Question 1
(a) Fig. 1.1 is a diagram of a food web in the sea. (Sub-topic: B18.2)
(i) Construct a food chain from the food web shown in Fig. 1.1. Your food chain must include four organisms.
▶️Answer/Explanation
Answer: green algae → limpets → crab → lobster / phytoplankton → mussels → crab → lobster
Explanation: A food chain represents the flow of energy from one organism to another. In this case, the food chain starts with a producer (green algae or phytoplankton), which is eaten by a primary consumer (limpets or mussels), which is then eaten by a secondary consumer (crab), and finally by a tertiary consumer (lobster).
(ii) Table 1.1 shows some terms that can be used to describe organisms in the food web shown in Fig. 1.1. Place ticks (✓) in the boxes to show all the terms that describe each organism. (Sub-topic: B18.2)
| carnivore | herbivore | producer | primary consumer | tertiary consumer | |
|---|---|---|---|---|---|
| crabs | |||||
| limpets | |||||
| lobsters | |||||
| phytoplankton |
▶️Answer/Explanation
Answer:
| carnivore | herbivore | producer | primary consumer | tertiary consumer | |
|---|---|---|---|---|---|
| crabs | ✓ | ||||
| limpets | ✓ | ✓ | |||
| lobsters | ✓ | ✓ | |||
| phytoplankton | ✓ |
Explanation:
- Crabs are carnivores as they eat other animals (limpets, mussels) and are tertiary consumers as they are at the top of the food chain.
- Limpets are herbivores as they eat producers (green algae) and are primary consumers as they are the first consumers in the food chain.
- Lobsters are carnivores as they eat other animals (crabs) and are tertiary consumers as they are at the top of the food chain.
- Phytoplankton are producers as they produce their own food through photosynthesis.
(iii) A disease kills all the limpets in the food web shown in Fig. 1.1. State why: (Sub-topic: B18.2)
- the population of green algae increases
- the immediate population of mussels decreases.
▶️Answer/Explanation
Answer:
- The population of green algae increases due to less predation (by limpets).
- The population of mussels decreases because there is more predation of mussels by crabs or lobsters.
Explanation:
- When limpets are removed from the food web, there are fewer organisms feeding on green algae, leading to an increase in their population.
- With the absence of limpets, crabs and lobsters may increase their predation on mussels, leading to a decrease in the mussel population.
(b) Disease can cause organisms to become extinct. Deforestation is another reason for extinction of organisms. List two other undesirable effects of deforestation. (Sub-topic: B19.1)
▶️Answer/Explanation
Answer:
- Loss of habitat
- Loss of soil
- Flooding
- Build-up of carbon dioxide in the atmosphere
Explanation:
- Loss of habitat: Deforestation destroys the natural habitats of many species, leading to a loss of biodiversity.
- Loss of soil: Trees help to hold soil together, and their removal can lead to soil erosion.
- Flooding: Trees absorb water, and their removal can lead to increased flooding.
- Build-up of carbon dioxide: Trees absorb carbon dioxide, and their removal contributes to increased levels of greenhouse gases in the atmosphere.
Question 2
The halogens chlorine, bromine and iodine are in Group VII of the Periodic Table.
(a)(i) Table 2.1 shows the melting points and boiling points of chlorine, bromine and iodine. Complete Table 2.1. (Sub-topic: C8.3)
| Halogen | Melting point /°C | Boiling point /°C | Solid, liquid or gas at 20°C |
|---|---|---|---|
| ….. | -7 | +59 | ….. |
| ….. | -101 | +34 | ….. |
| ….. | +114 | +184 | ….. |
▶️Answer/Explanation
Explanation: The halogens in Group VII have increasing melting and boiling points as you go down the group. Chlorine is a gas at room temperature, bromine is a liquid, and iodine is a solid. The melting and boiling points increase due to the increasing strength of the van der Waals forces between the molecules as the size of the halogen atoms increases.
(ii) Describe one other trend in the properties of the Group VII elements. (Sub-topic: C8.3)
▶️Answer/Explanation
Answer: The colour of the halogens becomes darker as you go down the group. Chlorine is pale green, bromine is red-brown, and iodine is dark grey or purple.
