General Science Mixed Quiz: Set 79

The correct answer is D, Ribosomes. Ribosomes stuck on the outer surface of the endoplasmic reticulum give it a grainy, rough look under the electron microscope.

The endoplasmic reticulum is a network of membrane tubes and sacs in the cytoplasm. The part carrying ribosomes is the rough ER, and it is busy making proteins, especially those to be secreted or placed in membranes. The part without ribosomes is the smooth ER, which makes lipids and steroid hormones and helps detoxify drugs in liver cells. Cells that secrete a lot of protein, such as pancreatic cells, have plenty of RER.

A is wrong: centrioles are paired cylinders near the nucleus that help in cell division; they are not on the ER.

B is wrong: plastids such as chloroplasts are large separate organelles of plant cells.

C is wrong: lysosomes are free membrane sacs of digestive enzymes, not particles fixed on the ER.

Exam tip: RER = ribosomes + protein synthesis; SER = no ribosomes + lipid synthesis and detoxification.

The correct answer is A, The ring has higher kinetic energy. Rotational kinetic energy is ½Iω², and the ring has the larger moment of inertia.

For a thin ring about the axis through its centre and perpendicular to its plane, all the mass sits at distance R, so I = MR². For a uniform disc, much of the mass lies closer to the axis, so I = ½MR². At the same angular velocity ω, the ring has KE = ½MR²ω² while the disc has only ¼MR²ω². The ring therefore carries twice the rotational kinetic energy of the disc. The farther mass lies from the axis, the harder a body is to spin and the more energy it stores.

B is wrong: the disc has the smaller moment of inertia, so it has less energy at the same ω.

C is wrong: equal mass and radius do not mean equal moment of inertia; mass distribution matters.

D is wrong: a spinning body has rotational kinetic energy even when its centre of mass is at rest.

Exam tip: ring I = MR², disc I = ½MR², solid sphere I = ⅖MR²; rotational KE = ½Iω².

The correct answer is C, apical meristem. Apical meristem sits at the growing tips of stems and roots, and its dividing cells make them longer.

Meristems are groups of cells that keep dividing throughout a plant's life. The shoot apex and root apex hold apical meristems, so a plant grows in length from its tips; this is primary growth. In the root the tip is shielded by a root cap as it pushes through soil. Lateral meristem (vascular cambium and cork cambium) adds girth instead, and intercalary meristem lengthens internodes and leaf bases in grasses and bamboo.

A is wrong: lateral meristem increases the thickness of stems and roots, not their length.

B is wrong: intercalary meristem works at the base of internodes and leaves, mainly in grasses; it does not lengthen roots.

D is wrong: secondary growth, by cambium, increases girth; growth in length is primary growth.

Exam tip: apical = length (tips); lateral = girth (cambium); intercalary = base of internodes (grasses, regrowth after grazing).

The correct answer is C, 2 × 10⁵ A.U. One parsec equals about 2,06,265 astronomical units, which rounds to 2 × 10⁵ A.U.

An astronomical unit is the mean distance between the Earth and the Sun, about 1·5 × 10¹¹ m. A parsec is the distance at which one astronomical unit subtends an angle of one second of arc; the name comes from "parallax of one arcsecond". Since one radian holds about 2,06,265 arcseconds, a parsec is that many astronomical units, roughly 3·26 light years or 3·1 × 10¹⁶ m. Astronomers use it for distances between stars.

A is wrong: 2,000 A.U. is about a hundred times too small.

B is wrong: 20,000 A.U. is still ten times smaller than a parsec.

D is wrong: 2 × 10⁶ A.U. is ten times larger than a parsec.

Exam tip: 1 parsec ≈ 2·06 × 10⁵ A.U. ≈ 3·26 light years; order of size is A.U. < light year < parsec.

The correct answer is B, Porifera. In sponges the cells are arranged loosely and work with a good deal of independence, with collar cells driving water through a canal system and other cells digesting the food particles, so the body never rises to the level of a true tissue. The skeleton is of spicules or spongin fibres.

Option A, Coelenterata, has reached the tissue level, with stinging cnidoblasts and contractile cells acting together. Option C, Ctenophora, also has the tissue level, with its eight rows of comb plates beating in order. Option D, Platyhelminthes, has gone further still, to the organ level, with definite reproductive and excretory organs. The ladder to remember is cellular, tissue, organ and organ-system, in that order of phyla, and the sponge is also the only one of the four that is usually asymmetrical in body form.

