BMAT 2014-S2

Explanation

The correct answer is C.

Statement 1 is incorrect – deoxygenated blood flows through the right side of the heart.

Statement 2 is incorrect because blood from the vena cava enters the atrium.

Statement 3 is incorrect because the pulmonary artery is one of the few arteries that carries deoxygenated blood.

Statement 4 is correct because there are valves in the base of the aorta to prevent the backflow of blood into the ventricle, when the ventricle relaxes.

Explanation

The correct answer is B.

Reaction 1 is a redox reaction because there are changes in oxidation states (ionic charges): the oxidation state of copper changes from +2 to 0 (Cu2+ + 2e– → Cu [reduction]), and zinc changes from 0 to +2 (Zn → Zn2+ + 2e– [oxidation]).

Reaction 2 is not a redox reaction because there is no electron transfer (no change in ionic charge, nor oxidation state).

Reaction 3 is a redox reaction because there are changes in oxidation states (ionic charges): the oxidation state of magnesium changes from 0 to +2 (Mg → Mg2+ + 2e– [oxidation]), and hydrogen changes from +1 to 0 (2H+ + 2e– → H2 [reduction]).

Reaction 4 is not a redox reaction because there is no transfer of electrons.

Explanation

The correct answer is D.

Statement 1 is incorrect; microwaves have a longer wavelength than infrared radiation and many other parts of the electromagnetic spectrum.

Statement 2 is incorrect; energy increases with frequency (and consequently decreases with wavelength), and so in fact the shortest wavelengths transfer the most energy.

Statement 3 is incorrect; the wavelength is inversely proportional to frequency, and the speed is the constant for this relationship ( u =  f × λ).

Statement 4 is correct; ultraviolet waves are higher frequency than visible light, so carry more energy and can damage corneas, causing cataracts.

Explanation

The correct answer is B.

Factorise both numerator and denominator.

Numerator: x is the common factor, hence:

x2 − 4x = x (x − 4)

Denominator: Via difference of two squares,x2− 16 = (x + 4) (x − 4)

Cancel both (x − 4) , as they appear in both numerator and denominator:

Explanation

The correct answer is D.

DNA synthesis doubles the DNA content in the cell, so the content will increase from 1 to 2 arbitrary units, which is M. The DNA separates within the cell. However, the total content is still 2, hence this is N or J. The cell divides in half, which halves the DNA content per cell back to 1, which is K.

Explanation

The correct answer is H.

When the temperature of a reaction is increased, the particles gain kinetic energy so they move faster and increase the frequency of collisions. The proportion of successful collisions will also increase because the proportion of particles with energy greater than the activation energy has increased. This is why a small increase in temperature results in a large increase in the rate of a reaction. The activation energy is the minimum energy required by colliding particles to result in a successful collision and, therefore, a chemical change. Activation energy is a measure of the energy required to break chemical bonds and is not affected by temperature. Hence, an increase in temperature will have no effect on the activation energy but it will increase the frequency of collisions as well as the proportion of successful collisions.

Explanation

The correct answer is F.

From power: power (watts) = current (amps) x voltage (volts)

current (amps)=power (watts)/voltage (volts) , so unit (ampere) = watt/volt

Explanation

The correct answer is B.

Express 4 and 8 as powers of 2: 4 =  2²,8²=2³

Hence: 4p x 8q= (2²)p x (2³)q = 2²p x 2³q = 2²p+³q

Hence, n = 2p + 3q

Explanation

The correct answer is D.

Explanation

The correct answer is C.

When balancing this chemical equation, you must have the same number of carbon atoms, hydrogen atoms and oxygen atoms on both the reactant side and the product side of the equation. This is only true for the correct answer, C. ‘a’ can be calculated first. With just one carbon on the right hand side of the equation it can be deduced that a=1. With this knowledge, the remainder of the equation can be balanced and ‘b’ found. For instance, recognising 7 oxygen atoms are present on the left, and therefore 7 oxygen atoms much be present on the right, means that b must be 5.

Explanation

The correct answer is F.