(b) In a naturally occurring sample of chlorine, one of the atoms contains 17 protons and 18 neutrons. The sentences about chlorine are either correct or incorrect. For each sentence, write a tick (✓) if it is correct or a cross (✗) if it is incorrect. (Sub-topic: C2.2)
▶️Answer/Explanation
Explanation:
- Protons are indeed contained in the nucleus, so this is correct.
- The nucleon number (mass number) is the sum of protons and neutrons, which is 17 + 18 = 35, not 18.
- A molecule of chlorine (Cl2) contains 2 chlorine atoms, each with 17 protons, so it has 34 protons in total. However, the question refers to a single atom, so this is incorrect.
- Not all chlorine atoms contain 18 neutrons; some isotopes have different numbers of neutrons.
- All chlorine atoms contain 17 protons, as this defines the element.
(c) Sodium reacts with chlorine to make sodium chloride. During the reaction, a sodium atom transfers one electron to a chlorine atom.
(i) State the type of chemical bonding in sodium chloride. (Sub-topic – C2.4)
▶️Answer/Explanation
Answer: Ionic bonding.
(ii) Explain in terms of electrical charges why sodium and chloride particles are strongly bonded in sodium chloride. (Sub-topic: C2.4)
▶️Answer/Explanation
Explanation: Sodium chloride is held together by strong electrostatic forces of attraction between the positively charged sodium ions (Na+) and the negatively charged chloride ions (Cl–). These oppositely charged ions attract each other, forming a strong ionic bond.
(d) A student knows that a white solid is either sodium chloride or potassium chloride. Describe a test she can do to identify whether the solid is sodium chloride or potassium chloride. Include the results she can expect. (Sub-topic: C12.5)
▶️Answer/Explanation
Answer: The student can perform a flame test. Sodium chloride will produce a yellow flame, while potassium chloride will produce a lilac flame.
Question 3 (Sub-topic: P1.2)
(a) A skydiver jumps from an aircraft high above the ground. Fig. 3.1 shows the speed–time graph of his descent.
Use the graph in Fig. 3.1 to calculate how far the skydiver falls from time \( t = 0 \, \text{s} \) to \( t = 10 \, \text{s} \).
▶️Answer/Explanation
Answer: 250 m
Explanation: The distance fallen by the skydiver can be calculated by finding the area under the speed-time graph from \( t = 0 \, \text{s} \) to \( t = 10 \, \text{s} \). The graph forms a triangle during this time interval. The area of a triangle is given by: \[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} \] Here, the base is 10 seconds, and the height is 50 m/s. Therefore: \[ \text{Distance} = \frac{1}{2} \times 10 \, \text{s} \times 50 \, \text{m/s} = 250 \, \text{m} \]
(b) When the skydiver opens the parachute at \( t = 10 \, \text{s} \), his speed decreases. Name the force that causes this decrease in speed. (Sub-topic: P1.5)
▶️Answer/Explanation
Answer: Air resistance (or friction)
Explanation: When the skydiver opens the parachute, the surface area exposed to air increases, leading to an increase in air resistance (or friction). This force opposes the motion of the skydiver, causing the speed to decrease.
(c) The skydiver has a mass of 85 kg. His weight is 850 N.
(i) State the size of the upwards force on the skydiver at \( t = 80 \, \text{s} \). Explain your answer. (Sub-topic: P1.3)
▶️Answer/Explanation
Answer: 850 N
Explanation: At \( t = 80 \, \text{s} \), the skydiver is descending at a constant speed, which means the forces acting on him are balanced. The upwards force (air resistance) must be equal to the downwards force (weight) to maintain this constant speed. Therefore, the upwards force is 850 N.
