Identify in which continent the fewest types of neonicotinoid were detected in honey samples.

Using the data, outline the different use of thiamethoxam in North and South America.

Identify the total percentage of honey samples contaminated with neonicotinoid pesticides in the continent with the lowest overall levels of contamination.

. . . . . . . . . . . . %

Deduce the conclusions that can be drawn from the data in the graph.

Suggest a reason for the effect of a diet reduced in acetylcholine on the larval survival rate.

Compare and contrast the effect of clothianidin and thiacloprid treatments on the concentration of acetylcholine in royal jelly.

Explain how neonicotinoids affect synaptic transmission in insects.

Companies that manufacture neonicotinoid pesticides have argued that they do not cause significant harm to honeybees. Construct an argument, based on the data in this question, for serious concern about the manufacture and use of neonicotinoid pesticides.

Oceania ✔

thiamethoxam is the most used in North America (but not in South America) / CONVERSE
OR
in South America they use different neonicotinoids to thiamethoxam ✔

OWTTE.

Allow numerical comparison.

57 (%) ✔

Allow range 56 % to 58 %.

a. reduced acetylcholine does not affect larval survival in the first two days ✔

b. reduced acetylcholine causes increased mortality from day 3 onwards ✔

c. 90 % versus 40 % survival/other valid numerical comparison by day 5
OR
(much) greater decrease in survival occurs between days 4 and 5/by day 5 for the reduced group ✔

Do not accept answers without times/ days.

(larvae lacking acetylcholine/with reduced AcH cannot survive because) acetylcholine is a neurotransmitter taking message from one neuron to another in synapses of nervous tissues
OR
messages would not pass from one neuron to the other
OR
(larvae) unable to synthesise/produce AcH, so need it from their diet ✔

OWTTE.

a. both neonicotinoids reduce the concentration of acetylcholine in royal jelly (compared to control) ✔

b. clothianidin reduces the concentration of acetylcholine in royal jelly more than thiacloprid (but perhaps not statistically different) ✔

c. clothianidin is used in smaller concentrations (than thiacloprid) so no firm conclusion can be obtained ✔

Need one similarity and one difference.

a. neonicotinoids bind to the (acetylcholine) receptor (in insects) ✔

b. (binding happens) in (cholinergic) synapses/at motor end plate/between motor neuron and muscles ✔

c. neonicotinoids bind irreversibly (to receptors)
OR
(receptors are blocked so) acetylcholine is unable to bind ✔

d. acetylcholinesterase/enzymes cannot break down neonicotinoids ✔

e. (synaptic) transmission prevented ✔

f. (causing) insect paralysis/death ✔

a. neonicotinoids are used in every continent ✔

b. the choice of specific neonicotinoid varies considerably around the world ✔

c. neonicotinoids contaminate honey (so must get into honeybees) ✔

d. only a minority of honey samples from around the world contain no neonicotinoids ✔

e. neonicotinoids reduce the acetylcholine (content of royal jelly)
OR
only a small amount of clothianidin can reduce acetylcholine in royal jelly ✔

f. survival of honeybee larvae is lower if the acetylcholine is lower/content of royal jelly is reduced ✔

In general, the data analysis question was well attempted by the majority of students.

Almost all were able to name Oceania.

In general, the data analysis question was well attempted by the majority of students.

Most identified that the proportion of the pesticide was greater in North than South America. This does not actually mean that a greater mass was used as these were relative frequency graphs.

In general, the data analysis question was well attempted by the majority of students.

Most read the graphs correctly, stating between 56 and 58 %.

In general, the data analysis question was well attempted by the majority of students.

An answer comparing the survival as the days progressed was expected. Answers tended to be too general.

In general, the data analysis question was well attempted by the majority of students.

At least half of the candidates did not know that acetylcholine is a neurotransmitter (section 6.5).

In general, the data analysis question was well attempted by the majority of students.

A compare and contrast question, that required one similarity and one difference. Most were able to state that both treatments reduce the acetylcholine concentration in the royal jelly and that clothianidin reduced it more than thiacloprid. The more astute also commented on the differences in concentrations of the insecticides.

In general, the data analysis question was well attempted by the majority of students.

Those students who had studied synaptic transmission scored well. However, many knew the role of acetylcholine here, but not in Q(1)(e).

In general, the data analysis question was well attempted by the majority of students.

