SEE Model Paper 1

Because the newton is made by combining fundamental units: 1 N = 1 kg × 1 m/s² = 1 kg m s⁻².

Echinodermata (for example, the starfish).

23: 22 autosomes and one sex chromosome (X or Y), half the 46 of a body cell.

$$\text{relative density} = \frac{W_1}{W_1 - W_2} = \frac{6}{6 - 4} = 3$$
It has no unit: the stone is 3 times as dense as water.

Because of refraction: light from the part under water bends away from the normal as it passes from water into air, so that part looks raised, and the pencil looks bent where it enters the water.

$$\frac{N_p}{N_s} = \frac{V_p}{V_s} \quad\Rightarrow\quad N_s = \frac{N_p \times V_s}{V_p} = \frac{2000 \times 11}{220} = 100$$
The secondary coil has 100 turns.

Gravity will win: the expansion will slow down, stop and turn into a collapse, ending in a Big Crunch (a closed universe).

Gold is very unreactive, so it does not combine with oxygen, sulphur or other elements to form compounds.

They are unsaturated: they have carbon–carbon double bonds, which open up and add hydrogen (hydrogenation), turning the liquid oil into a solid fat.

• i.The time the sugar takes to dissolve: it is what she measures, and it depends on the temperature she chooses.
• ii.Any one: the mass of sugar (5 g), the volume of water (100 mL), the kind and grain size of the sugar, or the way she stirs.

Any two:

• a.They have jointed legs.
• b.The body is covered by a hard exoskeleton made of chitin.
• c.The body is segmented, bilaterally symmetrical and triploblastic.
• d.The body is divided into head, thorax and abdomen (or cephalothorax and abdomen), with compound eyes and antennae on the head.

• i.A drone develops from an unfertilized egg. An egg developing into a new animal without being fertilized is called parthenogenesis.
• ii.The queen can no longer fertilize her eggs: the sperm she stored in her spermatheca when she mated has run out (or she never mated). Only drones can hatch, so no new workers replace the old ones as they die. With no workers to collect food, feed the larvae and guard the hive, the colony will die out, unless the beekeeper gives it a new, mated queen.

The hybrid (Yy) gives two kinds of gametes, Y and y; the green plant (yy) gives only y.

Yellow : green = 2 : 2 = 1 : 1.

Arteries carry the blood pushed out by the ventricles at high pressure; thick, elastic walls stand the pressure and stretch with each beat.
Capillaries are where substances (oxygen, food, carbon dioxide and wastes) pass between the blood and the cells; a wall one cell thick lets them pass through easily.

• i.Between 2000 and 2005, from 612 to 409. The most likely reason is poaching for their horns, which rose during the years of armed conflict, when the parks were less well guarded.
• ii.Any one: patrols by the army and park staff against poachers; strict punishment for poaching and for trading in horns; involving the local people of the buffer zones in protecting them; protecting the grasslands and forests where they live; moving some rhinos to other parks (Bardiya, Shuklaphanta) to start new groups.

• i.120 kg. Mass is the amount of matter in it, which doesn’t change from place to place.
• ii.$W = mg = 120 \times 1.62 = 194.4\ \text{N}$

Yes. On the surface, $g = \dfrac{GM}{R^2}$: g is inversely proportional to the square of the radius. With half the radius,
$$g' = \frac{GM}{(R/2)^2} = 4 \times \frac{GM}{R^2} = 4g$$
The person’s mass stays the same, so the weight, W = mg, also becomes four times as much.

• i.$f = \dfrac{1}{P} = \dfrac{1}{-2.5\ \text{D}} = -0.4\ \text{m} = -40\ \text{cm}$ (the minus sign: a diverging lens).
• ii.Short-sightedness (myopia): she sees near things clearly but not far ones. It is corrected with a concave lens, which is why the power is negative.

A transformer works by electromagnetic induction: an e.m.f. is induced in the secondary coil only while the magnetic flux through it changes. Alternating current keeps changing in size and direction, so the flux it makes in the core keeps changing and induces an e.m.f. in the secondary. A direct current is steady, so its flux doesn’t change, and no e.m.f. is induced in the secondary.

• i.It jumps the opposite way, into the gap. Reversing the current reverses the force on the wire (the motor effect).
• ii.It jumps out of the gap again, as at first. Reversing the current reverses the force, and reversing the field reverses it once more, so it points the original way.

