Question 1:
(a) Fig. 1.1 is a side view of a human skull indicating the four types of teeth and the jaws.
(i) State the function of human teeth.
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(ii) State the name of the visible outer layer of the teeth.
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(iii) Explain the process of tooth decay in humans.
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(b) Mammals can be classified according to the position and shape of their teeth.
Fig. 1.2 shows the skulls of seven mammals.
(i) Use the key to identify each species shown in Fig. 1.2.
Write the letter of each species (A to G) in the correct box in the key.
Key
(ii) Killer whales, Orcinus orca, are mammals.
State two internal features you would expect to find in a killer whale that you would not find in a fish.
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(iii) State the name of the group of animals that includes mammals and fish.
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▶️Answer/Explanation
Ans: 1(a)(i) mechanical / physical, digestion ;
1(a)(ii) enamel ;
1(a)(iii) any three from:
sugar / food / plaque, left on teeth ;
respiration (of sugar) by bacteria ;
produce (lactic) acid ;
dissolves, enamel / dentine / AW ;
AVP ;
1(b)(i)
1(b)(ii) any two from:
double circulation ;
four-chambered heart ;
lungs / any named part of lungs ;
diaphragm ;
red blood cells without nuclei ;
AVP ;
1(b)(iii) vertebrates ;
Question 2:
Digestive enzymes catalyse the breakdown of large insoluble molecules.
(a) (i) Explain why it is important that large insoluble molecules are broken down by chemical digestion.
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(ii) State the name of the substance that is the solvent for most molecules that have been digested by enzymes.
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(b) The activity of two protease enzymes, A and B, was measured at different pHs. Both enzymes are found in the human alimentary canal.
The results are shown in Fig. 2.1.
Describe and explain the roles of the two protease enzymes, A and B, in the alimentary canal.
Use the information in Fig. 2.1 to support your answer.
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(c) Maltase is a digestive enzyme that acts in the small intestine.
State the exact location of maltase in the small intestine.
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▶️Answer/Explanation
Ans: 2(a)(i) any two from:
become soluble ;
for absorption ;
small enough, for diffusion / active transport ;
2(a)(ii) water ;
2(b) any six from:
1 protein → amino acids ;
2 ref to specificity ;
3 both enzymes are active between pH 3 and pH5 ; A at pH4
4 A is pepsin ;
5 optimum pH at 2 ;
6 enzyme shows, no activity / is denatured, from pH 5 ;
7 (functions) in stomach ;
8 where HCl is present / in acid conditions ;
9 B is trypsin ;
10 optimum pH at 10 ;
11 enzyme shows, no activity / is denatured, from pH 3 ;
12 (functions) in small intestine / secreted from pancreas ;
13 bile neutralises (stomach) acid / in alkaline conditions ;
2(c) (membrane of) epithelium ;
Question 3:
(a) Fig. 3.1 shows some apparatus that was used to investigate water loss from a leafy shoot.
(i) State the name of the process by which leafy shoots lose water.
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(ii) Before the leafy shoot is inserted into the jar shown in Fig. 3.1, it must be recut under water.
Suggest why the end of the leafy shoot was cut under water.
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(iii) State the purpose of the oil layer on top of the water in the burette.
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(iv) Using the information in Fig. 3.1, describe one method that can be used to determine how much water is lost from the leafy shoot.
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(b) The apparatus shown in Fig. 3.1 was used to investigate the effect of temperature on the rate of water loss in a species of plant. The results are shown in Fig. 3.2.
(i) Using the information in Fig. 3.2, calculate how much water would be lost from 1m2 of leaves in 12 hours if the plants were kept at 35°C. Include the unit.
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(ii) Using the information in Fig. 3.2, describe and explain the effect of increasing temperature on the rate of water loss in this species of plant.
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(c) The apparatus shown in Fig. 3.1 can also be used to investigate the effects of changing humidity on water loss in plants.
