Live practice

Write elements in a consistent order. Then \[\begin{aligned}B &= \{1,2,3,4\}\\&= D\end{aligned}\], and \[\begin{aligned}E &= \{-1,1\}\\&= G\end{aligned}\]. Every other set has a different element list.

The impact differs because each trophic level performs a different function. Removing producers stops the entry of solar energy and ultimately collapses the whole food chain. Removing primary consumers allows producers to grow unchecked and deprives secondary consumers of food. Removing top consumers permits rapid growth of prey populations. Removing decomposers prevents nutrient recycling and causes dead matter to accumulate. Since levels are linked through feeding and nutrient cycles, no entire trophic level can be removed without affecting ecosystem balance.

Required current is

This exceeds 5 A, so the fuse should melt or MCB trip, disconnecting the circuit. Using it without suitable wiring would overheat conductors and be unsafe.

Join the three cells series-aiding to make 6 V. Connect the closed key and the 5 Ω, 8 Ω and 12 Ω resistors end-to-end with no branches. The same current passes through every resistor.

For a very near object, rays diverge strongly and require greater lens power. The ciliary muscles and elastic eye lens have a finite accommodation limit. Inside about \(25\,\mathrm{cm}\) the lens cannot become sufficiently convex, so the image would not focus sharply on the retina and viewing causes strain.

Lens power is \(P=\frac{1}{f}\) when focal length is in metres. A lens of focal length \(1\,\mathrm{m}\) has power 1 dioptre. Thus \(1\text{ D}=1\text{ m}^{-1}\).

No. A copper-T is an intrauterine contraceptive that impairs sperm function and prevents fertilisation/implantation, but it does not block exchange of body fluids or skin contact during intercourse. Condoms provide barrier protection and reduce transmission of many STIs.

Iodine is required to synthesise thyroxine in the thyroid gland. Thyroxine regulates metabolism, growth and development. Iodine deficiency can enlarge the thyroid (goitre) and, in children, impair physical and mental development. Iodised salt supplies a small regular dietary amount.

Oxygen diffuses from alveoli into blood and binds reversibly to haemoglobin in red blood cells as oxyhaemoglobin. It is released in tissues where oxygen concentration is low. Carbon dioxide from tissues is transported mainly as bicarbonate ions in plasma, with smaller amounts dissolved or bound to haemoglobin, and diffuses into alveoli for exhalation.

No. Detergents form lather in both soft and hard water because their charged ends do not form insoluble precipitates with calcium and magnesium ions. Soap, however, forms scum and little lather in hard water, so soap can be used for this comparison.