Fine dust has a very large surface area for its mass, so far more flour particles are in contact with the oxygen of the air than in a sack, where only the outside of the heap touches the air. With so much more surface, collisions between flour and oxygen particles happen far more often, and the burning is so fast that it becomes an explosion.

General formula: CₙH₂ₙ₊₂. The alkane with four carbon atoms is butane, C₄H₁₀ (2 × 4 + 2 = 10).

• i.He sold them the day after spraying, without waiting for the waiting period on the pesticide’s label. Poison left on the cauliflowers can harm the people who eat them.
• ii.Washing the sprayer in the stream put the insecticide into the water, and it poisoned the fish. He should have cleaned the sprayer away from any river, well or pond.

• i.Any one: respect others; protect other people’s privacy (he posted her photo without asking); use polite, decent language, not jokes that hurt; think before you post.
• ii.Yes. Anything posted online is permanent: others may already have saved it, taken a screenshot or shared it, and deleting his post doesn’t remove those copies.
• iii.It is short and made of his name and a year, which are easy to guess, and the same password for every account means that one stolen password opens all of them. A long password of random words, different for each account, is much safer.
• iv.Any one, with its reason: keep screen-free times, especially the hour before sleep, and put the phone away at night (late screen use causes sleeplessness, tired eyes and stress); set a daily limit in the phone’s settings; spend time on games, exercise and family instead (screen time crowds out physical and social health).

i. The father’s body cells are 44 + XY, and by meiosis he makes two kinds of sperm in equal numbers: 22 + X and 22 + Y. The mother’s cells are 44 + XX, and every egg she makes is 22 + X.

• ii.No. Every egg carries an X chromosome, so the mother cannot decide the child’s sex. It depends on whether the sperm that fertilizes the egg carries an X or a Y, which is a matter of chance; not even the father can choose it.
• iii.1 in 2 (50%). Each child is decided afresh, like a new toss of a coin, so the three daughters before make no difference.

• i.Right auricle → (tricuspid valve) → right ventricle → (pulmonary valve) → pulmonary artery → lungs, where the blood gives up carbon dioxide and takes in oxygen → pulmonary veins → left auricle → (bicuspid valve) → left ventricle → (aortic valve) → aorta.
• ii.In one complete round of the body, the blood passes through the heart twice: once through the right side, which sends it to the lungs (pulmonary circulation), and once through the left side, which sends it to the rest of the body (systemic circulation).

• i.A (water). Both took in the same heat in the same time, but A’s temperature rose by only 20 °C (20 °C to 40 °C), while B’s rose by 40 °C.
• ii.$Q = ms(T_2 - T_1) = 0.5 \times 4200 \times (40 - 20) = 42{,}000\ \text{J}$
• iii.$s = \dfrac{Q}{m(T_2 - T_1)} = \dfrac{42000}{0.5 \times (60 - 20)} = \dfrac{42000}{20} = 2{,}100\ \text{J/kg °C}$
• iv.Water (A). For each degree it cools, water gives out twice as much heat as B, so a bag of water gives out more heat and stays warm for longer.

• i.Between F₁ and 2F₁: more than 10 cm but less than 20 cm from the lens.
• ii.A ray from the top of the flame parallel to the principal axis passes, after the lens, through F₂; a ray through the optical center O goes straight on. They meet beyond 2F₂, where the image forms.

iii. It is real (it forms on the screen) and inverted; it is also magnified, and lies beyond 2F₂.

• i.X (magnesium): 1s², 2s² 2p⁶, 3s².
• ii.Y (chlorine) is 1s², 2s² 2p⁶, 3s² 3p⁵: seven electrons in the outer shell, the third shell. So it is in group VIIA (17), period 3.
• iii.X gives away two electrons (valency 2) and Y takes one (valency 1), so the formula is XY₂ (MgCl₂).
• iv.The element with atomic number 20 (calcium, 1s², 2s² 2p⁶, 3s² 3p⁶, 4s²). It is in the same group as X (IIA) but one period lower, so its atom is bigger: its two outer electrons are farther from the nucleus and are lost more easily.

Marble (or limestone) pieces in a Woulfe’s bottle react with dilute hydrochloric acid poured down the thistle funnel, whose end dips into the acid. The gas leaves by the delivery tube, whose end inside the bottle is above the acid, and collects at the bottom of an upright gas jar by upward displacement of air (it is heavier than air).
$$\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$$
Test: bubbled through lime water, carbon dioxide turns it milky.