Question 1 (a) (Subtopic – B15.4)
Scientists measure the length of sperm cells from different animals. The animals are placed in size from animal A (the smallest) to animal F (the largest). Fig. 1.1 shows the results.
(i) Using Fig. 1.1, state the length of a sperm cell in animal B.
(ii) State the animal with the shortest length of sperm.
(iii) State evidence from Fig. 1.1 that shows that the length of sperm does not increase with the size of the animal.
▶️Answer/Explanation
(i) 0.12 mm ;
(ii) A ;
(iii) animal F is the biggest but does not have the longest length of sperm / animal D has the longest sperm but is not the biggest animal / avp ;
Question 1 (b) (Subtopic – B2.1)
Plant and animal cells both contain a nucleus.
Name two other structures seen in both plant and animal cells.
▶️Answer/Explanation
any two from:
cell membrane ;
cytoplasm ;
AVP ; e.g. ribosomes / mitochondria
Question 1 (c) (Subtopic – B2.1)
The boxes on the left show some of the parts of a plant cell. The boxes on the right show the functions of the parts. Draw lines to link each part with its function.
Parts of Plant Cell:
- Cell wall
- Chloroplast
- Nucleus
- Vacuole
Functions:
- Contains genetic material
- Contains cell sap and supports the cell
- Site of photosynthesis
- Strengthens the cell
▶️Answer/Explanation
Question 1 (d) (Subtopic – B3.1)
Substances enter and leave cells. Name the process by which substances enter the cells.
▶️Answer/Explanation
The process by which substances enter the cells is diffusion.
Detailed Solution:
Diffusion is the process by which substances move from an area of higher concentration to an area of lower concentration across a semi-permeable membrane (e.g., the cell membrane). This process is passive and does not require energy. It is essential for the movement of gases (e.g., oxygen and carbon dioxide) and small molecules into and out of cells.
Question 1 (e) (Subtopic – B12.1)
Explain why muscle cells need high rates of respiration.
▶️Answer/Explanation
Muscle cells need high rates of respiration because:
- Respiration releases energy, which is required for muscle contraction and movement.
- Muscle cells are highly active and require a continuous supply of energy to perform their functions.
Detailed Solution:
Muscle cells are highly specialized for movement and require a significant amount of energy to contract and relax. This energy is provided through the process of respiration, which converts glucose and oxygen into ATP (adenosine triphosphate), the energy currency of the cell. High rates of respiration ensure that muscle cells have a constant supply of ATP to meet their energy demands, especially during physical activity or exercise.
Question 2 (a) (Subtopic – C6.1)
The thermal decomposition of calcium carbonate makes calcium oxide and carbon dioxide.
(i) Write the word equation for the thermal decomposition of calcium carbonate.
(ii) The production of lime (calcium oxide) from limestone (calcium carbonate) is one use of limestone. State one other use of limestone.
(iii) Calcium carbonate has the formula CaCO3. State the number of different elements present in calcium carbonate.
(iv) Explain why the thermal decomposition of calcium carbonate is a chemical change and not a physical change.
(v) The thermal decomposition of calcium carbonate is an endothermic reaction. State what is meant by an endothermic reaction.
▶️Answer/Explanation
(i) The word equation for the thermal decomposition of calcium carbonate is:
calcium carbonate → calcium oxide + carbon dioxide
(ii) Another use of limestone is neutralizing acidic soil or as a building material.
(iii) Calcium carbonate contains 3 different elements: calcium (Ca), carbon (C), and oxygen (O).
(iv) The thermal decomposition of calcium carbonate is a chemical change because new substances (calcium oxide and carbon dioxide) are formed, and the change is irreversible.
(v) An endothermic reaction is a reaction that takes in thermal energy from the surroundings, resulting in a decrease in temperature.
Detailed Solution:
(i) The thermal decomposition of calcium carbonate involves breaking down the compound into calcium oxide and carbon dioxide when heated. The word equation represents this process.
(ii) Limestone is widely used in agriculture to neutralize acidic soil and in construction as a building material or to produce cement.
(iii) The formula CaCO3 indicates that calcium carbonate consists of calcium (Ca), carbon (C), and oxygen (O), totaling 3 different elements.
(iv) A chemical change involves the formation of new substances with different properties. In this case, calcium carbonate decomposes into calcium oxide and carbon dioxide, which are chemically different from the original compound.
(v) Endothermic reactions absorb energy from the surroundings, often in the form of heat. This energy is used to break chemical bonds during the reaction.
Question 2(b) (Subtopic – C1.1)
(i) Carbon dioxide is a compound, but carbon is an element. State the difference between an element and a compound.
(ii) Carbon is a solid, and carbon dioxide is a gas. Complete Table 2.1 to describe the differences between a solid and a gas.