(ii) State the value of the gravitational field strength \( g \) that is used to determine the weight of the skydiver in (c). Give the units of \( g \). (Sub-topic: P1.3)
▶️Answer/Explanation
Answer: 10 N/kg
Explanation: The gravitational field strength \( g \) is calculated using the formula: \[ g = \frac{W}{m} \] where \( W \) is the weight and \( m \) is the mass. Given that the weight is 850 N and the mass is 85 kg: \[ g = \frac{850 \, \text{N}}{85 \, \text{kg}} = 10 \, \text{N/kg} \] The units of \( g \) are newtons per kilogram (N/kg).
(d) The skydiver lands in a pit full of sand. The dimensions of the sand pit are shown in Fig. 3.2. (Sub-topic: P1.4)
The density of sand is \( 1800 \, \text{kg/m}^3 \). Calculate the mass of the sand in the pit.
▶️Answer/Explanation
Answer: 27000 kg
Explanation: The mass of the sand can be calculated using the formula: \[ \text{mass} = \text{density} \times \text{volume} \] First, calculate the volume of the sand pit: \[ \text{Volume} = \text{length} \times \text{width} \times \text{height} = 6.0 \, \text{m} \times 5.0 \, \text{m} \times 0.5 \, \text{m} = 15 \, \text{m}^3 \] Then, calculate the mass: \[ \text{mass} = 1800 \, \text{kg/m}^3 \times 15 \, \text{m}^3 = 27000 \, \text{kg} \]
Question 4 (Sub-topic: B7.1)
(a) In Fig. 4.1, the boxes on the left show some of the components of a balanced diet for an adult. The boxes on the right show some principal sources of these components. Draw four lines to link each component with its principal source.
▶️Answer/Explanation
Answer:
carbohydrate → noodles
fat → olive oil
protein → fish
vitamin C → grapefruit
Explanation:
Carbohydrates are primarily found in foods like noodles, which are rich in starch. Fats are commonly found in oils, such as olive oil. Proteins are abundant in fish, which is a good source of lean protein. Vitamin C is found in fruits like grapefruit, which are known for their high vitamin C content.
(b) A person has to choose between two different menus, A and B. Fig. 4.2 shows each menu.
(i) A doctor advises a patient to eat menu B rather than menu A. Suggest two reasons why.
▶️Answer/Explanation
Answer:
1. Menu B contains a greater variety of nutrients and food types, including more fruits and vegetables.
2. Menu B contains less fat and sugar compared to Menu A, which is healthier for the patient.
Explanation:
Menu B includes chicken, rice, mixed salad, fruit, and yoghurt, which provide a balanced mix of proteins, carbohydrates, vitamins, and minerals. In contrast, Menu A consists of a meat burger, potato chips, and chocolate cake, which are high in fats and sugars, making Menu B a healthier choice.
(ii) Both meals contain water. Table 4.1 lists some statements. Place a tick (✓) to show the statement that describes why water is needed by the body.
▶️Answer/Explanation
Answer:
as a solvent
Explanation:
Water is essential as a solvent in the body because it dissolves nutrients, waste products, and other substances, allowing them to be transported and utilized efficiently. It also facilitates chemical reactions, including respiration, but its primary role is as a solvent.
(c) The food we ingest is absorbed and assimilated inside the body.
(i) State where ingestion occurs.
▶️Answer/Explanation
Answer:
Mouth
Explanation:
Ingestion is the process of taking food into the body, and it occurs in the mouth where food is chewed and mixed with saliva before being swallowed.
(ii) Describe one similarity and one difference between absorption and assimilation.
▶️Answer/Explanation
Answer:
Similarity: Both absorption and assimilation involve the movement of digested food.
Difference: Absorption is the process of nutrients passing into the blood, while assimilation is the process of nutrients being taken up by cells.
Explanation:
Absorption occurs in the small intestine where nutrients from digested food pass through the intestinal wall into the bloodstream. Assimilation happens when these nutrients are transported to cells and used for energy, growth, and repair.
(d) Nutrition is one of the characteristics of living things. Name two other characteristics.
▶️Answer/Explanation
Answer:
1. Movement
2. Respiration
Explanation:
Living things exhibit various characteristics, including movement (the ability to change position) and respiration (the process of releasing energy from food). These are essential for survival and are part of the defining features of living organisms.
