SL Paper 2
Consumption of dark chocolate has been shown to have health benefits. A study was undertaken to see the effects of epicatechin (Epi), a substance in dark chocolate, on the aerobic capacity of leg muscles of mice.
A group of adult mice was used to measure the effects of a low dose of Epi given over 15 days. The mice were divided into four groups and given either water or Epi and were either kept idle (no exercise) or made to exercise on a treadmill.
After 15 days, the results were analysed. The blood capillary density in leg muscle was measured under the light microscope.
Leg muscle tension was measured over time during a treadmill exercise in all four groups. The muscle is considered to reach a point of fatigue when there is a decrease in tension to 50 % of the initial tension.
The scientists tested the expression of four different mitochondrial proteins. The protein samples were taken from leg muscles. The technique that was used to quantify the amount of protein expressed was Western blotting. In this procedure the thickness of the band is an indicator of the amount of protein.
State the significance of the statement: p<0.05.
Outline the trends in capillary density in the results of this experiment.
Describe how increased capillary density could affect the aerobic capacity of muscle.
State the time when the point of fatigue occurred in the Epi–exercise group.
Compare and contrast the results for the water–no exercise group and the Epi–no exercise group.
Discuss the effect of exercise on the results of the experiment.
Analyse the effect of exercise on the presence of the mitochondrial proteins in the leg muscle.
Mitochondria are essential for aerobic respiration. Suggest one possible role of the proteins that were studied.
The scientists concluded that Epi significantly increased aerobic capacity in leg muscle.
Evaluate the strength of the evidence provided by all of the data for dark chocolate improving the aerobic capacity of athletes.
Three-toed sloths (Bradypus variegatus) are placental mammals that live in trees in Central and South America. They eat leaves and fruit and get almost all their water from succulent plants.
[Source: Adapted from Laube, S., 2003. Three-toed-sloth (Bradypus variegatus), Lake Gatun, Republic of Panama. [image online] Available at: https://meta.wikimedia.org/wiki/User:Bradipus#/media/File:Bradypus.jpg]
Three-toed sloths change their body posture in response to the temperature of their environment (ambient temperature). Researchers assessed posture on a scale from 1 to 6, with 1 being when the sloth was curled into a tight ball and 6 when it had all limbs spread. The percentage of time the sloths were observed in each position was recorded at ambient temperatures from 22 °C to 34 °C. The researchers also measured the body temperature of the sloths over the same range of ambient temperatures.
[Source: Adapted from Cliffe, R.N., Scantlebury, D.M., Kennedy, S.J., Avey-Arroyo, J., Mindich, D. and Wilson, R.P., 2018. The metabolic response of the Bradypus sloth to temperature. PeerJ, [e-journal] 6: e5600. http://dx.doi.org/10.7717/peerj.5600. Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
The daily food intake of three-toed sloths and daily ambient temperatures were monitored over a 160-day period from February to early July. The graphs show the mean results.
[Source: Cliffe et al. (2015), Sloths like it hot: ambient temperature modulates food intake in the brown-throated sloth (Bradypus variegatus). PeerJ 3:e875; DOI 10.7717/peerj.875 Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
State the relationship between sloth body temperature and ambient temperature.
Explain how this relationship differs from that in humans.
Describe the trend in body posture as ambient temperature rises from 22 to 34 °C.
Suggest reasons for this trend.
The mean daily food intake fluctuated from day to day. State the month that contains the day on which the mean intake of food was highest.
Outline the relationship between ambient daily temperature and food intake in March.
Suggest, with a reason, how the activity of the sloth varies with ambient temperature.
State one feature of the sloth that would indicate it is a mammal.
Edible insects have been a part of traditional human diets in many countries. For example, crickets are insects commonly eaten in Asia and Africa. Many studies have looked at the prospects of raising insects on a commercial scale for direct human consumption as food or indirectly by feeding insects to farm animals.
One factor to consider is which organisms are most efficient at converting the feed they eat into animal protein that can be consumed. A study compared the percentage of mass that was edible in two common farm animals and in crickets.
The yellow mealworm (Tenebrio molitor) is native to temperate regions of the world and has been studied as a possible means of producing food in countries with that type of climate. The amino acid content of yellow mealworms and cattle was analysed. The table shows the results for seven amino acids that are required in the human diet.
The environmental impact of producing protein from mealworms was compared with the impact of producing traditional protein sources. The graphs show the greenhouse gas production (global warming potential) and land use due to the production of 1 kg of protein from mealworms, chickens and cattle.
Identify which organism has the highest percentage of edible mass.
Calculate how much more feed is required by cattle than chickens to produce 1 kg of live mass.
Identify which organism requires the least feed to produce 1 kg of edible mass.
Distinguish between the amino acid contents of yellow mealworms and cattle.
Predict, with a reason, whether the amino acid composition of yellow mealworms or cattle is more suitable for a human diet.
Outline the differences between the environmental impact of using mealworms and traditional farm livestock for protein production.
Birds and mammals maintain constant body temperature despite considerable losses of body heat to the environment. In insects such as mealworms, body temperature is variable and is often the same as the temperature of the environment or only slightly above it. Analyse the data in the bar charts, using this information.