Table 2.1
| Particle Separation | Particle Arrangement | Particle Motion | |
|---|---|---|---|
| Solid | Vibrate about a fixed point | ||
| Gas | Move rapidly in all directions |
▶️Answer/Explanation
(i) An element contains only one type of atom, while a compound contains two or more elements chemically combined.
(ii) The completed table is:
| Particle Separation | Particle Arrangement | Particle Motion | |
|---|---|---|---|
| Solid | Close together | Regular | Vibrate about a fixed point |
| Gas | Far apart | Random | Move rapidly in all directions |
Detailed Solution:
(i) An element is a pure substance made up of only one type of atom (e.g., carbon). A compound is a substance formed when two or more elements are chemically bonded together (e.g., carbon dioxide).
(ii) In solids, particles are closely packed in a regular arrangement and vibrate about fixed positions. In gases, particles are far apart, arranged randomly, and move rapidly in all directions.
Question 2 (c) (Subtopic – C2.6)
Carbon exists in many forms, including diamond and graphite. Diamond and graphite are described as giant covalent structures. Fig. 2.1 shows three covalent structures, A, B, and C.
(i) State which structure represents diamond.
(ii) State which structure represents graphite.
(iii) State why the bonding between the carbon atoms in diamond is covalent and not ionic.
▶️Answer/Explanation
(i) Structure A represents diamond.
(ii) Structure B represents graphite.
(iii) The bonding between carbon atoms in diamond is covalent because the atoms share electrons to form strong covalent bonds, rather than transferring electrons as in ionic bonding.
Detailed Solution:
(i) Diamond has a tetrahedral structure where each carbon atom is bonded to four other carbon atoms, forming a rigid 3D network. This matches structure A.
(ii) Graphite has a layered structure where each carbon atom is bonded to three others, forming hexagonal rings. The layers are held together by weak forces, allowing them to slide over each other. This matches structure B.
(iii) Covalent bonding involves the sharing of electrons between atoms. In diamond, each carbon atom shares electrons with four neighboring carbon atoms, forming strong covalent bonds. Ionic bonding involves the transfer of electrons, which does not occur in diamond.
Question 3 (a) (Subtopic – P4.3.2)
A student constructs a circuit containing two lamps in parallel connected across two cells in series. Each lamp is controlled by a separate switch.
(i) Draw a circuit diagram for this circuit using standard electrical symbols.
(ii) State one advantage of connecting the lamps in parallel rather than in series.
▶️Answer/Explanation
(i) The circuit diagram should include:
- Two cells connected in series.
- Two lamps connected in parallel.
- Two switches, each controlling one lamp.
(ii) One advantage of connecting the lamps in parallel is that if one lamp fails, the other lamp will still light.
Detailed Solution:
(i) In a parallel circuit, each component has its own separate path for current flow. The circuit diagram should show two cells in series (connected end-to-end) and two lamps in parallel (each connected across the same two points in the circuit). Each lamp should have its own switch to control it independently.
(ii) In a parallel circuit, the failure of one component does not affect the operation of the other components. This is because each component has its own independent path for current flow. In contrast, in a series circuit, if one component fails, the entire circuit is broken, and no current flows.
Question 3 (b) (Subtopic – P2.3.1 and P3.3)
Fig. 3.1 shows a filament lamp.
(i) When the lamp is switched on, thermal energy is transferred from the filament through the metal base. Name the process that transfers the thermal energy.
(ii) Suggest one part of the electromagnetic spectrum emitted by the lamp.
▶️Answer/Explanation
(i) The process that transfers thermal energy is conduction.
(ii) One part of the electromagnetic spectrum emitted by the lamp is visible light or infrared radiation.
Detailed Solution:
(i) Conduction is the process by which thermal energy is transferred through a material (e.g., the metal base of the lamp) from a region of higher temperature to a region of lower temperature. In this case, thermal energy is transferred from the hot filament to the metal base.
(ii) A filament lamp emits electromagnetic radiation, including visible light (which allows us to see) and infrared radiation (which we feel as heat).
Question 3 (c) (Subtopic – P3.2.2)
Fig. 3.2 shows a ray of light from the lamp passing through a rectangular glass block.
(i) On Fig. 3.2, label the angle of incidence with the letter i and the angle of refraction with the letter r.
(ii) Explain why the ray of light changes direction as it is refracted through the glass block.
▶️Answer/Explanation
(i) The angle of incidence (i) is the angle between the incident ray and the normal. The angle of refraction (r) is the angle between the refracted ray and the normal.
(ii) The ray of light changes direction because light travels at different speeds in different media. When light enters the glass block, it slows down, causing it to bend towards the normal.
Detailed Solution:
(i) The angle of incidence (i) is measured between the incident ray and the normal (a line perpendicular to the surface of the glass block). The angle of refraction (r) is measured between the refracted ray and the normal.
