General Science Mixed Quiz: Set 47

The correct answer is C, the small intestine. At roughly six to seven metres it is by far the longest part of the nine-metre alimentary canal, it is where digestion is completed by pancreatic and intestinal juices, and its inner wall carries millions of finger-like villi that give a vast surface for absorbing glucose, amino acids, fatty acids and glycerol into the blood. Option A is wrong because the stomach is only a muscular bag about twenty-five centimetres long, and it absorbs almost nothing besides water, alcohol and some medicines. Option B is wrong because the oesophagus is a plain conducting tube about twenty-five centimetres long that only pushes food down by peristalsis. Option D is wrong because the large intestine, though wider, is much shorter and mainly absorbs water and salts from the undigested residue.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is B, the spleen. A red blood cell lives about one hundred and twenty days. As it ages its membrane grows stiff, and the narrow winding channels of the spleen trap such cells so that the macrophages lining them can break the cells down and salvage the iron of their haemoglobin. Because so many worn out red cells are destroyed there, the spleen is called the graveyard of red blood cells; it is also the largest lymphoid organ of the body and acts as a blood reservoir. Option A is wrong because the liver, although it does handle the bilirubin left from broken haemoglobin and turns it into bile pigment, is not the place where the cells are trapped and destroyed. Option C is wrong because the red bone marrow is the opposite: it is the birthplace of red blood cells, not their graveyard. Option D is wrong because the pancreas makes digestive juice and the hormones insulin and glucagon and has no role with red cells at all.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is B, Stoichiometry. Stoichiometry is the branch of chemistry that measures how much of each reactant is used up and how much of each product is formed in a reaction, working from the balanced chemical equation. The coefficients of a balanced equation give the ratio in moles, and from that ratio a chemist can work out masses, volumes of gases and numbers of particles, identify the limiting reagent and calculate the percentage yield. The word comes from the Greek stoicheion, meaning element, and metron, meaning measure. Option A is wrong because mole fraction is the ratio of the moles of one component to the total moles in a mixture, a way of stating concentration. Option C is wrong because mass per cent gives the mass of a component present in 100 units of mass of the solution. Option D is wrong because molarity is the number of moles of solute dissolved in one litre of solution. Exam tip: stoichiometry works from the balanced equation, while mole fraction, molarity and mass per cent only express concentration.

The correct answer is C, Avogadro. The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811. It says that equal volumes of all gases at the same temperature and pressure hold the same number of molecules, so the volume of a gas is directly proportional to the number of moles in it. This is why one mole of any gas occupies 22.4 litres at standard temperature and pressure, and why the number of particles in one mole, about 6.022 x 10 to the power 23, is named the Avogadro number after him. A is wrong because Charles law links the volume of a fixed mass of gas to its temperature at constant pressure. B is wrong because Boyle's law says that volume varies inversely with pressure at constant temperature. D is wrong because Gay-Lussac gave the law of combining volumes and the pressure-temperature law. Exam tip: Avogadro ties volume to the number of molecules, Boyle to pressure and Charles to temperature.

The correct answer is B. The gastric glands secrete hydrochloric acid, which makes the contents of the stomach strongly acidic; pepsin can work only in such a medium, and the acid also kills most of the bacteria swallowed along with food. The same glands secrete a layer of mucus that protects the stomach wall from being digested by this acid, and damage to that layer produces a peptic ulcer. Option A is wrong because no acid digests fat; fat is emulsified by bile and then split by lipase. Option C is wrong because the absorption of vitamins happens mainly in the small intestine, not through the action of stomach acid. Option D is wrong because emulsification is the work of the bile salts made in the liver, and bile in fact neutralises this acid when the food reaches the duodenum.

The correct answer is C, Stomata. Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them. Each stoma is bounded by two bean-shaped guard cells that swell to open the pore and shrink to close it, and this is how the plant controls its water loss. Most stomata lie on the lower surface of a leaf, so less water is lost to direct sunlight. Transpiration also happens largely through these pores. A is wrong because the cell membrane controls what enters and leaves a single cell, not the gas exchange of the whole plant. B is wrong because the nucleus carries the genetic material and directs the activities of the cell. D is wrong because guard cells only open and close the pore, while the exchange itself happens through the stomatal opening. Exam tip: stomata do the gas exchange and transpiration, guard cells only open and close them.

