SEE Model Paper 2

1 KB = 1024 bytes, so 3 KB = 3 × 1024 = 3072 bytes.

Before the cell divides, the DNA of every chromosome is copied, and each daughter cell then gets one exact copy of every chromosome. So both have the same number of chromosomes and the same genes as the parent cell.

About 120/80 mmHg: a systolic pressure of about 120 mmHg and a diastolic pressure of about 80 mmHg.

Water expands as it cools below 4 °C, and expands by about 9% more when it freezes. The ice needs more space than the bottle has, and it pushes on the glass hard enough to crack it.

From Q = ms(T₂ − T₁):
$$s = \frac{Q}{m(T_2 - T_1)} = \frac{18{,}000}{2 \times (30 - 20)} = 900\ \text{J/kg °C}$$

About 25 cm from the eye: the nearest point at which the eye can see clearly (the least distance of distinct vision).

Nothing would bend its path any more, so the Earth would stop going round the Sun and move off in a straight line, in the direction it was moving at that moment (along a tangent to its orbit), into space.

Carbon dioxide does not burn and does not help things burn, and it is heavier than air. It settles over the fire like a blanket and keeps the oxygen away, so the fire goes out.

Silver and gold are less reactive than copper, so they do not go into the solution as ions. As the impure copper anode wears away, they fall to the bottom below the anode as anode mud, from which these valuable metals can be collected.

• i.An analog signal carries the sound as the shape of a wave that can take any value. Noise from lightning, other waves and the atmosphere changes that shape on the way, and the receiver can’t tell the added noise from the sound, so it plays the hiss and crackle too.
• ii.A digital signal carries only 0s and 1s. The receiver only has to decide “is this a 0 or a 1?”, so a little noise doesn’t change the answer, and the data is recreated exactly.

Any two:

• a.A pollen basket on each hind leg, ringed with stiff hairs, to carry pollen home.
• b.Hairy legs and body that catch pollen.
• c.Wax glands under the abdomen, to make wax for the comb.
• d.A long proboscis to suck nectar, and mandibles to shape wax.
• e.A barbed sting to guard the hive.

• i.Tt. A dwarf offspring (tt) needs a t from each parent. The dwarf parent gives only t, so the tall plant must have given the other t. A TT plant gives only T, and all its offspring would have been tall.
• ii.Tt × tt: the tall plant’s gametes are T and t; the dwarf plant’s are all t.

The offspring are 1 tall (Tt) : 1 dwarf (tt), about half of each, as he found.

• i.Every individual has its own DNA (except identical twins), and every cell of an animal carries the same DNA. So if the DNA from the horn matches the DNA from the dead rhino’s body, the horn came from that rhino; if it doesn’t match, it came from another.
• ii.A DNA test is very sensitive: cells from his skin could contaminate the sample and give a wrong answer. He should have handled it with clean gloves, and sealed and labeled it carefully for the laboratory.

A woman’s body cells are 44 + XX, so every egg she makes is 22 + X. A man’s body cells are 44 + XY, so he makes two kinds of sperm in equal numbers: 22 + X and 22 + Y.
An X sperm and the egg give 44 + XX, a daughter; a Y sperm and the egg give 44 + XY, a son. Every egg carries an X, so which kind of sperm fertilizes it decides the baby’s sex.

• i.Clumping with anti-A shows antigen A, and with anti-D the Rh factor; no clumping with anti-B shows there is no antigen B. Her blood group is A+ve (A positive).
• ii.No. AB+ve red cells carry antigen B, which her own cells lack. The anti-B antibodies in her plasma would clump and destroy them (a transfusion reaction).

• i.Most likely a heart attack: a coronary artery has been blocked, and part of the heart muscle is getting no blood. An ambulance should be called at once (102 in Nepal), or he should be taken quickly to a hospital, sitting and resting, not walking.
• ii.Any two: smoking (stop smoking); fried food, rich in fat (eat more vegetables, fruit, whole grains and pulses, and less fried food, salt and sugar); high blood pressure for years (have it checked and treated regularly); sitting all day as a driver (exercise for at least 30 minutes on most days).

Any two:

• a.Neem juice and paste are used for skin problems.
• b.Neem twigs are used as toothbrushes (datiun).
• c.Neem leaves are kept with stored grain and clothes to keep insects away.
• d.Neem oil is used as a natural pesticide.
• e.Its leaves, root, bark, flowers and fruit are used in Ayurvedic medicines.

• i.$\dfrac{C}{100} = \dfrac{F - 32}{180} = \dfrac{104 - 32}{180} = \dfrac{72}{180}$, so $C = 0.4 \times 100 = 40\ °\text{C}$: a high fever.
• ii.$K = C + 273 = 40 + 273 = 313\ \text{K}$

• i.No. The eye gets red light only from drops at about 42° from the line from the Sun through the head, so the rainbow is a circle centered on the point directly opposite the Sun. At noon in June the Sun is very high, much more than 42° above the horizon, so that circle lies wholly below the horizon. A rainbow is seen only when the Sun is low: in the morning or the late afternoon.
• ii.Each color leaves the drops at its own angle to the sunlight: red at about 42° and violet, which bends most, at about 40°. So red reaches the eye from drops on a bigger circle, and violet from a slightly smaller circle inside it.

