An object is released from a certain height above the ground. Just at the time it touches the ground, it will possess ______.

The correct answer is A, During respiration. Plants respire day and night, breaking glucose down to release energy, and carbon dioxide is the waste product of that process. Photosynthesis does the opposite: the plant takes in carbon dioxide and water and, using sunlight trapped by chlorophyll, makes glucose while releasing oxygen as its waste product. During the day photosynthesis runs faster than respiration, so a green plant gives out oxygen on balance; at night only respiration continues, so carbon dioxide is released. These gases move in and out through the stomata of leaves and the lenticels of woody stems. B is wrong because photosynthesis uses carbon dioxide up instead of producing it. C is wrong for the same reason, as oxygen and not carbon dioxide is the waste of photosynthesis. D is wrong because transpiration is the loss of water vapour from the plant and involves no carbon dioxide. Exam tip: respiration takes oxygen and gives carbon dioxide; photosynthesis takes carbon dioxide and gives oxygen.

The correct answer is B, the same, opposite. The same magnet moves at the same speed in both cases, so the rate of change of magnetic flux through the coil is equal and the induced potential difference has the same magnitude. But turning the other pole towards the coil reverses the direction of the field through it, so the induced voltage takes the opposite sign. This follows from Faraday's law of electromagnetic induction, which says the induced emf equals the rate of change of flux, and from Lenz's law, which fixes the direction so that the induced current opposes the change causing it. A is wrong because the sign must flip once the pole facing the coil is reversed. C is wrong because the speed, and therefore the rate of flux change, is unchanged, so the two magnitudes match. D is wrong on both counts. Exam tip: speed decides how big the induced emf is, the field direction decides its sign - Faraday for magnitude, Lenz for direction.

The correct answer is D, Fibrous roots. Fibrous roots are the mark of monocotyledonous plants such as wheat, maize, rice and grasses, not of dicots. A dicot seed carries two cotyledons, and its seedling sends down one strong primary root that thickens into a tap root with smaller lateral branches; gram, pea, mustard, neem and mango are familiar examples. Dicot leaves show reticulate or net-like venation, their flowers usually have petals in fours or fives, and their vascular bundles stand in a ring with cambium, so the stem can thicken year after year. A is wrong because the tap root is precisely what a dicot has. B is wrong because reticulate venation is a dicot feature, while monocots show parallel venation. C is wrong because two cotyledons is the very definition of a dicotyledonous plant. Exam tip: dicot - two cotyledons, tap root, reticulate venation; monocot - one cotyledon, fibrous roots, parallel venation.

The correct answer is D, 80 J. The work done in moving a charge across a potential difference is W = QV, so W = 5 × 16 = 80 joules. Potential difference is itself defined as the work done per unit charge in carrying that charge from one point to another, which is why one volt means one joule of work for every coulomb moved. Here five coulombs are carried across sixteen volts, so the source must supply 80 J of energy. A is wrong because 65 J does not follow from any correct use of 5 C and 16 V. B is wrong because 45 J would need a potential difference of 9 V for the same charge. C is wrong because 40 J would need either 2.5 C at 16 V or 5 C at 8 V. Exam tip: remember V = W/Q, so W = QV; in this chapter joules are simply coulombs multiplied by volts.

The correct answer is A, Peacock. The peacock is a bird, and all birds, like mammals, have a heart of four chambers: two atria and two ventricles. Four chambers keep oxygen-rich blood and oxygen-poor blood completely apart, so the body gets fully oxygenated blood. Birds and mammals need this because they are warm-blooded and burn a great deal of energy to hold a steady body temperature; flight makes the demand greater still. Crocodiles are the only reptiles with a four-chambered heart. B is wrong because a sea horse is a fish and has a two-chambered heart, one atrium and one ventricle. C is wrong because a frog, being an amphibian, has three chambers, two atria and a single ventricle in which the two kinds of blood mix. D is wrong for the same reason as the sea horse. Exam tip: fish 2 chambers, amphibians and most reptiles 3, birds and mammals 4; the peacock is India's national bird.