The correct answer is B, the liver. When the body breaks down more protein than it needs, the amino acids are stripped of their amino group and the ammonia so released is highly poisonous. The liver converts this ammonia into urea, a far less toxic compound, through a series of reactions known as the urea cycle or the ornithine cycle. The urea then travels in the blood to the kidney, which only filters it out and concentrates it in the urine. Option A is wrong for exactly that reason: the kidney removes urea but does not make it, and this separation of the site of manufacture from the site of removal is what the question tests. Option C is wrong because the urinary bladder is only a muscular sac that stores urine until it is passed out. Option D is wrong because the spleen destroys worn out red blood cells and stores blood. Because human beings pass out mainly urea they are described as ureotelic animals, unlike ammonotelic bony fishes and uricotelic birds and reptiles.

The correct answer is B, In the same direction. In a class 3 lever the fulcrum is at one end, the effort is applied in the middle and the load sits at the far end. Since both the effort and the load lie on the same side of the fulcrum, the beam turns one way and they move in the same direction. The effort arm is shorter than the load arm, so the mechanical advantage is less than one and more effort is needed than the load; what such a lever gains is speed and a wider sweep of movement. The human forearm, a pair of sugar tongs, a fishing rod and a stapler work this way. A is wrong because effort and load move oppositely in a class 1 lever, where the fulcrum lies between them, as in a see-saw or scissors. C is wrong because a lever turns about a fixed point and its two ends never move at right angles to each other. D is wrong because the size of the load changes the force needed, not the direction of motion. Exam tip: class 1 has the fulcrum in the middle, class 2 the load, class 3 the effort.

The correct answer is C, 6. The balanced equation for the complete combustion of glucose is C6H12O6 plus 6O2 gives 6CO2 plus 6H2O, so one mole of glucose needs six moles of oxygen gas. Balancing it is quick: glucose has six carbon atoms, so six molecules of carbon dioxide are formed, and its twelve hydrogen atoms give six molecules of water. That calls for eighteen oxygen atoms on the right, and since glucose itself supplies six, the remaining twelve must come from oxygen gas, which is six molecules of O2. The same reaction runs in our cells as aerobic respiration and releases about 2870 kilojoules of energy per mole of glucose. Option A is wrong because one mole of oxygen could not even oxidise the carbon present. Option B is wrong because three moles would leave the reaction half complete, giving carbon monoxide instead. Option D is wrong because twelve moles counts oxygen atoms, not molecules. Exam tip: for glucose the carbon dioxide, water and oxygen coefficients are all 6.

The correct answer is C, 2 s. A simple pendulum about one metre long completes one full swing in roughly two seconds, and a pendulum of this length is called the seconds pendulum. The time period of a simple pendulum is T = 2 pi times the square root of L divided by g, where L is the length of the thread and g is the acceleration due to gravity, about 9.8 metres per second squared. Putting L = 1 metre gives T = 2 x 3.14 x the square root of 1 divided by 9.8, which comes to about 2.01 seconds. The period depends only on the length and on g, not on the mass of the bob or on how far it is pulled aside, so long as the swing is small. A is wrong because a 6 second period needs a thread about 9 metres long. B is wrong because a 4 second period needs a thread about 4 metres long. D is wrong because a 1 second period belongs to a thread of only about 25 centimetres. Exam tip: the period doubles only when the length becomes four times.

The correct answer is B, three. The right lung is divided into three lobes, an upper, a middle and a lower, while the left lung has only two, because the heart is tilted towards the left side of the chest and takes up room there; the left lung even carries a notch called the cardiac notch for the heart. Option A is wrong because two is the number of lobes in the left lung, and it is offered here precisely as the trap for a student who remembers the pair but not which side is which. Option C is wrong because no human lung has four lobes. Option D is wrong because a single undivided lung is not the human arrangement at all. Remember the rule that the right lung is the bigger of the two, with three lobes, and the left the smaller, with two.

The correct answer is D, Neon. When electricity is passed through a sealed tube holding neon at low pressure, the gas atoms are excited and give out a bright orange-red glow, which is why advertising signs are still called neon signs. Neon is a noble gas discovered in 1898 by Ramsay and Travers; it is chemically inert, forms no ordinary compounds, and is also used in voltage testers, high-voltage indicators and lightning arresters. Every gas glows in its own colour in a discharge tube, and that colour is the fingerprint of its atomic energy levels. Option A is wrong because helium gives a pale pinkish-white glow and is better known for filling balloons and airships. Option B is wrong because argon glows a pale violet-blue and is used to fill electric bulbs and to shield welding. Option C is wrong because nitrogen glows bluish, and its common uses are as an inert packing gas and as a liquid coolant. Exam tip: neon gives red light in a discharge tube, while argon is the gas that fills ordinary electric bulbs.

