General Science GK Questions with Answers – Page 20

Glycolysis spends two molecules of ATP in the preparatory steps that phosphorylate glucose and fructose, and produces four by substrate level phosphorylation in the later steps, so the net gain is two ATP along with two molecules of reduced NAD.

Sugar is actively loaded into the sieve tubes at the source, water follows from the xylem by osmosis and raises the pressure there, and the resulting gradient pushes the whole solution to the sink, where sugar is unloaded and water returns to the xylem.

In yeast the pyruvic acid formed by glycolysis is decarboxylated and then reduced to ethyl alcohol, a process called alcoholic fermentation, which is the basis of brewing and of the rising of dough.

The respiratory quotient is the volume of carbon dioxide released divided by the volume of oxygen used. When glucose is oxidised completely, six molecules of oxygen are used and six of carbon dioxide are released, so the ratio is one.

Pyruvic acid formed in glycolysis enters the mitochondrion, is converted to acetyl coenzyme A and is oxidised completely in the matrix through the cycle named after Hans Krebs, who received the Nobel Prize for the discovery; the cycle releases carbon dioxide and reduced coenzymes.

Glycolysis, also called the Embden Meyerhof Parnas pathway, splits one molecule of glucose into two molecules of pyruvic acid in the cytoplasm, needs no oxygen and gives a net gain of two ATP along with two molecules of reduced NAD.

Ganong's potometer and the simpler bubble potometer measure the water absorbed by a cut shoot in a given time, and since almost all of that water is lost as vapour, the reading is taken as the rate of transpiration.

In light, potassium ions are actively pumped into the guard cells, their solute concentration rises, water enters by osmosis, the cells swell and because their inner walls are thicker they bend apart, opening the pore; when potassium leaves, the cells lose water and the pore closes.

Its sieve tubes, helped by companion cells, carry sucrose and other soluble food from a source such as a mature leaf to a sink such as a root, fruit or bud, and the movement can be upward or downward.

It occurs through pores called hydathodes at the leaf margin or tip, usually in the early morning when the soil is moist, the air is humid and transpiration is low, so root pressure forces out drops of water with dissolved salts; Colocasia, grasses and tomato show it well.

Dixon and Joly explained that water molecules cling to one another by cohesion and to the xylem walls by adhesion, forming an unbroken column; evaporation from the leaf surface creates a suction at the top that pulls this column upward.

Egg white is mostly water and protein, and heat denatures these proteins so that they set into an opaque white solid.

By mass, an adult human body has the most oxygen, then carbon, hydrogen and nitrogen. Oxygen makes up about 65 percent of body mass, carbon about 18 percent, hydrogen about 10 percent and nitrogen about 3 percent.

Near the horizon, sunlight crosses a much thicker layer of air, and scattering removes most of the blue light before it reaches us.

The glass of a glowing bulb is heated mainly by radiation from the white-hot filament, not by convection. Conduction passes heat through a solid from particle to particle, convection carries heat by the actual movement of a fluid, and radiation sends heat as electromagnetic waves that need no medium.

Caesium melts at about 28.5 °C, the lowest of these alkali metals, so it can turn liquid on a warm day or in the hand.

The girth, or thickness, of a stem increases only through the lateral meristems, the vascular cambium and the cork cambium.

The gastric glands in the stomach wall secrete pepsin, which begins the digestion of proteins into smaller peptides. The chief cells of the gastric glands release pepsin in an inactive form, pepsinogen.

The blue colour comes from water of crystallisation: blue vitriol is CuSO4·5H2O, and heating drives off these five water molecules to leave white anhydrous copper sulphate.

Zinc lies in the middle of the reactivity series, so its oxide can be reduced to the metal by heating it with carbon (coke): ZnO + C → Zn + CO.