General Science Previous Year Questions (PYQ) with Answers – Page 27

Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.

Reversing the pole that approaches the loop reverses the change in magnetic flux, so the induced current reverses too. When a magnet moves towards a closed loop, the magnetic flux through the loop changes and an electric current is induced (Faraday's law of electromagnetic induction).

Iron is more reactive than copper, so it pushes copper out of copper sulphate, and the freed copper coats the nail brown.

Benzene and water do not mix, so they form two layers that a separating funnel can draw off one after the other.

In the alkane series the boiling point rises as the carbon chain gets longer, and this order goes from 3 to 4 to 5 to 8 carbons.

Lemon juice is acidic and rich in vitamin C, which together slow the enzyme reaction that browns cut apple. When an apple is cut, the enzyme polyphenol oxidase in its cells meets oxygen in the air and oxidises the fruit's phenolic compounds into brown pigments (melanins).

When oxygen runs short during hard exercise, muscle cells break glucose down anaerobically, and lactic acid is the by-product. In glycolysis, which takes place in the cytoplasm, one molecule of glucose splits into two molecules of pyruvate and yields a little ATP.

The pancreas pours amylase, trypsin and lipase into the duodenum in its juice, so all three classes of food are digested there.

Lymph is plasma that has leaked out of the capillaries, and red blood cells are too large to pass through the capillary walls.

Urea is the form in which the body gets rid of the nitrogen left over when amino acids from proteins are broken down.

Sexual reproduction mixes the genes of two parents, so the young differ from each other and from their parents, and variation helps a species survive changing conditions.

Besides the nucleus, these are the only organelles of a plant cell that carry their own DNA. Mitochondria and chloroplasts have small circular DNA molecules and their own 70S ribosomes, so they can make some of their own proteins and divide on their own.

Brine is a concentrated solution of common salt, sodium chloride (NaCl), in water. Brine occurs naturally in seawater, salt lakes and underground deposits.

Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas: Zn + H2SO4 gives ZnSO4 + H2.

Graphite, fullerene, diamond and graphene are all allotropes of carbon, made only of carbon atoms arranged in different ways. Allotropes are different structural forms of the same element.

An alloy is made by melting and mixing its components, which keep their own properties and are not joined in a fixed ratio by chemical bonds.

Prokaryotic cells, such as bacteria, have no true nucleus; their DNA lies free in the cytoplasm in a region called the nucleoid.

While collecting nectar, a honey-bee carries pollen from one flower to the stigma of another, which lets the plant form seeds.

Bacteria have peptidoglycan walls and animal cells have no wall, but fungal walls are made of chitin, not cellulose. Statement 1 is correct: peptidoglycan, also called murein, is a mesh of sugars cross-linked by short peptides; penicillin works by blocking its formation.

Meiosis halves them in the gametes, and fertilisation restores them in the offspring. Each parent makes gametes by meiosis, so a human egg or sperm carries 23 chromosomes instead of 46.