JUPEB Biology
Past Questions

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**The reasoning** Gregor Mendel discovered several fundamental laws of inheritance. His **First Law** (also called the Law of Segregation) states that: *During gamete formation (making sperm or egg cells), the two alleles (gene variants) for each trait separate, so each gamete carries only ONE allele for each gene.* Think of it this way: If you're heterozygous Tt (tall), your body doesn't pass "Tt" to your child. Instead, the T and t **segregate** (separate) during meiosis, so each sperm/egg gets either T *or* t — never both. **Why the wrong options tempt you** - **Independence** is Mendel's *Second* Law (different genes assort independently) - **Dominance** describes how one allele masks another (Tt looks tall), but it's not called Mendel's First Law - **Heredity** is the general concept of traits passing down, too broad to be a specific law **Quick takeaway** Remember: **"FIRST = SEGREGATION"** — allele pairs split up during gamete formation, one allele per sex cell. This is the foundation of everything else in genetics!

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**The reasoning** Think of protein synthesis like building a house. The **nucleus** holds the blueprints (DNA), but the actual construction happens elsewhere. The blueprints are copied into mRNA (messenger RNA), which then travels out of the nucleus to the **ribosome** — the cellular factory where proteins are assembled. Ribosomes read the mRNA code and link amino acids together in the correct sequence to form proteins. This process is called **translation**. So ribosomes are literally the workbenches where proteins are built, piece by piece. **Why the wrong options tempt you** - **Nucleus (A)** — You might pick this because DNA is here, and DNA contains genetic information for making proteins. But the nucleus only *stores* instructions; it doesn't build proteins. - **Golgi body (C)** — This one modifies and packages proteins *after* they're made, like a post-office sorting parcels. - **Lysosome (D)** — This actually *breaks down* proteins and waste materials — the opposite of building them! **Quick takeaway** Nucleus = blueprint storage; Ribosome = construction site where proteins are actually assembled from amino acids.

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A gene is a unit of DNA that codes for a specific trait — the basic unit of heredity.

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Most DNA is in the nucleus. Mitochondria also contain a small amount of their own DNA.

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Chloroplasts contain chlorophyll and are the site of photosynthesis in plants and algae.

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White blood cells (leucocytes) are the primary defenders of the immune system.

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Osmosis is specifically the diffusion of WATER across a semi-permeable membrane.

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Mushrooms are fungi — they lack chlorophyll and feed on decaying organic matter.

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Humans have 46 chromosomes (23 pairs) in each somatic cell. Gametes have 23.

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UV light converts 7-dehydrocholesterol in the skin to vitamin D₃.

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Beta cells in the islets of Langerhans in the pancreas secrete insulin to regulate blood glucose.

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Distilled water is hypotonic to the cell contents, so water enters by osmosis. Because an animal cell has no cell wall to resist the pressure, the cell swells and eventually bursts (haemolysis). Crenation occurs in a hypertonic solution, and plasmolysis is a term for plant cells only.

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Mitochondria carry out the Krebs cycle and oxidative phosphorylation on their folded inner membranes (cristae), releasing most of the cell's ATP. Ribosomes make proteins, the Golgi packages them, and the nucleus stores DNA.

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Proteins from the rough endoplasmic reticulum pass to the Golgi apparatus in vesicles, where they are modified (for example by adding carbohydrate), sorted and packaged into secretory vesicles. Lysosomes digest, centrioles organise spindle fibres, and the nucleolus makes ribosomal RNA.

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Mitosis is a single division that separates identical sister chromatids, giving two daughter cells with the same chromosome number and the same genes as the parent, which is what growth and repair require. Four genetically different haploid cells are produced by meiosis.

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The levels of organisation run cell → tissue → organ → organ system → organism. A tissue is a group of similar cells with a common function; an organ (such as the stomach) is made of several tissues working together.

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Magnification $= \dfrac{\text{image size}}{\text{actual size}} = \dfrac{50}{0.05} = 1000$. Both measurements must be in the same unit before dividing; mixing millimetres and micrometres gives the wrong power of ten.

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Active transport uses carrier proteins powered by ATP to pump substances from low to high concentration, for example the uptake of mineral ions by root hairs and the sodium-potassium pump in neurones. Diffusion is passive and moves substances down the gradient.

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Water leaves the cell by osmosis into the hypertonic solution, the vacuole shrinks, and the protoplast pulls away from the cell wall, a state called plasmolysis. Turgidity is the opposite condition in a hypotonic solution, and haemolysis refers to bursting of red blood cells.

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Plant cells have a rigid cellulose cell wall outside the cell membrane, as well as chloroplasts and a large central vacuole; animal cells have none of these. Both cell types have a membrane, mitochondria and a nucleus.