Biology 4BI1 | Paper 2 Mock 01 | Written Paper 2
Question 1 Report
The diagram shows the route of nerve impulses when a person touches the metal cap of a hot saucepan. This response happens before the person has time to decide to move their hand. The labelled structures are part of a reflex arc.
(a) Complete the sequence below using words from the diagram.
receptor → sensory neurone → ________ → ________ → muscle [2]
(b) Describe what happens at a synapse between two neurones. [2]
(c) Explain why the hand is withdrawn before the brain produces a conscious sensation of pain. [3]
(d) Suggest two advantages of this rapid response to the person. [3]
(a) The sequence is:
receptor → sensory neurone → relay neurone → motor neurone → muscle. [2]
(b) At a synapse, the first neurone releases a chemical neurotransmitter. The neurotransmitter diffuses across the gap and starts an impulse in the next neurone. [2]
(c) Impulses from the receptor travel to the spinal cord. A relay neurone transfers the impulse to a motor neurone, which causes the arm muscle to contract. This happens before impulses are processed by the brain to produce conscious pain. [3]
(d) The rapid response reduces the time the hand contacts the hot cap, reducing burns and other damage to skin or body cells. Avoiding injury improves chances of survival. Any three valid points. [3]
Answer Details
(a) The sequence is:
receptor → sensory neurone → relay neurone → motor neurone → muscle. [2]
(b) At a synapse, the first neurone releases a chemical neurotransmitter. The neurotransmitter diffuses across the gap and starts an impulse in the next neurone. [2]
(c) Impulses from the receptor travel to the spinal cord. A relay neurone transfers the impulse to a motor neurone, which causes the arm muscle to contract. This happens before impulses are processed by the brain to produce conscious pain. [3]
(d) The rapid response reduces the time the hand contacts the hot cap, reducing burns and other damage to skin or body cells. Avoiding injury improves chances of survival. Any three valid points. [3]
Question 2 Report
A fertility clinic records the stages of one IVF procedure in Fig. 1. The woman is given hormones so that several eggs mature. Mature eggs are collected and mixed with sperm cells in a laboratory dish. The dish is kept at body temperature. Two days later, scientists choose one healthy early embryo and place it in the woman’s uterus. The clinic explains that the remaining embryos may be frozen, with consent, for a later attempt. This treatment can help when a couple cannot achieve fertilisation inside the female reproductive system.
(a) Describe the sequence of events between collecting the eggs and placing an embryo in the uterus. [3]
(b) Explain why the eggs, sperm cells and early embryos are kept close to 37 degrees C. [4]
(c) Suggest three reasons why a clinic may transfer only one embryo during this treatment. [3]
(d) Explain one advantage and two concerns of freezing unused embryos. [3]
(a) Eggs are mixed with sperm cells in a laboratory dish. A sperm fertilises an egg, and the fertilised egg then divides by mitosis to form an early embryo before it is transferred to the uterus. [3]
(b) \(37\,^{\circ}\text{C}\) is close to normal human body temperature. Enzymes work efficiently at or close to their optimum temperature, allowing respiration, metabolism and cell division to occur at suitable rates. At much higher temperatures enzymes can denature; at lower temperatures reactions are slowed. [4]
(c) Transferring one embryo reduces the chance of a multiple pregnancy. This reduces risks to the mother during pregnancy or birth and lowers the risk of premature or low-mass babies. It also reduces pressure on hospital care. [3]
(d) Freezing unused embryos means they may be used in a later attempt without another egg-collection procedure. Concerns include decisions about how long embryos are stored or what happens to them if unused, and ethical or religious objections or possible consent and identity disputes. [3]
Answer Details
(a) Eggs are mixed with sperm cells in a laboratory dish. A sperm fertilises an egg, and the fertilised egg then divides by mitosis to form an early embryo before it is transferred to the uterus. [3]
(b) \(37\,^{\circ}\text{C}\) is close to normal human body temperature. Enzymes work efficiently at or close to their optimum temperature, allowing respiration, metabolism and cell division to occur at suitable rates. At much higher temperatures enzymes can denature; at lower temperatures reactions are slowed. [4]
(c) Transferring one embryo reduces the chance of a multiple pregnancy. This reduces risks to the mother during pregnancy or birth and lowers the risk of premature or low-mass babies. It also reduces pressure on hospital care. [3]
(d) Freezing unused embryos means they may be used in a later attempt without another egg-collection procedure. Concerns include decisions about how long embryos are stored or what happens to them if unused, and ethical or religious objections or possible consent and identity disputes. [3]
Question 3 Report
The diagram shows a model used by a class to demonstrate breathing. The bell jar represents the chest, two balloons represent the lungs and the rubber sheet represents the diaphragm. A student pulls the rubber sheet down while another student watches the balloons. The tube is sealed through the cap at the top of the jar so that air can enter only through the tube.