Only electrons are transferred when an object becomes charged. Hence options C, D, G and H are all incorrect. The object becomes negatively charged if it gains electrons and positively charged if it loses electrons. For repulsion to occur, two objects must have like charges, so either rod X gained electrons from the cloth and rod Y was negatively charged (which is not one of the options) or rod X lost electrons to the cloth and rod Y was positively charged, option F.

Explanation

The correct answer is F.

Extend north line down at L and recall that alternate angles between parallel lines are equal, so angle SLT = 90 + x

Because the interior angles of any triangle add up to 180°, LTS + LST = 180 − (90 + x)

LTS + LST = 90 − x.

Triangle SLT is isosceles so both angles LTS and LST = (90−x)/2

Bearing S from T = 270 – ( (90−x)/2) = 270 − 45 + x/2 = 225 + x/2

Explanation

The correct answer is B.

The water content in the blood is detected by the brain, which controls how much ADH is released by the pituitary gland. When the water content is too low, the pituitary gland releases more ADH. This causes an influx in water reabsorption by the kidneys, hence a high volume of water passes into the blood.

Explanation

The correct answer is C.

But-1-ene is an alkene, and alkenes can form addition polymers, so statement 1 is true.

But-1-ene contains 1 C=C (carbon-carbon double bond), so statement 2 is false.

Alkenes have twice as many hydrogen atoms as carbon atoms, so they, and hence but-1-ene, conform to the general formula CnH2n, so statement 3 is true.

Alkenes decolourise bromine water, so statement 4 is true.

But-1-ene contains 1 C=C bond, so is unsaturated, so statement 5 is false.

Therefore, only statements 1, 3 and 4 are true.

Explanation

The correct answer is B.

Cooled water will become more dense and fall, causing a convection current in the container. The cooling unit should be positioned at the top to ensure that all the water is cooled, including the warmer, less dense water at the top. The water starts at room temperature, and will soon become cooler than its surroundings. This means that a dark surface would absorb more infra-red from the surroundings than it would emit. A shiny surface reduces this effect and will help to keep the water cooler than the surroundings.

Explanation

The correct answer is D.

Class 1 contains twice as many students as Class 2 – if there are n students in Class 2, then there are 2n students in Class 1. The total of all of the scores in Class 1 must be 61 × 2n = 122n. The total of all of the scores in Class 2 must be 63n. If there are m students in Class 3, then the total of all the scores in Class 3 must be 70m. The total score of all of the students must be 65 × (2n + n + m), so 195n + 65m = 122n + 63n + 70m. This simplifies to 10n = 5m, so m = 2n. The number of students in Class 3 is 2n, which is the same as the number of students in Class 1.

Explanation

The correct answer is B.

Emulsification is the breakdown of large lipid globules into smaller droplets by the action of bile salts. Each single droplet has a smaller surface area than a single large droplet, but collectively the many more smaller droplets formed have a higher surface area to volume ratio than fewer large droplets. Therefore statement 1 is correct.

Bile is alkalic, but this increases the pH of the material from the stomach rather than decreasing it, therefore statement 2 is incorrect.

Lipase does hydrolyse bonds in lipids to produce glycerol and fatty acids, but lipase is not secreted in bile, it is secreted from the pancreas into pancreatic fluid, which enters the small intestine via the pancreatic duct. So statement 3 is also incorrect.

Hence, the only correct statement is 1.

Explanation

The correct answer is B.

You need to find: the molecular mass, from the mass, volume and mole information, and then dividing this mass over the 3 elements to figure out how many atoms of each are present in the molecule.

Using the molar gas volume given (1 mole = 24dm3 ), we can deduce that 2.4 dm3 of the compound must contain 0.1 moles.

Hence, 0.1 moles of the compound weighs 6g. So, 1 mole of the compound would weigh 60g.

Hence the relative molecular mass must be 60.

The ratio of C : H : O by mass is 6 : 1 : 8; dividing the mass into this ratio gives us the mass of each element in the molecule. C: 6 15 × 60 H: 1 15 × 60 O: 8 15 × 60

The relative masses are: C: 24 H: 4 O: 32 Using the Ar values, we can see this relates to 2 carbons, 4 hydrogens, and 2 oxygens. The molecular formula is C2H4O2.

Explanation

The correct answer is C.

