BMAT 2015-S2

Explanation

The correct answer is E.

The brain does not take part in the autonomic nervous system. The response to touching a hot plate, gives an involuntary and reflex response. The brain is not involved in such responses, as they are unconscious and involuntary. The electrical impulse is passed onto the relay neurone, after the sensory neurone, across a synapse.

Explanation

The correct answer is C.

Alkenes (the presence of a C=C bond) causes bromine water to change colour from orange to colourless. 1) is ethene, an alkene, so would decolourise bromine water. 2) is a polymer, which is formed from many propene monomers joined together to form a saturated compound, so does not contain any C=C bonds and will not decolourise bromine water. 3) is 2-methylprop-1-ene, which is another alkene so will decolourise bromine water. 4) is a haloalkane so will not decolourise bromine water. Therefore only compounds 1 and 3 will decolourise bromine water.

Explanation

The correct answer is B.

Black coated surfaces are the best absorbers and emitters of infrared radiation. In order to keep a person warm in the winter, infrared radiation needs to be prevented from being emitted from the person. White is the worst emitter and absorber of infrared radiation, and so restricts heat lost.

Explanation

The correct answer is B.

The probability of getting a black in the first selection, is 3/8. As the ball is not replaced, the sample size: 7. Hence, the probability of getting a black ball in the second selection is 2/7. The probability of getting 2 black balls, BB, is 3/8 X 2/7 = 6/56 = 3/28.

Explanation

The correct answer is A.

Anaerobic respiration occurs in the absence of oxygen – when insufficient oxygen is available for aerobic respiration to occur.

Hence, glucose is broken down to lactic acid; no carbon dioxide nor water is produced.

Explanation

The correct answer is A.

The energy change for the forward reaction would be the difference from the reactants to the products, which is a. The magnitude of the energy change for the reverse reaction would be the same but the sign would reverse, making the energy change of the reverse reaction -a.

Explanation

The correct answer is D.

P=VI; as the voltage decreases, the current is increased. Hence, as the voltage decreases and the current increases, the power must remain the same.

Explanation

The correct answer is E.

As PQR is an isosceles triangle, we can split the shape into 2 right angled triangles. PQ=PR=6cm is the hypotenuse of both triangles, and QR is split into the base of 4cm each. As Tan θ= Opposite/Adjacent, we already have the adjacent length of 4cm. As we have the hypotenuse too, we can use the Pythagorean Theorem: √(62-42)=√20 = 2√5

Tan θ= Opposite/Adjacent à tan θ = 2√5/4 = √5/2

Explanation

The correct answer is D.

As the offspring of the first breeding experiment are all black, and it is known that Mouse 1 is homozygous, the white mouse has to be homozygous recessive for the white colour to be expressed. The offspring are all heterozygous dominant black, Cc.

First breeding experiment

Second breeding experiment

When Mouse 1 (CC) is bred with Mouse 2 (Cc), the offspring produced are all black as they all have the dominant C. Half (50%) of the offspring are heterozygous dominant (Cc) and 50% are homozygous dominant (CC). Hence, there are 2 genotypes in the population of offspring: homozygous and heterozygous.

Explanation

The correct answer is D.

A Rubidium and chlorine are formed when an aqueous solution of rubidium chloride is electrolysed. – This statement is too vague, as it does not specify whether the electrodes are inert or of a suitable metal. If the metal is Rubidium, Rubidium will form. However, if it’s a metal of higher reactivity, i.e. Francium or Caesium, they will form.

B Rubidium has higher melting and boiling points than sodium. – This is incorrect, as Rubidium has lower melting and boiling points than sodium. This is as, when moving down the group 1 elements, the atomic size increases, leading to the decrease of nuclear force of attraction. This is as, there are more shells shielding the nuclear attraction from the outermost electron, which is lost more easily for delocalisation. Hence, less energy is required to overcome the attraction between the loosely bound electrons and rubidium ions. Hence, the boiling and melting points are low.

C Rubidium reacts more slowly with water than sodium, forming hydrogen gas. – This is incorrect, as rubidium reacts more vigorously, violently and almost instantaneously in water. It does form hydrogen gas; it’s more reactive than sodium.

D Rubidium is stored under oil. – This is correct, as exposure to air causes instantaneous ignition, forming rubidium oxide and oxygen. To prevent this, it is stored under oil, as with most group 1 alkaline metals.

E Rubidium sulfate has the formula RbSO₄ – Rubidium is a group 1 element, hence it has only 1 electron in its outermost shell. When ionised, it forms Rb+ Whereas, the charge on SO₄ is -2: SO₄2-. Hence, the formula is rather: Rb2SO₄

Explanation

The correct answer is A.

