively, the removal of oxygen or any other electronegative element from a compound is also classified as reduction, as seen in the extraction of metals from their oxides.
• From the electronic perspective, reduction occurs when an atom, ion, or molecule gains one or more electrons; this is commonly remembered by the mnemonic GER (Gain of Electrons is Reduction).
• A fundamental characteristic of reduction is the decrease in the oxidation state or oxidation number of an element, reflecting a reduction in its positive charge or an increase in its negative charge.
• In a typical redox reaction, the species that undergoes reduction is called the oxidizing agent because it facilitates the oxidation of another substance by accepting its electrons.

 Additional Information

• Oxidation: This process is the direct opposite of reduction and is characterized by specific chemical changes.
• It involves the gain of oxygen or the loss of hydrogen.
• In electronic terms, it is the loss of electrons (LEO: Loss of Electrons is Oxidation), resulting in an increase in oxidation state.
• Reducing Agent: This is a substance that loses electrons and is itself oxidized during a chemical reaction.
• Common examples include Hydrogen (H₂), Carbon (C), and reactive metals like Sodium (Na) or Magnesium (Mg).
• These agents are essential in metallurgical processes to convert metallic oxides into pure metals by removing the oxygen component.

The correct answer is Both (ii) and (iii).

Key Points

• Amplitude is the maximum displacement of the particles of a medium from their original undisturbed positions when a sound wave passes through. The loudness of a sound is directly determined by its amplitude; specifically, a larger vibrational force creates a larger amplitude, resulting in a louder sound. Hence, statement (i) is correct.
• A sound wave is a form of mechanical energy. The intensity and loudness of sound are dependent on the energy carried by the wave per unit area per unit time. Therefore, a loud sound wave carries significantly more energy than a soft or faint sound wave. Hence, statement (ii) is incorrect.
• Loudness is a physiological sensation and refers to the degree of sensation produced in the human ear. It is a measure of the sensitivity and auditory response of the ear to the sound intensity, rather than a measure of the heart's response. Hence, statement (iii) is incorrect.

 Additional Information

• Loudness vs Intensity:
• Loudness is proportional to the square of the amplitude of the vibration produced by the sound source.
• The unit used to measure the level of sound is the Decibel (dB).
• The threshold of hearing for a healthy human ear is typically 0 dB, while sounds above 80 dB are considered noise pollution and can be harmful to the ear.
• While intensity is an objective physical quantity (measured in Watts per square meter), loudness is a subjective quantity that varies from person to person.
• Frequency and Pitch:
• While amplitude determines loudness, the frequency of the sound wave determines its pitch or shrillness.
• A high-frequency wave has a high pitch (e.g., a whistling sound), whereas a low-frequency wave has a low pitch (e.g., a drum beat).

The correct answer is (Initial velocity + Final velocity)/2.

Key Points

• Uniform acceleration describes motion where the velocity of an object changes by equal amounts in equal time intervals, meaning the rate of change of velocity is a constant.
• The average velocity of an object is defined as the total displacement divided by the total time elapsed during its motion.
• For a body undergoing constant acceleration, the velocity-time graph is a straight line. In such linear relationships, the average value over an interval is mathematically equal to the arithmetic mean of the start and end values.
• The specific formula for average velocity (v_avg) under these conditions is v_avg = (u + v) / 2, where u is the initial velocity and v is the final velocity.
• This derivation is a foundational principle in Newtonian mechanics and was historically verified by Galileo Galilei through experiments with inclined planes and free-falling bodies.

 Additional Information

• Core Kinematic Variables:
• Initial Velocity (u): The velocity at the beginning of the observation (t = 0).
• Final Velocity (v): The velocity at the end of the duration t, calculated as v = u + at.
• Acceleration (a): The constant rate at which velocity changes, defined as (v − u) / t.
• Displacement and Average Velocity:
• The second equation of motion, s = ut + (1/2)at², represents the total displacement.
• Since displacement = average velocity × time, substituting the kinematic relationships proves that the average velocity must be (u + v) / 2 to satisfy the equations of motion.
• In idealized physics problems, such as an object falling under gravity (where g ≈ 9.8 m/s²), this formula simplifies calculations of distance and time.
• Context of Other Options:
• Zero: The average velocity is only zero if the object returns to its starting position (zero net displacement), regardless of its acceleration.
• Initial/Final Velocity: The average velocity only equals these specific values if acceleration is zero, meaning the object is in uniform motion with a constant speed.