UPSC CDS-1

31. Which one of the following is the ‘energy currency’ for cellular

Which one of the following is the ‘energy currency’ for cellular processes?

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Glucose
ATP
ADP
Pyruvic acid
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UPSC CDS-1 – 2020
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ATP (Adenosine Triphosphate) is widely considered the main energy currency of the cell. Energy released from the breakdown of fuels like glucose is used to synthesize ATP. ATP then provides the energy for most cellular processes, such as muscle contraction, nerve impulse transmission, and chemical synthesis, by breaking one of its phosphate bonds to form ADP (Adenosine Diphosphate) and inorganic phosphate, releasing energy.
– ATP is a molecule that stores and releases energy in cells.
– Energy from metabolic processes (like glucose breakdown) is stored in ATP.
– Cells directly use the energy released from the hydrolysis of ATP for their activities.
While glucose is a primary source of energy, it is metabolized through processes like glycolysis and cellular respiration to produce ATP. ADP is a lower-energy molecule produced when ATP is hydrolyzed. Pyruvic acid is an intermediate product of glycolysis. Therefore, ATP is the direct molecule that powers most cellular work.

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32. When air is blown from mouth into a test tube containing limewater, th

When air is blown from mouth into a test tube containing limewater, the limewater turns milky. This is due to the presence of

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water vapour
oxygen
carbon dioxide
carbon monoxide
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Limewater is a solution of calcium hydroxide (Ca(OH)₂). When carbon dioxide (CO₂) is passed through limewater, it reacts to form insoluble calcium carbonate (CaCO₃), which precipitates out of the solution, causing it to turn milky or cloudy. Human exhaled air contains a higher concentration of carbon dioxide compared to inhaled air.
– Limewater (Calcium hydroxide solution) is a test for carbon dioxide.
– The reaction is: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l).
– Calcium carbonate (CaCO₃) is insoluble, causing the milky appearance.
– Human breath contains significant amounts of carbon dioxide.
The reaction is reversible. If excess carbon dioxide is passed through the milky solution, the calcium carbonate can react further with water and carbon dioxide to form soluble calcium bicarbonate (Ca(HCO₃)₂), causing the milkiness to disappear.
CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)

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33. Which one of the following is the correct sequence of events during se

Which one of the following is the correct sequence of events during sexual reproduction in plants?

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Seedling, formation of embryo, pollination, fertilization, division of zygote
Formation of embryo, seedling, pollination, fertilization, division of zygote
Pollination, fertilization, division of zygote, formation of embryo, seedling
Seedling, formation of embryo, division of zygote, pollination, fertilization
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Sexual reproduction in flowering plants typically begins with pollination, which is the transfer of pollen. This is followed by fertilization, where the male gamete (from pollen) fuses with the female gamete (in the ovule) to form a zygote. The zygote then undergoes cell division and development (embryogenesis) to form an embryo. The embryo is enclosed within a seed, and the seed germinates under favorable conditions to grow into a seedling.
– The correct sequence starts with the interaction of gametes or their carriers: Pollination.
– Fusion of gametes: Fertilization.
– The result of fertilization: Zygote.
– Development from zygote: Division of zygote leading to embryo formation.
– Subsequent stage: Seedling growth from the seed containing the embryo.
The order presented in option C (Pollination, fertilization, division of zygote, formation of embryo, seedling) correctly represents the major sequential steps from the start of reproduction to the establishment of a new plant from seed. The division of the zygote is the initial step in the formation of the embryo.

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34. Which one of the following animals has a three-chambered heart?

Which one of the following animals has a three-chambered heart?

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Scoliodon
Salamander
Pigeon
Human being
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Salamanders are amphibians. Most amphibians have a three-chambered heart consisting of two atria and one ventricle. This contrasts with fish (Scoliodon), which have a two-chambered heart, and birds (Pigeon) and mammals (Human being), which have a four-chambered heart.
– Scoliodon (fish) has a two-chambered heart.
– Salamander (amphibian) has a three-chambered heart.
– Pigeon (bird) has a four-chambered heart.
– Human being (mammal) has a four-chambered heart.
The evolution of the heart chambers reflects adaptations for more efficient circulation. Two-chambered hearts pump deoxygenated blood to the gills for oxygenation. Three-chambered hearts allow for some mixing of oxygenated and deoxygenated blood in the single ventricle before pumping it to both the lungs and the body. Four-chambered hearts completely separate oxygenated and deoxygenated blood, allowing for more efficient oxygen delivery, which is necessary for the high metabolic rates of birds and mammals.

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35. Which one of the following is not an epidemic disease?

Which one of the following is not an epidemic disease?

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Cholera
Malaria
Smallpox
Elephantiasis
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Elephantiasis (lymphatic filariasis) is typically classified as a chronic disease, often endemic in certain regions, caused by parasitic worms. While local outbreaks can occur, it is not usually referred to as an ‘epidemic’ in the same sense as diseases like cholera, malaria, or smallpox, which can spread rapidly through a population in a short period. Cholera, malaria, and smallpox (historically, before eradication) are well-known examples of epidemic or pandemic diseases characterized by rapid spread and increased incidence.
– Epidemic diseases are characterized by a sudden increase in the number of cases of a disease in a specific population or region.
– Cholera, malaria, and smallpox fit the description of diseases that can occur in epidemics.
– Elephantiasis is a chronic parasitic infection leading to swelling, which is usually endemic rather than primarily epidemic.
An endemic disease is one that is constantly present in a population, while an epidemic involves a widespread occurrence of an infectious disease in a community at a particular time. A pandemic is an epidemic that has spread across a large region, multiple continents or worldwide. Elephantiasis, caused by filarial worms transmitted by mosquitoes, results in long-term disability and is primarily a public health problem in tropical and subtropical regions where the parasites are endemic.