This question was a good discriminator, with better students using the data presented to construct an argument as asked. Weaker students wrote about the function of bees in pollination etc., which is a consequence, but does not answer the question.

Calculate the difference in the mean dry mass of mayflies upstream and downstream of Cement Creek pond 9 for female and male mayflies.

Describe the effect dams have on water temperature.

The graph shows the mean dry mass of mayflies relative to the water temperature in their habitats.

Using the graph, discuss evidence for the hypothesis that mayflies grow to greater dry mass in cooler water.

Analyse the data to find the effect of flooding and tree felling by beavers on the activity of bats.

The trout, Oncorhynchus mykiss, that live in West Brush Creek and Cement Creek also feed on the mayflies. Fishermen come to Colorado to catch and eat trout. Draw a diagram of part of a food web for the creeks in Colorado, including mayflies, humans, trout and bats.

Identify an example of competition between organisms in this food web.

The North American beaver (Castor canadensis) was introduced to islands adjacent to Argentina and Chile where they have become an invasive species. Discuss one ecological criterion (a basis for deciding) whether beavers are harmful or helpful to the ecosystems there.

I. female: «+» 0.04 «mg»
AND
II. male: «–» 0.12 «mg»

Both needed.

a. height of dam affects the temperature

b. high dams tend to cool the water

c. low dams tend to warm the water

d. pond 5/one pond shows no change/stays the same

a. trend lines support «the hypothesis»
OR
trend shows a negative correlation shown «between increased temperature and size»

Do not credit answers with just numbers.
Accept “line of best fit” wtte.

b. the trend line is shallow / small slope
OR
there is a large amount of scatter at higher temperatures (reducing the certainty)
OR
wide/overlapping ranges so no significant difference «(at» 9^oC )

Note that it is only the trend line that indicates support.

c. (hypothesis not supported because) females in water over 10^oC have the highest «mean dry» mass

Words other than “hypothesis not supported” may be used: “as opposed to”, “whereas”, to express deviation from support.

a. both flooding and tree felling increases bat passes/activity / WTTE

b. flooding has greater/increase on bat passes/activity / WTTE
OR
flooding has the greater impact than tree felling on bat passes

c. supporting argument from the data

a. arrow pointing from trout to human

b. arrows pointing from mayflies to trout and bats

Award [1 max] if answer does NOT show all 4 organisms.

bats and trout compete for mayflies

a. criterion

b. reason that beavers damage

c. reason that beavers help

eg,

a. biodiversity

b. if indigenous species are eliminated biodiversity is reduced, then the beavers would be seen as damaging

c. if biodiversity increases (due to the engineering of waterways), then beavers could be a benefit

Consider criteria something that may be dealt with from a range of perspectives.

Other possible criteria: abiotic disturbance changes to food webs diversity

Outline how acidified sea water could affect the shells of the oyster.

Outline the trends shown in the data in the graph.

Estimate how much smaller drilled oysters raised in seawater at a high CO₂ concentration were than drilled oysters raised in seawater at a normal CO₂ concentration.

Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.

Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.

The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO₂ concentrations.

Using all the data, evaluate how CO₂ concentrations affect the development of oysters and their predation by gastropods.

Shells might dissolve/deteriorate / become smaller/thinner/weaker / OWTTE
OR
shell formation reduced / more difficult

a. positive correlation between shell thickness and shell size
OR
as shell thickness increases, shell size «also» increases 

b. (positive correlation) occurs at two different CO₂ concentrations / both high and normal concentrations 

c. trend for thickness is «slightly» lower with high CO₂

«approximately» 0.2 mm²
OR
«approximately» 40 % «smaller» 

unit required

a. significant factor: concentration of CO₂ in which oysters were raised 

b. insignificant factor: concentration of CO₂ at which oysters were presented to gastropods

a. (because) shells are thinner/smaller when the oyster is raised in high CO₂/lower pH
OR
«because» lower pH/higher acidity prevents/reduces deposition of calcium carbonate 

b. gastropods target smaller/thinner-shelled oysters more 

c. gastropods can eat/drill thin-shelled/smaller oysters at a faster rate (and move onto another) 

d. eating smaller oysters «from high CO₂ environments» means given population of gastropods require more oysters for same food intake

a. data shows that similar numbers are drilled regardless of conditions 

b. since radulas are not affected by acidification
OR
radulas not made of calcium carbonate so (remain) strong/successful at drilling

a. the data/trend lines indicate that a higher CO₂ concentration diminishes the shell thickness, making gastropod predation more successful
OR
the bar graphs suggest that oysters raised in a higher CO₂ concentration are smaller, making gastropod predation more successful 

b. CO₂ concentrations «during feeding» do not change the occurrence of drilling/predation «by gastropods» 

c. «limitation» no information about how exaggerated the CO₂ concentrations were
OR
«limitation» no information about numbers of gastropods used «in each setting»

State one process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.

