General Science GK Questions with Answers – Page 43

Sponges belong to the phylum Porifera, a name that means "pore bearers", because their bodies are full of tiny pores.

Nitrogen dioxide has an unpaired electron, so two of its molecules join to form dinitrogen tetroxide, N 2 O 4.

Tincture of iodine is a true solution, which is homogeneous, so statement I is wrong, while II and III are right.

Xerophytes are plants adapted to live in deserts and other places with very little water; the Greek word "xeros" means dry.

Genetic engineering uses recombinant DNA, cloning and gene transfer, and restriction enzymes cut DNA at specific sites; but they do not unzip DNA into two strands, so statement 3 is wrong.

Cholesterol is a sterol, a kind of lipid (fat-like substance) that does not dissolve in water. Cholesterol is made mainly in the liver and also comes from animal foods such as eggs, meat and butter; plants do not contain it.

Mammals have a four-chambered heart, so blood passes through the heart twice in each round, once for the lungs and once for the body, without oxygenated and deoxygenated blood mixing.

The coronary arteries carry oxygen-rich blood to the muscle of the heart wall itself. The heart pumps blood to the whole body, but its own thick muscle (the myocardium) needs a separate supply.

Natural selection needs variation among members of a species; without variation there is nothing for nature to select, so statement A is the incorrect one.

In plant cells RNA is found in the nucleus, the cytoplasm, mitochondria, chloroplasts and ribosomes. RNA is made in the nucleus, where DNA is copied into messenger, transfer and ribosomal RNA; the nucleolus in particular is rich in ribosomal RNA.

The tapeworm is an animal, and animal cells have no cell wall, only a cell membrane. A rigid cell wall lies outside the cell membrane in plants, fungi, most bacteria and many protists, giving the cell shape and protection.

In the liver, methanol is oxidised to methanal (formaldehyde), which coagulates protoplasm and damages cells. Methanol, CH3OH, is the simplest alcohol and is sometimes mixed into illicit liquor.

Adipocytes are the fat cells of adipose tissue, a loose connective tissue that stores fat in animals. Adipose tissue lies mainly beneath the skin and around organs such as the kidneys and heart.

Seeds are carried away from the parent plant by wind, water and animals, but fungi play no part in seed dispersal.

Thyroxine is an iodine-containing hormone, so the thyroid gland cannot make it without iodine from the diet. The thyroid is a butterfly-shaped gland in the neck.

Mitochondria carry out respiration, chloroplasts photosynthesis, ribosomes make proteins and the rough endoplasmic reticulum transports them. Mitochondria are called the powerhouse of the cell because aerobic respiration in them releases energy as ATP.

This follows the order of these metals in the reactivity series, and hydrochloric acid reacts fastest with the metal highest in it.

Apical meristems sit at the tips of roots and shoots, and their dividing cells make the plant grow in length.

Xylem is made of more than one type of cell working together, which is what makes a tissue complex. Plant permanent tissues are of two kinds.

In the sodium-calcium exchanger, Na+ ions enter the cell while Ca2+ ions are pushed out, so the two ions cross the membrane in opposite directions.