The correct answer is B, Ion-exchange. An ion-exchange resin or zeolite swaps the calcium and magnesium ions that cause permanent hardness for sodium or hydrogen ions.

Permanent hardness comes from the chlorides and sulphates of calcium and magnesium, which do not break down on heating. In the zeolite (permutit) process, sodium aluminium silicate takes up Ca2+ and Mg2+ and gives out Na+, which does not harden water; the exhausted zeolite is renewed by washing it with brine. Synthetic resins work the same way. Washing soda and Calgon also remove permanent hardness.

A is wrong: boiling removes only temporary hardness, by turning soluble bicarbonates into insoluble carbonates.

C is wrong: lime treatment, Clark's method, also removes only temporary (bicarbonate) hardness.

D is wrong: bubbling sulphur dioxide only makes the water acidic; it does not take out calcium or magnesium.

Exam tip: temporary hardness = bicarbonates, removed by boiling or Clark's lime; permanent = chlorides and sulphates, removed by washing soda, Calgon or ion exchange.

The correct answer is C, peptidoglycan, also called murein, a mesh of sugar chains cross-linked by short peptides. It is the target of penicillin, which blocks its formation, and the amount of it in the wall is what makes a bacterium stain Gram-positive or Gram-negative. Option A is wrong because cellulose is the wall material of plant cells and of some algae. Option B is wrong because chitin forms the wall of fungi and also the exoskeleton of insects and other arthropods, and this is the pair most often interchanged in examinations. Option D is wrong because lignin strengthens the walls of woody plant tissue and is not a microbial wall material. The wall is absent in a virus altogether, since a virus is not a cell.

The correct answer is C, Stapedius. The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body. When a very loud sound reaches the ear, the stapedius contracts and damps the vibration of the stapes, protecting the delicate inner ear; this is called the acoustic reflex. It is supplied by the facial nerve, so damage to that nerve can make ordinary sounds seem painfully loud. Option A is wrong because the biceps is a large muscle at the front of the upper arm that bends the elbow. Option B is wrong because the sartorius, which runs across the thigh, is the longest muscle of the body, not the smallest. Option D is wrong because the triceps at the back of the upper arm straightens the elbow and is a large muscle. Exam tip: smallest muscle stapedius, smallest bone stapes, longest muscle sartorius, largest muscle gluteus maximus.

The correct answer is C, Pericycle. The pericycle is a layer of cells around the vascular cylinder of the root and stem; it is not part of xylem or phloem.

The conducting tissues of plants are xylem and phloem. Xylem, which carries water and minerals upward, is made of tracheids, vessels, xylem fibres and xylem parenchyma. Phloem, which carries food, is made of sieve tubes, companion cells, phloem fibres and phloem parenchyma. The pericycle lies just inside the endodermis and outside the vascular tissue; in roots it gives rise to lateral roots and later to the vascular cambium.

A is wrong: fibres (xylem fibres and phloem fibres, also called bast fibres) are a component of both conducting tissues.

B is wrong: tracheids are elongated dead cells of xylem that conduct water.

D is wrong: sieve tubes are the main food-conducting elements of phloem.

Exam tip: xylem has four elements (tracheids, vessels, fibres, parenchyma) and phloem has four (sieve tubes, companion cells, fibres, parenchyma); lateral roots arise from the pericycle.

The correct answer is B, Fallopian tube. In human beings the sperm meets and fuses with the egg inside the fallopian tube, also called the oviduct.

The ovary releases one egg in a month, and the funnel shaped mouth of the fallopian tube collects it. Sperms swim up from the vagina through the cervix and the uterus into the tube, and fusion usually happens in its wider upper part. The fertilised egg, now a zygote, begins to divide as the tube's lining pushes it along, and reaches the uterus in a few days as a ball of cells that implants in the thick uterine wall and grows there with the help of the placenta.

Option A is wrong because the uterus is where the embryo implants and develops, after fertilisation. Option C is wrong because the ovary only makes and releases the egg. Option D is wrong because the vagina is the passage the sperms enter through.

