SEE Model Paper 8

The mole (mol), one of the seven fundamental units.

A karyotype is a picture of all the chromosomes of one cell, sorted into pairs by size (for a human, 22 pairs of autosomes and the pair of sex chromosomes).

Because the number of chromosomes is halved: a diploid mother cell (2n) gives four haploid daughter cells (n), each with one chromosome of every pair.

The Moon’s gravity pulls the near side of the ocean more strongly than the Earth’s center, and the Earth’s center more strongly than the far side, so the oceans bulge on both sides of the Earth. As the Earth turns once a day, a coast passes through both bulges: two high tides.

$$Q = ms(T_1 - T_2) = 2 \times 4200 \times (80 - 30) = 420{,}000\ \text{J}$$
It gives out 420,000 J (420 kJ).

$$\mu = \frac{\text{speed of light in air}}{\text{speed of light in alcohol}} = \frac{3.00 \times 10^8}{2.21 \times 10^8} \approx 1.36$$
It has no unit.

A current flowing in a wire makes a magnetic field around it (the magnetic effect of current, found by Oersted), and this field turns the compass needle.

Gravity pulls everything towards the center of the Earth, not towards a fixed direction in space. At each pole the Earth’s center is below the thrower’s feet, so each ball falls back to the ground.

Dissolved sugar is still sugar (the water can be dried off to get it back): no new substance is formed. Charred sugar has become new substances, black carbon and water vapor, and can’t be turned back into sugar.

Unit of momentum = unit of mass × unit of velocity = kg × m s⁻¹ = kg m s⁻¹.
Unit of force × time = N × s = (kg m s⁻²) × s = kg m s⁻¹.
Both are kg m s⁻¹, so they have the same unit.

Any two:

Any two:

• i.Both parents are Rr (hybrid round). A wrinkled seed is rr, so it got an r from each parent; and both parents are round, so each also has an R.
• ii.Each parent gives gametes R and r:

Round : wrinkled = 3 : 1, as found: 90 round and 30 wrinkled out of 120.

• i.Her red blood cell count is below normal: she has anemia. Red cells carry oxygen with their hemoglobin, so with too few of them less oxygen reaches her cells, and she tires and gets out of breath easily. (Her white cells and platelets are normal.)
• ii.The most common cause is too little iron in the food: iron is part of hemoglobin, the part that grabs oxygen. The doctor is likely to advise her to eat more iron-rich food (or take iron tablets).

• i.White snow and ice reflect most of the sunlight falling on them (the Earth as a whole reflects about 30 % back to space). When they melt, the darker rock and ground below absorb more sunlight, which warms them more and melts still more ice.
• ii.He is wrong. Satellites have measured the Sun since 1978, and it has not got brighter, so it can’t explain today’s warming. The warming comes mainly from the greenhouse gases released by human activities (burning fossil fuels, cutting forests).

From $h = ut + \tfrac{1}{2}gt^2$ with u = 0, $t = \sqrt{\dfrac{2h}{g}}$.

• i.$t = \sqrt{\dfrac{2 \times 20}{9.8}} = \sqrt{4.08} \approx 2.0\ \text{s}$
• ii.$t = \sqrt{\dfrac{2 \times 20}{1.62}} = \sqrt{24.7} \approx 5.0\ \text{s}$

On the Moon it falls for about two and a half times as long, because g there is about six times smaller.

Any two:

• i.P is convex. With the print closer than its focus (between F₁ and O), a convex lens forms a virtual, upright, magnified image. Q is concave: wherever the object is, a concave lens forms a virtual, upright, diminished image.
• ii.Q, the concave lens. Its small, upright image takes in a wide view, so the whole doorstep can be seen through the small hole.

• i.The powers of thin lenses put together add: P = +4 D + (−1.5 D) = +2.5 D. It is positive, so the pair acts as a converging (convex) lens.
• ii.$f = \dfrac{1}{P} = \dfrac{1}{+2.5\ \text{D}} = +0.4\ \text{m} = 40\ \text{cm}$

• i.Across the period the number of valence electrons rises from 1 to 8. Elements with 1 to 4 valence electrons give (or share) that many, so the valency rises 1, 2, 3, 4. Elements with 5 to 7 take (or share) the number still needed to make eight, 8 − 5 = 3, then 2, then 1. Argon has a full octet and needs none: 0.
• ii.Down a group, each element has one more shell, but the number of valence electrons stays the same, and valency is set by the valence electrons.

(Any other correct examples, such as Zn + H₂SO₄ → ZnSO₄ + H₂ and NaCl + AgNO₃ → AgCl↓ + NaNO₃.)

• i.Ammonia turns damp red litmus blue: it dissolves in the water on the paper to make an alkali (it is the only common basic gas). Carbon dioxide turns damp blue litmus red: it dissolves to make a weak acid, carbonic acid.
• ii.Ammonia is lighter than air, so it would rise out of a jar with its mouth up; carbon dioxide is about 1.5 times heavier than air, so it stays at the bottom of an upright jar.

