BLE Model Paper 7

OCR (optical character recognition) software recognizes the letters in a scanned picture of a page and turns them into text that can be edited and searched.

At the low temperature of a refrigerator (about 4 °C), most microorganisms become inactive: they grow very slowly or not at all, so the food doesn’t spoil quickly.

The number and kinds of species living in a particular place; for example, the many kinds of trees in Chitwan’s forest.

A first-class lever: the fulcrum (the screw joining the blades) is between the effort (the fingers in the handles) and the load (the paper or cloth between the blades).

A hand pump only lowers the pressure inside the pipe; it is the atmospheric pressure on the water in the well that pushes the water up. The air can push water up only about 10 m, so it can’t lift it 15 m.

The Moon has no air. Sound is a mechanical wave and needs a medium to travel, so it can’t cross the empty space between them; radio waves are electromagnetic waves, which can travel through a vacuum.

Period 3 means 3 shells, and group 2 means 2 valence electrons, so its electrons are 2, 8, 2: atomic number 12 (magnesium).

Bronze (kansa), an alloy of copper and tin. The bronze used for bells, with a lot of tin in it, is called bell metal.

• i.A fume cupboard (fume hood) has a fan that sucks the fumes away and out of the building, so nobody in the lab breathes them in.
• ii.Traces of chemicals and microbes stay on the hands after the work, and could get into the mouth and eyes; soap and water wash them off.

X: Fungi. It has a cell wall but no chlorophyll, its body is made of threads (hyphae), and it absorbs its food from dead matter (a saprophyte).
Y: Protista. It is a single cell with a proper nucleus, a unicellular eukaryote (it is like Paramecium).

No, I don’t agree.

• a.The air and the oceans are shared by the whole world, so damage to the environment in one place affects the whole Earth, Nepal included: climate change brings it more floods, landslides, droughts and forest fires and harms its biodiversity. The goals can be reached only with the support of every country.
• b.A small country’s efforts do work. Since community forestry began, more than 22,000 user groups have come to manage about a third of Nepal’s forests, and forest and shrubland grew from about 40% of the country in the mid-1990s to about 45% by 2015, which helps Goal 15, Life on land.

i. The tongs are a third-class lever (the effort is between the hinge and the load). By the principle of the lever,
$$E \times \text{E.D.} = L \times \text{L.D.} \quad\Rightarrow\quad E = \frac{2 \times 0.3}{0.1} = 6\ \text{N}$$
ii. $$\text{MA} = \frac{L}{E} = \frac{2\ \text{N}}{6\ \text{N}} \approx 0.33$$
The MA is less than 1: tongs need more effort than the load, but they keep her hand far from the fire.

• i.The larger the vibrating surface, the more air it pushes, so the more intense the sound. A big bell has a much larger vibrating area than a small one.
• ii.As the sound travels out from the bell, its energy spreads over a larger and larger area, so less of it passes through each square meter: the intensity falls with the distance from the source.

• i.The man speaking (120 Hz) and the sarangi (440 Hz): a healthy human ear hears frequencies from about 20 Hz to 20,000 Hz (20 kHz). The elephant’s rumble is below that range and the bat’s call above it.
• ii.The elephant’s rumble (below 20 Hz) is infrasound; the bat’s call (above 20 kHz) is ultrasound.

• i.Citric acid in lemon juice is a weak organic acid: it gives only a few hydrogen ions in water. Sulphuric acid is a strong mineral acid: almost all of it splits up and gives many hydrogen ions, so it burns the skin.
• ii.Caustic soda is a strong base. It reacts with grease and oils, turning them into a kind of soap, and dissolves grease and hair, which clears the blocked drain.

• i.The Paleozoic, Mesozoic and Cenozoic eras (“old life”, “middle life” and “new life”).
• ii.The Mesozoic era, when forests of conifers and other gymnosperms (cycas, pines, ginkgo) replaced the fern forests.

• i.The longer he used the phone after 9 p.m., the later he fell asleep and the more tired he was the next day; on the days without the phone he slept early and felt fresh.
• ii.Screens give out a lot of blue light, which holds back the body’s making of melatonin, the hormone that makes us feel sleepy at night as part of our body clock. So sleep comes late.
• iii.Any one: health problems such as depression, anxiety and insomnia; fake accounts; leaks of private information (a photo showing a home address); targeted phishing; cyberbullying.
• iv.Any one: set a time limit in the phone’s settings; turn off notifications he doesn’t need; keep the phone out of the bedroom at night; stop using screens about an hour before sleeping; decide before opening an app what he wants to do on it.

• i.Binary fission (transverse binary fission: the cell splits across).
• ii.Multiple fission: the cell divides into many pieces at once, while in binary fission it splits into only two.
• iii.Fragmentation: the body breaks into pieces, and each piece grows into a new plant.
• iv.They are sori. Each sorus is a cluster of sporangia full of spores, which drift away and grow into new plants: sporulation.

• i.In parallel: each lamp is on its own branch between the live and the neutral wire, with its own switch, so each gets the full 230 V and works on its own.
• ii.The blown fuse breaks only the neutral side. With S1 on, the lamp holder is still joined to the live wire at about 230 V, so a person touching it is a path for the current from the live wire, through the body, to the ground.
• iii.Different colors (live red or brown, neutral black or blue, earth green or green and yellow) make it easy to see which wire is which, so the fuse and the switches can be put in the live wire, and a damaged wire found quickly. (Colors can be wrong in old wiring, so an electrician still checks with a tester.)
• iv.An MCB (miniature circuit breaker), an automatic switch that is just switched back on after the fault is fixed. Like a fuse, it must be connected in the live wire, so that when it trips, the whole circuit is cut off from the live supply.

• i.Atomic weight = number of protons + number of neutrons. A: 11 + 12 = 23 amu; C: 13 + 14 = 27 amu.
• ii.B has 8 electrons: 2, 6. With 6 valence electrons it gains 2 to make 8, so its valency is 2 (8 − 6). (B is oxygen.)
• iii.C has 13 electrons, 2, 8, 3, so its valency is 3 (C is aluminium). By the criss-cross method, C’s valency 3 goes to B and B’s valency 2 goes to C: C₂B₃, that is Al₂O₃ (aluminium oxide).
• iv.Molecular weight of Al₂O₃ = 2 × 27 + 3 × 16 = 54 + 48 = 102 amu.