Which one among the following is not a part of vascular bundle in plants ?

The correct answer is C, Fat of food is digested by lipases. Lipases split fats into fatty acids and glycerol.

Fat digestion happens mainly in the small intestine. Bile from the liver, stored in the gall bladder, first breaks large fat globules into tiny droplets, a step called emulsification; bile itself has no enzyme. Pancreatic lipase then acts on these droplets and breaks the fats into fatty acids and glycerol, which are absorbed into the lacteals of the villi. Each enzyme in the gut acts on one kind of food: amylases on starch, proteases on proteins, lipases on fats and nucleases on nucleic acids.

Option A is wrong because trypsin and chymotrypsin are pancreatic proteases that digest proteins, not fats. Option B is wrong because starch is digested by amylases, salivary amylase in the mouth and pancreatic amylase in the intestine. Option D is wrong because nucleic acids, DNA and RNA, are broken down by nucleases, not amylases.

Exam tip: amylase–starch, protease (pepsin, trypsin)–protein, lipase–fat, nuclease–nucleic acid; bile only emulsifies.

The correct answer is A. A single-celled organism has no organs at all; the one cell takes in food through its surface or by forming temporary structures.

In organisms like Amoeba, Paramecium or bacteria, the whole body is one cell, so every life process happens within it. Amoeba engulfs food with finger-like pseudopodia and digests it in a food vacuole; Paramecium sweeps food into a groove with its cilia. Oxygen and carbon dioxide simply diffuse across the cell membrane because the whole surface touches the surroundings. Waste such as ammonia also diffuses out, and freshwater forms push out extra water with a contractile vacuole. Organs are needed only in large multicellular bodies whose inner cells are far from the outside.

Option B is a correct statement, since gas exchange happens by diffusion through the cell surface. Option C is correct, because metabolism in any living cell produces waste that must be removed. Option D is correct, as the single cell is directly exposed to its environment on all sides.

Exam tip: unicellular = no organs; diffusion across the membrane handles gases and waste.

The correct answer is B, 20 Hz - 20 kHz. A healthy young human ear can hear sounds with frequencies from about 20 hertz to about 20,000 hertz.

Frequency is the number of vibrations per second, measured in hertz, and our ears sense it as pitch. Sound below 20 Hz is called infrasound; elephants and whales use it to communicate over long distances, and it is produced by earthquakes. Sound above 20 kHz is called ultrasound; bats and dolphins use it for echolocation, and doctors use it for sonography, while ships use it in SONAR. The upper limit of hearing falls with age, so older adults often cannot hear sounds much above 15 kHz.

Option A is wrong because 20 to 200 kHz lies entirely in the ultrasonic range, which humans cannot hear. Option C is wrong because 35 kHz is well into ultrasound; it is closer to the hearing range of dogs. Option D is wrong because 40 kHz is also beyond human hearing, though cats and some rodents can hear near it.

Exam tip: below 20 Hz infrasound, 20 Hz–20 kHz audible, above 20 kHz ultrasound.

The correct answer is C. A muscle contracts when calcium ions are released from the sarcoplasmic reticulum, and it relaxes when they are pumped back into it.

When a nerve signal reaches a muscle fibre, it spreads into the fibre and triggers the sarcoplasmic reticulum, the fibre's internal calcium store, to release Ca++ ions. Calcium binds to troponin, which moves tropomyosin aside and uncovers the binding sites on actin. Myosin heads then attach, pull the actin filaments inward using ATP, and the sarcomere shortens; this is the sliding filament theory. For relaxation, calcium pumps that also use ATP move Ca++ back into the reticulum, the binding sites are covered again and the filaments slide apart.

Option A is wrong because zinc ions play no part in contraction. Option B is wrong because the calcium that triggers each contraction comes from the store inside the fibre, not directly from the blood. Option D is wrong because the exchange of sodium and potassium carries the electrical signal along the membrane but does not by itself make the filaments slide.

Exam tip: contraction = Ca++ out of SR binds troponin; relaxation = Ca++ pumped back; both need ATP.

The correct answer is A, Tropolone. Tropolone is aromatic, but its seven-membered ring is made only of carbon atoms, so it is not heterocyclic.

A heterocyclic compound has at least one atom other than carbon, such as oxygen, sulphur or nitrogen, inside its ring. Tropolone, C7H6O2, is a seven-carbon ring carrying a ketone group and a hydroxyl group outside the ring. It is counted among the non-benzenoid aromatic compounds because its ring has six delocalised pi electrons, the same number that makes benzene aromatic, but every ring atom is carbon.

Option B is wrong because furan is a five-membered aromatic ring with one oxygen atom. Option C is wrong because thiophene is a five-membered aromatic ring with one sulphur atom. Option D is wrong because pyridine is a six-membered aromatic ring like benzene in which one CH unit is replaced by a nitrogen atom; it is a common solvent and base.

Exam tip: hetero = O, S or N in the ring: furan (O), thiophene (S), pyridine (N); tropolone is all-carbon.