(ii) Refraction occurs because light changes speed when it passes from one medium (e.g., air) to another (e.g., glass). When light enters a denser medium (like glass), it slows down and bends towards the normal. This change in speed and direction is described by Snell’s Law.
Question 4 (Sub-topic – B15.4)
(a) Fig. 4.1 is a diagram of the male reproductive system in humans.
Identify the letter from Fig. 4.1 that represents the:
- part where sperm is produced
- part which secretes the fluid that sperm swim in
- tube which carries both semen and urine
▶️Answer/Explanation
Answer:
1. E (Testes)
2. C (Seminal vesicle)
3. A (Urethra)
Explanation:
– The testes (E) are responsible for producing sperm.
– The seminal vesicle (C) secretes a fluid that mixes with sperm to form semen.
– The urethra (A) is the tube that carries both semen and urine out of the body.
(b) State the name of the part of the female reproductive system that releases gametes.
▶️Answer/Explanation
Answer:
Ovary
Explanation:
The ovary is the part of the female reproductive system that releases gametes (eggs) during ovulation.
(c) The statements in Table 4.1 describe either asexual or sexual reproduction.
Complete Table 4.1 to identify the type of reproduction each statement describes.
| Statement | Type of Reproduction |
|---|---|
| Offspring are genetically identical to each other | …… |
| Produces zygotes | …… |
| Involves the fusion of nuclei | …… |
▶️Answer/Explanation
Answer:
| Statement | Type of Reproduction |
|---|---|
| Offspring are genetically identical to each other | Asexual |
| Produces zygotes | Sexual |
| Involves the fusion of nuclei | Sexual |
Explanation:
– Asexual reproduction produces offspring that are genetically identical to each other because there is no fusion of gametes.
– Sexual reproduction involves the fusion of male and female gametes to form a zygote, which develops into a new organism.
(d) Fig. 4.2 is a diagram representing the reproduction of a type of organism called a hydra.
Identify if this organism is reproducing asexually or sexually. Use evidence from Fig. 4.2 to give a reason for your answer.
Type of reproduction
Reason
▶️Answer/Explanation
Answer:
Type of reproduction: Asexual
Reason: Offspring are produced by only one parent.
Explanation:
In asexual reproduction, offspring are produced from a single parent without the fusion of gametes. The diagram shows a hydra producing a bud, which is a form of asexual reproduction.
(e) Reproduction and respiration are characteristics of living things.
State two other characteristics of living things.
▶️Answer/Explanation
Answer:
1. Movement
2. Growth
Explanation:
– Movement is a characteristic of living things, as organisms can move to find food, escape predators, or respond to stimuli.
– Growth is another characteristic, as living organisms increase in size and complexity over time.
Question 5 (Sub-topic – C9.4)
(a) Iron is an element in Period 4 of the Periodic Table.
- Name the collection of metals in Period 4 that contains iron.
- An atom of iron has a proton number of 26 and a nucleon number of 56. State the number of electrons in this atom.
Number of electrons - Iron is obtained from iron oxide by reaction with carbon. The word equation for the reaction is shown.
iron oxide + carbon → iron + carbon dioxide
Name the substance that is reduced in this reaction. Explain your answer.
Substance reduced
Explanation
▶️Answer/Explanation
Answer:
1. Transition metals
2. 26
3. Iron oxide
Explanation: Iron oxide loses oxygen, which is reduction.
Explanation:
– Iron is part of the transition metals in Period 4 of the Periodic Table.
– The number of electrons in an atom is equal to the proton number, which is 26 for iron.
– In the reaction, iron oxide (Fe₂O₃) loses oxygen to form iron (Fe), which is a reduction process.
(b) Steel is an alloy of iron.
- State what is meant by an alloy.
- State why steel is used rather than pure iron for making cars.
- Table 5.1 shows the percentage composition of an alloy.
Element Percentage Copper 33 Iron …… Nickel 60 Calculate the percentage of iron in the alloy.
Percentage of iron = …… %
▶️Answer/Explanation
Answer:
1. An alloy is a mixture of a metal with one or more other elements.
2. Steel is stronger and more resistant to corrosion than pure iron.
3. 7%
Explanation:
– An alloy is a mixture of metals or a metal with another element to improve its properties.
– Steel is preferred over pure iron because it is stronger and less prone to rusting.
– The percentage of iron in the alloy is calculated as follows:
Total percentage = 100%
Percentage of iron = 100% – (33% + 60%) = 7%.
(c) A student investigates the rusting of iron nails.
Fig. 5.1 shows the student’s experiments.
