የባዮሎጂ መግቢያ ፈተና፣ 2018 ዓ.ም. (2026)

Plants store energy as starch and build their cell walls from cellulose. Both are chains of glucose, but the glucose units in cellulose are joined by beta 1,4 links, and the human gut makes no enzyme that can cut that link. So cellulose passes through us as dietary fibre. Glycogen tempts because it is also a glucose polymer, but it is the animal storage carbohydrate and our amylase and maltase break it down without trouble.

The words saturated and unsaturated describe how much hydrogen the carbon chain carries. A saturated fatty acid has only single carbon to carbon bonds, so every carbon holds all the hydrogen it can. An unsaturated one has at least one \( \text{C}=\text{C} \) double bond, and each double bond means two fewer hydrogens. Option A states the same idea backwards, which is why it catches students who read fast.

Bile is made in the liver and stored in the gall bladder, and it contains no enzymes at all. Its bile salts break large fat drops into many tiny droplets, which multiplies the surface area that lipase can work on. Faster fat digestion is the result. Option D is not invented, because bile is alkaline and does help raise the pH of the food leaving the stomach, but the role the question is asking about is emulsification.

Pancreatic juice is the one secretion that carries all three enzyme classes at once: amylase for starch, trypsin and other proteases for protein, and lipase for fat. It empties into the duodenum through the pancreatic duct. The small intestine tempts because its lining does make enzymes such as maltase and peptidases, but those finish the job on small molecules rather than supply the full set.

The diaphragm is a dome of muscle stretched across the base of the chest, and it forms the floor of the thoracic cavity above the abdomen. When it contracts it flattens, the chest volume rises, the pressure inside falls below atmospheric pressure and air flows in. The trachea tempts because it is central to breathing too, but it is the tube that carries air, not the partition between the two cavities.

When exercise outruns the oxygen supply, muscle cells keep making ATP by glycolysis alone. The pyruvate that piles up is reduced to lactic acid, and that step regenerates the \( \text{NAD}^+ \) glycolysis needs to keep going. The acid builds up and contributes to muscle fatigue. Ethanol is the wrong choice because alcoholic fermentation belongs to yeast and some plant tissue, not to animal muscle.