Grade 9 Final Exam Model Paper 1

Every single reading has a small error (from reaction time, the eye or the instrument). Some readings are a little too high and some too low, so their average is closer to the true value than any one reading.

A body at rest stays at rest, and a moving body keeps moving in a straight line with uniform velocity, unless an unbalanced (external) force acts on it.

$\lambda = \dfrac{v}{f} = \dfrac{3 \times 10^8}{96 \times 10^6} = 3.125\ \text{m}$

Nichrome has a high resistance, so a current heats it strongly, and a high melting point, so it glows red-hot without melting; it also doesn’t oxidize (burn away) in air when hot.

The TV satellite is geostationary: it goes round once in the time the Earth takes to turn once, in the same direction, above the equator, so it stays above the same place and seems still in the sky.

He should not send the OTP (or any PIN or password) to anyone: it is a trick to get into his bank or wallet account. He should ignore or delete the message, and may report it.

Manganese dioxide (MnO₂).

Gold is a very unreactive metal (near the bottom of the reactivity series): it does not react with the oxygen and water around it, so it keeps its shine. Iron is more reactive and slowly reacts with oxygen and water to form rust.

Compost adds humus to the soil, which holds water and air, keeps the soil loose and feeds useful microbes, and it gives its nutrients slowly over a long time, while chemical fertilizer only adds a few nutrients quickly and, used alone for years, harms the soil.

0.0000075 m: move the point 6 places right to get 7.5; the number is less than 1, so the power is −6: 7.5 × 10⁻⁶ m.
384,000,000 m: move the point 8 places left to get 3.84; the power is +8: 3.84 × 10⁸ m.

Any two:

• a.They have no chlorophyll, so they can’t make their own food (heterotrophic).
• b.Most are saprophytic: they absorb food from dead and decaying matter; some are parasites.
• c.Their cell wall is made of chitin.
• d.The body of most is made of thread-like hyphae, forming a mycelium (yeast is unicellular).
• e.They store food as glycogen and reproduce mainly by spores.

No, she is not right.

• a.Insects and other animals eat mushrooms that are poisonous to people, so insect bites prove nothing.
• b.The silver spoon test is a myth: deadly mushrooms do not blacken silver, and cooking does not destroy the most dangerous mushroom poisons. Only an expert or a laboratory test can tell; she should eat only farmed or expertly identified mushrooms.

• a.Fossils are the remains or marks of living things of long ago, preserved in sedimentary rocks. In the deeper (older) layers there are fossils of simpler organisms, and in the upper (newer) layers more complex ones, which shows that complex living things came later from simpler ones.
• b.Some fossils show a mixture of features of two groups (such as Archaeopteryx, part reptile, part bird), and some, such as the ammonites found as shaligram, are of organisms that no longer exist: living things have changed over time.

The intercalary meristem. It is a meristematic tissue at the base of the internodes (near the nodes) in grasses, and its cells keep dividing, so the stem grows again in length from below even after its top has been cut off.

When the jumper lands, her body must be brought to rest. On hard ground she stops in a very short time, so her retardation is very large, and by $F = ma$ the force on her body is very large, which hurts. The soft mattress sinks under her and makes her stop over a longer time, so her retardation, and so the force on her (F = ma), is much smaller, and she is not hurt.

The pulse goes down and comes back, so it travels twice the depth:
$d = \dfrac{v \times t}{2} = \dfrac{1500 \times 2.4}{2} = 1800\ \text{m}$

Any two:

• a.Open the site by typing the bank’s address himself (or use the bank’s official app), never from a link in an SMS, email or social media message.
• b.Check that the address is exactly the bank’s own, spelled correctly, and that it starts with https and shows a padlock (connection is secure).
• c.Do it on his own device, not a shared computer, and sign out afterwards.