Neutrons emitted in nuclear fission can cause further fission, as they can be absorbed by more fission fragments, causing them to split up further. Statement 2 is incorrect – the half-life = the time taken for half of the nuclei to decay. Statement 3 is incorrect – nuclear fusion occurs in the Sun, not nuclear fission.

Explanation

The correct answer is B.

a<c<b

Comparing a and c first: a<c:

3 / 5+X < 3+X / 5+X

This statement is true – as the denominators are the same, only the numerators need to be compared. 3<3+X is always true, as X>0 and the addition of 3 with a whole number greater than 0 is always greater than 3.

Comparing b and c:

3+X / 5+X < 3+X / 5

This statement is also true – as the numerators are the same, only the denominators need to be compared. However, in this case, the smaller the denominator, the greater the value of the fraction (quotient rule: For the same numerator, a larger denominator will give a smaller value). 5+X is always greater than 5, as X>0. Hence, the c<b is true. As c<b is true, a<b is also true.

Explanation

The correct answer is B.

Explanation

The correct answer is C.

A They have the general formula CnH2n+2 – This is incorrect, as although they are alkanes, they are cyclic. Alkanes obey the formula CnH2n+2, whereas cycloalkanes obey CnH2n.

B They react rapidly with bromine water – This is incorrect, as alkenes react with bromine water, through electrophilic substitution, due to being unsaturated compounds, containing a double C=C bond. However, cycloalkanes are saturated compounds, with only single C-C bonds.

C They are saturated compounds – This is correct, as cycloalkanes are saturated compounds, with only single C-C bonds.

D They burn in excess oxygen to form CO2 and H2 – This is partially correct. The combustion of cycloalkanes and alkanes forms CO2 and H2O – not H2.

E They are not members of a homologous series – This is incorrect. All alkenes, alkanes and cycloalkanes are members of a homologous series. This is as, they have almost same chemical properties due to presence of same functional group (CH2). The physical properties (i.e. solubility, melting point, boiling point, state) of members of a homologous series either gradually increases or decrease with increase in molecular mass. This increase in molecular mass is uniform, often an increase in a multiple of CH2.

F They are giant covalent compounds – This is incorrect, as they are simple molecular compounds. They are held together by strong covalent bonds, yet there exist weak intermolecular forces between the molecules.

Explanation

The correct answer is A.

Horizontal acceleration: Resultant force 50N – 40N = 10N

a = F/m 10/2 = 5 ms-²

Vertical acceleration: Resultant force 25N – 20N = 5N UPWARDS

a = F/m 5/2 = 2.5 ms-²

Explanation

The correct answer is E.

Multiply the ratio by the lowest common multiple, to eliminate denominators. The lowest common multiple of 1,3 and 5 is 15.

Hence, 1 : 2/3 : 4/5 

15: 10: 12

Compare this with A:B:3000

The multiplying factor is, 3000/12 = 250

10 X 250 = 2500

15 X 250 = 3750

Hence, 3750: 2500: 3000

Adding them up: 3750 + 2500 + 3000 = 9250

Explanation

The correct answer is H.

Firstly, digestive enzymes are used in Process 2. This is when plants animals eat plants, and so digestive enzymes break down long chains of carbon compounds into their smaller organic forms (fatty acids, glycerol, amino acids, glucose etc), to be assimilated in the body as fat, muscle etc. When animals die, they are decomposed by saprobiotic decomposers, which are microorganisms that release digestive enzymes. These enzymes catalyse the breakdown of organic compounds that have been ingested by the animals, thus releasing carbon containing compounds into the soil. Respiratory enzymes are only used in Process 4, which is respiration. Saprobiotic decomposers respire aerobically as they assimilate the products of digestion, thus releasing carbon dioxide into the atmosphere.

Explanation

The correct answer is C.

A is incorrect as catalysts increase the rate of reaction. B is incorrect as gases react faster than solids. C is correct because it would take longer for more molecules to have energy equal to or greater than a higher activation energy compared to a lower one. D is incorrect as increasing the temperature gives reacting particles more kinetic energy and means more will have at least the activation energy and there will be an increased frequency of successful collisions between particles, so the rate would increase. E is incorrect because there are an equal number of moles of gas in the reactants as in the products, and the same number of moles of any ideal gas occupies the same volume, so there would be no change in gas volume.

Explanation

The correct answer is G.