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36. The unit of the force constant $k$ of a spring is

The unit of the force constant $k$ of a spring is

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N-m
N/m
N-m$^2$
N/m$^2$
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According to Hooke’s Law, the force (F) required to extend or compress a spring by a distance (x) is proportional to that distance, i.e., $F = kx$, where k is the force constant (also known as the spring constant). To find the unit of k, we can rearrange the formula: $k = F/x$. The standard unit of force (F) is Newtons (N), and the standard unit of displacement (x) is meters (m). Therefore, the unit of the force constant k is Newtons per meter (N/m).
– Hooke’s Law: $F = kx$.
– F is force (unit: N).
– x is displacement (unit: m).
– k is the force constant.
The force constant k is a measure of the stiffness of the spring; a higher value of k means the spring is stiffer and requires more force to extend or compress it by a given distance.

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37. Which one of the following types of radiation has the shortest

Which one of the following types of radiation has the shortest wavelength?

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Radio waves
Visible light
Infrared (IR)
Ultraviolet (UV)
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The electromagnetic spectrum consists of various types of radiation ordered by frequency or wavelength. From longest wavelength to shortest wavelength, the order is typically: Radio waves, Microwaves, Infrared (IR), Visible light, Ultraviolet (UV), X-rays, Gamma rays. Comparing the options given: Radio waves have the longest wavelength, followed by Infrared, then Visible light. Ultraviolet (UV) light has a shorter wavelength than visible light. Therefore, among the given options, Ultraviolet (UV) radiation has the shortest wavelength.
– The electromagnetic spectrum is ordered by wavelength and frequency.
– Wavelength and frequency are inversely related ($c = f\lambda$).
– Order of increasing frequency/decreasing wavelength: Radio, Micro, IR, Visible, UV, X-ray, Gamma.
Visible light covers wavelengths from approximately 400 nm (violet) to 700 nm (red). UV wavelengths are shorter than visible light, typically ranging from 10 nm to 400 nm. Infrared wavelengths are longer than visible light, typically from 700 nm to 1 mm. Radio waves have wavelengths ranging from about 1 mm to very long distances.

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38. If the speed of light in air is $3 \times 10^8$ m/s, then the speed of

If the speed of light in air is $3 \times 10^8$ m/s, then the speed of light in a medium of refractive index $\frac{3}{2}$ is

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$2 imes 10^8$ m/s
$ rac{9}{4} imes 10^8$ m/s
$ rac{3}{2} imes 10^8$ m/s
$3 imes 10^8$ m/s
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The refractive index (n) of a medium is defined as the ratio of the speed of light in a vacuum (c) to the speed of light in that medium (v). The formula is $n = c/v$. Given the speed of light in air (approximately equal to the speed in vacuum) $c = 3 \times 10^8$ m/s and the refractive index of the medium $n = 3/2$, we can find the speed of light in the medium ($v$) by rearranging the formula: $v = c/n$.
$v = (3 \times 10^8 \, \text{m/s}) / (3/2) = (3 \times 10^8 \, \text{m/s}) \times (2/3) = 2 \times 10^8$ m/s.
– Refractive index $n = c/v$.
– $c$ is the speed of light in vacuum (or air).
– $v$ is the speed of light in the medium.
The refractive index is a dimensionless quantity and is always greater than or equal to 1. A higher refractive index indicates a slower speed of light in the medium. The speed of light is maximum in vacuum.

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39. In a periscope, the two plane mirrors are kept

In a periscope, the two plane mirrors are kept

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parallel to each other
perpendicular to each other
at an angle of 60° with each other
at an angle of 45° with each other
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In a simple periscope, two plane mirrors are used to change the direction of light twice. To achieve this, the mirrors are placed parallel to each other. Each mirror is typically oriented at a 45-degree angle relative to the line of sight (or the tube of the periscope) to reflect light at a 90-degree angle. The parallelism of the two mirrors ensures that the final image observed is upright relative to the object.
– A simple periscope uses two plane mirrors.
– The mirrors are placed parallel to each other.
– Each mirror is tilted at 45 degrees to the axis of the periscope.
More complex periscopes use prisms instead of mirrors to avoid issues with coatings and ensure total internal reflection, but the principle of directing light through successive reflections remains the same, often with parallel optical elements.

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40. Which one of the following is not true about the image formed by a pla

Which one of the following is not true about the image formed by a plane mirror?

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It is of the same size as the subject.
It is laterally inverted.
It is real image.
It is formed as far behind the mirror as the object is in front.
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A plane mirror forms a virtual image. A virtual image is one that cannot be projected onto a screen because the light rays do not actually converge at the location of the image; they only appear to diverge from that point. A real image, conversely, is formed where light rays actually converge and can be projected onto a screen (like the image formed by a projector or on the retina of the eye). All other statements are true properties of images formed by plane mirrors.
– Plane mirrors form virtual images.
– Virtual images cannot be projected onto a screen.
– Real images are formed by converging rays and can be projected.
Properties of image formed by a plane mirror: virtual, erect, laterally inverted, same size as object, and same distance behind the mirror as the object is in front.

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