Question 5
Aluminium is used in industry to make many different products.
(a) Fig. 5.1 shows stages in the production of aluminium food containers. (Sub-topic: C9.2)
(i) State the physical property of aluminium which allows it to be made into thin sheets.
▶️Answer/Explanation
Answer: Malleability / it is malleable.
Explanation: Aluminium is malleable, meaning it can be hammered or rolled into thin sheets without breaking. This property is essential for manufacturing thin aluminium sheets used in food containers.
(ii) Describe the property of aluminium which means it is safe to use for food containers.
▶️Answer/Explanation
Answer: Unreactive / does not react with food.
Explanation: Aluminium is unreactive, meaning it does not easily react with food or other substances. This makes it safe for use in food containers as it won’t contaminate the food.
(b) Table 5.1 shows information about the composition of an aluminium alloy, A.
(i) Calculate the mass of aluminium in 100.0 g of alloy A. (Sub-topic: C9.3)
▶️Answer/Explanation
Answer: 94.2 g
Explanation: The mass of aluminium is calculated by subtracting the masses of the other elements from the total mass of the alloy: 100.0 g – (4.0 g + 0.6 g + 0.7 g + 0.5 g) = 94.2 g.
(ii) Identify the two transition elements in alloy A. (Sub-topic: C8.4)
▶️Answer/Explanation
Answer: Copper and chromium.
Explanation: Copper (Cu) and chromium (Cr) are transition elements, which are typically found in the d-block of the periodic table.
(iii) Aluminium alloys and pure aluminium have low densities. Suggest why aircraft parts are made from aluminium alloys rather than from pure aluminium. (Sub-topic: C9.3)
▶️Answer/Explanation
Answer: Alloy is stronger.
Explanation: Aluminium alloys are stronger than pure aluminium, making them more suitable for use in aircraft parts where strength and durability are crucial.
(c) Aluminium is extracted from its ore using electrolysis. Fig. 5.2 shows how this is done in industry.
(i) Aluminium forms at the negative electrode. The negative electrode is the carbon lining of the apparatus. State the name of this electrode. (Sub-topic: C4.1)
▶️Answer/Explanation
Answer: Cathode.
Explanation: In electrolysis, the negative electrode is called the cathode, where reduction occurs, and aluminium ions gain electrons to form aluminium metal.
(ii) Oxygen gas is made at the positive electrode. The positive electrode is made of carbon and is very hot. Suggest, in terms of a chemical reaction, why the positive electrode becomes smaller. (Sub-topic: C4.1)
▶️Answer/Explanation
Answer: Carbon oxidises / carbon burns / C + O2 → CO2.
Explanation: The positive electrode, made of carbon, reacts with oxygen to form carbon dioxide gas. This reaction causes the electrode to gradually erode and become smaller over time.
(iii) State the name of the ore from which aluminium is extracted. (Sub-topic: C9.6)
▶️Answer/Explanation
Answer: Bauxite.
Explanation: Bauxite is the primary ore from which aluminium is extracted. It contains aluminium oxide, which is then processed to obtain pure aluminium.
(iv) Aluminium ore is removed from the Earth’s crust and is not replaced. Describe one way in which humans can reduce the rate at which aluminium ore is being used. (Sub-topic: C9.6)
▶️Answer/Explanation
Answer: Recycle (waste) aluminium.
Explanation: Recycling aluminium reduces the need to extract new aluminium from bauxite ore, conserving natural resources and reducing environmental impact.
Question 6
(a) A torch (flashlight) contains a cell, a switch, and a lamp connected in series. (Sub-topic: P4.2.2)
(i) Complete the circuit diagram in Fig. 6.1. The lamp has been drawn for you.
(ii) The cell is a store of chemical energy. Complete the sentences to describe the energy transfers when the circuit is switched on and the lamp is lit.
In the cell, …… energy is transferred to electrical energy in the circuit.
Electrical energy in the circuit is transferred to …… energy and …… energy emitted from the lamp.
(iii) The lamp has a resistance of 8.0 Ω and the potential difference (p.d.) across the lamp is 12 V. Calculate the current in the lamp.