(a) Name the structures labelled A, B and C. [3]
(b) Describe what happens to the volume of the box, the pressure of air inside it and the balloons when the rubber sheet is pulled down. [4]
(c) Explain how breathing in allows oxygen to be used by human cells to release energy. [5]
(d) Use Fig. 3 to explain three limitations of this model of breathing. [3]
(e) Suggest how the students could use limewater to show that exhaled air contains more carbon dioxide than inhaled air. [3]
(a) A is the bell jar, representing the chest. B is a balloon, representing a lung. C is the rubber sheet, representing the diaphragm. [3]
(b) Pulling the rubber sheet down increases the volume inside the bell jar. The pressure of air inside decreases, so air enters through the tube. The balloons inflate and increase in volume. [4]
(c) Air containing oxygen enters the lungs during inhalation. Oxygen reaches the alveoli, then diffuses into capillary blood. The blood transports oxygen to body cells, where oxygen is used in aerobic respiration to release energy. [5]
(d) The model has limitations: the bell jar is rigid, whereas the rib cage moves during breathing; the rubber sheet is pulled, whereas the real diaphragm is a muscle that contracts and becomes flatter; and the balloons do not show alveoli, capillaries or gas exchange. It also does not show blood flow or transport by the heart. Any three are required. [3]
(e) Pass equal volumes of inhaled and exhaled air through separate equal volumes of limewater, keeping conditions the same. Exhaled air makes limewater turn cloudy faster or become cloudier. This indicates that exhaled air contains more carbon dioxide. [3]
Answer Details
(a) A is the bell jar, representing the chest. B is a balloon, representing a lung. C is the rubber sheet, representing the diaphragm. [3]
(b) Pulling the rubber sheet down increases the volume inside the bell jar. The pressure of air inside decreases, so air enters through the tube. The balloons inflate and increase in volume. [4]
(c) Air containing oxygen enters the lungs during inhalation. Oxygen reaches the alveoli, then diffuses into capillary blood. The blood transports oxygen to body cells, where oxygen is used in aerobic respiration to release energy. [5]
(d) The model has limitations: the bell jar is rigid, whereas the rib cage moves during breathing; the rubber sheet is pulled, whereas the real diaphragm is a muscle that contracts and becomes flatter; and the balloons do not show alveoli, capillaries or gas exchange. It also does not show blood flow or transport by the heart. Any three are required. [3]
(e) Pass equal volumes of inhaled and exhaled air through separate equal volumes of limewater, keeping conditions the same. Exhaled air makes limewater turn cloudy faster or become cloudier. This indicates that exhaled air contains more carbon dioxide. [3]
Question 4 Report
Table 2 shows the number of species recorded by scientists in two habitats on the same farm. Each habitat was searched on five dry mornings in June. The old hedge had not been cut for eight years, whereas the grass verge was mown every three weeks. Organisms were identified using field guides and placed into groups. The results show the variety of animals, plants and fungi in each place.
| group of organisms | old hedge | mown grass verge |
|---|---|---|
| flowering plants | 18 | 7 |
| ferns | 4 | 0 |
| fungi | 11 | 3 |
| insects | 26 | 14 |
| arachnids | 9 | 4 |
| birds | 7 | 5 |
(a) Calculate the total number of species recorded in the old hedge. [2]
(b) Use Table 2 to describe three differences between the variety of organisms in the two habitats. [3]
(c) Explain why the scientists used the same number of searches in each habitat. [3]
(d) Suggest two changes to the management of the grass verge that could increase the variety of organisms there. [4]
(e) Describe two limitations of using these results alone to decide which habitat has the greater biodiversity. [4]
(a)
\[18+4+11+26+9+7=75\]
The total number of species recorded in the old hedge is 75 species. [2 marks]
(b) Three valid comparisons are:
- The hedge has more flowering plant species, 18 compared with 7. [1 mark]
- Ferns were found in the hedge, 4 species, but none were recorded on the verge. [1 mark]
- The hedge has more fungi, 11 compared with 3. [1 mark]
The hedge also has more insects, 26 compared with 14, and more arachnids, 9 compared with 4; bird species are only slightly higher, 7 compared with 5.
(c) Using five searches in each habitat gives equal sampling effort and makes the comparison fair. [1 mark] Differences are then less likely to be caused by one habitat being searched more often. [1 mark] Equal numbers of searches allow totals or mean results to be compared more reliably. [1 mark]
(d) Four suitable changes are: mow less frequently [1 mark]; leave some areas uncut [1 mark]; sow native flowering plants [1 mark]; avoid herbicides and pesticides [1 mark]. Leaving dead wood or leaf litter, creating a pond or damp area, and planting shrubs or a hedge are also acceptable.
(e) The surveys were carried out only in June. [1 mark] Some organisms are seasonal and may not have been present then. [1 mark] Five searches may not represent the entire habitat. [1 mark] Organisms may have been missed or misidentified, and species number does not show the number of individuals of each species. [1 mark] Weather and differences in habitat area are further limitations.