When a beta particle (electron) is emitted, a neutron turns into a proton, hence the atomic number (proton number) increases, hence W (atomic number of M) + 1 = X (atomic number of X). When an alpha particle is emitted, 2 protons and 2 neutrons are released. Hence, the mass number decreases by 4. (Y = V – 4).

Explanation

The correct answer is D.

 Let X = total score.

Mean Score = Total Score/Number of pupils → m = x/n → mn = x

Inclusion of another pupil’s test score: m-2 =  x+n/n+1

For every X substitute mn= x

m-2 = mn+n/n+1(multiply both sides by (n+1) to get rid of denominator)

(m-2)(n + 1)=mn+n

Expand brackets on Left Hand Side: mn – 2n + m – 2 = mn + n

As we want to express in terms of n, rearrange equation with all ‘n’s on one side:

3n=m-2

Divide both sides by 3: n = m-2/3

Explanation

The correct answer is A.

Statements 1 and 4 are correct. Statement 2 is incorrect, as although aerobic bacteria (prokaryotic cells) would possess a cell wall, human white blood cells do not have a cell wall. Statement 3 is incorrect, as although a human white blood cell would contain a nucleus, prokaryotic cells do not have a nucleus – their DNA is chromosomal, with no true nucleus, commonly circular as a plasmid. Both their DNA are double helixes, and both eukaryotic and prokaryotic cells possess a cell membrane.

Explanation

The correct answer is C.

For this question, you must calculate the electron number of each ion/element given. This can be found on the atomic number. The charges – positive and negative – change the electron numbers from their elements, as these elements have been ionised. If the atom is negatively charged, add 1 electron to the atomic number, and if the atom is positively charged, subtract 1 from the atomic number.

Cl- : 17 + 1 = 18 ; Cl+ : 17 – 1 = 16 ; Ar : 18 ; K+ : 19 – 1 = 18, Ca+: 20 – 1 = 19,

K- : 19 + 1 = 20

Hence, Cl- , Ar and K+ have the same electron arrangement: 18 electrons.

Explanation

The correct answer is D.

Distance traveled in reaction time:

s = vt

s = 20(2(0.7))

s = 28 m

Distance traveled while braking:

s = 1⁄2 (u+v)t

s = [(20 + 0)/2]x3.3

s = 33 m

Hence, Total distance:

d = 38 + 33

d = 61 m

Explanation

The correct answer is D.

Lowest common multiple of all 3 fractions is: (2x− 3)(2x + 3) Hence, rewrite equation, using cross multiplication:

Simplify the numerators:

(2x+3)2= 4x2+ 12x + 9

(2x-3)2 =4x2− 12x + 9

Hence, (2x+3)2+(2x-3)2= 8x2+ 18

2(2x − 3)(2x + 3) = 8x2− 18

8x2 + 18 −(8x2− 18) = 8x2+ 18 −8x2+ 18 = 36

Hence,

Explanation

The correct answer is G.

A fruit fly will be male if X: A = 0.5:1 and female if X: A = 1: 1. Here, the determination of sex is clearly stated by the X:A ratio. Although the Y chromosome contains genes for sperm production, the determination of sex is only controlled by the X:A ratio. The genes for sperm production can be activated or be dormant, depending on the X:A ratio. Hence, the presence of a Y chromosome has no effect on sex determination.

XAA – 1X:2A (1:2 ratio), 0.5:1 = 1:2 hence male

XYAA – 1:2 ratio (no effect of Y) = male

XXAA – 2X:2X (2:2 ratio) = female

XXYAA – 2:2 ratio (no effect of Y) = female

XXYYAA – 2:2 ratio (no effect of 2Y either) = female

Explanation

The correct answer is B.

To answer this question, firstly, work out the moles on the CH₄.

n(CH₄) = m/Mr = 1.6/(12+4)= 0.1

CH₄:2H₂O – ratio of 2:1 (compare these ratios, as the mass of water is unknown)

Hence, moles of water = 2 x 0.1 = 0.2

Mass of water = n x Mr(water) = 0.2 x 18 = 3.6

Form an equation of mass, where (8-x) represents the quantity of reacted oxygen; x = unreacted oxygen

Hence: 1.6 + (8 – x) = 4.4 + 3.6

1.6 + 8 – x = 8

Hence, x = 1.60g.

Explanation

The correct answer is D.

Statement 1 is correct – F = ma 4 x 1.25 = 5

Statement 2 is correct – c= f� ; 5 = 4 x 1.25

Statement 3 is incorrect – V = IR, As 4 NOT EQUAL to 5 x 1.25