Live practice

(i) \[\begin{aligned}x^2+5x+6 &= (x+2)(x+3)\\&= 0\end{aligned}\], so \(B=\{-2,-3\} e\{2,3\}\).

(ii) Repetition is ignored: FOLLOW and WOLF both give \(\{F,O,L,W\}\). Hence the sets are equal.

Organisms at the next higher level would lose a major food source and their population would decline or move away. Organisms at the immediately lower level would face less predation and could increase excessively, overusing the level below them. Energy transfer through that food chain would be interrupted and connected food webs would also be disturbed. The resulting imbalance can destabilise the ecosystem.

A correctly rated fuse or miniature circuit breaker opens the live wire during excess current. Earthing provides a low-resistance route from a metal casing to ground so a fault current trips protection. Either pair, together with proper insulation, is acceptable.

Lower resistivity means better conduction. Iron has much lower resistivity than mercury, so iron is better. Silver has the lowest listed resistivity and is the best conductor.

The lens must make an object at \(25\,\mathrm{cm}\) appear at the unaided near point \(1.0\,\mathrm{m}\). Therefore \(u=-0.25\) m and \(v=-1.0\) m.

A convex lens provides the required convergence.

It means the ratio of light speed in vacuum to that in diamond is 2.42:

Thus light travels 2.42 times faster in vacuum than in diamond, and its speed in diamond is about \(1.24\times10^8\text{ m s}^{-1}\).

The embryo implants in the thick uterine lining and develops a placenta. Maternal blood spaces and foetal capillaries lie close but normally do not mix. Oxygen and nutrients diffuse or are transported across the placenta into foetal blood; carbon dioxide and wastes move to maternal blood. The umbilical cord connects the foetus to the placenta.

Endocrine glands release hormones directly into blood. Blood carries them throughout the body, but only target cells with matching receptors respond. Hormones change activities such as metabolism, growth and reproduction. Feedback mechanisms adjust secretion, for example blood glucose regulates insulin release.

Glucose is first split in the cytoplasm into two three-carbon pyruvate molecules:

With oxygen, pyruvate is completely oxidised in mitochondria to CO2 and water, releasing much ATP. Without oxygen, yeast forms ethanol and CO2; muscle cells during oxygen shortage form lactic acid. Anaerobic routes release much less energy.

An oxidising agent causes another substance to be oxidised by supplying oxygen, removing hydrogen or accepting electrons. It is itself reduced. Alkaline potassium permanganate and acidified potassium dichromate are common oxidising agents.