Post-UTME Biology
Past Questions

AI Explanation

**The reasoning** Human somatic cells (body cells like skin, muscle, liver cells — basically any cell except sperm and egg) contain the **diploid number** of chromosomes. "Diploid" means two complete sets: one inherited from your mother, one from your father. In humans, each parent contributes **23 chromosomes** through their gametes (sex cells). When sperm meets egg during fertilization: 23 + 23 = **46 chromosomes total**. These 46 exist as 23 pairs in every somatic cell throughout your body. **Why the wrong options tempt you** - **A) 23** — This is the haploid number found only in gametes (sperm and egg cells). Students mix up somatic cells with sex cells. - **B) 44** — These are just the autosomes (non-sex chromosomes). You're forgetting the 2 sex chromosomes (XX or XY). 44 + 2 = 46. - **D) 48** — This might come from confusing humans with other species, like chimpanzees, which have 48 chromosomes. **Quick takeaway** Remember: **Somatic = 46 (diploid, two sets); Gametes = 23 (haploid, one set)**. Your body cells always have the full double set from both parents.

AI Explanation

## The reasoning Genes are **segments of DNA** (Deoxyribonucleic Acid) that contain the instructions for making specific proteins. Think of DNA as the "recipe book" of life — each gene is like one recipe that tells your cells how to build a particular protein. The structure goes like this: DNA → Gene → Protein. DNA is the raw material that *makes up* genes. When your body needs to produce a protein (say, hemoglobin for blood or melanin for skin), it reads the gene (DNA sequence) and follows those instructions. ## Why the wrong options tempt you **A) Protein** — This is backwards! Genes *code for* proteins, but they're not made of protein themselves. It's like confusing the recipe with the cake. **B) Lipid** — Lipids (fats) make up cell membranes and store energy, but have nothing to do with genetic information. **D) Sugar** — Tricky! DNA does contain a sugar (deoxyribose) in its backbone, but the gene itself is the *entire DNA molecule*, not just the sugar component. ## Quick takeaway **Genes ARE DNA segments that CODE FOR proteins** — the blueprint is DNA, the product is protein. Never confuse the instruction manual with what it builds!

AI Explanation

**The reasoning** DNA replication is **semi-conservative** because each new DNA molecule contains one original (old) strand and one newly synthesized strand. Think of it like this: the double helix unzips down the middle. Each separated strand then serves as a template to build its complementary partner. So from one DNA molecule, you get two identical copies — but each copy is half-old, half-new. This was brilliantly proven by the Meselson-Stahl experiment in 1958 using heavy nitrogen isotopes to track which strands were original. **Why the wrong options tempt you** - **Conservative** sounds logical but would mean the original DNA stays completely intact while an entirely new copy forms separately (doesn't happen). - **Dispersive** suggests DNA breaks into fragments with old and new bits randomly mixed throughout both strands (too messy and inaccurate). - **Random** implies no organized pattern at all (chaos wouldn't preserve genetic information!). **Quick takeaway** Remember: **"Semi" = half** — each daughter DNA is half-parent, half-child, like inheriting one eye color from each parent. That's semi-conservative replication!