Answer Details
(a)
\[18+4+11+26+9+7=75\]
The total number of species recorded in the old hedge is 75 species. [2 marks]
(b) Three valid comparisons are:
- The hedge has more flowering plant species, 18 compared with 7. [1 mark]
- Ferns were found in the hedge, 4 species, but none were recorded on the verge. [1 mark]
- The hedge has more fungi, 11 compared with 3. [1 mark]
The hedge also has more insects, 26 compared with 14, and more arachnids, 9 compared with 4; bird species are only slightly higher, 7 compared with 5.
(c) Using five searches in each habitat gives equal sampling effort and makes the comparison fair. [1 mark] Differences are then less likely to be caused by one habitat being searched more often. [1 mark] Equal numbers of searches allow totals or mean results to be compared more reliably. [1 mark]
(d) Four suitable changes are: mow less frequently [1 mark]; leave some areas uncut [1 mark]; sow native flowering plants [1 mark]; avoid herbicides and pesticides [1 mark]. Leaving dead wood or leaf litter, creating a pond or damp area, and planting shrubs or a hedge are also acceptable.
(e) The surveys were carried out only in June. [1 mark] Some organisms are seasonal and may not have been present then. [1 mark] Five searches may not represent the entire habitat. [1 mark] Organisms may have been missed or misidentified, and species number does not show the number of individuals of each species. [1 mark] Weather and differences in habitat area are further limitations.
Question 5 Report
The diagram in Fig. 1 shows part of the alimentary canal of a patient who has had surgery. Food enters at the mouth and passes through several organs. The surgeon explained that removing a short section of the small intestine can reduce the amount of digested food absorbed into the blood. The patient must therefore eat smaller meals and follow advice from a dietitian.
(a) Name the organ where most absorption of soluble food molecules takes place. [1]
(b) Describe two features of this organ that make absorption efficient. [2]
(c) Explain why absorbed glucose is carried in the blood to body cells. [2]
(a) Most absorption of soluble digested food molecules occurs in the small intestine, especially the ileum. [1]
(b) Any two adaptations are:
- many villi provide a large surface area;
- the villi have a thin, one-cell-thick surface, giving a short diffusion distance;
- a good blood supply in capillaries maintains a concentration gradient.
These features allow absorbed molecules to enter the blood efficiently. [2]
(c) Glucose is transported in the blood to body cells. Cells use glucose in respiration to release energy for their activities. [2]
Answer Details
(a) Most absorption of soluble digested food molecules occurs in the small intestine, especially the ileum. [1]
(b) Any two adaptations are:
- many villi provide a large surface area;
- the villi have a thin, one-cell-thick surface, giving a short diffusion distance;
- a good blood supply in capillaries maintains a concentration gradient.
These features allow absorbed molecules to enter the blood efficiently. [2]
(c) Glucose is transported in the blood to body cells. Cells use glucose in respiration to release energy for their activities. [2]
Question 6 Report
Fig. 1 shows a small sewage-treatment works beside a river containing fish and water plants. Waste water enters the works from nearby homes. The treated water is released through an outlet pipe downstream. Scientists found that the river water had fewer fish below the outlet during a period when a filter was damaged. They also recorded a strong smell and a large amount of decaying plant material on the river bed.
(a) Name the type of pollution caused when untreated sewage enters a river. [1]
(b) Describe two changes likely to occur in the river water below the outlet when sewage is not treated properly. [2]
(c) Explain why the number of fish may decrease when bacteria decompose sewage in the river. [3]
(d) Suggest one improvement to the treatment works that would reduce pollution of the river. [2]
(a) Untreated sewage entering a river causes water pollution. [1]
(b) Below the outlet, water may become more cloudy and have a lower dissolved oxygen concentration. Other acceptable changes include more bacteria or microorganisms, increased growth of algae or water plants, and a bad smell. Any two are required. [2]
(c) Bacteria feed on and decompose the organic material in sewage. They respire while doing this, using oxygen dissolved in the water. Too little oxygen may then remain for fish respiration, so fish numbers decrease. [3]
(d) The works could repair or replace the damaged filter. This prevents inadequately treated sewage being released. Other acceptable improvements include adding biological treatment tanks, removing solids before discharge, disinfecting waste water, or monitoring the outlet and stopping releases when treatment fails. [2]
Answer Details
(a) Untreated sewage entering a river causes water pollution. [1]
(b) Below the outlet, water may become more cloudy and have a lower dissolved oxygen concentration. Other acceptable changes include more bacteria or microorganisms, increased growth of algae or water plants, and a bad smell. Any two are required. [2]
(c) Bacteria feed on and decompose the organic material in sewage. They respire while doing this, using oxygen dissolved in the water. Too little oxygen may then remain for fish respiration, so fish numbers decrease. [3]
(d) The works could repair or replace the damaged filter. This prevents inadequately treated sewage being released. Other acceptable improvements include adding biological treatment tanks, removing solids before discharge, disinfecting waste water, or monitoring the outlet and stopping releases when treatment fails. [2]
