SEE Model Paper 5

The ampere (A).

Because every egg and every sperm is genetically different: in meiosis, crossing over swaps pieces between the chromosomes of each pair, and the pairs line up by chance. So each sister came from a different egg and a different sperm, with a different mix of the parents’ genes. (Their surroundings, such as food, also shape them.)

Hemoglobin in the red blood cells carries oxygen: it joins with oxygen in the lungs (forming oxyhemoglobin) and gives it up to the cells of the body.

The air resistance on the big canopy grows with her speed until it equals her weight. The two forces then balance, the net force is zero, so there is no acceleration and she falls at a steady speed, the terminal velocity.

$$Q = ms(T_2 - T_1) = 0.8 \times 385 \times (70 - 20) = 15{,}400\ \text{J}$$

Because of the anomalous expansion of water: water is densest at 4 °C, so the water at 4 °C sinks to the bottom, while the colder water and the ice, which are lighter, stay on top. The lake freezes from the top down, and the ice keeps the heat in, so the water below stays liquid, near 4 °C at the bottom, where the fish live.

The faster wheel spins the dynamo’s magnet faster, so the magnetic flux through its coil changes faster. By Faraday’s law the induced e.m.f. depends on the rate of change of flux, so a larger e.m.f. and current are induced, and the lamp glows brighter.

Its gravity squeezes it inwards, while the heat released by the nuclear fusion of hydrogen into helium in its core pushes outwards. The two balance each other, so the star stays the same size and shines steadily.

Silver is an unreactive metal, so its oxide is unstable and heat alone breaks it up (2Ag₂O → 4Ag + O₂). Zinc is more reactive and holds oxygen tightly, so a reducing agent, carbon, is needed to take the oxygen away (ZnO + C → Zn + CO).

• i.Argument 2. Only the length (the independent variable) should change, so that any change in the time of a swing is caused by the length alone; everything else, the mass of the bob included, is kept the same, so it is a controlled variable. Argument 1 is wrong: the dependent variable is what she measures, not what she keeps the same.
• ii.The time of one swing (the time period): it is what she measures, and it depends on the length she chooses.

• i.A QR code is a picture of binary data: each small black or white square stands for one bit (1 or 0), and the pattern spells out the shop’s account details for the payment app to read.
• ii.Advantage, any one: she needn’t carry cash; the money goes straight to the shop’s account in seconds; she can also pay bills or book tickets the same way.

Care, any one: keep her PIN or password secret; check the amount and the shop’s name before she confirms; don’t scan codes sent by strangers, as digital payment can be misused for fraud (cybercrime).

i. The places, from the right, are worth 1, 2, 4, 8, 16, 32. 45 = 32 + 8 + 4 + 1, so
45 = (1 × 32) + (0 × 16) + (1 × 8) + (1 × 4) + (0 × 2) + (1 × 1) = 101101.
ii. No. Five bits make only 2⁵ = 32 patterns, the numbers 0 to 31 (11111). 45 is more than 31, so it needs a sixth bit, worth 32.

• i.She builds the comb and seals the cells of the larvae and of the honey. Her four pairs of wax glands, under her abdomen, develop at about this age (days 12 to 17) and make the wax.
• ii.The ages at which workers do each job are not fixed. When the colony suddenly lacks foragers, young workers start flying out to forage earlier than usual, so food is collected again.

• i.Artificial insemination. Semen is collected from a bull of an improved breed (in Nepal, frozen semen from the National Livestock Breeding Centre is carried to the villages in liquid nitrogen), and a trained technician places it with instruments into the cow’s reproductive tract at the right time, when she is ready to conceive.
• ii.No. The offspring of artificial insemination are as normal and healthy as those of natural mating, since the calf comes from an ordinary sperm and egg. Advantage, any one: there is no need to keep an expensive bull; the semen of one excellent bull can be used for many cows; the semen is tested, so the bull’s fertility is checked; it stops diseases that spread during mating; stored semen can be used even after the bull has died.

The upper chambers are the right and left auricles (atria); the lower, thicker-walled chambers are the right and left ventricles, the left ventricle having the thickest wall. The valves, the vena cavae, the pulmonary artery and veins and the aorta may also be labeled.

