Image formation

The governing concept is micelle formation by amphiphilic soap molecules. In water, their hydrophobic hydrocarbon tails point inward and attach to oily dirt, while their hydrophilic ionic heads point outward toward water. This arrangement encloses grease in a dispersed droplet. Agitation breaks the dirt into smaller suspended particles, which can then be carried away during rinsing. Therefore option A correctly explains cleansing; the other options describe impossible changes.

The governing concept is the dependence of thyroid hormone synthesis on iodine. The thyroid gland produces thyroxine, and iodine is an essential raw material in that hormone’s structure. Inadequate iodine can reduce thyroxine production and may lead to enlargement of the thyroid, called goitre, along with other effects of deficiency. Hence A is the correct pair. The pancreas is associated with insulin, the adrenal gland with adrenal hormones, and bile is linked to the liver.

The governing concept is the emergency, or fight-or-flight, response. During fear, the adrenal glands release adrenaline, which increases heart rate and breathing and helps make more glucose available for rapid energy production. These changes support the muscles and prepare the body for quick action. Therefore A is correct. Adrenaline does not reduce blood sugar to zero, grow roots, or destroy dendrites, so B, C, and D are inappropriate.

The governing concept is hormonal control of body growth and the effect of an imbalance. Growth hormone from the pituitary promotes growth of bones and other body tissues, especially during childhood. If it is secreted excessively, growth may become abnormally high; in a growing child this can produce gigantism, while excess in adults has different effects. Thus A is correct. The other options describe impossible or unrelated biological events.

Human gametes are haploid: the egg contributes 23 chromosomes and the sperm contributes another 23. Fertilisation combines these two sets in the zygote, the first cell formed after fertilisation. Therefore, 23 + 23 = 46 chromosomes, arranged in 23 pairs. Option B is correct. Twenty-three is the number in one gamete, while 92 and 11 do not represent the normal human zygote number.

The governing concept is autotrophic nutrition. Autotrophs manufacture organic food from simple inorganic substances, commonly carbon dioxide and water, using light energy captured by chlorophyll. Green plants are the standard example. Option A is correct. Heterotrophs obtain food from other organisms, decomposers break down dead matter, and parasites draw nourishment from hosts.

Leaves are usually source organs because they manufacture sugars by photosynthesis. Phloem distributes these soluble food materials from sources to sinks, including roots, tubers, bulbs, fruits, and other storage organs. If phloem is damaged, the transported food supply to those organs may fall, reducing storage and growth. Therefore option A is correct; the other options assign animal organ functions to plants.

A plane mirror forms a virtual and erect image. It cannot be obtained on a screen because the reflected rays do not actually meet behind the mirror; they only appear to come from there. The image is also the same size as the object. A real, inverted image is not formed by a plane mirror. Exam tip: Remember ‘virtual, erect, same size’ for a plane mirror.