Live practice

At an intersection, two tangents could be drawn, implying two different magnetic field directions at the same point. A compass north pole cannot point simultaneously in two directions. Therefore field lines cannot intersect.

An electric cell converts chemical energy into electrical energy and maintains a potential difference. Several connected cells form a battery.

The student has myopia (short-sightedness): distant rays are focused in front of the retina, often because the eyeball is too long or the eye lens too powerful. A concave lens of suitable negative power diverges the rays so the eye focuses them on the retina.

A convex mirror always gives a virtual, erect and diminished image and has a wide field of view. The driver can therefore see a larger region behind the vehicle while objects remain upright.

In a dihybrid cross of round yellow and wrinkled green seeds, F1 plants were round yellow. Selfing F1 produced four F2 combinations in about 9:3:3:1: round yellow, round green, wrinkled yellow and wrinkled green. The two new combinations show that alleles for seed shape separated independently of alleles for seed colour during gamete formation.

Very large numbers of tiny spores are produced, so dispersal by air or water is wide. Each spore has a resistant wall and can remain dormant through adverse conditions. When moisture, temperature and nutrients become suitable, it germinates, enabling rapid colonisation with little parental energy per offspring.

Volatile molecules from the incense dissolve in mucus and stimulate olfactory receptors in the nasal epithelium. Receptor cells generate electrical impulses that travel through the olfactory nerve to the forebrain, where the pattern is interpreted as a particular smell.

The principal maintenance processes are nutrition, respiration, internal transport of materials and excretion. Control and coordination regulate them, while cellular synthesis and repair maintain body organisation. Reproduction ensures continuation of the species but is not required for survival of one individual.

Tetravalency: carbon forms four stable covalent bonds with carbon and many other elements. Catenation: carbon atoms form strong C-C bonds and join into long chains, branched chains and rings, with single, double or triple bonds. Together these properties create enormous structural variety.

(i) Hot iron reacts with steam to form magnetite and hydrogen:

(ii) Calcium:

Potassium:

The potassium reaction is extremely vigorous.