የ12ኛ ክፍል ባዮሎጂ መግቢያ ፈተና፣ 2018 ዓ.ም. (2026)፣ እትም 1

Dr. Melaku Worede built and ran Ethiopia's national gene bank, and his work was to collect, store and multiply the seeds farmers had already been growing for generations. Those landraces are adapted to the local soil, rainfall and pests, so they give a harvest without bought fertiliser or chemical sprays. He received the Right Livelihood Award for protecting that seed heritage. Professor Gebisa Ejeta is the tempting choice because he is also a famous Ethiopian plant scientist, but his work was breeding new sorghum varieties that resist drought and the Striga weed, which is a different kind of research.

Resolution means the smallest gap between two points that still appear as two separate points. A light microscope is limited by the wavelength of visible light, so it cannot separate anything closer than about 200 nm. Electrons have a far shorter wavelength, so an electron microscope reaches about 0.2 to 0.3 nm, roughly a thousand times finer. Option D carries the same two numbers but swapped, which would make the light microscope the sharper instrument, and the physics of wavelength does not allow that.

The cell membrane is the layer that decides what enters and leaves. It is selectively permeable, so it lets in nutrients, holds them inside and pushes waste out. If it stops working, that control is lost and materials move both ways freely, exactly as described. The cell wall is the tempting answer because a plant has one, but the wall is fully permeable to water and small dissolved substances and its job is shape and support, not selection.

Iodine solution is the test for starch and it turns blue-black, so test tube 3 with a positive result holds starch. The other two are matched wrongly in the options: Biuret reagent tests for protein and turns purple, and Benedict's solution heated with a reducing sugar gives an orange to brick-red precipitate. Option A is tempting because test tube 1 really does contain protein, but the colour given there belongs to Benedict's test, not to Biuret.

Food leaving the stomach is soaked in hydrochloric acid, with a pH near 2. Bile from the liver is alkaline because it carries hydrogen carbonate, and it neutralises that acid so the small intestine sits at about pH 7 to 8. Pancreatic and intestinal enzymes such as amylase, trypsin and lipase work fastest at that pH, so they can now act. Option C is tempting because bile really does act on fat, but bile is not an enzyme: it breaks large fat drops into tiny ones, and lipase does the chemical splitting into fatty acids and glycerol.

The alveoli are millions of tiny air sacs at the end of the airways. Their walls are one cell thick, they are moist, they are wrapped in capillaries and together they give a huge surface area, so oxygen and carbon dioxide diffuse across quickly. The bronchi are the tempting answer because air passes through them on the way in, but their walls are thick and held open by cartilage and they have no capillary network, so they only conduct air.