SainsScience

The medulla oblongata controls involuntary actions such as heartbeat, breathing and peristalsis. Swinging the arms and deciding to sprint are voluntary (brain); pulling the foot away from a sharp object is a reflex controlled by the spinal cord.

The rays meet in front of the retina, so distant objects are blurred: short-sightedness. A concave lens spreads the rays out first so that they focus on the retina. A convex lens corrects long-sightedness (image behind the retina).

The only difference between X and Y is the water in the sponge, and the roots grow towards the moist sponge: positive hydrotropism. Both boxes are dark, so light is not the stimulus; the roots in Y still grow down (positive geotropism), not up.

Carbon monoxide combines with haemoglobin to form stable carboxyhaemoglobin, so less oxyhaemoglobin forms. Sulphur dioxide and nitrogen dioxide irritate the air passages; carbon dioxide does not form a stable compound with haemoglobin.

Efficient gaseous exchange surfaces are thin, moist and have a large surface area. Insects do not use blood to carry oxygen (A), only insects have spiracles (C), and only fish gills stay in water (D).

Group O has no antigens but its plasma has both Anti-A and Anti-B antibodies. Anti-B attacks the B antigens on donated group B cells and makes the blood clump.

Water lost = 480 − 444 = 36 g. Time = 2 × 60 = 120 minutes. Rate = 36 ÷ 120 = 0.30 g per minute. 0.60 uses 60 minutes, 3.33 divides time by mass and 18.0 is the rate per hour.

Diamond is made of carbon atoms only, so it is a mineral element (like gold, silver and graphite). Quartz (silicon dioxide), bauxite (aluminium oxide) and calcite (calcium carbonate) are compounds.

Carbon can only reduce the oxides of metals below it in the reactivity series (zinc, iron, tin, lead). Magnesium, aluminium and calcium are above carbon and are extracted by electrolysis.

The temperature drops, so heat is taken from the water around it: an endothermic reaction (heat absorbed from the surroundings).

A cold pack contains a salt such as ammonium nitrate. Dissolving it is endothermic: it absorbs heat, so the pack becomes cold and reduces swelling.

A wave that rises and falls above and below zero is alternating current. The crest is 2.5 divisions above the centre line, so the peak voltage = 2.5 × 4 = 10 V.

Energy = 1.5 kW × 2 h × 30 = 90 kWh. Cost = 90 × 25 sen = 2 250 sen = RM22.50.

72 km h⁻¹ = 72 ÷ 3.6 = 20 m s⁻¹. E = ½mv² = ½ × 1 200 × 20² = 240 000 J. 480 000 J forgets the ½, 12 000 J forgets to square the speed, and 3 110 400 J uses 72 without converting to m s⁻¹.

Loss of gravitational P.E. = gain in K.E.: mgh = ½mv², so v² = 2gh = 2 × 10 × 1.8 = 36 and v = 6.0 m s⁻¹. 36 is v², not v.

Gamma rays have no charge (not deflected) and the highest penetration power, so thick lead is needed. Alpha and beta particles are charged and deflected.

The atom starts with 13 electrons (neutral). After losing 3 it has 10 electrons. Charge = protons − electrons = 13 − 10 = +3 (a positive ion).

Sunspots are dark regions on the photosphere because they are cooler than the granules around them. Granules are grainy structures, prominences are loops of gas above the surface and flares are explosions.

The more sunspots, the more CME. 2025 has the most sunspots and CME, so more charged particles reach Earth and telecommunication is most likely to be disturbed.

Both put the Sun at the centre (heliocentric). Copernicus used circular orbits; Kepler changed them to elliptical orbits with the Sun at one focus.