የ12ኛ ክፍል ባዮሎጂ መግቢያ ፈተና፣ 2017 ዓ.ም. (2025)፣ እትም 1

Dr Zeresenay Alemseged led the team that recovered the fossil child known as Selam from the Dikika area in the Afar region, and the full description was published in 2006. The skeleton is about 3.3 million years old and belongs to Australopithecus afarensis, the same species as Lucy. Dr Berhane Asfaw is the tempting choice because he is also a well known Ethiopian palaeoanthropologist, but his famous work is on Ardipithecus and on the Herto skulls, not on the Dikika child.

Row 2 is the only line that states the difference the right way round: the electron microscope forms its image with a beam of electrons, and the light microscope uses a beam of light. Row 3 is the tempting one, but it is reversed. Electrons have a far shorter wavelength than light, so the electron microscope has the higher resolving power, not the lower. Row 1 and row 4 are reversed in the same way, because it is the electron microscope that needs a vacuum and therefore cannot show a living cell.

The cell theory has three parts: all living things are made of cells, the cell is the basic unit of structure and function in life, and new cells come only from cells that already exist. Option D states that middle part, so it is the best statement of the theory. Option A is the idea the theory replaced. Spontaneous generation was disproved by the work of Pasteur, and the theory insists instead that every cell comes from another cell.

One vacuole that fills most of the cell and stays there for the whole life of the cell is a plant feature. It holds cell sap and pushes outward on the cell wall, and that turgor pressure is what keeps a soft plant stem upright. Animal cells are the tempting answer because they can have vacuoles too, but theirs are small, few and temporary, so they never fill the cell the way a plant vacuole does.

A hypertonic solution holds more dissolved solute and less free water than the inside of the cell. Water moves by osmosis from where there is more of it to where there is less, so water leaves the cell and the cell shrinks. Bursting is the tempting answer, but that happens in the opposite case: an animal cell placed in a hypotonic solution takes water in until the membrane gives way.

Benedict's solution starts blue and moves through green, yellow and orange to a brick red precipitate as the amount of reducing sugar rises. Sample 1 gave the red precipitate, so it holds a lot of reducing sugar. Option B is the trap: sample 2 turned only yellow, so it does hold some reducing sugar, but less than sample 1, not more. Biuret stayed blue in both samples, so neither has much protein, and iodine stayed brown, so neither contains starch.