Table 5.2 shows the student’s observations after one week. Complete Table 5.2 to explain the student’s observations.
| Test-tube | Rusts/Does not rust | Explanation |
|---|---|---|
| X | Does not rust | …… |
| Y | Rusts | …… |
| Z | Does not rust | …… |
▶️Answer/Explanation
Answer:
| Test-tube | Rusts/Does not rust | Explanation |
|---|---|---|
| X | Does not rust | No water present |
| Y | Rusts | Oxygen (air) and water present |
| Z | Does not rust | No air and water can reach the nail |
Explanation:
– In test-tube X, there is no water, so rusting cannot occur.
– In test-tube Y, both oxygen and water are present, which are necessary for rusting.
– In test-tube Z, the nail is painted, preventing air and water from reaching it, so rusting does not occur.
Question 6 (a) (Subtopic – P4.5.4)
Fig. 6.1 shows a copper wire connected to a battery and placed between the poles of a strong magnet.
(i) Describe two ways to change the apparatus so that the wire moves downwards when the switch is closed.
To make the wire move downwards when the switch is closed, you can:
- Reverse the polarity of the battery, which will reverse the direction of the current flowing through the wire.
- Reverse the polarity of the magnet, which will change the direction of the magnetic field.
▶️Answer/Explanation
Answer:
- Reverse the battery polarity / current.
- Reverse the magnet polarity.
Explanation: The direction of the force on the wire depends on the direction of the current and the magnetic field. By reversing either the current or the magnetic field, the force will act in the opposite direction, causing the wire to move downwards.
(Subtopic – P4.2.2)
(ii) State the term that describes a flow of electrons in a metal conductor.
The term that describes the flow of electrons in a metal conductor is “current.”
▶️Answer/Explanation
Answer: Current Explanation: In a metal conductor, the flow of electrons constitutes an electric current. The direction of conventional current is opposite to the direction of electron flow.
Question 6 (b) (Subtopic – P5.2.2)
A β-particle is an electron. α-particles and β-particles are radioactive emissions released during the radioactive decay of isotopes.
(i) State the meaning of the terms:
1. Radioactive decay: The process by which an unstable atomic nucleus loses energy by emitting radiation, such as α-particles or β-particles.
2. Isotopes: Atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses.
▶️Answer/Explanation
Answer:
- Radioactive decay is the process by which an unstable nucleus loses energy by emitting radiation.
- Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
Explanation: Radioactive decay is a spontaneous process that occurs in unstable nuclei, leading to the emission of particles or energy. Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, which affects their stability and radioactive properties.
(Subtopic – P5.2.2)
(ii) Complete the sentences below using the symbols α and β.
β particles are less ionising than α particles.
α particles are less penetrating than β particles.
▶️Answer/Explanation
Answer:
β particles are less ionising than α particles.
α particles are less penetrating than β particles.
Explanation: α-particles are helium nuclei and are highly ionising but have low penetration power due to their large mass and charge. β-particles are electrons or positrons and are less ionising but more penetrating than α-particles.
Question 6 (c) (Subtopic – P4.2.1)
A plastic ruler and a piece of cloth are both uncharged. A student rubs the plastic ruler with the cloth. The plastic ruler becomes positively charged.
(i) Describe in terms of electrons how the plastic ruler becomes positively charged.
When the plastic ruler is rubbed with the cloth, electrons are transferred from the ruler to the cloth. This leaves the ruler with a deficiency of electrons, resulting in a positive charge.
▶️Answer/Explanation
Answer: The ruler loses electrons.
Explanation: When two materials are rubbed together, electrons can be transferred from one material to another. In this case, electrons are transferred from the plastic ruler to the cloth, leaving the ruler with a positive charge due to the loss of electrons.
(Subtopic – P4.2.1)
(ii) State which row from Table 6.1 shows the charge on the cloth compared to the charge on the plastic ruler.
Row 4 shows the charge on the cloth compared to the charge on the plastic ruler. The cloth has a negative charge equal in magnitude to the positive charge on the ruler.
▶️Answer/Explanation
Answer: Row 4
Explanation: Since the ruler loses electrons and becomes positively charged, the cloth gains those electrons and becomes negatively charged. The charges are equal in magnitude but opposite in sign, which corresponds to row 4 in Table 6.1.
Question 7
Sub-topic – B16.3
(a) A student has two peas.
Pea A is green. Pea B is yellow. The colour of peas is controlled by a single gene.
- The allele for green-coloured peas is g.
- The allele for yellow-coloured peas is G.
- Circle two words that can be used to describe the genotype of pea A.
allele dominant heterozygous homozygous phenotype recessive - State the two possible genotypes of pea B.
…… and ……
▶️Answer/Explanation
Answer:
1. Homozygous and recessive
2. GG and Gg
Explanation:
– Pea A is green, which is the recessive trait, so its genotype must be homozygous recessive (gg).
– Pea B is yellow, which is the dominant trait. It can be either homozygous dominant (GG) or heterozygous (Gg).
