IGCSE Science - Combined (0653) — May–June 2025, Paper 21
40 questions · every question answerable online with instant point-by-point AI marking against the official mark scheme.
Start with Question 1 →Osmosis can be defined as the net movement of ......1...... molecules from a region of ......2...... water potential to a region of ......3...... water potential, through a…
Answer this question and get it marked →The diagrams show four root hair cells. Each cell is surrounded by soil with the same volume of water present. Which root hair cell absorbs water the most rapidly? A a root hair…
Answer this question and get it marked →Which statement explains how an increase in pH affects enzyme activity? A The active site changes shape. B The substrate is denatured. C There is an increase in the kinetic…
Answer this question and get it marked →What is the balanced equation for photosynthesis? A CO2 + H2O → C6H12O6 + O2 B CO2 + 6H2O → 6C6H12O6 + O2 C 6CO2 + 6H2O → C6H12O6 + 6O2 D 6CO2 + 12H2O → 6C6H12O6 + 6O2
Answer this question and get it marked →The diagram shows a transverse section through a leaf, with four labelled layers: layer 1 (waxy cuticle on the upper surface), layer 2 (upper epidermis), layer 3 (palisade…
Answer this question and get it marked →What is the purpose of physical digestion? A break down food into smaller pieces B break down insoluble food into soluble molecules C change food so that it can be absorbed into…
Answer this question and get it marked →The diagram shows the human alimentary canal and other organs, with four labelled positions: A (stomach), B (pancreas region), C (small intestine) and D (large intestine). Which…
Answer this question and get it marked →Which row describes aerobic respiration? Key: ✓ = true, ✗ = false nutrient molecules broken down produces water releases energy --- --- --- --- A ✓ ✓ ✓ B ✓ ✓ ✗ C ✓ ✗ ✓ D ✗ ✓ ✓
Answer this question and get it marked →Which row about the anther and stigma of a wind-pollinated flower is correct? anther position stigma position stigma description --- --- --- --- A inside flower inside flower…
Answer this question and get it marked →Which row shows the effect of deforestation on oxygen and carbon dioxide concentrations in the atmosphere? oxygen concentration carbon dioxide concentration --- --- --- A…
Answer this question and get it marked →Which term describes an area that contains all the organisms and their environment interacting together? A community B ecosystem C food chain D food web
Answer this question and get it marked →Which row shows how active immunity is gained? Key: ✓ = yes, ✗ = no from antibodies supplied in an injection by vaccination after an infection by a pathogen --- --- --- --- A ✓ ✗…
Answer this question and get it marked →Which statements about antibiotics are correct? 1 An antibiotic is a drug. 2 Antibiotics kill bacteria and viruses. 3 MRSA is a type of bacteria resistant to antibiotics. A 1 and…
Answer this question and get it marked →Which diagram represents a mixture of elements? A particles each made of two identical (open) atoms joined together, all the same kind B a mixture of different molecules,…
Answer this question and get it marked →A neutral atom of chlorine contains 17 electrons and 18 neutrons. What is the atomic number and what is the mass number of this atom? atomic number mass number --- --- --- A 17 35…
Answer this question and get it marked →The elements in Period 2 and Period 3 of the Periodic Table are shown. Period 2: Li, Be, B, C, N, O, F, Ne Period 3: Na, Mg, Al, Si, P, S, Cl, Ar Which statement about atoms of…
Answer this question and get it marked →Which statement describes the formation of ions? A Metal atoms gain electrons to form cations and non-metal atoms lose electrons to form anions. B Metal atoms gain electrons to…
Answer this question and get it marked →The formula of sodium phosphate is Na3PO4. The formula of calcium nitrate is Ca(NO3)2. Which row shows the formula for calcium phosphate and the formula for sodium nitrate?…
Answer this question and get it marked →Which row shows what forms at the electrodes during electrolysis of an aqueous compound? anode cathode --- --- --- A metal non-metal B non-metal metal C hydrogen metal D hydrogen…