Exam tip: egg made in the ovary, fertilised in the fallopian tube, developed in the uterus.

The correct answer is B, Bengaluru. The Central Silk Board was constituted under the Central Silk Board Act, 1948 and works under the Ministry of Textiles with its headquarters in Bengaluru, from where it runs the country's sericulture research and seed organisation. Option A is wrong, though Mysuru is the seat of a Central Sericultural Research and Training Institute, the other two being at Berhampore in West Bengal and Pampore in Jammu and Kashmir. Option C is wrong because Ranchi, or more exactly Namkum near it, is the home of the lac research institute, not of the silk board. Option D is wrong because Guwahati is in the muga belt but is not the board's headquarters. Keep the three cities separate: Bengaluru for silk administration, Mysuru for silk research and Ranchi for lac.

The correct answer is C, Hepatitis B. The hepatitis B vaccine was the first vaccine made by recombinant DNA technology. Scientists cut out the gene for the surface protein of the hepatitis B virus and put it into yeast cells; the yeast then made that protein in large amounts, and the purified protein is injected as the vaccine. Because only one viral protein is used and no whole virus is involved, the vaccine cannot cause the disease, which is what makes recombinant vaccines safe. It was licensed in the mid 1980s and in India it is part of the pentavalent shot given to infants. A is wrong because the polio vaccine is either the killed virus of Salk or the weakened live virus of Sabin. B is wrong because no vaccine against AIDS has been licensed so far. D is wrong because the smallpox vaccine used the live vaccinia virus, and the disease was declared eradicated in 1980. Exam tip: hepatitis B, first recombinant vaccine, made in yeast from the surface antigen gene.

The correct answer is A, The motion repeats after time T only once. This is the incorrect statement, because periodic motion repeats after every interval T, again and again.

The time period T of a pendulum is the time for one complete oscillation, that is, the smallest interval after which the bob returns to the same position moving in the same direction. Since the motion is periodic, it repeats after T, 2T, 3T and so on, without limit as long as no energy is lost. The formula T = 2π√(L/g) also assumes small swings; for large angles the period grows a little, so T stays constant only when the angular displacement is small.

B is correct: the period is by definition the least time after which motion repeats.

C is correct: if the motion repeats after T, it also repeats after any whole multiple nT.

D is correct: the period is independent of amplitude only for small angular displacements.

Exam tip: period = shortest repeat time; motion also repeats at every nT; isochronism holds only for small swings.

The correct answer is A, Ashwagandha. Ashwagandha, whose botanical name is Withania somnifera, is called winter cherry in English because of the small red berry it bears inside a papery cover; it is also called Indian ginseng. The part used is the root, which in Ayurveda is given as a tonic for weakness, stress and sleeplessness, and the plant's Sanskrit name comes from the horse-like smell of the fresh root. It is a hardy shrub of dry regions, so Rajasthan, Madhya Pradesh and Gujarat are the main growing states; the Nagauri type from Nagaur in Rajasthan and the crop around Mandsaur and Neemuch in Madhya Pradesh are the best known. B is wrong because rose is an ornamental and perfume crop, not a winter cherry. C is wrong because lily is a garden flower grown from bulbs. D is wrong because chandni is an ornamental flowering shrub grown for its white flowers. Exam tip: Ashwagandha, Withania somnifera, winter cherry or Indian ginseng, root used.

The correct answer is B, dust particles in the air scatter light into our eyes. A beam seen from the side is visible only because tiny particles send some of its light sideways.

Light travelling in a straight line cannot enter our eyes unless something redirects it towards us. Fine dust, smoke and water droplets in the air scatter light in all directions, so part of each sunbeam reaches an observer standing to one side. This is the Tyndall effect, the same reason a torch beam shows up in fog or sunlight looks like shafts in a dusty room or a forest. In perfectly clean air the beam would be invisible from the side.

A is wrong: reflection needs a smooth surface and sends light in one fixed direction; tiny particles scatter it everywhere.

C is wrong: refraction is bending at a boundary between two media and does not light up a beam's path.

D is wrong: scattering can partly polarise light, but polarisation is not what makes the particles visible.

Exam tip: sunbeams in a dusty room and a headlight beam in fog are both examples of the Tyndall effect.