Period= 2s hence, frequency =(1/ 2) = 0.5 Hz u =  f × λ = 0.50 × 1.5 = 0.75cm/s

Explanation

The correct answer is A.

The angle required is XRP. Using the Pythagorean Theorem PR = √2, since PR is a diagonal of square PQRS. Then triangle XPR is a right angled triangle as X is vertically above P, and by Pythagoras XR = √18 = 3√2

Hence, cos(XRP) = PR/XR = √2/(3√2) = 1/3

Explanation

The correct answer is G.

Statement 1 is not true. In the opening paragraph, it is stated that oxygen supply is essential for neurons in the brain to function for more than 5 – 10 seconds. Hence, anaerobic respiration cannot be used for prolonged periods of time.

Statement 2 is true because a by-product of aerobic respiration is heat so as respiration occurs, the body will have to work to counteract the corresponding increase in temperature.

Statement 3 is true – too much insulin will lower body glucose levels and this could prevent sufficient respiration from occurring, resulting in a lack of energy and therefore brain function.

Statement 4 is true because carbon dioxide is produced during aerobic respiration.

Explanation

The correct answer is D.

The graphene description indicates that it has a giant covalent structure. Typically, substances with a giant covalent structure have high melting and boiling points; they do not dissolve in water and they do not conduct electricity. However, the structure of graphene is very similar to that of graphite in that each C atom is covalently bonded to only 3 other C atoms which means that each C atom has a ‘free’ electron. This ‘free’ electron can migrate within the structure, so enabling graphene to conduct electricity. Graphene should have a high melting point and good electrical conductivity but not dissolve in water.

Explanation

The correct answer is E.

The total mass number of the particles before fission is 235 + 1 = 236 (uranium + neutron). As the total mass number is conserved, the total mass number of the particles after fission must also be 236. E) is the only statement in which the products have a total mass of 236 units.

A) has products with a total mass of 235 units.

B) has products with a total mass of 238 units.

C) has products with a total mass of 235 units.

D) has products with a total mass of 237 units.

F) has products with a total mass of 239 units.

Explanation

The correct answer is E.

Hence, 8 + 99 = 107 people test positive, of which 8 have the condition, so the probability that someone has the condition, given that they test positive, is 8/107.

This is only about 7.5%, so the test is quite poor on this population: over 90% of the positive test results are false positives. Tests for rare conditions which are applied indiscriminately will often suffer from this problem, and can lead to costly treatments (physically, financially and emotionally) for many perfectly healthy people.

Explanation

The correct answer is E.

In order to have the condition, the woman must have 2 copies of the recessive allele, as stated in the question. In order to inherit 2 copies, she must have inherited a recessive copy from each of her parents. As neither of them have the disorder, they must be heterozygous, hence A is true. Her parents must have inherited a recessive allele each from their parents (the woman’s grandparents) so they could all be carriers (D), one of each set of grandparents could be a carrier (C) or they may have the condition (B). In order for the woman to develop a condition that requires two copies of the recessive allele, however, the DNA mutation in one gamete is not sufficient. DNA in the gametes from both parents would have had to mutate if neither of them possessed the recessive allele to start with. Therefore E cannot be true.

Explanation

The correct answer is E.

The number of electrons is equal to the number of protons for a neutral atom. For a negative ion, add on the magnitude of the ion’s charge to the proton number to calculate the number of electrons it has, and for a positive ion subtract the magnitude of the charge of the ion from the proton number of the element. O has 8 electrons, S has 16 electrons, Cl has 17 electrons, Cl- has 17+1=18 electrons and Ca2+ has 20-2=18 electrons. Therefore only Cl- (4) and Ca2+ (5) have 18 electrons.

Explanation

The correct answer is D.

Power output in this question is about the change in potential energy (mgh) per unit time. The mass and gravitational field strength are constant, so the change in potential energy with time is directly related to the change in height with time. In the graph we can see that the change in height with time (the gradient) is constant from 15s to 35s (which includes the time at which it is at the height of 10 m). Hence, we can use this as the time interval from which to calculate the power and energy change. The change in height is 10 m (15–5m) in this interval of 20s. This relates to a change in potential energy of 2000 J (mgh = 20×10×10) in the interval. The power output is given by change in potential energy, divided by the time interval: 2000/20 = 100W.