(b) Two pea plants are crossed.
Fig. 7.1 is an incomplete genetic diagram showing a genetic cross of two pea plants.
- Complete the genetic diagram in Fig. 7.1 to show the expected genotypes of the offspring.
Parental gametes G g Parental gametes G …… …… g …… …… - State the percentage chance of the parent plants in Fig. 7.1 producing offspring that have the genotype gg.
…… %
▶️Answer/Explanation
Answer:
1.
| Parental gametes | G | g | |
|---|---|---|---|
| Parental gametes | G | GG | Gg |
| g | Gg | gg |
2. 25%
Explanation:
– The genetic cross is between two heterozygous parents (Gg x Gg).
– The Punnett square shows the possible genotypes of the offspring: GG, Gg, Gg, and gg.
– The genotype gg has a 1 in 4 (25%) chance of occurring.
(c) Chromosomes, DNA, and genes are involved in inheritance.
- List these structures in order of size from smallest to largest.
…… → …… → …… - State the phenotype of a person with the sex chromosomes XX.
……
▶️Answer/Explanation
Answer:
1. DNA → genes → chromosomes
2. Female
Explanation:
– DNA is the smallest unit, followed by genes (which are segments of DNA), and chromosomes (which are made up of DNA and proteins).
– The sex chromosomes XX determine the female phenotype in humans.
Question 8 (a) (Subtopic – C11.3)
Petroleum is a fossil fuel.
(i) Name one other fossil fuel.
(ii) Petroleum is separated into fractions to make it more useful. Complete the sentences using words from the list.
List: compound, distillation, electrolysis, filtration, mixture, molecule
Petroleum is a …… of different hydrocarbons. Petroleum is separated by fractional …….
(iii) Gasoline is obtained from petroleum. State the two products of the complete combustion of gasoline.
▶️Answer/Explanation
(i) Another fossil fuel is coal or natural gas.
(ii) The completed sentences are:
- Petroleum is a mixture of different hydrocarbons.
- Petroleum is separated by fractional distillation.
(iii) The two products of the complete combustion of gasoline are:
- Carbon dioxide (CO2)
- Water (H2O)
Detailed Solution:
(i) Fossil fuels are formed from the remains of ancient plants and animals. Examples include coal, natural gas, and petroleum.
(ii) Petroleum is a complex mixture of hydrocarbons. Fractional distillation is the process used to separate these hydrocarbons based on their boiling points. This process occurs in a fractionating column, where different fractions (e.g., gasoline, diesel) are collected at different heights.
(iii) Complete combustion of gasoline (a hydrocarbon) occurs in the presence of sufficient oxygen. The products are carbon dioxide (CO2) and water (H2O), as the hydrocarbon reacts with oxygen to form these compounds.
Question 8 (b) (Subtopic – C11.5)
Ethane, C2H6, is an alkane. Ethene, C2H4, is an alkene.
(i) Explain why ethene is described as an unsaturated hydrocarbon.
(ii) Describe the chemical test and the positive result for an unsaturated hydrocarbon.
▶️Answer/Explanation
(i) Ethene is described as an unsaturated hydrocarbon because it contains a carbon-carbon double bond, which allows it to undergo addition reactions.
(ii) The chemical test for an unsaturated hydrocarbon is:
- Test: Add aqueous bromine (bromine water) to the hydrocarbon.
- Positive Result: The bromine water changes from orange/brown to colorless.
Detailed Solution:
(i) Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond. Ethene (C2H4) has a double bond between the two carbon atoms, making it unsaturated. This double bond allows ethene to react with other substances in addition reactions.
(ii) The bromine water test is used to identify unsaturated hydrocarbons. When bromine water is added to an unsaturated hydrocarbon, the double bond reacts with the bromine, causing the orange/brown color of bromine to disappear. This indicates the presence of an unsaturated hydrocarbon.
Question 8 (c) (Subtopic – C11.7)
Ethene molecules react together to form a polymer.
(i) Describe what happens to the ethene molecules when they form a polymer.
(ii) Name the polymer made from ethene.
▶️Answer/Explanation
(i) When ethene molecules form a polymer, they join together in long chains through a process called addition polymerization. The double bonds in ethene break, and the molecules link together to form a polymer.
(ii) The polymer made from ethene is polyethene (also called polyethylene).
Detailed Solution:
(i) In addition polymerization, the double bonds in ethene molecules break, and the carbon atoms form single bonds with other ethene molecules. This creates a long chain of repeating units, known as a polymer.
(ii) The polymer formed from ethene is called polyethene (or polyethylene). It is a widely used plastic in packaging, containers, and other applications due to its durability and flexibility.
Question 9 (Subtopic – P2.3 )
Fig. 9.1 shows a refrigerator.