(i) Suggest why the mass of water in the apparatus does not change when the leafy shoot is kept at 100% relative humidity.
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(ii) Even at extremely low relative humidities the leafy shoot did not wilt.
Explain why the leafy shoot shown in Fig. 3.1 did not wilt.
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(iii) The investigation on the effect of temperature was done at a relative humidity of 20%.
The investigation was repeated at a relative humidity of 80% and all other conditions were kept the same.
Predict how the water loss will differ from the trend shown in Fig. 3.2.
Sketch your prediction on Fig. 3.2.
▶️Answer/Explanation
Ans: 3(a)(i) transpiration ;
3(a)(ii) ensure continuous column of water / prevents air bubbles / prevents airlock ;
3(a)(iii) prevent, evaporation / condensation (from the top of the burette,
affecting the volume of water in the burette) / AW ;
3(a)(iv) measure the decrease in the volume of water (in burette over a
period of time) / record the decrease in mass (over time) ;
3(b)(i) 12 096 g (per m2 ) / 12.096 kg (per m2 ) ;;;
3(b)(ii) any five from:
1 as temperature increases, (rate of) water loss increases ;
2 ref to steeper rate / greater loss of water, after 37 / 38 oC ;
3 any correct comparative data quote (with units at least once) ;
4 water vapour lost, through stomata / between guard cells ;
5 evaporation from mesophyll into air spaces ;
6 (diffusion) down a, water potential, gradient ;
7 increasing temperature increases kinetic energy (of water molecule) ;
8 faster (rate of) more, diffusion ;
9 stomata open wider / more stomata open in high(er) temperatures ;
10 AVP ;
3(c)(i) no diffusion (of water vapour) ;
(because) no water potential gradient / described ;
3(c)(ii) (it has a) continuous supply of water / AW ;
3(c)(iii) line drawn below original line ;
Question 4:
Chromosomes are made of DNA.
(a) Describe the structure of a DNA molecule.
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(b) (i) Outline how antibiotic resistance develops in a population of bacteria.
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(ii) Scientists use differences in antibiotic-resistance genes to distinguish between different strains of the bacterium, methicillin-resistant S. aureus (MRSA).
Suggest why scientists use differences in base sequences to classify the strains of MRSA rather than using other methods.
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(iii) Explain why scientists are concerned that some strains of bacteria, such as S. aureus, have become resistant to antibiotics.
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(c) (i) Describe how the use of antibiotics can be managed to reduce the development of resistant strains of bacteria.
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(ii) Suggest why MRSA is unlikely to be transmitted from a mother to her unborn fetus.
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(d) Many species of bacteria do not cause disease. Bacteria are very important in many biological processes.
State the names of three natural processes involving bacteria that are important to ecosystems.
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▶️Answer/Explanation
Ans: 4(a) any four from:
two strands ;
formed into (double) helix ;
ref. to four bases / A and T and C and G ;
pairing of, A with T / C with G ;
cross links between bases ;
4(b)(i) any three from:
1 variation (in the bacteria) ;
2 ref. to mutations / described ;
3 mutations, give bacteria an advantage ;
4 non-resistant bacteria, killed / inhibited / AW (by antibiotic) ;
5 competition with non-resistant bacteria ;
6 resistant bacteria reproduce ;
7 pass on, gene / allele (for resistance) ;
8 natural selection ;
9 AVP ;
4(b)(ii) any one from:
1 no difference in appearance (of different strains of MRSA) / AW ;
2 no need to culture the bacteria ;
3 (gene sequencing is an) automated process / AW ;
/ easy to do / AW ;
4 only need small, number / quantity / amount (of bacteria) ;
5 more, accurate / precise (than traditional methods) / AW ;
6 explained in terms of comparing base sequences of
different, strains / AW ;
7 AVP ;
4(b)(iii) any two from:
(resistant) bacteria will not be killed by antibiotics / AW ;
idea that no antibiotic of last resort / AW ;
(bacterial diseases) cannot be treated / AW ;
infection / disease / (resistant) bacteria, will spread ;
AVP ;;
4(c)(i) any two from:
antibiotics used only when essential ;
ensuring people, follow instructions / complete course of
antibiotics ;
do not prescribe antibiotics for, viral / fungal, infections ;
AVP ;;
4(c)(ii) placenta forms a barrier between mother and fetus / AW ;
4(d) any three from:
nitrogen fixation ;
decomposition / decay ;
nitrification ;
denitrification ;
deamination ;
fermentation ;
AVP ;;
Question 5:
Fires release carbon dioxide into the atmosphere.