(b) (i) Name the instrument used to measure current in a circuit. (Sub-topic: P4.2.3)
(ii) The wires in the circuit are made of copper. State the name of the particles that flow when there is a current in the wires.
(c) A student connects a 3 Ω and a 4 Ω resistor in series. Calculate the combined resistance of these two resistors in series. (Sub-topic: P4.3.2)
▶️Answer/Explanation
6(a)(i) The circuit diagram should show the cell, switch, and lamp connected in series. The cell should be represented by a long and short line, the switch by a break in the line, and the lamp by a circle with a cross inside.
6(a)(ii) In the cell, chemical energy is transferred to electrical energy in the circuit. Electrical energy in the circuit is transferred to light energy and thermal energy emitted from the lamp.
6(a)(iii) Using Ohm’s Law, \( V = IR \), the current \( I \) can be calculated as: \[ I = \frac{V}{R} = \frac{12}{8} = 1.5 \, \text{A} \] So, the current in the lamp is 1.5 A.
6(b)(i) The instrument used to measure current in a circuit is an ammeter.
6(b)(ii) The particles that flow when there is a current in the wires are electrons.
6(c) When resistors are connected in series, their resistances add up. Therefore, the combined resistance is: \[ R_{\text{total}} = R_1 + R_2 = 3 + 4 = 7 \, \Omega \] So, the combined resistance is 7 Ω.
Question 7
(a) Fig. 7.1 is a diagram of the human gas exchange system.
(i) State the letters in Fig. 7.1 that identify the: (Sub-topic: B11.1)
- bronchus
- diaphragm
- ribs
- trachea
▶️Answer/Explanation
Answer: The letters in Fig. 7.1 identify the following parts of the human gas exchange system:
- Bronchus: F
- Diaphragm: C
- Ribs: G
- Trachea: B
Explanation: The bronchus is a passage that leads air into the lungs, the diaphragm is a muscle that helps in breathing, the ribs protect the lungs, and the trachea is the windpipe that carries air to the bronchi.
(ii) Table 7.1 contains some statements. Place ticks (✓) next to the statements that correctly describe diffusion. (Sub-topic: B3.1)
| Statement | ✓ |
|---|---|
| Diffusion occurs due to random movement of particles. | |
| Particles move up a concentration gradient. | |
| Substances move into cells by diffusion. | |
| The net movement of particles is from low to high concentration. | |
| Water does not diffuse into cells. |
▶️Answer/Explanation
Answer: The correct statements that describe diffusion are:
- Diffusion occurs due to random movement of particles.
- Substances move into cells by diffusion.
Explanation: Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration due to random motion. It is a passive process that allows substances to move into and out of cells.
(b) Inspired air contains more oxygen than expired air. Oxygen is used in the process of respiration.
(i) State two other ways that inspired air is different from expired air. (Sub-topic: B11.1)
▶️Answer/Explanation
Answer: Two other ways that inspired air is different from expired air are:
- Inspired air contains less carbon dioxide than expired air.
- Inspired air contains less water vapor than expired air.
Explanation: During respiration, oxygen is used by the body, and carbon dioxide is produced as a waste product. Therefore, expired air has more carbon dioxide and water vapor compared to inspired air.
(ii) State why respiration enables protein synthesis to take place. (Sub-topic: B12.1)
▶️Answer/Explanation
Answer: Respiration enables protein synthesis to take place because it releases energy.
Explanation: Protein synthesis is an energy-consuming process. The energy required for this process is provided by respiration, which breaks down glucose to release energy in the form of ATP.
(iii) State the substance that reacts with oxygen in aerobic respiration. (Sub-topic: B12.1)
▶️Answer/Explanation
Answer: The substance that reacts with oxygen in aerobic respiration is glucose.
Explanation: In aerobic respiration, glucose is broken down in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP.
Question 8 (Sub-topic: C2.5)
Fig. 8.1 shows hydrogen burning in air. Water is made during the reaction.
(a) Describe one test and its positive result to show that the liquid in the U-tube is water.