The crustacean and the jellyfish obtain carbon compounds by feeding. State one source of carbon for marine organisms, other than feeding.

Explain how energy enters, flows through and is lost from marine food chains.

Deduce whether jellyfish or crustacea are a richer source of carbon in a food chain.

Suggest with a reason whether having a large body mass is an advantage or disadvantage for jellyfish.

a. (aerobic/cellular) respiration ✔

b. gas exchange / diffusion ✔

Do not accept photosynthesis.

Do not accept breathing

Organism is taken to be a living thing.

a. photosynthesis ✔

b. absorption of (dissolved) carbon dioxide / (hydrogen)carbonate directly from the oceans ✔

Accept reference to carbonate or hydrogencarbonate ions.

a. light energy is converted to chemical energy (in carbon compounds/sugars) by photosynthesis ✔

b. (chemical) energy (in carbon compounds) flows by means of feeding/through food chains/webs ✔

c. only (approximately) 10 % of energy is passed to the next trophic level ✔

d. energy released as heat (by respiration) ✔

e. energy is not recycled ✔

f. after death, energy may remain trapped as undigested detritus/fossils/fossil fuels ✔

crustacean as they have more carbon per unit volume
OR
crustacean as jellyfish has little carbon per total body size ✔

OWTTE.

The conclusion must be supported from the information given.

a. advantage of large size is ability to eat /catch large prey ✔

b. (advantage as) lower rates of predation of large jellyfish ✔

c. (advantage as) can produce more reproductive cells ✔

d. (disadvantage as) can move slower to escape from predators/capture prey ✔

e. (disadvantage as) needs more energy/nutrients to maintain structure/move/grow ✔

f. (disadvantage as) low surface area to volume ratio and thus possibly difficulty with materials/gas/nutrient exchange ✔

g. (disadvantage as) more prone to mechanical damage during storms ✔

Accept other reasonable answer.

Must say advantage or disadvantage.

In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO₂ or HCO₃ from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.

In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO₂ or HCO₃ from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.

In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO₂ or HCO₃ from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.

In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO₂ or HCO₃ from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.

In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO₂ or HCO₃ from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.

State the immediate consequence of a species producing more offspring than the environment can support.

Explain the consequence of overpopulation on the survival and reproduction of better adapted individuals within a population.

competition/lack of resources/death/exceeding carrying capacity ✔

Allow a description of it.
Do not allow “overpopulation” or “natural selection”.

a. «better adapted» tend to survive more ✔

b. «better adapted» reproduce/produce more offspring ✔

c. pass on characteristics to their offspring «when they reproduce» ✔

d. their frequency increases «within the population» due to natural selection ✔

e. leading to evolution ✔

Identify the site with the highest incidence of diseased colonies.

Deduce whether there is a trend in the incidence of white syndrome over the north-south range of latitude.

Describe the evidence that is provided by the data in the table for the harmful effects of rising sea temperatures on corals.

The researchers concluded that there was a threshold coral cover percentage, below which infection rates tended to remain fairly low. Using the data in the table, identify this threshold level.

Suggest a reason for a larger percentage of corals being infected with white syndrome on reefs with a higher cover of corals.

Compare and contrast the data for 1998–1999 and 2002–2003.

Suggest a reason for the correlation between coral cover and WSSTA in 1998–1999.

Some scientists predict that, if humans continue to produce carbon dioxide at the current rate, the pH of the oceans will become more acidic. Suggest possible effects on the coral reefs.

This study was carried out over six years on the Australian Great Barrier Reef. State one advantage of field investigations compared with mesocosm experiments to study ecological processes.

