General Science GK Questions with Answers – Page 59

Deep-sea divers breathe a mixture of oxygen and helium because helium does not dissolve much in blood under high pressure.

Besides the nucleus, these are the only organelles of a plant cell that carry their own DNA. Mitochondria and chloroplasts have small circular DNA molecules and their own 70S ribosomes, so they can make some of their own proteins and divide on their own.

A body sinks when its weight is greater than the buoyant force of the water it displaces, which happens when it is denser than water.

At uniform speed the net force is zero, so the upward force must equal the skydiver's weight. Weight is mass times the acceleration due to gravity: 60 kg × 9.8 m/s² = 588 N, acting downward.

With no external force on the system, its centre of mass cannot start moving. The throw is an internal force: X pushes the tool forward and the tool pushes X backward with an equal and opposite force (Newton's third law).

Sphagnum is a bog moss, a bryophyte, whose dead cells hold many times their own weight of water; in waterlogged and acidic bogs its remains decay only partly and pile up as peat, which is cut, dried and burnt as fuel and is also used in nurseries to keep soil…

An angiosperm shows double fertilisation: of the two male gametes brought by the pollen tube, one fuses with the egg to give a diploid zygote, and the other fuses with the two polar nuclei of the central cell.

The word itself means naked seed: the ovules are not enclosed in an ovary, so after fertilisation the seeds lie exposed on the surface of the scales of a cone and no fruit is formed.

It is the only surviving species of its order, has remained almost unchanged for many millions of years and is known from fossils of the age of the dinosaurs, which is why it is called a living fossil; it is a gymnosperm with fan-shaped leaves, grown widely as an ornamental…

Besides its normal roots, Cycas bears small branched roots that grow upward near the surface and look like coral; these coralloid roots hold cyanobacteria such as Anabaena and Nostoc, which fix atmospheric nitrogen and supply it to the plant.

Brown algae of the class Phaeophyceae contain chlorophyll a and c along with the xanthophyll pigment fucoxanthin, and because fucoxanthin masks the green chlorophyll the plant looks olive green to deep brown; Laminaria, Sargassum, Fucus, Ectocarpus and Dictyota are examples, and many of them bear air bladders that keep the…

The green algae owe their colour to chlorophyll a and chlorophyll b, which are not masked by any other pigment; Chlamydomonas, Volvox, Spirogyra, Ulothrix and Chara belong here, and their stored food is starch.

Agar is obtained chiefly from Gelidium and Gracilaria, members of the Rhodophyceae, and it is used to prepare the solid media on which microbes and plant tissues are grown, as well as in jellies and ice cream.

Ferns and their relatives, such as Selaginella, Lycopodium, Equisetum, Pteris, Adiantum and Marsilea, are the first plants with xylem to conduct water and minerals and phloem to conduct food, and the first with a true root, stem and leaf; for that reason they are also called the vascular cryptogams.

Bryophytes such as Marchantia, Riccia, Funaria and Sphagnum grow on soil, rocks and tree trunks, but their male gametes are flagellate and must swim through a film of water to reach the egg, so fertilisation cannot take place in dry conditions.

Eichler divided the plant kingdom into two: the Cryptogamae, meaning plants with hidden reproductive organs and no seeds, which include the algae or thallophytes, the bryophytes and the pteridophytes; and the Phanerogamae, the seed bearing plants.

An alkali is a base that dissolves in water, so all alkalis are soluble, but not all bases are alkalis; statement 1 has it the wrong way round.

The water at the bottom warms, becomes lighter and rises, while cooler water sinks to take its place, and these convection currents carry heat through the pot.

Dolomite is a carbonate of calcium and magnesium, a base that neutralises soil acidity and so raises the pH. Dolomite, CaMg(CO₃)₂, is a common liming material.

Three equal resistors R in parallel have a combined resistance of R/3, and at the same voltage the power, V²/R, becomes three times as large.