Answer this question and get it marked →The reaction pathway diagrams for reaction X and for reaction Y are shown. In reaction X the products are at a lower energy than the reactants (energy released). In reaction Y the…
Answer this question and get it marked →Which statement about catalysts is correct? A Catalysts decrease the rate of reaction. B Catalysts increase the concentration of reactants. C Catalysts are unchanged at the end of…
Answer this question and get it marked →Which processes involve a chemical change? 1 cracking of an alkane 2 polymerisation of ethene 3 corrosion of iron A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only
Answer this question and get it marked →A chromatogram of dyes X, Y and Z is shown. The baseline is at 0 cm and the solvent front is at 8 cm. Dye X has one spot at 4 cm. Dye Y has spots at about 2.5 cm and 7 cm. Dye Z…
Answer this question and get it marked →An excess of an insoluble metal carbonate is mixed with an acid. A salt is produced. Which row shows steps to obtain a pure salt from the reaction mixture? step 1 step 2 --- ---…
Answer this question and get it marked →Which type of reaction occurs when alkenes react with bromine? A addition B combustion C displacement D polymerisation
Answer this question and get it marked →Which substances are initially placed in the blast furnace during the production of iron? 1 carbon 2 carbon monoxide 3 hematite A 1 and 3 B 1 only C 2 and 3 D 3 only
Answer this question and get it marked →Which row correctly explains a strategy to reduce the effects of climate change? strategy explanation --- --- --- A plant more trees trees use up land for growing crops B reduce…
Answer this question and get it marked →The graph shows how the speed of a car changes with time. The car travels at constant speed from 0 to 5 s, then accelerates (a straight line) from 5 s to 20 s, then brakes to a…
Answer this question and get it marked →The diagrams show all the forces acting on different objects. The masses of the objects are shown. Which object has an acceleration of 3.0 m/s^2? A mass 27 kg, with a 3.0 N force…
Answer this question and get it marked →Which row shows what the weight of an object depends on? Key: ✓ = depends on this, ✗ = does not depend on this mass gravitational field strength --- --- --- A ✓ ✓ B ✓ ✗ C ✗ ✓ D ✗ ✗
Answer this question and get it marked →The temperature of a gas increases. Which row is correct for the particles of the gas? force between particles average speed of particles --- --- --- A strong decreases B strong…
Answer this question and get it marked →The diagrams show two identical wide beakers and two identical narrow measuring cylinders. One of the beakers and one of the measuring cylinders contain hot water. The other…
Answer this question and get it marked →Which row shows the main method of thermal conduction in metallic and in non-metallic solids? metallic solids non-metallic solids --- --- --- A molecular vibrations molecular…
Answer this question and get it marked →A student moves one end of a long rope up and down through a short distance. A transverse wave travels along the rope in the direction shown. The student now moves the rope up and…
Answer this question and get it marked →The diagram shows a ray of light reflected at a plane mirror, X. The reflected ray strikes another plane mirror, Y. Mirror Y is at 90° to mirror X. The angle between the incident…
Answer this question and get it marked →Sound travels in solids, liquids and gases. The speed of sound is different in each state. Which row shows the state with the lowest and highest speed? lowest speed highest speed…
Answer this question and get it marked →In which unit is charge measured? A ampere B coulomb C volt D watt
Answer this question and get it marked →There is a current of 2.0 A in a resistor of resistance 7.5 Ω. What is the power and energy transferred in the resistor in 5.0 s? power / W energy / J --- --- --- A 15 3.0 B 15 75…
Answer this question and get it marked →A student determines the resistance of resistor R. Which circuit is used to obtain the readings needed? A an ammeter connected in series with R and a voltmeter connected in…
Answer this question and get it marked →What is a possible set of stages in the life cycle of stars? A protostar → black hole → red supergiant B protostar → interstellar cloud of gas and dust → new stars C supernova →…
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