Which cell organelle is called the Master of the Cell?

The correct answer is A, Aedes - Chikungunya - Bacteria. This set is wrong because chikungunya is caused by a virus, the chikungunya virus, and not by bacteria. It is spread by Aedes mosquitoes, the same day-biting mosquitoes that carry dengue and Zika, and it causes high fever with severe joint pain. The name comes from a word in the Makonde language of East Africa meaning 'that which bends up', describing patients bent over with pain. Aedes breeds in clean water stored in coolers, tyres, pots and tanks, which is why dengue and chikungunya cases rise after the monsoon. Option B is a correct set because the Culex mosquito spreads lymphatic filariasis, or elephantiasis, caused by parasitic worms such as Wuchereria bancrofti. Option C is correct because the female Anopheles mosquito spreads malaria, caused by the Plasmodium parasite, a protozoan. Option D is correct because Aedes also spreads dengue, which is caused by the dengue virus. Exam tip: Aedes carries dengue, chikungunya and Zika, all viruses; Anopheles carries malaria; Culex carries filariasis and Japanese encephalitis.

The correct answer is A, Protein. The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina. With age, and faster with diabetes, ultraviolet light, smoking or an injury, these proteins break down and clump together. The clumps scatter light, so the lens turns cloudy and vision becomes blurred, dim and glary. This clouding is a cataract, and it is one of the leading causes of blindness in India. It is treated by a short operation in which the cloudy lens is removed and replaced by an artificial intraocular lens. Option B is wrong because carbohydrate changes are not what clouds the lens, although high blood sugar in diabetes speeds up the protein damage. Option C is wrong because fat does not form the clear structure of the lens. Option D is wrong because the tear glands keep the eye moist and have nothing to do with the lens. Exam tip: cataract = cloudy lens from clumped proteins; glaucoma = raised pressure inside the eye.

The correct answer is B, Falciparum. Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed. Malaria spreads through the bite of the female Anopheles mosquito; the parasite first multiplies in the liver and then in red blood cells, and the bursting of these cells brings the cycles of chills and high fever. Ronald Ross proved the mosquito link in 1897 while working in India and won the Nobel Prize in 1902. Option A is wrong because P. vivax causes benign tertian malaria, which can relapse from dormant stages in the liver but is rarely fatal. Option C is wrong because P. ovale causes a mild tertian malaria found mainly in Africa. Option D is wrong because P. malariae causes quartan malaria, with fever every fourth day. Exam tip: falciparum = malignant; vivax = benign but relapsing; female Anopheles = vector.

The correct answer is D, A and D. Vitamins A, D, E and K dissolve in fat, while the B group and vitamin C dissolve in water. Fat-soluble vitamins are absorbed along with the fat in our food and are stored in the liver and fatty tissue, so the body can build up a reserve; for the same reason, too much of them, especially A and D taken as supplements, can be harmful. Most water-soluble vitamins are not stored in large amounts, the extra is passed out in urine, and so they must be eaten regularly. Vitamin A keeps the eyes healthy and its lack causes night blindness, while vitamin D is made in the skin in sunlight and its lack causes rickets in children. Option A is wrong because vitamin B12 is water-soluble, even though D is fat-soluble. Option B is wrong because vitamin C is water-soluble. Option C is wrong because it pairs fat-soluble A with water-soluble C. Exam tip: remember the fat-soluble group as 'ADEK'; the B group and C are water-soluble.

The correct answer is C, Stapedius. The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body. When a very loud sound reaches the ear, the stapedius contracts and damps the vibration of the stapes, protecting the delicate inner ear; this is called the acoustic reflex. It is supplied by the facial nerve, so damage to that nerve can make ordinary sounds seem painfully loud. Option A is wrong because the biceps is a large muscle at the front of the upper arm that bends the elbow. Option B is wrong because the sartorius, which runs across the thigh, is the longest muscle of the body, not the smallest. Option D is wrong because the triceps at the back of the upper arm straightens the elbow and is a large muscle. Exam tip: smallest muscle stapedius, smallest bone stapes, longest muscle sartorius, largest muscle gluteus maximus.