Live practice

A cloth bag avoids repeated single-use packaging, switching off unused appliances saves electrical energy, and walking avoids fuel consumption and air pollution. Since every listed practice reduces resource use or pollution, all are environment-friendly.

For a positive charge, \(\vec F=q\vec v\times\vec B\). Applying Fleming's left-hand rule with motion/current west and force north makes the field vertically upward.

Alloys such as nichrome have higher resistivity, high melting point and resist oxidation at red heat. A practical length produces substantial heat \(H=I^2Rt\) without melting or burning rapidly.

For an object at infinity, the corrective lens must form a virtual image at the far point. Thus \(u=-\infty\), \(v=-0.80\) m and \(f=-0.80\) m.

Since \(v=\frac{c}{n}\), the smallest refractive index gives the greatest speed. Water has about 1.33, lower than kerosene and turpentine. Light therefore travels fastest in water.

Meiosis produces haploid gametes containing one chromosome from each homologous pair. At fertilisation, one haploid sperm nucleus and one haploid ovum nucleus fuse. The diploid zygote therefore receives one set of chromosomes, and one allele for each autosomal gene, from each parent. Cytoplasmic contribution is not equal, but the nuclear chromosome contribution is.

Ovaries begin to mature ova and secrete oestrogen/progesterone; menstruation and ovulation begin. Breasts develop, hips broaden, pubic and underarm hair appears, and a growth spurt occurs. Reproductive organs mature, sweat/oil glands become more active and emotional changes may accompany hormonal adjustment.

Place germinating seeds in a trough filled with dry soil. Put a porous pot containing water on one side, keep light and gravity conditions uniform, and allow roots to grow. In a control trough, keep moisture uniform. Roots in the experimental trough curve towards the porous pot, whereas control roots show no sideways curvature. This directed growth towards moisture demonstrates positive hydrotropism.

Air contains much more oxygen than water and oxygen diffuses faster through air. A terrestrial organism therefore expends less energy ventilating its respiratory surface to obtain a given amount of oxygen. Aquatic organisms must move large volumes of water over gills.

Litmus test: a carboxylic acid turns moist blue litmus red; an alcohol gives no change.

Hydrogencarbonate test: add sodium hydrogencarbonate. A carboxylic acid gives brisk carbon dioxide effervescence:

Ethanol does not react in this way. The evolved gas turns lime water milky.