(a) The freezing compartment at the top of the refrigerator cools all the air in the refrigerator.
State the main method of thermal energy transfer used in this cooling process.
▶️Answer/Explanation
Answer:
Convection
Explanation:
Convection is the main method of thermal energy transfer in the refrigerator. Cold air from the freezing compartment sinks, and warmer air rises, creating a convection current that cools the entire refrigerator.
(b) The volume of air in the refrigerator is 210 000 cm3.
The density of air is 0.00126 g/cm3.
Calculate the mass of air in the refrigerator. Show your working.
Mass = …… g
▶️Answer/Explanation
Answer:
265 g
Explanation:
Mass = Density × Volume
Mass = 0.00126 g/cm3 × 210,000 cm3
Mass = 265 g
(c) A liquid-in-glass thermometer is placed inside the freezing compartment to measure a temperature of –20 °C.
- Name a suitable liquid to use in the thermometer.
- State the physical property of the liquid that varies with temperature in a liquid-in-glass thermometer.
▶️Answer/Explanation
Answer:
1. Mercury or alcohol
2. Volume
Explanation:
– Mercury or alcohol is commonly used in liquid-in-glass thermometers because they expand and contract predictably with temperature changes.
– The volume of the liquid changes with temperature, causing it to rise or fall in the thermometer’s narrow tube.
(d) The refrigerator emits a quiet sound with a low pitch.
- Describe the amplitude and frequency of this sound.
Amplitude
Frequency - State the unit of frequency.
▶️Answer/Explanation
Answer:
1. Small amplitude, low frequency
2. Hertz (Hz)
Explanation:
– A quiet sound has a small amplitude, and a low-pitched sound has a low frequency.
– The unit of frequency is hertz (Hz), which measures the number of vibrations per second.
(e) The refrigerator contains two lamps connected in series.
Lamp A has a resistance of 4000 Ω and lamp B has a resistance of 5000 Ω.
- Calculate the combined resistance of the two lamps connected in series.
Resistance = …… Ω - The potential difference across the lamps is 240 V. Use your answer to (e)(i) to calculate the current in the lamps. Show your working.
Current = …… A
▶️Answer/Explanation
Answer:
1. 9000 Ω
2. 0.027 A
Explanation:
1. Combined resistance in series = R1 + R2
Combined resistance = 4000 Ω + 5000 Ω = 9000 Ω
2. Current (I) = Voltage (V) / Resistance (R)
I = 240 V / 9000 Ω = 0.027 A
Question 10 (a) (Subtopic – B18.3)
Fig. 10.1 is a diagram showing part of the carbon cycle.
(i) Name the process occurring at X in Fig. 10.1.
▶️Answer/Explanation
(i) The process occurring at X is fossilisation.
Detailed Solution:
(i) Fossilisation is the process by which dead organisms are converted into fossil fuels (e.g., coal, oil, and natural gas) over millions of years. This process involves the burial and decomposition of organic matter under high pressure and temperature.
Question 10 (b) (Subtopic – B19.1)
When deforestation occurs, there is a build-up of carbon dioxide in the atmosphere.
(i) List two other negative effects of deforestation.
(ii) Stopping deforestation will reduce the build-up of carbon dioxide in the atmosphere. Use the information in Fig. 10.1 to suggest two other ways we can reduce the build-up of carbon dioxide in the atmosphere.
▶️Answer/Explanation
(i) Two other negative effects of deforestation are:
- Loss of biodiversity: Many species lose their habitats, leading to extinction.
- Soil erosion: The removal of trees exposes soil to wind and rain, leading to erosion.
(ii) Two other ways to reduce the build-up of carbon dioxide in the atmosphere are:
- Plant more trees: Trees absorb carbon dioxide during photosynthesis, reducing its concentration in the atmosphere.
- Reduce the combustion of fossil fuels: Using renewable energy sources (e.g., solar, wind) instead of fossil fuels can reduce carbon dioxide emissions.
Detailed Solution:
(i) Deforestation has several negative impacts on the environment:
- Loss of biodiversity: Forests are home to many species, and their destruction leads to habitat loss and extinction.
- Soil erosion: Trees help hold soil in place. Without them, soil is easily washed or blown away, leading to reduced soil fertility and increased sedimentation in rivers.
(ii) To reduce carbon dioxide levels, we can:
- Plant more trees: Trees act as carbon sinks, absorbing carbon dioxide from the atmosphere and storing it in their biomass.
- Reduce fossil fuel use: Burning fossil fuels releases carbon dioxide. Switching to renewable energy sources can significantly reduce emissions.
Question 10 (c) (Subtopic – B6.1 and B12.1)
Table 10.1 shows some features of respiration and photosynthesis.
