General Science GK Questions with Answers – Page 82

Malaria is caused by the protozoan parasite Plasmodium, of which several species infect human beings, and it is transmitted by the bite of an infected female Anopheles mosquito, the male feeding on plant juices.

He noticed that a mould of the genus Penicillium growing by accident on a culture plate had stopped the growth of Staphylococcus around it, and Howard Florey and Ernst Chain later turned that observation into a usable drug, the three sharing the Nobel Prize.

This bacterium ferments the lactose of milk into lactic acid, and the acid makes the milk protein coagulate, which is why a spoonful of old curd added to warm milk sets the whole vessel.

Its salivary glands secrete hirudin, an anticoagulant that keeps the host's blood flowing while the leech feeds, and the same property made leeches a part of old medical practice and a subject of modern research on blood thinners.

In animals such as Branchiostoma, also called Amphioxus or the lancelet, the notochord extends from the head to the tail and remains there for the whole of life, which is why the group is treated as the clearest surviving picture of the basic chordate plan.

It belongs to the monotremes, the only mammals that lay eggs, the other being the spiny anteater or echidna. The young hatch from the eggs and are then fed on milk from the mother's mammary glands, which is why the animal is still a mammal.

Reptiles in general have a three-chambered heart, with two atria and a ventricle that is only partly divided, so that oxygenated and deoxygenated blood mix to some extent.

Bony fishes of the class Osteichthyes fill or empty a gas-filled air bladder and so hover at any depth without effort.

These are fine blind tubules that float in the body fluid of an insect and open into the gut, where they take up nitrogenous waste and pass it out as nearly dry uric acid, so that very little water is lost.

It belongs to the phylum Mollusca and the class Cephalopoda, so it is a relative of the squid and the cuttlefish rather than of any fish, and the common name devil fish came from its appearance and its eight arms with suckers.

Each cnidoblast holds a capsule called a nematocyst with a coiled thread that shoots out and injects a toxin when touched, and it is found in Hydra, the sea anemone, the jellyfish and the corals.

In sponges the cells are arranged loosely and work with a good deal of independence, with collar cells driving water through a canal system and other cells digesting the food particles, so the body never rises to the level of a true tissue.

Flame cells, also called solenocytes, are specialised cells with a tuft of beating cilia that drives waste fluid into a system of tubules, and they handle both the removal of nitrogenous waste and the balance of water in animals such as Planaria, Taenia and Fasciola.

Starfishes, sea urchins, sea cucumbers, brittle stars and sea lilies are found only in the sea, and their water vascular system, which works by taking in sea water, is one reason they never colonised fresh water or land.

More than three-fourths of all described animal species are arthropods, that is insects, spiders, scorpions, centipedes, crabs and prawns. A hard chitinous exoskeleton, jointed appendages, small body size and, in insects, the power of flight allowed the group to spread into almost every habitat on earth.

A large central vacuole filled with sap presses the cytoplasm against the cell wall, keeping the cell firm, or turgid.

Annelids such as the earthworm, leech and Nereis are the first coelomates in the usual sequence: their body cavity is lined on all sides by mesoderm.

No pathway of respiration in living cells turns glucose into methanol. Glucose is first split in the cytoplasm into two molecules of pyruvate; this step, glycolysis, is common to all cells.

Of the four options, oxygen is by far the most plentiful element; it makes up about 46% of the Earth's crust by mass.

The melting point is the minimum temperature at which a solid melts to become a liquid at atmospheric pressure, not the maximum.