Capricorn and Bunkers group;

there is no clear trend;

a. effects (generally) increase with temperature anomalies/WSSTA;
b. effects increase for all different coral covers
OR
in the 25-49 cover there is an anomaly/is not an increasing trend;
c. harmful effect is higher in coral covers between1 50-75 % / vice versa;

50 % / 25 % / 49 %
OR
25–49 % (coral cover);

a. the closer the corals are (to each other) the easier the transmission;
b. other organisms in the community may act as vectors/carriers / OWTTE;

Similarities
a. similar range of cover in both periods
OR
weak correlation/no correlation in either;

Differences
b. higher WSSTA range/more WSSTA in 1998–1999 than 2002–2003
OR
positive (2002–2003) versus negative correlation (98–99)
OR
more coral reefs with very low % of coral cover (0–20 %) in 2002–2003;

Must respond with one similarity and one difference for full marks.

coral cover lower on reefs with higher temperature;

a. corals would not be able to maintain their skeletons;
b. (if coral reefs are lost) habitat will be lost;
c. some organisms/coral can decline if the water becomes too acidified;
d. coral bleaching could occur/become worse
OR
coral could expel their mutualistic alga/zooxanthellae;
e. enzymes could be denatured;

real environmental conditions / larger scale investigations / more variables studied;

In general, the data analysis question was well attempted by the majority of students. In 1a almost all were able to correctly name the Capricorn and Bunkers Group.

In 1b many just described the incidence at various points, instead of stating that there was no clear trend. There were a few G2 comments that the map did not include compass points, which, perhaps, has some justification. However, by convention maps are usually shown with North at the top.

The expression ‘coral cover’ did confuse some of the weaker students who imagined that the corals somehow has a sort of cover over them. Most students gained at least 1 mark in 1b (i), despite the criticism from the G2 forms that it was very complex.

Most were able to able to gain the mark in 1b (ii) for saying that the threshold level was 25 – 49 %.

In 1b (iii) the better students realised that it was to do with higher density of corals, not just the more vague ‘higher cover’ given in the stem.

In 1c contrasts were common, but few gained the comparison mark as well.

In 1d weaker students incorrectly wrote about the sea becoming acidic as the pH was increasing (sic). Indeed, it is becoming more acidic, as the pH is decreasing slightly, leading to more bleaching and the decrease in population of some creatures.

In 1e most were able to give a reason why the study was better than a mesocosm.

State the haploid number for horses.

Explain reasons that mules cannot reproduce.

Discuss whether or not horses and donkeys should be placed in the same species.

A mule was born at the University of Idaho in the USA with 64 chromosomes. Suggest a mechanism by which this could happen.

32

a. because the chromosome number is not an even number/63

b. (so) cannot divide by two during meiosis/cannot perform meiosis/chromosomes cannot pair up during meiosis

c. one chromosome has no homologue/WTTE

d. because unlikely to/cannot produce viable gametes/sperm/egg cells

a. to be in same species two organisms must have the same genes arranged on the same chromosomes
OR
must have the same number of chromosomes

b. members of same species produce fertile offspring and a mule is not fertile

non-disjunction

Accept description of non-disjunction.

State the type of wavelength of the radiation labelled X and Y.

X: 

Y: 

Outline reasons for the change occurring at Z. 

The short-tailed albatross (Phoebastria albatrus) nests and breeds on remote low-lying coral islands in the Pacific Ocean. Predict how global warming may threaten the survival of such an ocean bird.

X: short-/ultraviolet/UV/visible/EMR/electromagnetic radiation 

Y: long-/infrared/IR

a. greenhouse gases present (at Z) 

b. greenhouse gases «CO₂, methane, nitrous oxide, water vapour» absorb long-wavelengths/infrared
OR
long wavelengths/infrared waves blocked from leaving the atmosphere 

c. (long-wavelengths/infrared absorbed and) reradiated/re-emitted (heat Earth)

a. rising ocean levels/more extreme weather «due to global warming» may destroy breeding/nesting sites 
OR 
rising sea level may put island underwater causing young birds/chicks to drown 

b. populations may not find/adapt to new colony sites 

c. warming seas may affect the food supply

Compare and contrast the mode of nutrition of detritivores and saprotrophs.

The image shows an example of a soil food web.

[Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/
photogallery/soils/health/biology/gallery/?cid=1788&position=Promo [Accessed 11 March 2020].]

Draw a food chain from this food web, showing at least three organisms.

Explain the reasons for food chains rarely containing more than four or five trophic levels.