Table 10.1
| Process | Produces Carbon Dioxide | Produces Oxygen | Requires Light Energy | Produces Carbohydrates |
|---|---|---|---|---|
| Photosynthesis | ||||
| Respiration |
Place ticks (✓) in the boxes to show the features of each process.
▶️Answer/Explanation
The completed table is:
| Process | Produces Carbon Dioxide | Produces Oxygen | Requires Light Energy | Produces Carbohydrates |
|---|---|---|---|---|
| Photosynthesis | ✓ | ✓ | ✓ | |
| Respiration | ✓ |
Detailed Solution:
Photosynthesis:
- Produces Oxygen: Oxygen is released as a byproduct of photosynthesis.
- Requires Light Energy: Photosynthesis uses light energy to convert carbon dioxide and water into glucose.
- Produces Carbohydrates: Glucose (a carbohydrate) is produced during photosynthesis.
Respiration:
- Produces Carbon Dioxide: Carbon dioxide is released as a waste product of respiration.
- Does not produce oxygen: Respiration consumes oxygen and releases carbon dioxide.
- Does not require light energy: Respiration occurs in all living cells, regardless of light availability.
- Does not produce carbohydrates: Respiration breaks down glucose to release energy, rather than producing it.
Question 10 (d) (Subtopic – B8.3)
Water is one of the substances required by plants and is also lost by plants during transpiration.
(i) State the name of the vessels that transport water through a plant.
(ii) Complete the sentences to define the term transpiration.
Transpiration is the loss of water vapour from plant …… by evaporation of water at the surfaces of the mesophyll ……, followed by diffusion of water vapour through the …….
▶️Answer/Explanation
(i) The vessels that transport water through a plant are called xylem.
(ii) The completed sentences are:
- Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells, followed by diffusion of water vapour through the stomata.
Detailed Solution:
(i) The xylem is a specialized tissue in plants that transports water and dissolved minerals from the roots to the leaves. It also provides structural support to the plant.
(ii) Transpiration is the process by which water is lost from the leaves of a plant in the form of water vapour. This occurs when water evaporates from the surfaces of mesophyll cells inside the leaf and diffuses out through tiny pores called stomata.
Question 11 (Subtopic – C8.2)
(a) Table 11.1 shows the melting points of some Group I elements.
| Element | Melting point/°C |
|---|---|
| Lithium | 181 |
| Sodium | 98 |
| Potassium | …… |
| Rubidium | 39 |
| Caesium | 28 |
Predict the melting point of potassium.
…… °C
▶️Answer/Explanation
Answer:
63 °C
Explanation:
The melting points of Group I elements decrease as you move down the group. Sodium (Na) has a melting point of 98 °C, and rubidium (Rb) has a melting point of 39 °C. Potassium (K) is between sodium and rubidium, so its melting point is approximately 63 °C.
(b) Potassium reacts with chlorine to make potassium chloride.
Potassium chloride is an ionic compound. Fig. 11.1 shows the electronic structure of a potassium atom and of a chlorine atom.
- Complete the diagrams in Fig. 11.2 to show the ions in potassium chloride.
Potassium ion:
Chloride ion: - Balance the symbol equation for the reaction between potassium and chlorine.
…… K + Cl2 → …… KCl
▶️Answer/Explanation
Answer:
1. Potassium ion: K+, Chloride ion: Cl–
2. 2 K + Cl2 → 2 KCl
Explanation:
– Potassium (K) loses one electron to form a K+ ion, and chlorine (Cl) gains one electron to form a Cl– ion.
– The balanced equation for the reaction is 2 K + Cl2 → 2 KCl, as two potassium atoms react with one chlorine molecule to form two potassium chloride molecules.
(c) Universal indicator is added to water.
The water is neutral.
- State the pH of the water.
pH - A teacher reacts potassium with the water. Potassium hydroxide solution is made in the reaction. Suggest the pH of the resulting potassium hydroxide solution and the colour of the universal indicator.
pH
Colour of universal indicator - The teacher reacts lithium with water. Compare the reactivity of lithium with the reactivity of potassium.
▶️Answer/Explanation
Answer:
1. pH 7
2. pH 14, Purple
3. Lithium is less reactive than potassium.
Explanation:
– Neutral water has a pH of 7.
– Potassium hydroxide is a strong alkali, so the pH of the solution will be 14, and the universal indicator will turn purple.
– Lithium is less reactive than potassium because reactivity increases as you move down Group I of the Periodic Table.
Question 12 (a) (Subtopic – P1.5.1)
An astronaut travels to the Moon in a spacecraft. The weight of the spacecraft at take-off is 25,000,000 N. When the spacecraft blasts off from Earth, it is pushed upwards by a force of 32,000,000 N.
Calculate the resultant upward force on the spacecraft.
The resultant upward force can be calculated by subtracting the weight of the spacecraft from the upward force applied during take-off.
