BLE Model Paper 3

A search engine is a software system that searches the information on the internet and shows the web pages most useful for the keywords typed, for example Google (or Bing, Yahoo!, DuckDuckGo).

Because when a cell is old or badly damaged, its lysosomes burst, and their strong digestive enzymes digest the cell itself.

Development that meets the needs of the present without compromising the ability of future generations to meet their own needs: it takes care of the economic, social and environmental sides of a project, so that it lasts.

By the wind. The cotton adds a lot of surface but almost no weight, so the seeds float in the air and the wind carries them far.

Cross-pollination: the stigma can’t receive the flower’s own pollen, which is already gone, so it must get pollen from another flower, usually of another plant, carried by an agent such as insects or the wind.

Yes. The rays reflected from a convex mirror always spread out, so they never really meet; they only seem to come from a point behind the mirror. So the image is always virtual (and erect and diminished), and a virtual image can’t be caught on a screen.

At each step one proton is added to the nucleus as well as one electron, but the new electron goes into the same shell. The nucleus, with more and more positive charge, pulls the electrons of that shell more strongly, closer in.

22-carat gold. It is an alloy of gold with a little copper and silver, which is much harder and stronger than pure (24-carat) gold, so the bangle keeps its shape. Pure gold is soft and would bend and scratch.

• i.Hot glass looks exactly like cold glass. Put straight on the table, it can burn the table, crack, or burn the next person who touches it, so it is put on a heat-proof mat or a wire gauze.
• ii.Many laboratory chemicals are poisonous or burn the nose and throat. To notice a smell, the air above the tube is wafted (fanned) towards the nose with the hand, so only a little of it is breathed.

Any two:

• a.Bacteria decompose dead bodies and wastes into simple minerals, which make the soil fertile.
• b.Rhizobium in the root nodules of beans, peas and lentils fixes nitrogen from the air, which makes the soil fertile.
• c.Lactobacillus turns milk into curd (dahi) and yoghurt; other bacteria make cheese.
• d.Yeast ferments sugar into alcohol and carbon dioxide, which makes bread and sel roti dough rise.
• e.Antibiotics (penicillin from the fungus Penicillium), vaccines, vitamins and insulin are made with microbes.
• f.Lactic acid bacteria ferment gundruk, sinki and pickles.

No, I don’t agree.

• a.Development must be sustainable: it should meet our needs without spoiling the chance of future generations to meet theirs. Trees take many years to grow back, so cutting them all now leaves nothing for our children, and the money is soon spent.
• b.The forest is the habitat of many plants and animals, so clearing it causes biodiversity degradation. The bare slopes are washed away by the rain (soil erosion and landslides), and the sources of water dry up. The forest should be used sensibly instead: only mature trees cut, and new ones planted.

• i.If all the seeds fell right under the parent plant, the seedlings would compete with it and with each other for light, water and space. Seeds carried away grow where there is room, and the plant spreads to new places.
• ii.Its seed has stored food (starch and protein) in the cotyledons or the endosperm. The young plant lives on this food until its leaves are green and can make food by photosynthesis.

• i.The heater warms the air next to it. Warm air is less dense, so it rises, and cooler air from the room comes down to the heater to take its place. This convection current carries the heat round the whole room. A heater near the ceiling would only warm the air at the top, which would stay there.
• ii.The warm, stale air we breathe out, and the hot air from a stove or a lamp, is less dense, so it rises to the top of the room and goes out through the ventilator near the ceiling. Fresh, cooler air comes in lower down, through the doors and windows, so a convection current keeps fresh air moving through the room.

• i.A dark, dull surface is a good absorber of radiation: it takes in most of the Sun’s heat rays that fall on it, so the cooker gets hotter.
• ii.A white surface reflects most of the sunlight that falls on it, so it absorbs less heat, and the rooms inside stay cooler on hot days.

• i.Each knock on the floor jolted the molecular magnets out of line, and the push between the like poles kept pressed together slowly turned them too. Bit by bit the molecular magnets turned in random directions (closed chains), so the magnets were demagnetized. (Kept without keepers, they also lost some magnetism naturally.)
• ii.In pairs, side by side, with the north pole of one beside the south pole of the other and a piece of wood between them, and two soft iron keepers across their ends; kept away from heat, and never dropped.

• i.Acid rain. Smoke from vehicles, brick kilns and factories puts oxides of sulphur and nitrogen into the air, which form sulphuric acid and nitric acid with the water in the clouds. Marble is calcium carbonate, which reacts with these acids, so the rain eats away the surface layer by layer.
• ii.Any one: use less fossil fuel (walk, cycle, use public transport, keep vehicles well maintained); use renewable energy such as hydroelectricity and solar energy instead of coal and oil; make factories clean their smoke before it leaves the chimney and build them away from where people live.

• i.Robotics is the branch of science and engineering that designs, builds, operates and uses robots, machines that help humans and can copy human actions.
• ii.Hardware, the physical body that can be touched (frame, motors, arms, sensors, computer), and software, the program of instructions that tells the hardware what to do.
• iii.Artificial intelligence means computer programs or machines that can do tasks that normally need human intelligence, such as understanding language, recognizing faces and objects, making decisions and solving problems.
• iv.Narrow (weak) AI, because it is made for one particular task, recognizing crop diseases, and can’t do anything outside it.

i. From the graph, $u$ = 0, $v$ = 15 m/s and $t$ = 10 s.
$$a = \frac{v - u}{t} = \frac{15 - 0}{10} = 1.5\ \text{m/s}^2$$

• ii.From 10 s to 30 s (A to B), where the velocity stays 15 m/s. Its velocity isn’t changing, so its acceleration is zero.
• iii.From B to C, $u$ = 15 m/s, $v$ = 0 and $t$ = 35 s − 30 s = 5 s.

$$a = \frac{v - u}{t} = \frac{0 - 15}{5} = -3\ \text{m/s}^2$$
The acceleration is −3 m/s², so the retardation is 3 m/s².
iv. The velocity rises steadily, so
$$\bar v = \frac{u + v}{2} = \frac{0 + 15}{2} = 7.5\ \text{m/s}, \qquad s = \bar v \times t = 7.5 \times 10 = 75\ \text{m}$$

• i.Group 2 (2 valence electrons) and period 4 (4 shells).
• ii.No. Y has 5 valence electrons. Gaining 3 electrons to make 8 is far easier than losing 5, so it gains 3: its valency is 8 − 5 = 3.
• iii.X has valency 2 and Y valency 3. Crossing them over gives X₃Y₂, and no number divides both 3 and 2, so the formula is X₃Y₂ (calcium nitride, Ca₃N₂).
• iv.Ca₃N₂ has 3 calcium atoms and 2 nitrogen atoms.

$$\text{Molecular weight} = 3 \times 40 + 2 \times 14 = 120 + 28 = 148\ \text{amu}$$

• i.Because it contains iron (Latin ferrum): iron can be got from it, as from hematite and magnetite.
• ii.Any one: it is rare; it is very valuable; it is chemically unreactive, so it doesn’t rust or tarnish easily.
• iii.Limestone is a raw material of industry (the cement industry), and slate is used in construction (roofs).
• iv.A mineral is a natural, solid, pure substance with a definite chemical composition. Granite is a mixture of minerals (grains of quartz, feldspar and mica), so it is a rock, not a single mineral.