The amount of food passing into food chains can be affected by the rate of photosynthesis. Explain the effect of one limiting factor on photosynthesis.

All of the leaves in the image are from Solanum, a wild genus of tomato.

[Source: Courtesy: National Science Foundation, Credit Leonie Moyle.]

State one cause of variation in a plant such as the tomato.

Accept not autotrophic/not photosynthetic instead of heterotrophic.

Do not accept that both groups are decomposers or consumers for the similarity.

food chain of three or more organisms starting with plants;

a. energy is lost between the trophic levels;
b. transfer between levels is only usually 10% efficient
OR
energy transformations take place in living organisms / the process is never 100% efficient;
c. energy is lost by the organism/used in respiration / released as heat/movement;
d. energy is lost as waste/feces/urine/undigested food/uneaten parts;
e. as energy is lost between trophic levels and so (higher ones) have less biomass / less biomass available for next level;

a. the rate of reaction will be limited by the limiting factor that is nearest to its minimum value;

temperature:
b. enzymes that control photosynthesis are influenced by temperature;
c. as temperature increases, reaction rate will increase;
d. above a certain temperature, the rate of photosynthesis will decrease;
e. (where temperature is limiting) essential enzymes begin to denature/not working to optimum;

light intensity:
f. light is source of energy / converted into chemical energy;
g. as light intensity increases reaction rate will increase;
h. at a certain light intensity, rate of photosynthesis will plateau;
i. another factor becomes limiting;

CO₂ concentration:
j. CO₂ is fixed to form organic molecules;
k. as CO₂ concentration increases, reaction rate will increase;
l. at a certain concentration of CO₂, rate of photosynthesis will plateau;
m. another factor becomes limiting;

Accept answers using an annotated graph to explain

Only accept the first factor described

Do not accept pH as a limiting factor

a. mutations;
b. meiosis/crossing over/random assortment of homologous pairs;
c. sexual reproduction/recombination/random fertilisation;

Knowledge of detritivores and saprotrophs was good in 3a, with many of the poorer answers describing them as feeding on inorganic material.

Many took the word ‘draw’ literally in the food chain, and the drawings of the nematodes and fungi amused the examiners. A food chain must start with a plant. The stem did say “three organisms”. Detritus was not taken as an organism, so negated the mark.

Most were able to gain at least two marks for the explanation of energy loss through the trophic levels.

In 3c, most knew that temperature/CO₂ concentration/light affect photosynthesis but could not explain the idea of acting as a limiting factor. Only the better students gained all 3 marks.

In 3d there was a great deal of variety in the leaf shape, so an answer in terms of sexual reproduction was looked for.

Describe anaerobic respiration in humans and in yeast.

Distinguish between the thermal properties of water and methane.

Explain the role of methane in climate change.

1. (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;
2. anaerobic respiration occurs when there is no oxygen;
3. anaerobic respiration in yeast produces ethanol and carbon dioxide/alcoholic fermentation;
4. anaerobic respiration in humans (in muscle) produces lactate/lactic acid/lactic acid fermentation;
5. both undergo glycolysis;

Do not accept mpd if CO₂ also included.

1. water has higher boiling/melting point;
2. water has a higher specific heat capacity;
3. water has a higher latent heat of vaporization;
4. differences due to water having many H-bonds/polarity between the molecules while methane has no H-bonds/polarity;

1. methane is a greenhouse gas
   OR
   methane causes an increase in temperature of the atmosphere;
2. methane is one of the most powerful greenhouse gases / more powerful than CO₂;
3. methane has a relatively short lifespan compared to CO₂/decomposes to CO₂;

Other verifiable sources.

In 3a. the top candidates scored all three marks with ease, but many, especially in Spanish scored zero. A common mistake was to say that humans produce lactic acid and CO₂. In bi, many were confused by the term ‘thermal properties’, but most were able to gain at least one point for comparing their boiling/freezing temperatures, specific heat capacities and latent heat of fusion. The best candidates also explained the differences in terms of hydrogen bonds between the water molecules. In bii, few got past stating that methane is a greenhouse gas/causes an increase in temperature of the atmosphere. The better candidates stated that it was a powerful greenhouse gas, but it had a relatively short life span compared to CO₂. A surprising number thought that methane’s main danger was that it destroyed the ozone layer.

Calculate the increase in mean global temperature between 1880 and 2010.