▶️Answer/Explanation
Answer: 7,000,000 N Explanation: The resultant upward force is calculated as follows: \[ \text{Resultant Force} = \text{Upward Force} – \text{Weight} \] \[ \text{Resultant Force} = 32,000,000 \, \text{N} – 25,000,000 \, \text{N} = 7,000,000 \, \text{N} \] Therefore, the resultant upward force on the spacecraft is 7,000,000 N.
Question 12 (b) (Sub-topic – P1.6.1)
The spacecraft has solar panels to gather energy from the Sun. This energy is stored in batteries on the spacecraft.
(i) Complete the sentences to describe the energy conversion that takes place in this process.
The Sun’s light energy is transformed into electrical energy by the solar panels. This energy is stored as chemical potential energy in the batteries.
▶️Answer/Explanation
Answer:
The Sun’s light energy is transformed into electrical energy by the solar panels.
This energy is stored as chemical potential energy in the batteries.
Explanation: Solar panels convert sunlight (light energy) into electrical energy through the photovoltaic effect. This electrical energy is then stored in batteries as chemical potential energy, which can be later converted back into electrical energy when needed.
(Subtopic Code: P1.6.3)
(ii) Solar energy is a renewable energy source. State one other renewable energy source.
One other renewable energy source is wind energy.
▶️Answer/Explanation
Answer: Wind energy Explanation: Wind energy is a renewable energy source that harnesses the kinetic energy of wind to generate electricity using wind turbines. It is sustainable and does not deplete natural resources.
Question 12 (c) (Subtopic – P1.2)
(c) The spacecraft travels 386,000 km from Earth to the Moon in 72 hours. Calculate the average speed of the spacecraft in km/s.
To calculate the average speed, divide the total distance traveled by the total time taken, converting hours to seconds.
▶️Answer/Explanation
Answer: 1.49 km/s Explanation: First, convert 72 hours into seconds: \[ 72 \, \text{hours} = 72 \times 60 \times 60 = 259,200 \, \text{seconds} \] Then, calculate the average speed: \[ \text{Average Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{386,000 \, \text{km}}{259,200 \, \text{s}} \approx 1.49 \, \text{km/s} \] Therefore, the average speed of the spacecraft is approximately 1.49 km/s.
Question 12 (d) (Subtopic – P1.3)
On Earth, the astronaut has a mass of 80 kg and a weight of 800 N. On the Moon, the astronaut has a mass of 80 kg and a weight of 135 N. Describe the difference between mass and weight.
Mass is a measure of the amount of matter in an object and is constant regardless of location. Weight is the force exerted on an object due to gravity and varies depending on the gravitational field strength.
▶️Answer/Explanation
Answer:
Mass is the actual amount of material contained in a body (measured in kg or g).
Weight is the force exerted by gravity on that object.
Explanation: Mass is an intrinsic property of an object and does not change with location. Weight, however, depends on the gravitational force acting on the object. On the Moon, the gravitational field strength is weaker than on Earth, so the astronaut’s weight is less, even though their mass remains the same.
Question 12 (e) (Subtopic – P3.3)
The astronaut communicates with Earth using radio waves.
(i) Fig. 12.1 shows an incomplete electromagnetic spectrum.
Place radio waves in the correct place in Fig. 12.1.
Radio waves should be placed in the right-hand box of the electromagnetic spectrum, as they have the longest wavelength and lowest frequency.
▶️Answer/Explanation
Answer: Radio waves in the right-hand box. Explanation: The electromagnetic spectrum is arranged in order of increasing frequency and decreasing wavelength. Radio waves have the longest wavelengths and lowest frequencies, so they belong on the far right of the spectrum.
(Sub-topic Code: P3.4)
(ii) Explain why it is not possible for the astronaut to communicate with Earth using sound waves.
Sound waves require a medium (such as air, water, or solids) to travel through. In space, there is no medium, so sound waves cannot propagate, making communication using sound waves impossible.
▶️Answer/Explanation
Answer: Sound waves need a medium and cannot travel through a vacuum. Explanation: Sound waves are mechanical waves that require a medium (like air or water) to travel through. In the vacuum of space, there is no medium for sound waves to propagate, so they cannot be used for communication.
(Sub-topic Code: P3.4)
(iii) Fig. 12.2 shows a sound wave. On Fig. 12.2, label with a double-headed arrow (↔) one wavelength of the sound wave.
One wavelength of the sound wave can be labeled by drawing a double-headed arrow from one peak to the next peak or from one trough to the next trough.
▶️Answer/Explanation
Answer: Double-headed arrow from peak to peak or trough to trough. Explanation: The wavelength of a wave is the distance between two consecutive peaks (crests) or troughs. Labeling this distance with a double-headed arrow indicates one complete cycle of the wave.