• i.A mineral is any natural, inorganic solid with a fixed formula found in the Earth’s crust; an ore is a mineral from which a metal can be extracted in large amounts, easily and at low cost. All ores are minerals, but not all minerals are ores. Iron pyrite is not used because of its sulphur, which makes getting good iron from it hard and costly.
• ii.Molecular mass of Fe₂O₃ = 2 × 56 + 3 × 16 = 112 + 48 = 160.

$$\%\ \text{of iron} = \frac{112}{160} \times 100\% = 70\%$$

• i.P: as radio waves through the air, from a tall transmitter to an antenna on the roof. Q: down from a satellite far above the Earth, to a dish on the roof. R: a modulated signal.
• ii.Dish TV. The signal comes down from a satellite, so it needs no cable, and it reaches even remote places where antenna signals are weak (the waves spread out, lose energy and are blocked by hills) and cables can’t reach.
• iii.Our eyes and ears can’t use 0s and 1s: the signal must become the analog signals that make light on the screen and sound in the speaker.
• iv.A digital copy is made of 0s and 1s, and each 0 stays a 0 and each 1 stays a 1, so every copy is exactly the same, bit for bit. An analog (cassette) copy adds a little noise (hiss) each time, and the noise builds up.

• i.P: Porifera (a sponge: pores, fixed, no tissues). Q: Coelenterata (tentacles with stinging cells round the only opening, radial symmetry). R: Platyhelminthes (a flatworm: flat, a sucker round the mouth, no anus). S: Nemathelminthes (a roundworm: long, round, pointed ends, a complete gut).
• ii.P → Q → R → S. Any one reason: P and Q have two germ layers, R and S three (a third layer makes complex organs possible); P has no gut at all, Q and R a gut with one opening, and S a complete gut with a mouth and an anus, so different parts of the tube can do different jobs.
• iii.Hookworm. Its larvae live in damp soil and burrow straight through the skin of bare feet. In the intestine it bites the wall and sucks blood, which causes anemia. (Wearing shoes prevents it.)

i.

• ii.His sister (O−ve). A donor’s red cells must carry no antigen that the patient’s own cells lack. O−ve cells carry none of A, B or D. His mother’s cells carry A and D, his father’s D (Rh positive; an Rh-negative patient should get Rh-negative blood), and his uncle’s A.
• iii.His plasma has anti-A antibodies. They would stick to his mother’s red cells, which carry antigen A, glue them into clumps (agglutination) and destroy them; the clumps can block small vessels and the kidneys. This transfusion reaction can kill, which is why blood is cross-matched before it is given.

• i.Upthrust = real weight − apparent weight: in water 5.0 − 3.0 = 2.0 N; in kerosene 5.0 − 3.4 = 1.6 N; in salt water 5.0 − 2.6 = 2.4 N.
• ii.By Archimedes’ principle the upthrust equals the weight of the liquid displaced. The same volume of a denser liquid weighs more, so the upthrust is directly proportional to the density of the liquid: largest in salt water, least in kerosene.
• iii.$\text{relative density} = \dfrac{W_1}{W_1 - W_2} = \dfrac{5.0}{5.0 - 3.0} = 2.5$ (no unit).
• iv.The stone displaces the same volume of kerosene as of water, so the ratio of the upthrusts is the ratio of the densities:

$$\text{relative density of kerosene} = \frac{\text{upthrust in kerosene}}{\text{upthrust in water}} = \frac{1.6}{2.0} = 0.8$$

i. Any two:

• ii.The e.m.f. is largest when the plane of the coil is parallel to the field lines (its sides cut the lines fastest), and zero when the plane is perpendicular to them (its sides move along the lines, not across them).
• iii.To keep turning the same way, the current in a motor’s coil must reverse every half turn. In a d.c. motor the commutator and brushes do this; in an a.c. motor the a.c. supply reverses the current by itself, 100 times a second, so no commutator is needed.

i. Any two:

ii. Ethene, C₂H₄: two carbon atoms joined by a double bond, each also holding two hydrogen atoms (H₂C=CH₂). Ethyne, C₂H₂: two carbon atoms joined by a triple bond, each holding one hydrogen atom (H–C≡C–H).

iii. General formula CₙH₂ₙ. With n = 3: C₃H₆ (propene, CH₂=CH–CH₃).

• i.Cauliflower (20 %): below 35 %, so it is safe and may be sold. Tomatoes (41 %): between 35 % and 45 %, so they must wait a few days before they are sold. Beans (62 %): above 45 %, so the load is destroyed.
• ii.The commonest insecticides (organophosphates and carbamates) kill insects by blocking this enzyme. So the more insecticide a vegetable’s juice carries, the more of the enzyme it blocks.
• iii.A biodegradable (non-persistent) pesticide, such as malathion or dimethoate, is broken down into harmless compounds in a fairly short time, by microbes and helped by water, air, light and heat; a persistent one, such as DDT, stays in the environment and food chains for years. So in a few days the biodegradable residue on the tomatoes breaks down and falls below the safe limit (waiting would not help with a persistent pesticide, which is why they are banned in Nepal).
• iv.Without protection he takes the poison into his body through his skin and lungs. He should wear protective clothing covering the whole body, gloves, a mask over the nose and mouth, and goggles, and wash and bathe right after spraying.