.......... °C

Outline how changes in temperature over short time periods could give a misleading impression of changes to the Earth’s climate. 

Explain how increased carbon dioxide in the air leads to the greenhouse effect.

0.87; (accept values between 0.8 and 0.9)

short-term reading could show global temperatures falling while the trend is rising
OR
fluctuations from year to year may not show long-term trend;

1. short wave radiation from sun passes through atmosphere / is not absorbed by CO₂;
2. infrared/long wave (radiation) / heat emitted from/released from (surface of) Earth;
3. CO₂ in the atmosphere absorbs infrared/long wave (radiation)/heat / cannot pass through the greenhouse gases;
4. this results in warm/increased temperatures on Earth/global warming;

Do not accept “reflected” for mpb.

Many candidates got the calculations right.

Answers to this question suffered due to poor expression of an answer. Other candidates answers were succinct and to the point as they used the data to make the point clear.

There were elegant answers to this question demonstrating a high level of understanding. Many other candidates mixed up all sorts of ideas here, including the idea of ozone being a cause of global warming and stating as a "fact" that heat travels from the sun to the earth. Among the confused ideas was the notion that carbon dioxide is a toxic pollutant.

Draw a labelled diagram to show the fluid mosaic model of the plasma membrane.

Unicellular and multicellular organisms share the same functions of life. Outline four functions of life.

The structure of organisms is based on organic molecules containing carbon. Explain the cycling of carbon in an ecosystem.

a. two correctly oriented layers of phospholipids/phospholipid bilayer shown with heads facing in opposite directions 

b. phospholipids shown with two parts labelled hydrophilic/phosphate head AND hydrophobic/hydrocarbon tail

c. protein (any) shown as a globular structure embedded in one/both layers of phospholipid 

d. peripheral protein, shown as globular structure at the surface of the membrane AND integral protein shown as embedded globular structures 

e. glycoprotein shown as embedded globular structure with antenna-like carbohydrate protruding / carbohydrate shown as a branched/antenna-like structure either on a protein or on a phospholipid
OR
channel protein(s) shown with a pore passing through it
OR
pump protein shown as a transmembrane globular structure 

f. cholesterol shown in between adjacent phospholipids

Do not award the mark unless the structure is labelled with the underlined name.

a. nutrition: process by which organisms take in and make use of food//nutrients OWTTE 

b. metabolism: conversion of organic molecules/chemical reactions in an organism 

c. growth: increase in size/mass/number of cells within an organism

d. response/irritability/sensitivity: reactions/responsiveness to stimuli/factors 

e. homeostasis: regulating/maintaining constant/stable interior environment 

f. reproduction: production of similar cells/organisms from existing ones/offspring 

g. excretion: elimination of (metabolic) wastes

a. autotrophs/producers absorb carbon (dioxide} from atmosphere/air/water 

b. autotrophs make carbohydrates/organic compounds / perform photosynthesis 

c. carbon (compounds) pass along food chains/trophic levels (as consumers feed) 

d. respiration releases carbon (dioxide) into atmosphere/water 

e. carbon (dioxide} is released from dead matter /by decomposition/respiration 

f. methane is produced during anaerobic respiration of organic matter / by methanogens in cattle/herbivores

g. methane is oxidized into carbon dioxide in the atmosphere 

h. fossil fuels/peat were made from partially decomposed organic matter 

i. combustion of fossil fuels/forest fires/biomass releases carbon (dioxide} into the atmosphere 

j. volcanic eruptions may add large quantities of carbon (dioxide) into the atmosphere 

k. limestone (from shells/reefs)/trees/permafrost are sinks of carbon

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.

body temperature increases with ambient temperature / positive correlation;

Since direct can be either –/+, no credit for direct correlation alone.

humans maintain/regulate a constant body temperature at different ambient temperatures/maintained by homeostasis;

As ambient temperature increases, the sloth spends more time with limbs spread
OR
as ambient temperature increases the sloth spends less time curled in a ball
OR
as ambient temperature rises, the posture changes from 1 to 6;

1. less surface area is exposed when curled up
   OR
   more surface area is exposed when all limbs spread;
2. curled position prevents heat loss/provides warmth
   OR
   stretched out position allows more heat loss/body cooled;

May;

1. food intake rises as daily temperature increases / positive correlation;
2. the lowest food intake corresponds to the lowest temperature;

1. the sloth will be more active at higher temperatures as it takes in more food for energy;
2. as temperature rises, the sloth uncurls to dissipate/lose heat;

Reason required.