• i.$\mu = \dfrac{c}{v} = \dfrac{3 \times 10^8}{2.25 \times 10^8} = 1.33$
• ii.$v = \dfrac{c}{\mu} = \dfrac{3 \times 10^8}{1.6} = 1.875 \times 10^8\ \text{m/s}$

• i.Potassium (39.1) would come before argon (39.9). Potassium, a very reactive metal, would then fall among the noble gases, and argon, an unreactive gas, among the alkali metals: each would sit in a group whose properties it doesn’t share.
• ii.The modern periodic law arranges the elements by atomic number, not atomic weight. Argon (18) comes before potassium (19), so argon falls in group 0 with the noble gases and potassium in group IA with the alkali metals, where their properties belong.

• i.Ammonia is very soluble in water: the first few drops dissolve so much of it that the pressure inside the flask falls far below the air pressure outside. The air pressing on the water in the beaker pushes the water up the tube.
• ii.The ammonia dissolves to make ammonium hydroxide, an alkali (a base), and phenolphthalein turns pink in a base.

First-class (from natural sources, used in the amount needed): vinegar and sugar.
Second-class (chemicals made in factories, used only in small amounts set by law): sulphur dioxide and potassium nitrate.

• i.Unit of W = kg × m s⁻² × m = kg m² s⁻² (the joule).
• ii.Unit of pressure = unit of force ÷ unit of area = kg m s⁻² ÷ m² = kg m⁻¹ s⁻² (the pascal).
• iii.1 N = 1 kg m s⁻², so N/kg = kg m s⁻² ÷ kg = m s⁻², the unit of acceleration.
• iv.Density is measured in kg m⁻³, but m × V would be in kg × m³ = kg m³. The two sides have different units, so the formula is wrong. (The correct one is ρ = m/V.)

• i.P belongs to Bryophyta (it is a moss) and Q to Pteridophyta (it is a fern).
• ii.R is a gymnosperm and S an angiosperm. A gymnosperm’s seeds are naked (on the cone scales, with no fruit); an angiosperm’s seeds are enclosed in a fruit.
• iii.Q has true roots, and with them true stems and leaves with vascular tissue (xylem and phloem); P has only rhizoids and no vascular tissue.
• iv.A monocot: its leaves have parallel veins (it also has fibrous roots, and its flower parts are in threes).

• i.$g = \dfrac{v - u}{t} = \dfrac{29.4 - 0}{3} = 9.8\ \text{m/s}^2$
• ii.$g_{\text{Mars}} = \dfrac{11.1 - 0}{3} = 3.7\ \text{m/s}^2$, a little over a third of the Earth’s.
• iii.$h = ut + \tfrac{1}{2}gt^2 = 0 + \tfrac{1}{2} \times 9.8 \times 3^2 = 44.1\ \text{m}$. (The area under line A gives the same: $\tfrac{1}{2} \times 3 \times 29.4 = 44.1$ m.)
• iv.$W = mg = 2 \times 3.7 = 7.4\ \text{N}$. (Its mass is still 2 kg; only its weight changes.)

• i.By Pascal’s law, $\dfrac{F_1}{A_1} = \dfrac{F_2}{A_2}$, so $F_1 = F_2 \times \dfrac{A_1}{A_2} = 30{,}000 \times \dfrac{4}{600} = 200\ \text{N}$.
• ii.The lifting piston has 600 ÷ 4 = 150 times the area, so the oil pushed out by the small piston raises it only 1/150 as far. To raise it 2 cm, the small piston must go down 150 × 2 = 300 cm (3 m) in all, stroke after stroke. The jack multiplies force, not energy.
• iii.No. Air can be compressed: pushing the piston would only squeeze the air, and very little of the push would reach the lifting piston. Oil can’t be compressed, so it passes on the pressure fully.
• iv.Any one: the release valve is open, so the oil flows back into the reservoir; the oil has leaked out or the reservoir is empty; air has got into the jack.

• i.End A. By Maxwell’s right-hand grip rule: hold the coil in the right hand with the fingers curling the way the current goes round the turns (up the front of each turn), and the thumb points to the north pole, at A.
• ii.The pins fall off. The magnetism of soft iron is temporary: when the current stops, the coil makes no field and the nail loses its magnetism.
• iii.Any two: increase the current (use two or more cells); wind more turns of wire round the nail; use a thicker soft iron core.

• i.$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$. It is a single displacement reaction: magnesium, above hydrogen in the reactivity series, displaces hydrogen from the acid.
• ii.A rise in temperature makes the reaction faster: 10 °C more halved the time. Hotter particles move faster, so they collide more often, and many more of the collisions have enough energy (the activation energy) to react.
• iii.The acid in R is more concentrated: there are more acid particles in the same volume, so they collide with the magnesium more often.
• iv.About 30 s. In P and Q, a rise of 10 °C halved the time (doubled the rate), so another 10 °C should halve it again: 60 ÷ 2 = 30 s.

• i.A homologous series is a series of organic compounds that can be written with the same general formula, in which each member differs from the next by a –CH₂– group (for example, the alkanes CH₄, C₂H₆, C₃H₈…).
• ii.Any two:
• a.They have the same general formula (CₙH₂ₙ₊₂ for the alkanes).
• b.Neighboring members differ by CH₂, and by 14 in molecular mass.
• c.They have the same functional group, so they have similar chemical properties.
• d.Their physical properties change gradually: the bigger the molecule, the higher the boiling point.
• iii.Methyl alcohol: any one, such as making methylated spirit, as a solvent for paints and varnishes, or making formaldehyde. Ethyl alcohol: any one, such as sterilizing skin and wounds (hand sanitizers), preserving biological specimens, in red thermometers, or as a fuel in spirit lamps.