• i.Veins carry blood back towards the heart. The band presses the thin-walled veins near the skin shut, so the blood coming up from the hand can’t pass it and collects in the veins below, which swell. (The arteries lie deeper and their high pressure keeps pushing blood into the arm.)
• ii.By the time blood reaches the veins it has lost most of its pressure, so it flows slowly and could slip backwards, especially uphill from the legs; the valves let it flow only towards the heart. In arteries the high pressure from the ventricles keeps the blood moving forward, so no valves are needed.

Any two:

• a.Loss of habitat, as forests, grasslands and wetlands are cleared for farms, roads and towns (the biggest cause).
• b.Overuse: taking plants and animals from the wild faster than they can grow back (including poaching and smuggling).
• c.Weather and climate change, which shift where they can live.
• d.Invasive plants, such as banmara and mikania, crowding out the native plants.
• e.New animals reared without research, which push out the native animals or bring them diseases.
• f.Pollution of the air, water and soil.

i. M = 3.30 × 10²³ kg, R = 2,440 km = 2.44 × 10⁶ m
$$g = \frac{GM}{R^2} = \frac{6.67 \times 10^{-11} \times 3.30 \times 10^{23}}{(2.44 \times 10^{6})^2} = \frac{2.20 \times 10^{13}}{5.95 \times 10^{12}} \approx 3.70\ \text{m/s}^2$$
ii. $W = mg = 60 \times 3.70 = 222\ \text{N}$

No. Sand has a specific heat capacity of about 800 J/kg °C, about five times less than water’s (4,200 J/kg °C), so in the sunshine the land heats up much faster than the sea. The air over the hot land warms, expands, becomes lighter and rises, and cooler air from over the sea flows in to take its place. So in the daytime the wind blows from the sea to the land (a sea breeze). Only at night, when the land has cooled faster than the sea, does a land breeze blow out to sea.

i. Light enters the top prism square on through one short face, without bending; it meets the long face at 45°, is totally reflected and turns through 90°, down the tube. The bottom prism turns it through 90° again, level, into the eye.

ii. Inside the prism, the light travels from glass (denser) towards air (rarer) and meets the long face at 45°, which is greater than the critical angle of glass, 42°. Both conditions for total internal reflection are met.

• i.The split-ring commutator reverses the current in the coil every half turn, so that the forces on its sides reverse at the right moment and the coil keeps turning the same way, instead of rocking to and fro.
• ii.The brushes (usually of carbon) press against the split rings and carry the current from the battery into the coil while it turns.

• i.X (sulphur): 1s², 2s² 2p⁶, 3s² 3p⁴. It has six electrons in its outer shell and needs two more to fill it, so its valency is 2.
• ii.Sodium gives one electron (valency 1) and X takes two, so two sodium atoms join one atom of X: Na₂X (Na₂S, sodium sulphide).

• i.Argument 2. Light gives the hydrogen peroxide molecules energy to break apart, so in sunlight it decomposes faster; a dark bottle keeps the light out and the reaction slow. Argument 1 is wrong: the glass takes no part in the reaction, and a catalyst would speed it up, not slow it down.
• ii.$2\text{H}_2\text{O}_2 \xrightarrow{\text{light}} 2\text{H}_2\text{O} + \text{O}_2$

Characteristics of Pisces, any two:

• a.The body is streamlined and covered with scales, and divided into head, trunk and tail, with no neck.
• b.They breathe through gills, covered by an operculum.
• c.They swim with paired and unpaired fins.
• d.Most have a swim bladder (air sac), which lets them float at any depth.
• e.The heart has two chambers.
• f.They are poikilothermic (cold-blooded), and most are oviparous with external fertilization.

• i.The TTRR parent gives only TR gametes and the ttrr parent only tr, so every F₁ plant is TtRr: tall with round seeds.
• ii.TR, Tr, tR and tr, in equal numbers.

iii.