The correct answer is B, the proximal convoluted tubule. Filtration at the glomerulus is blind: it pushes out useful glucose and amino acids along with the waste. The tubule that immediately follows the Bowman's capsule, the proximal convoluted tubule, has a brush border of microvilli that gives it an enormous surface, and it takes back practically all the glucose and amino acids and about seventy to eighty per cent of the water and salts. Option A is wrong because the Bowman's capsule is the site of ultrafiltration, where the filtrate is formed rather than reabsorbed. Option C is wrong because the loop of Henle does something different: by its counter-current arrangement it builds a salt gradient in the medulla so that concentrated urine can be produced, and it reabsorbs water and sodium, not glucose. Option D is wrong because the collecting duct carries out the last adjustment of water under the influence of antidiuretic hormone. Note the clinical link: glucose appears in the urine only when the blood sugar exceeds what the proximal tubule can carry back.

The correct answer is B, are long chain molecules held together by secondary bonds. In a thermoplastic the polymer exists as long linear or lightly branched chains, and one chain is held to the next only by weak secondary forces such as van der Waals attraction. Heat gives enough energy to loosen those weak links, so the material softens, can be moulded into a new shape and hardens again on cooling, and the cycle can be repeated, which is why thermoplastic waste is recyclable. Polyethylene, polypropylene, PVC, polystyrene and nylon all belong to this group. A is wrong because a three-dimensional network of strong primary bonds describes a thermosetting plastic such as bakelite, which sets once and cannot be remoulded. C is wrong because the ability to deform plastically rises with temperature instead of falling. D is wrong because the secondary bonds do break as thermal energy rises, and that is exactly why the plastic softens. Exam tip: thermoplastic means weak secondary bonds and remoulding, thermosetting means cross-linked primary bonds and a shape set for good.

The correct answer is B, the diaphragm. It is a dome-shaped sheet of muscle that separates the chest cavity from the abdomen, and when it contracts it flattens, which increases the volume of the chest, lowers the pressure inside the lungs and draws air in; the intercostal muscles between the ribs assist by lifting the rib cage up and out. Option A is wrong because cardiac muscle is found only in the wall of the heart and its job is to pump blood, not air. Option C is wrong because the biceps is a skeletal muscle of the arm and has no role in respiration. Option D is wrong because the smooth muscle of the stomach churns food and has nothing to do with the breathing movement. A sudden involuntary spasm of the diaphragm is what we experience as hiccups.

The correct answer is B, antidiuretic hormone. Antidiuretic hormone, also called vasopressin, is released by the posterior lobe of the pituitary gland and makes the distal tubule and the collecting duct of the nephron pull water back into the blood. If it is lacking, that water is not recovered and the patient passes litres of very dilute urine and is constantly thirsty, which is the disease diabetes insipidus. Option A is wrong because a shortage of insulin causes diabetes mellitus, an entirely different disorder in which blood glucose rises and sugar spills into the urine; sharing the word diabetes is the trap here. Option C is wrong because aldosterone, from the adrenal cortex, controls the reabsorption of sodium and the excretion of potassium, and its lack disturbs salt balance rather than causing floods of dilute urine. Option D is wrong because thyroxine from the thyroid gland regulates the rate of metabolism, and its deficiency causes cretinism in children and myxoedema in adults. Remember that insipidus means tasteless and mellitus means honey sweet.

The correct answer is B, as bicarbonate ions. Most of the carbon dioxide produced by the tissues enters the red blood cells, where the enzyme carbonic anhydrase combines it with water to form carbonic acid, which at once splits into hydrogen and bicarbonate ions; the bicarbonate then travels in the plasma to the lungs, where the reaction is reversed and the gas is breathed out. A smaller share is carried bound to haemoglobin as carbaminohaemoglobin and a little stays dissolved. Option A is wrong because oxyhaemoglobin is the form in which oxygen, not carbon dioxide, is carried. Option C is wrong because free bubbles of gas in the blood would cause an embolism and are dangerous, not the normal mode of transport. Option D is wrong because carbon monoxide is a poison from incomplete burning that blocks haemoglobin, and the body does not make it for transport.

The correct answer is B, the bicuspid valve. The opening between the left atrium and the left ventricle is guarded by a valve with two flaps or cusps, which is why it is called the bicuspid valve; it is also known as the mitral valve because its shape resembles a bishop's mitre. Its job is to stop blood from being pushed back into the atrium when the powerful left ventricle contracts. Option A is wrong because the tricuspid valve, with three cusps, sits on the other side of the heart, between the right atrium and the right ventricle; swapping the two sides is the commonest error in this question. Option C is wrong because the pulmonary semilunar valve stands at the mouth of the pulmonary artery, where blood leaves the right ventricle for the lungs. Option D is wrong because the aortic semilunar valve stands at the mouth of the aorta, where blood leaves the left ventricle, that is after the bicuspid valve and not between the chambers. A useful memory aid is that the left side has two cusps and the left lung has two lobes.