BLE Model Paper 8

Cyberbullying is using social media, messages or other electronic means to threaten, frighten, harass or humiliate someone, or to torture them mentally.

A firewall, which blocks the connections that shouldn’t get into a computer or a network.

Nepal’s varied plants, animals and landscapes attract tourists (ecotourism): visitors to national parks such as Chitwan and Sagarmatha bring money and jobs for local people.

The cell formed when the nucleus of a male gamete fuses with the nucleus of a female gamete in fertilization. It is the first cell of the new organism.

Light is not needed for the seeds to germinate, but the seedling needs light to make its own food by photosynthesis once its stored food is used up.

With a strong magnet (an electromagnet): it attracts the iron cans, because iron is a magnetic material, and leaves the aluminium cans, which are not magnetic.

Because an atom has as many electrons as protons: the positive and negative charges are equal and cancel each other, so the atom is electrically neutral.

Protons = 31 − 16 = 15, so it has 15 electrons, arranged 2, 8, 5 (phosphorus). It has 5 valence electrons, so its valency is 8 − 5 = 3.

• i.Survey. The answer is with the people of the tole, so the data are collected directly from them, by a questionnaire, interviews or a discussion.
• ii.Test. A hypothesis (“the powder is a base”) is checked by a set procedure: a little of the powder is dissolved in water and tested with red litmus paper, which turns blue in a base.

• i.A website must be open to anyone, from anywhere, at any time. If the computer holding its files were switched off or offline, nobody could reach the site. So its files are kept on a web server, usually space rented from a web hosting company.
• ii.The URL is the address the browser uses to find a website. If two websites had the same address, the browser could not tell which one to open, just as two houses with one address would confuse a postman.

No, I don’t agree.

• a.People use far more natural resources than any other living thing. Twice as many people need more land for houses and farms, more firewood and timber, and more water, and make more waste and sewage, so forests are cut and rivers are polluted. That is why the principle of population control and human resource management says the population must be kept within limits.
• b.The same principle says people’s knowledge and skills should be developed through education and training, so that people become a resource that looks after the forests and rivers (as community forest groups do), not a burden on them.

• i.In cross-pollination, the pollen comes from another plant, so the young get a new combination of qualities from two parents. Some of these varied young are more likely to survive a change, such as a new disease or a drier year.
• ii.The male gametes must reach the egg cell inside the ovule, deep in the ovary, but the pollen grain sits on the stigma, far above. The pollen tube grows down through the style, carries the male gametes and releases them into the ovule, so fertilization can take place.

• i.Trees take in carbon dioxide, a greenhouse gas. With fewer trees, more carbon dioxide stays in the air, it traps more of the heat given out by the Earth, and the Earth’s average temperature rises.
• ii.As the Earth warms, the glaciers melt faster, and the lakes below them fill up and grow. If a lake’s natural dam of rock and ice breaks, the water rushes down the valley as a glacial lake outburst flood (GLOF), destroying villages downstream.

i. $P$ = 150 W = 150/1000 kW = 0.15 kW, $N$ = 20, $t$ = 5 h
$$\text{E.C.} = P \times N \times t = 0.15 \times 20 \times 5 = 15\ \text{units (kWh)}$$
ii. Saved in a day = 0.15 × 20 × 1 = 3 units. In 25 days = 3 × 25 = 75 units. Money saved = 75 × Rs 10 = Rs 750.

i. There are 2 O on the left and 3 on the right; 6 is the smallest number both go into. Put 3 before O₂ and 2 before Al₂O₃: Al + 3O₂ → 2Al₂O₃. Now there are 4 Al on the right, so put 4 before Al:
$$4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3$$
Check: 4 Al and 6 O on each side.
ii. There are 3 Mg on the right, so put 3 before Mg:
$$3\text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2$$
Check: 3 Mg and 2 N on each side.

A galaxy is a huge collection of stars, with clouds of gas and dust (nebulae), held together by gravity. Our Solar System is in the Milky Way galaxy.
Any two shapes: spiral (like the Milky Way and Andromeda), elliptical, lenticular (lens-shaped), ring-shaped, irregular.

i. A round nucleus with a double nuclear membrane with pores, the liquid nucleoplasm inside, a dark nucleolus, and fine threads of chromatin.

• ii.It controls and coordinates the work of all the other parts of the cell: its metabolism, its growth and the movement of materials in it. It also carries the genetic characters.
• iii.Ribosomes, which pass out through the pores of the nuclear membrane into the cytoplasm.
• iv.DNA wound around proteins (histones). A human body cell has 46 chromosomes, in 23 pairs.

i. 1 km/h = 5/18 m/s, so
$$u = 36 \times \frac{5}{18} = 10\ \text{m/s}, \qquad v = 90 \times \frac{5}{18} = 25\ \text{m/s}$$

• ii.$$a = \frac{v - u}{t} = \frac{25 - 10}{6} = \frac{15}{6} = 2.5\ \text{m/s}^2$$
• iii.It speeds up steadily, so its average velocity is

$$\bar v = \frac{u + v}{2} = \frac{10 + 25}{2} = 17.5\ \text{m/s}$$
and the distance covered is $s = \bar v \times t = 17.5 \times 6 = 105\ \text{m}$.
iv. 18 km/h = 18 × 5/18 = 5 m/s. So $u$ = 25 m/s, $v$ = 5 m/s, $t$ = 4 s:
$$a = \frac{v - u}{t} = \frac{5 - 25}{4} = -5\ \text{m/s}^2$$
The acceleration is −5 m/s², so the retardation is 5 m/s².

• i.The sound of the knock travels to Suman along two paths, through the iron of the pipe and through the air. Sound travels much faster in a solid like iron than in air, so the sound through the iron arrives first and the sound through the air later.
• ii.Distance = 1.02 km = 1,020 m.

$$t_{\text{air}} = \frac{\text{distance}}{\text{speed}} = \frac{1020\ \text{m}}{340\ \text{m/s}} = 3\ \text{s}$$
iii. $$t_{\text{iron}} = \frac{1020\ \text{m}}{5100\ \text{m/s}} = 0.2\ \text{s}$$
So he hears the second sound 3 − 0.2 = 2.8 s after the first.
iv. No. The frequency is set by the source (the knock of the hammer on the pipe), and it doesn’t change from one medium to another. From $v = f\lambda$, with the same frequency and a higher speed, it is the wavelength that is longer in the iron (15 times as long, since 5,100 ÷ 340 = 15).

• i.$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$. An acid reacts with a metal to form a salt (magnesium chloride) and hydrogen gas.
• ii.$\text{H}_2\text{SO}_4 + 2\text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}$. An acid and a base react to form a salt (potassium sulphate) and water: neutralization.
• iii.$\text{H}_2\text{SO}_4 + 2\text{NaCl} \rightarrow \text{Na}_2\text{SO}_4 + 2\text{HCl}$. A salt reacts with an acid to form a new salt (sodium sulphate) and a new acid (hydrochloric acid).
• iv.$\text{Ca(HCO}_3)_2 + \text{Ca(OH)}_2 \rightarrow 2\text{CaCO}_3 + 2\text{H}_2\text{O}$. This is Clark’s method: calcium hydroxide (lime) turns the dissolved calcium bicarbonate into insoluble calcium carbonate, which settles out, so the temporary hardness of water is removed.