1. mammals have mammary glands;
2. produce milk for their offspring;
3. bodies covered in hair/fur;

Characteristic must be exclusive to mammals.

If more than one answer, use the first one given.

Often steady or constant body temperatures for humans was given rather than homeostasis. Some candidates erroneously described humans as warming up in response to cold ambient temperatures.

There were a few beautiful responses where surface area was specifically incorporated into the answer achieving maximum marks.

Good reasoning was not seen often, best answers needed some of the elements in this linkage: higher temperature led to uncurling which led to movement which led to eating because of energy needs; "sloth prefers staying curled up so cold does not affect them" or "sloth enjoys staying curled up" were not acceptable

Have hair/fur or feed young with milk were the best answers. Many students wrote "give birth to live young;" While this is true of most mammals, monotremes lay eggs. Furthermore, some other animals give birth to live young (ovoviviparous) such as some reptiles and some groups of fish. We credited only characteristics exclusive to all mammals.

State the reason that O. sativa and O. rufipogon are classified as different species.

Determine which type of rice has the lowest overall diversity index.

Compare and contrast the trends for O. rufipogon and O. sativa indica.

State the proportion of the ancestral allele for the gene GS3 in the O. rufipogon-III population.

Distinguish between the proportion of ancestral and derived alleles for all three genes in O. sativa indica and O. sativa japonica.

State one reason for having a control group. 

Using all of the data, discuss whether there is evidence that the two sub-species of O. sativa might have evolved independently from O. rufipogon.

cannot interbreed to produce fertile offspring ✔

Accept converse or a good explanation.

«O. sativa» japonica ✔

Similarities
both show diversity
OR
similar pattern/peaks and troughs in the first part of the chromosome / up to «approximately» 1.5 megabases
OR
similar diversity between 2.4 to 2.7 mb
OR
both highest at 0.7 mb ✔

Differences
there are «two» major drops in diversity for O. sativa indica whereas none for O. rufipogon/much wider fluctuations in O. s. indica
OR
O.s. indica much lower at PROG1
OR
O.rufipogon does not drop < 2.5 whereas O. s. indica approaches 0
OR
O.rufipogon generally higher than O. s. indica after 1.4-1.5 ✔

One answer from mpa and one from mpb required for 2 [max].

Accept a statement of where the drops occur.

$\frac{3}{4}$ /0.75/75% ✔

Do not accept 0.75% or 75 or ratios

a. O.s. indica has more of the ancestral allele «for all three genes» ✔ Accept converse.

b. lower/higher values for ancestral/derived are not for the same genes ✔ Allow specific gene examples.

c. for O. s. indica the highest proportion is for DPL2 ancestral, but for O. s. japonica is GS3 derived allele ✔ Allow converse for smallest derived.

any reference to comparison ✔

a. large difference in diversity index between O. s. indica and O. s. japonica «suggests independent evolution» ✔

b. «some of the» peaks/troughs for O. s. indica and O. s. japonica in different positions «suggests independent evolution» ✔

c. O.s. indica has a similar diversity index to O. rufipogon «which suggests closer relationship/recent divergence» ✔
Allow converse for japonica

d. O.s. japonica has very different proportions of ancestral and derived alleles compared to O. s. indica ✔

e. O.s. indica has similar large number of ancestral alleles to O. rufipogon I/II ✔ Allow converse for derived

f. O.s. japonica has a large number of derived alleles similar to O. rufipogon III
OR
«but» the number of derived alleles is greater in O. s. japonica than in O.rufipogon III ✔ Allow converse for ancestral

g. O.s. indica and O. s. japonica are in different clades ✔
OR
O.s. indica and O. rufipogon I are in the same clade ✔

h. evidence from one chromosome/3 genes/2 studies is not sufficient to form a conclusion ✔

State the phylum of this plant.

State two characteristics of plants from the phylum you stated in (a)(i).

Outline why the number of trophic levels is limited in a food chain.

Filicinophyta/Filicinophytes/Pteridophytes

Reject “ferns”

a. have roots, stem and leaves

All three, roots, stem and leaves required

b. pinnate leaves/leaves divided «repeatedly» into leaflets

c. have vascular tissue/xylem and phloem

d. produce spores/sporangia

    OR

    no flowers/fruits/seeds

[Max 2 Marks]

energy losses between trophic levels

OR

only part of the energy in one trophic level will become part of the next trophic level

State the name of the structures labelled I and II.