The correct answer is B, Nitrogen. An ordinary incandescent bulb is filled with an unreactive gas, nitrogen usually mixed with argon, so that the white-hot tungsten filament does not burn away. The filament works at about 2500 degrees Celsius, and in air the tungsten would oxidise within seconds. Nitrogen and argon do not react with tungsten, and the gas pressure inside also slows the evaporation of the metal, so the filament lasts longer and the glass does not blacken quickly. A is wrong because halogens such as iodine and bromine are added only in halogen lamps, a special high-temperature type, not in the common bulb. C is wrong because carbon dioxide would release oxygen at that temperature and attack the filament. D is wrong because hydrogen is highly inflammable and would make the bulb dangerous. Exam tip: filament is tungsten, melting point about 3400 degrees Celsius, and the bulb is filled with nitrogen and argon.

The correct answer is D, vacuoles full of cell sap. A large central vacuole filled with sap presses the cytoplasm against the cell wall, keeping the cell firm, or turgid.

In a mature plant cell the central vacuole can take up 50 to 90% of the cell's volume. Its membrane, the tonoplast, controls what enters it, and the sap holds water, sugars, salts, pigments and wastes. When the vacuole is full, water pressure inside pushes outward on the wall; this turgor pressure keeps leaves spread out and soft stems upright. When the plant loses water, vacuoles shrink and the plant wilts.

A is wrong: ribosomes are tiny particles that make proteins; they give no shape or firmness.

B is wrong: mitochondria release energy through respiration; they are not concerned with turgidity.

C is wrong: the Golgi apparatus packages and secretes materials, including those for the cell wall, but it does not keep the cell turgid.

Exam tip: turgidity = central vacuole (turgor pressure); its membrane = tonoplast; animal cells have small or no vacuoles.

The correct answer is B, Large number of stomata. Xerophytes live where water is scarce, so they have few stomata to cut down water loss.

Xerophytes are plants of deserts and dry habitats, such as cacti, Opuntia, Calotropis and Acacia. Most of their water is lost through transpiration from the stomata, so every adaptation aims to save water: leaves reduced to scales or spines, thick fleshy stems that store water, deep or widely spread roots, a thick waxy coating on the surface and stomata sunk in pits lined with hairs. Many also open their stomata only at night. A large number of stomata would speed up transpiration, which is the opposite of what a dry-land plant needs.

A is wrong: small or spiny leaves reduce the surface that loses water, a typical xerophytic feature.

C is wrong: a thick waxy cuticle stops water escaping from the leaf surface.

D is wrong: sunken stomata in pits trap moist air and slow transpiration.

Exam tip: xerophytes save water (few, sunken stomata); hydrophytes grow in water; halophytes grow in saline soil.

The correct answer is A, Coelenterata, also called Cnidaria, and the phylum takes its name from these cells. Each cnidoblast holds a capsule called a nematocyst with a coiled thread that shoots out and injects a toxin when touched, and it is found in Hydra, the sea anemone, the jellyfish and the corals.

Option B, Echinodermata, defends itself with spines and with pincer-like structures, not with stinging cells. Option C, Mollusca, has a shell and a rasping radula, and in the cone snails a venomous dart, but no cnidoblasts. Option D, Porifera, has spicules that make the body gritty and unpleasant to eat. The presence of cnidoblasts, radial symmetry and a diploblastic body are the three marks of the coelenterates, and the phylum also shows two body forms, the fixed polyp and the free-swimming medusa.

The correct answer is B, measles, a viral disease spread by droplets, which is why it is prevented by vaccination and not treated with antibiotics. Option A is wrong because tuberculosis is caused by the bacterium Mycobacterium tuberculosis, identified by Robert Koch, and is treated with a long course of antibiotics. Option C is wrong because typhoid is caused by the bacterium Salmonella typhi and spreads through contaminated food and water. Option D is wrong because cholera is caused by the bacterium Vibrio cholerae and also spreads through contaminated water. Other viral diseases worth listing together are influenza, the common cold, mumps, chickenpox, smallpox, poliomyelitis, rabies, hepatitis, dengue and the acquired immune deficiency syndrome. The simple test in such a question is whether a vaccine or an antibiotic is the remedy: a vaccine points to a virus and a course of antibiotics to a bacterium.