General Science GK Questions with Answers – Page 95

It hastens the ripening of fruit, encourages leaves and flowers to drop and is used commercially in the form of ethephon to ripen mangoes, bananas and tomatoes evenly; a ripe fruit kept with unripe ones ripens them because it gives off ethylene.

The potato is an underground stem tuber, and the proof is on its skin: the hollows called eyes are axillary buds with tiny scale leaves, and buds of this kind are never found on a true root.

Once fertilisation is complete, the ovary enlarges and ripens into the fruit, and its wall becomes the pericarp that may be fleshy, as in a mango, or dry, as in a pea pod.

Their pollen tube carries two male gametes into the ovule; one fuses with the egg to form the diploid zygote, which is syngamy, and the other fuses with the two polar nuclei to form the triploid primary endosperm nucleus, which is triple fusion.

A stamen is the male reproductive unit of a flower and has just two parts: a stalk called the filament and a swollen head called the anther, in which pollen grains are produced.

The gas is first fixed in the mesophyll cells by the enzyme PEP carboxylase on to a three-carbon acceptor, and the pathway is named after Hatch and Slack.

Here the ATP and NADPH made in the light reaction are spent on fixing carbon dioxide into carbohydrate.

In the light reaction, water absorbed by the roots is split in the presence of light and chlorophyll, a step called photolysis of water or the Hill reaction.

Chlorophyll is built on a ring structure with a single magnesium atom held at its centre, and because magnesium is needed to make the pigment, a plant short of magnesium develops chlorosis, the yellowing of leaves between the veins.

In photosynthesis a green plant absorbs sunlight through chlorophyll and uses that energy to join carbon dioxide and water into carbohydrate.

Haemophilia is an inherited disorder in which a clotting factor is missing, so bleeding continues for a long time after an injury.

The thyroid gland needs iodine to make the hormones thyroxine and triiodothyronine, and when the supply is short the gland enlarges in an attempt to trap more of it, which appears as a swelling in the neck.

Rabies is caused by a virus present in the saliva of an infected animal, usually a dog, and it travels along the nerves to the brain, where it causes inflammation, fear of water and almost certain death once the symptoms begin; it is prevented by vaccination after the bite, a…

Kala-azar, also called visceral leishmaniasis, is caused by the protozoan Leishmania donovani and is passed on by the bite of the female sandfly, which breeds in cracks of mud walls and damp soil.

Filariasis is caused by the thread-like nematode Wuchereria bancrofti, which is carried by the Culex mosquito.

Vitamin A is used to make rhodopsin, the pigment of the rod cells of the retina that allows sight in dim light, so a shortage of it makes a person unable to see properly at dusk or in a dark room.

Vitamin C, or ascorbic acid, is needed to make collagen, the protein that holds tissues together, so its absence weakens the gums and blood vessels and delays the healing of wounds.

This mosquito, marked by white stripes on a dark body, bites during the day and breeds in clean stored water in coolers, tyres and flower pots, which is why dengue control campaigns concentrate on emptying household containers.

Four species of Plasmodium commonly infect human beings, of which Plasmodium falciparum is the most dangerous and Plasmodium vivax the most widespread in India.

Rust of wheat is indeed a fungal disease, caused by species of Puccinia, and it is named from the reddish brown spores that appear in streaks on the leaves and stem.