▶️Answer/Explanation
Answer: The test involves using anhydrous copper(II) sulfate. When the liquid is added to the anhydrous copper(II) sulfate, it turns from white to blue, confirming the presence of water.
Test: Use anhydrous copper(II) sulfate.
Result: The white anhydrous copper(II) sulfate turns blue, indicating the presence of water.
(b) Look at the symbol equation for the reaction of hydrogen burning. This equation is not balanced.
H2 + O2 → H2O
(i) Explain why this equation is not balanced.
▶️Answer/Explanation
Answer: The equation is unbalanced because there are 2 oxygen atoms on the left side (O2) and only 1 oxygen atom on the right side (H2O).
Explanation: The equation is not balanced because the number of oxygen atoms on the left side (2) does not match the number of oxygen atoms on the right side (1).
(ii) Rewrite the equation correctly balanced.
▶️Answer/Explanation
Answer: The balanced equation is 2H2 + O2 → 2H2O.
(c) Fig. 8.2 shows the electrons in an atom of hydrogen and an atom of oxygen.
In the space below, draw the dot-and-cross diagram for a water molecule, H2O. In your diagram, show:
- the chemical symbols of the elements
- all of the outer shell electrons
▶️Answer/Explanation
Answer: The dot-and-cross diagram for H2O shows two hydrogen atoms each sharing one electron with the oxygen atom, which has six outer shell electrons. The oxygen atom forms two covalent bonds with the hydrogen atoms, resulting in a water molecule.
(d) A student places 100 cm3 of aqueous potassium chloride into the distillation apparatus shown in Fig. 8.3.
She boils the solution gently until the flask contains only solid potassium chloride.
(i) Explain why it is possible to separate water from potassium chloride by distillation. In your answer, use ideas about:
- types of bonding
- boiling points
▶️Answer/Explanation
Answer: Water, being a covalent molecule, has a lower boiling point (100°C) compared to potassium chloride, which is an ionic compound with a much higher boiling point. When the solution is heated, water evaporates first, leaving behind solid potassium chloride, allowing for their separation.
Explanation: Water and potassium chloride can be separated by distillation because water is a covalent compound with a low boiling point (100°C), while potassium chloride is an ionic compound with a much higher boiling point. When the solution is heated, water evaporates first, leaving behind solid potassium chloride.
(ii) The mass of solid potassium chloride in 100 cm3 of aqueous potassium chloride is 2.5 g. Calculate the concentration of potassium chloride, in g/dm3, in this aqueous solution.
▶️Answer/Explanation
Answer: The concentration of potassium chloride is 25 g/dm3.
Calculation: Concentration = (mass of solute / volume of solution) × 1000
Concentration = (2.5 g / 100 cm3) × 1000 = 25 g/dm3
(iii) The student tests the purity of the water in the beaker in Fig. 8.3. Describe a test that she can use to show whether or not the water in the beaker contains any chloride ions.
▶️Answer/Explanation
Answer: The test involves adding acidified silver nitrate solution to the water. If chloride ions are present, a white precipitate of silver chloride will form, indicating the presence of chloride ions.
Test: Add acidified silver nitrate solution to the water.
Result if chloride ions are present: A white precipitate of silver chloride will form.
Question 9 (Subtopic: 2.3.2)
(a) A building is kept warm by heating its solid concrete floor.
(i) Describe the change in the motion of molecules in a solid as the temperature rises.
(ii) Some water spills onto the warm floor and evaporates. Describe evaporation in terms of the motion of the water molecules.
▶️Answer/Explanation
9(a)(i) increased vibration; 1
9(a)(ii) escape of more energetic molecules;
from the surface of the liquid;
(b) Thermal energy from the warm floor is transferred to the air which rises. State the name of this process.
▶️Answer/Explanation
9(b) convection;
(c) An infrared camera is used to measure the rise in temperature of the concrete floor. Place infrared into the incomplete electromagnetic spectrum in Fig. 9.1.
▶️Answer/Explanation
(d) A worker in the building is using a hammer. Hammering on concrete produces sound waves.