Tall round (at least one T and one R): 9; tall wrinkled (T with rr): 3; dwarf round (tt with R): 3; dwarf wrinkled (ttrr): 1.
Phenotypic ratio = 9 : 3 : 3 : 1.
iv. Tall wrinkled is 3 out of every 16: $\tfrac{3}{16} \times 800 = 150$ plants. Tall wrinkled and dwarf round are new combinations that neither parent had; they are explained by the law of independent assortment: the alleles of one gene go into the gametes independently of the alleles of the other.

i.

ii. A₁ = 1.5 cm² = 1.5 × 10⁻⁴ m², F₁ = 60 N
$$P = \frac{F_1}{A_1} = \frac{60}{1.5 \times 10^{-4}} = 400{,}000\ \text{Pa}$$
iii. By Pascal’s law the same pressure acts on the caliper piston, A₂ = 6 cm² = 6 × 10⁻⁴ m²:
$$F_2 = P \times A_2 = 400{,}000 \times 6 \times 10^{-4} = 240\ \text{N}$$
iv. No. By Pascal’s law, a pressure applied to a liquid in a closed container is transmitted equally in all directions, throughout the liquid. The same pressure reaches the brake at every wheel at the same moment, however long its pipe; each brake’s force depends only on the area of its own piston.

• i.Long-sightedness (hypermetropia). Causes: the eyeball is too short, so the retina is too close to the lens; or the eye lens cannot become thick enough (its focal length stays too long).
• ii.Without glasses, light from a near object (25 cm away) would be focused behind the retina, so the image is blurred. A convex lens bends the light from 25 cm as if it came from his own near point, farther away, and the eye focuses it on the retina.

iii. $f = \dfrac{1}{P} = \dfrac{1}{+2.5\ \text{D}} = +0.4\ \text{m} = +40\ \text{cm}$: a convex (converging) lens.

i. Sunlight, mostly short waves (visible light), passes through the air and warms the ground; the warm ground gives out long waves (infrared); greenhouse gases (carbon dioxide, water vapor, methane …) absorb much of the infrared and send part of it back down, so the ground is warmed twice.

• ii.Argument 1. With greenhouse gases the Earth’s average temperature is about 15 °C; without them it would be about −18 °C, with frozen oceans and no life as we know it. Argument 2 is wrong: greenhouse gases absorb infrared from the ground; it is the ozone layer that absorbs the Sun’s ultraviolet rays.
• iii.Any two: use less petrol, diesel and coal; use renewable energy (hydroelectricity, solar, wind), such as electric vehicles and induction stoves in Nepal; plant trees and protect forests; stop using CFCs; walk, cycle or use public transport.

i. X is methane, CH₄, also called marsh gas. Its structural formula: one carbon atom joined to four hydrogen atoms by single bonds.
$$\begin{array}{c} \text{H} \\ | \\ \text{H}-\text{C}-\text{H} \\ | \\ \text{H} \end{array}$$

• ii.$\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} + \text{heat}$
• iii.Butane and propane. Butane turns into a liquid easily when it is squeezed (its boiling point is about 0 °C), so a lot of it fits in a cylinder. Methane cannot be liquefied by pressure alone at room temperature, so natural gas is sold as compressed gas (CNG).
• iv.A small amount of a strong-smelling sulphur compound (ethyl mercaptan) is added on purpose, so that a leak is noticed. A switch can make a spark inside it, which could set the leaked gas on fire or make it explode.

• i.The caterpillars are killed by an internal (stomach) pesticide, which kills pests that eat leaves or fruits carrying the poison; the aphids by a systemic pesticide, absorbed by the roots or leaves and carried through the plant in its sap.
• ii.Argument 2. The pesticide is inside the plant, in its sap, not only on its surface, so washing cannot remove it; the farmer must wait for the waiting period on the label before harvesting. Argument 1 describes a contact pesticide, not a systemic one.
• iii.With moisture, aluminium phosphide gives off phosphine, a poisonous gas that kills people as well as insects and rats, and there is no antidote. It must only be used by trained people, in sealed stores away from where anyone lives or sleeps.
• iv.Any one: spray neem leaves or neem oil, or a jholmal of cow urine and bitter leaves; put up yellow sticky traps; let ladybirds, which eat aphids, live in the field; rotate or mix crops and grow resistant varieties; remove and burn badly affected plants.