Symbols: Ca, Cl; valencies 2 and 1. Criss-crossing the valencies gives Ca₁Cl₂, that is CaCl₂.
Molecular mass = 40 + 2 × 35.5 = 40 + 71 = 111 amu.

No. The match only starts the reaction. Once the wood is burning, it gives out much more heat and light than it took in, and keeps burning by itself, so burning is an exothermic reaction. In an endothermic reaction, heat must be taken in all the time (as when limestone is decomposed by heating), and the reaction stops when the heating stops.

The gas is nitrogen. It neither burns nor supports burning, so the splint goes out; carbon dioxide would do the same, but it would turn lime water milky, so the gas is not carbon dioxide. Burning magnesium reacts with nitrogen to form magnesium nitride, the yellowish powder: 3Mg + N₂ → Mg₃N₂.

• i.Insulin: the pancreas (its islets of Langerhans). Thyroxine: the thyroid gland. Adrenaline: the adrenal glands.
• ii.It works as both kinds of gland: it sends digestive juice through a duct to the intestine (exocrine), and releases the hormones insulin and glucagon straight into the blood (endocrine).

• i.Any one: rice plant → rat → snake → eagle; rice plant → grasshopper → frog → snake (or rice → grasshopper → frog → snake → eagle, five links, also shows it).
• ii.The rats will increase, because their predator is gone, and they will eat more rice, so the harvest will fall. (The frogs will increase too, and the grasshoppers then fall.)
• iii.At each step of a food chain only about 10% of the energy passes on to the next level; the rest is used for life processes or lost as heat. The eagle is at the end of the chain, so it gets the smallest share.
• iv.Let the snakes (and owls and eagles) live, since they keep the rats in check for free, and keep rats down in other ways, such as clearing their hiding places and storing grain safely, rather than with poison. This keeps the food web balanced, while rat poison also kills the animals that eat the poisoned rats and can harm people.

• i.Any two: biogas burns with a clean blue flame and gives no smoke, so the kitchen stays clean and the family’s eyes and lungs are protected; it saves the time and work of collecting firewood and saves the forest; it uses dung that is otherwise wasted and is renewable; it is cheap once the plant is built; the spent slurry is a good fertilizer.
• ii.Put it in the compost pit and use it as manure in the fields, because it is an excellent fertilizer that returns nutrients to the soil.
• iii.Biogas is made by bacteria that break down the dung in the absence of oxygen; if air got in, they would not make the gas (and the gas would escape).

i.

• i.In series: $R = R_1 + R_2 = 4 + 6 = 10\ \Omega$. Current $I = \dfrac{V}{R} = \dfrac{12}{10} = 1.2\ \text{A}$.
• ii.In parallel: $\dfrac{1}{R} = \dfrac{1}{4} + \dfrac{1}{6} = \dfrac{3 + 2}{12} = \dfrac{5}{12}$, so $R = \dfrac{12}{5} = 2.4\ \Omega$. Current $I = \dfrac{12}{2.4} = 5\ \text{A}$ (3 A through the 4 Ω and 2 A through the 6 Ω).

• i.A magnesium atom has two valence electrons and gives both to an oxygen atom. Magnesium becomes Mg²⁺ (2, 8: an octet) and oxygen becomes O²⁻ (2, 8: an octet). The oppositely charged ions attract each other strongly, and this electrostatic attraction is the electrovalent bond in MgO.
• ii.Oxygen (2, 6) needs two more electrons for an octet, and each hydrogen atom (1) needs one more for a duplet. The oxygen atom shares one pair of electrons with each of two hydrogen atoms: two single covalent bonds (H–O–H). Then oxygen has an octet and each hydrogen a duplet.

• i.20% of 50 kg = $\dfrac{20}{100} \times 50 = 10\ \text{kg}$ of nitrogen.
• ii.$40 \div 10 = 4$ bags.
• iii.Nitrogen (the plant moves its scarce nitrogen to the young leaves, so the older leaves turn yellow first).
• iv.Potassium.