(i) Label with the letter A the double-headed arrow on Fig. 9.2 that shows the amplitude of the sound wave.
(ii) State the approximate range of audible frequencies for a healthy human ear.
▶️Answer/Explanation
9(d)(i) A on the arrow from the x axis to the top of the crest; 1
9(d)(ii) 20 (Hz) to 20 000 (Hz);
(e) The roof of the building is fitted with solar cells.
State one advantage and one disadvantage of generating electricity using solar cells apart from cost.
▶️Answer/Explanation
9(e) advantage: renewable ;
disadvantage: does not work in the dark / less electricity produced when it is cloudy;
Question 10 (Sub-topic: B13.2)
(a) Adrenaline is released in ‘fight or flight’ situations.
The concentration of adrenaline in the blood was monitored in three different people for 24 hours.
The results are shown in Fig. 10.1.
(i) Suggest which person is under the most stress during this time.
Give a reason for your answer.
▶️Answer/Explanation
Answer: Person A
Explanation: Adrenaline is a hormone released during stressful situations, and its concentration in the blood is directly related to the level of stress. Person A has the highest concentration of adrenaline, which suggests they are experiencing the most stress compared to Persons B and C.
(ii) State the time with the lowest release of adrenaline for all three people.
▶️Answer/Explanation
Answer: 03:00
Explanation: The graph shows that the concentration of adrenaline in the blood is lowest at 03:00 for all three individuals, indicating the lowest release of adrenaline at this time.
(iii) Describe two effects of adrenaline on the body.
▶️Answer/Explanation
Answer:
1. Increased heart rate
2. Widened pupils
Explanation: Adrenaline prepares the body for a ‘fight or flight’ response by increasing the heart rate to pump more blood to muscles and widening the pupils to improve vision in low light conditions.
(iv) State which part of the blood transports hormones such as adrenaline.
▶️Answer/Explanation
Answer: Plasma
Explanation: Hormones like adrenaline are transported throughout the body via the plasma, which is the liquid component of blood.
(b) Table 10.1 shows the number of new infections of human immunodeficiency virus (HIV) in one country in the years 2002 and 2009.
| Year | Number of new HIV infections |
|---|---|
| 2002 | 6980 |
| 2009 | 3100 |
(i) Calculate the decrease in new infections between 2002 and 2009.
▶️Answer/Explanation
Answer: 3880
Explanation: The decrease in new infections is calculated by subtracting the number of new infections in 2009 from the number in 2002: 6980 – 3100 = 3880.
(ii) Describe two methods of transmission of HIV.
▶️Answer/Explanation
Answer:
1. Sexual contact
2. Sharing needles
Explanation: HIV can be transmitted through unprotected sexual contact with an infected person or by sharing needles or syringes contaminated with the virus.
(iii) State the name of the deficiency syndrome that HIV can lead to.
▶️Answer/Explanation
Answer: Acquired Immune Deficiency Syndrome (AIDS)
Explanation: HIV can lead to AIDS, which is a condition where the immune system is severely weakened, making the body vulnerable to infections and diseases.
Question 11 (Sub-topic: B11.1)
Fig. 11.1 shows the molecular structures of four carbon compounds, A, B, C and D.
(i) State which of the compounds are alkanes. Explain your answer.
▶️Answer/Explanation
Compounds B and D are alkanes. Alkanes are hydrocarbons that contain only single bonds between carbon atoms. In the molecular structures shown, compounds B and D have only single bonds between carbon atoms, which is characteristic of alkanes.
(ii) Fig. 11.2 shows two bottles, E and F, containing carbon compounds.
State which bottle contains a hydrocarbon. Explain your answer.
▶️Answer/Explanation
Bottle E contains a hydrocarbon. Hydrocarbons are compounds that contain only hydrogen and carbon atoms. The name “heptane” indicates that it is an alkane, which is a type of hydrocarbon. Bottle F contains heptanol, which is an alcohol and contains an oxygen atom, making it not a hydrocarbon.
(b) Ethene is made when ethanol vapour passes over a heated catalyst. Fig. 11.3 shows apparatus used to produce ethene from ethanol.