(a) (i) State one other natural process that releases carbon dioxide into the atmosphere.
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(ii) Carbon dioxide is a greenhouse gas.
State the name of one other greenhouse gas.
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(b) Data scientists used satellite images to analyse the occurrence of fires globally, during a 14-year period.
They tracked all fires that were larger than 0.21km2 and therefore visible from space.
Table 5.1 summarises some of their data, categorising the fires by location. The locations
include natural ecosystems and land that is managed by people. The expansion rate is the
speed at which each fire becomes larger.
(i) Using the information in Table 5.1, compare the data for the two managed locations with the data for the three natural locations.
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(ii) Describe how the data in Table 5.1 could be used to estimate the total area that was burnt during the 14-year period, for each location.
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(iii) Burning large areas of forest is a cause of habitat destruction.
Describe the possible consequences of habitat destruction.
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▶️Answer/Explanation
Ans: 5(a)(i) any one from:
respiration ;
decomposition ;
volcanic eruptions ;
release of carbon dioxide from oceans (ocean-atmosphere exchange) ;
5(a)(ii) methane / AVP ;
5(b)(i) any three from:
1 (total) number of fires in natural ecosystems is higher than
(total) number of fires in managed land
or
idea that the savannah (alone) has more fires than the
(total) fires in managed land ;
2 fires on managed land, have a lower expansion rate / spread
more slowly (than other fires) ;
3 fires on managed land, have a shorter duration / last less
time (than other fires) ;
4 more fires on land being deforested than in natural forest ;
5 comparative data quote (with units at least once) ;
6 AVP ;
5(b)(ii) multiply ;
number of fires by expansion rate by duration (for each row) ;
5(b)(iii) any three from:
1 reduction in population sizes of organisms ;
2 organisms / animals / plants, become endangered ;
3 organisms / animals / plants, become extinct ;
4 loss of biodiversity ;
5 loss of genetic diversity ;
6 ref. to negative effect on, food chains / food webs ;
7 ref. to negative effect on, nutrient / water, cycling ;
8 AVP ;
Question 6:
(a) Fig. 6.1 shows part of the human gas exchange system.
(i) Table 6.1 shows the names of some parts of the human gas exchange system, their functions and the letters in Fig. 6.1 that identify the parts.
Complete Table 6.1.
(ii) Describe and explain how the alveoli are adapted for gas exchange.
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(b) (i) Explain the differences in composition between inspired and expired air.
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(ii) Physical activity changes the concentration of carbon dioxide in the body.
State where this change is detected and how the body responds to the change.
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(iii) State the name of a solution that can be used to test for the presence of carbon dioxide gas.
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▶️Answer/Explanation
Ans: 6(a)(i)
6(a)(ii) any three from:
thin / one cell thick ;
large surface area ;
(which) reduces diffusion distance / AW ;
good blood supply ;
AVP ;
6(b)(i) any three from:
less oxygen and more carbon dioxide in expired air (than inspired air) ;
(as) oxygen is required for aerobic respiration ;
carbon dioxide is released by respiration ;
water vapour increases (as it is released by respiration) ;
AVP ;
6(b)(ii) detected:
either
(carbon dioxide is) in the blood
or
by the brain ;
response:
either
increases, rate / depth, of breathing
or
increases heart rate / AW ;
6(b)(iii) limewater / hydrogencarbonate indicator (solution) / AVP ;