Using all the relevant data in this question, discuss the use of insects as a major food source for humans.
There is growing evidence of a decrease in bee populations. This decrease is a serious problem because of their valuable role as pollinators in the ecosystems where they live. Neonicotinoid pesticides have been implicated in this decrease because they have been found at trace levels in the nectar and pollen of crop plants and in the bee colonies.
Scientists placed colonies of a species of bumblebee, Bombus terrestris, in the laboratory to test the effects of different levels of a neonicotinoid on their development. They divided the colonies into three groups:
- The control colonies were given a solution of water and sugar that resembled nectar produced by flowers.
- A second group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at low concentrations, similar to those found in nature.
- A third group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at high concentrations, similar to those found in nature.
After two weeks, all colonies were placed in the field to allow the bumblebees to feed naturally.
The mass of the colonies, including adult bumblebees, wax, honey and larvae, was recorded every week. The cumulative increase in mass was calculated and is shown on the graph.
[Source: Adapted from Whitehorn, P.R., O’Connor, S., Wackers, F.L. and Goulson, D., 2012.
Bumble Bee Colony Growth and Queen Production. Science, [e-journal] 336(6079), pp. 351–352.
http://dx.doi.org/10.1126/science.1215025.]
The number of queen bumblebees produced in each colony was recorded. New bumblebee colonies are started by a queen.
[Source: Adapted from Whitehorn, P.R., O’Connor, S., Wackers, F.L. and Goulson, D., 2012.
Bumble Bee Colony Growth and Queen Production. Science, [e-journal] 336(6079), pp. 351–352.
http://dx.doi.org/10.1126/science.1215025.]
A similar study compared the effect of a different neonicotinoid on four different species of bumblebees. The queens were exposed to either control conditions (with no pesticide), or low or high doses of neonicotinoid. The scientists then measured the average length of the developing eggs in the ovaries of the queens.
[Source: Baron GL, Raine NE, Brown MJF. 2017 General and species-specific impacts of a neonicotinoid insecticide
on the ovary development and feeding of wild bumblebee queens. Proc. R. Soc. B 284: 20170123.
http://dx.doi.org/10.1098/rspb.2017.0123 Licensed under a Creative Commons Attribution 4.0
International License https://creativecommons.org/licenses/by/4.0/ Source adapted.]
Describe the effect of neonicotinoid pesticides on the nervous system of insects.
State the cumulative increase in the mass of control colonies at 7 weeks.
Compare and contrast the cumulative increase in mass of the three groups of colonies once they were placed in the field.
Suggest a reason for the changes in mass in the colonies between weeks 6 and 8.
Using the data in the graph, predict how the use of neonicotinoid pesticides will affect bumblebee populations.
Identify the species whose eggs are most affected by a high dose of neonicotinoid.
Describe the overall effects of low and high doses of neonicotinoid on the egg lengths of all four species.
Deduce, based on the data presented, whether the levels of neonicotinoids used in agriculture cause direct harm to B. terrestris.
The graph shows the change in the membrane potential of an axon during an action potential.
State the approximate value of the membrane potential at X.
Y is the threshold potential. State what happens when the threshold potential is reached.
Describe the movements in ions that occur during time t.
Explain how a nerve impulse is passed on to other neurons.
Chronic Obstructive Pulmonary Disease (COPD) is characterized by progressive airflow limitation. Classification of COPD as mild, moderate or severe is based on measurement of Forced Expiratory Volume (FEV), which is the maximum volume of air that can be exhaled in one second.
The table shows the numbers of individuals in each COPD class and their mean FEV for a Swedish study of 349 people.
[Source: Reproduced with permission of the © ERS 2012. European Respiratory Journal Apr 2012, 39 (4) 839–845; DOI: 10.1183/09031936.00064611]
The elasticity and resilience of the lungs are mainly provided by the protein elastin. Degradation of elastin produces peptides called desmosines.
Desmosines in urine or blood plasma have been proposed as biomarkers of lung degradation. The relationship between urine desmosines, plasma desmosines and COPD severity in patients was assessed.
[Source: Reproduced with permission of the © ERS 2012. European Respiratory Journal Apr 2012, 39 (4) 839–845; DOI: 10.1183/09031936.00064611]
The graph shows the relationship between the diffusion capacity of the lungs for carbon monoxide (CO) and urine desmosines.
[Source: Reproduced with permission of the © ERS 2012. European Respiratory Journal Apr 2012, 39 (4) 839–845; DOI: 10.1183/09031936.00064611]
State the level of COPD that has the lowest FEV.
Explain how a low FEV can be used to indicate emphysema.
State the disease severity group that has the highest range of plasma desmosines.
Evaluate which of the two biomarkers would be the most useful indicator of COPD severity.
Elastin is also an important component of other tissues such as arteries and ligaments. Evaluate how these other sources of elastin could affect the interpretation of the biomarker as an indicator of COPD.
State the relationship between diffusion capacity and urine desmosines.
Other studies on pulmonary diseases have shown a wide variety of results. Apart from age, sex and severity of COPD, list two other factors that may explain the inconsistent results between studies.
Discuss whether measurements of desmosine concentration would be useful for monitoring changes in the health of a patient.