(i) Suggest the purpose of the catalyst in this reaction.
▶️Answer/Explanation
The catalyst increases the rate of the reaction by providing an alternative pathway with a lower activation energy. This allows the reaction to proceed faster at a given temperature.
(ii) The ethene passes through an orange solution which becomes colourless. Identify the orange solution.
▶️Answer/Explanation
The orange solution is aqueous bromine (bromine water). Ethene reacts with bromine water, causing it to decolorize as the bromine is used up in the reaction.
(iii) An ethene molecule is described as unsaturated. Explain why.
▶️Answer/Explanation
Ethene is described as unsaturated because it contains a double bond between the carbon atoms. Unsaturated compounds have at least one double or triple bond, which allows them to undergo addition reactions.
(c) Fig. 11.4 shows an ethanol burner. The balance measures the mass of the burner and ethanol.
(i) Complete the word equation for the complete combustion of ethanol.
▶️Answer/Explanation
ethanol + oxygen → carbon dioxide + water
(ii) Predict how the balance reading changes while the ethanol is burning. Explain your answer.
▶️Answer/Explanation
The balance reading decreases as the ethanol burns. This is because ethanol is being converted into carbon dioxide and water, which are gases and escape into the air, reducing the mass of the burner and ethanol.
Question 12
(a) Fig. 12.1 shows a block of glass with a ray of light passing through it. The ray of light is passing from the air into the glass. (Sub-topic: P3.2.2)
(i) On Fig. 12.1, label the angle of incidence with the letter i and the angle of refraction with the letter r.
(ii) On Fig. 12.1, complete the diagram to show how the ray of light continues through the glass and out into the air.
▶️Answer/Explanation
(i) The angle of incidence (i) is the angle between the incident ray and the normal (a line perpendicular to the surface of the glass at the point of incidence). The angle of refraction (r) is the angle between the refracted ray and the normal. Both angles should be labeled on the diagram.
(ii) When the ray of light enters the glass, it bends towards the normal (since glass is denser than air). When it exits the glass, it bends away from the normal. The ray should continue in a straight line parallel to the original incident ray but displaced due to refraction.
(b) Fig. 12.2 shows rays of light from an object projected onto a screen through a thin converging lens. (Sub-topic Code: P3.2.3)
(i) State the name of the distance M.
(ii) Circle two words or phrases that correctly describe the image on the screen.
diminished enlarged inverted same size upright
▶️Answer/Explanation
(i) The distance M is the focal length of the lens, which is the distance from the lens to the focal point where parallel rays of light converge.
(ii) The correct words to describe the image on the screen are enlarged and inverted. A converging lens can produce an enlarged and inverted image when the object is placed between the focal point and twice the focal length from the lens.
(c) A robot is used to collect samples of radioactive material from a nuclear storage facility. (Sub-topic: P5.2.4)
(i) Explain why the robotic vehicle is more suitable to collect the radioactive material than a human being.
(ii) Fig. 12.3 is a graph of the radioactive decay curve for a sample of the radioactive material. Use the graph in Fig. 12.3 to determine the half-life of the sample.
▶️Answer/Explanation
(i) The robotic vehicle is more suitable for collecting radioactive material because it can operate in high-radiation environments without risking human health. Robots can be designed to handle hazardous materials safely, reducing the risk of exposure to harmful radiation.
(ii) The half-life of the radioactive material can be determined from the graph by finding the time it takes for the activity to decrease to half of its initial value. For example, if the initial activity is 1000 counts/s and it decreases to 500 counts/s after 2 years, the half-life is 2 years.
(d) The robot has a d.c. motor. State two ways in which the turning effect of the current-carrying coil in the magnetic field of a d.c. motor can be increased. (Sub-topic: P4.5.5)
▶️Answer/Explanation
Two ways to increase the turning effect (torque) of the current-carrying coil in a d.c. motor are:
- Increase the current flowing through the coil, as the force on the coil is directly proportional to the current.
- Increase the strength of the magnetic field, either by using stronger magnets or by increasing the number of turns in the coil.