የባዮሎጂ መግቢያ ፈተና፣ 2012 ዓ.ም. (2020)

H1N1 is a strain of the influenza virus, and influenza viruses carry their genetic information as RNA. Herpes simplex is a DNA virus, and the well studied bacteriophages such as the T-even phages also carry DNA.

HIV also holds RNA, but it is usually placed in its own group, the retroviruses, because it first copies its RNA into DNA inside the host cell. That is why H1N1 is the expected answer here.

Textbook: Biology Grade 12, Unit 2 Microorganisms, section 2.5.3 Classification of Viruses (page 84).

The earth holds a fixed amount of matter. Carbon, nitrogen and other nutrients must be used again and again, so decomposers break down dead bodies and wastes and return the nutrients to the soil, water and air. This keeps nutrients available for new life, which is why recycling matters for the whole planet.

Options A, B and C all describe recycling as harmful or wasteful, which is the opposite of its real role. Energy flows one way through an ecosystem, but matter cycles.

Textbook: Biology Grade 10, Unit 6 Ecological Interactions, section 6.1.2 Flow of energy and matter through ecosystems.

Coal and oil contain sulphur. When people burn these fossil fuels, the sulphur is released into the air as sulphur dioxide gas, which can later fall as acid rain. This extra input is the main human impact on the sulphur cycle.

The other options describe natural steps of the cycle: rocks weather to release sulphate, and decomposers free sulphur from dead matter without any human help.

During succession, pioneer organisms such as lichens and mosses break down rock, and their dead remains add organic matter. Over time the soil becomes deeper and richer, so larger plants can grow and the land becomes more productive.

The other options say the opposite of what really happens: the environment grows more stable, the abiotic conditions keep improving, and species diversity rises rather than falls.

Textbook: Biology Grade 9, Unit 6 Ecology, section 6.1.6 Ecological succession (page 153).

AIDS mostly strikes adults of working age. When these people fall sick or die, the country loses workers who produce goods, earn income and pay tax, so the taxable population shrinks and the economy weakens.

The other options claim benefits: AIDS does not raise life expectancy, does not add public resources, and forces families to spend savings on treatment rather than encouraging saving.

Textbook: Biology Grade 12, Unit 2 Microorganisms, section 2.5 Viruses (page 84).

A biome is a very large geographic region defined by its climate and soil, with plants and animals that share similar adaptations. Examples are desert, taiga and tropical rainforest.

A habitat is only the place where one organism lives, a niche is the role an organism plays, and an ecosystem is a community of organisms together with its non living surroundings, which can be as small as a pond.

Textbook: Biology Grade 9, Unit 6 Ecology, section 6.1.5 Biomes.