Outline the function of the structure labelled III.

The plant from which this cell was taken is in the group angiospermophyta. State one characteristic that is unique to this group of plants.

Distinguish between autotrophic nutrition and heterotrophic nutrition.

Explain how energy and nutrients are transferred in ecosystems.

I. cell wall 

II. nucleus/chromatin

Both needed.

a. necessary for photosynthesis/converts light energy into chemical energy

b. contains chlorophyll to absorb light

c. (contains enzymes) for production of carbohydrate/glucose/starch

a. produce flowers 

b. enclosed seeds/have fruit

Table format not required.
Must be paired statements.

a. energy enters ecosystems from the Sun / continuous supply from the Sun 

b. light energy is converted into chemical energy and lost with movement along food chains
OR
energy needs to be «constantly» added «to ecosystem» as lost with movement along food chains / energy lost as heat with movement along food chains 

c. nutrients are recycled within ecosystems / nutrients in an ecosystem are finite and limited 

d. nutrients not lost but transformed into different compounds 

e. nutrients «carbon compounds»/energy flow through food chains by means of feeding

Describe how detritivores obtain nutrition and the effects they have in ecosystems.

Outline the role of amylase in digestion in humans.

Explain how plants capture and use light in photosynthesis.

a. «detritivores» obtain nutrition from detritus/waste/dead bodies ✔

b. are heterotrophic ✔

c. removes large waste/cleans up the ecosystem
OR
helps control spread of disease ✔

d. facilitates further decomposition ✔

e. contribute to the supply of «inorganic» nutrients for autotrophs/nutrient cycling
OR
improve soil conditions/aeration ✔

a. amylase is an enzyme ✔

b. secreted by salivary glands/pancreas ✔

c. active/released into the mouth/small intestine ✔

d. acts on starch/polysaccharides ✔

e. breaks «glycosidic» bond by hydrolysis/adding water ✔

f. converts insoluble/large molecule to soluble/small molecules ✔

g. product is maltose/disaccharide/sugar molecule ✔

a. plants convert light energy into chemical energy by photosynthesis ✔

b. photosynthesis takes place in chloroplasts ✔

c. chloroplasts «are organelles that» contain the pigment chlorophyll ✔

d. chloroplasts/chlorophyll «in plants» absorb sunlight ✔

e. «chlorophyll» absorbs red AND blue light most effectively ✔

f. light causes photolysis/splits water molecule ✔

g. carbon dioxide AND water are reactants «in photosynthesis» ✔

h. glucose AND oxygen are products «of photosynthesis» ✔

i. light intensity is a limiting factor for the rate of photosynthesis ✔

j. organic/carbon compounds/glucose provide food/stored energy «for plant itself, animals,food chains» ✔

k. up to one additional mark for an accurate detail from AHL ✔

Most candidates got max 2 for mp a (nutrition of detritivores) and mp e (recycling of nutrients). Candidates getting high marks were able to provide correct examples of detritivores and correctly link to their role in enriching the soil and remove dead material. The biggest problem was the notion that detritivores recycle energy.

The name, location and correct function of the enzyme was very common making 3 max the most common marks. Students who got fewer marks gave generic explanations of the process of digestion. Some students made incorrect references to amylase digesting proteins. A few candidates ignored amylase and discussed digestion in general.

Generally well done with some very knowledgeable answers from the Higher Level programme sometimes to the detriment of the more basic answers required by the standard level examination. Many candidates who attempted this response got more than 4 marks for mp b, d, g and h which were the most common. Students getting higher marks were able to focus on correct conversion of energy, efficiency of red and blue light absorption, and photolysis. Some egregious misconceptions exist among candidates such as plants are green because they absorb green light. The idea that during photosynthesis light energy is converted to chemical energy was frequently neglected.

Draw a section of the Singer-Nicolson model of an animal cell membrane.

Outline the principles used by scientists to classify organisms.

Explain the movement of energy and inorganic nutrients in an ecosystem.

a. bilayer of phospholipids with both “tails” towards the inside «of the bilayer» ✔ This can be taken unlabeled from diagram.

b. hydrophilic/polar and hydrophobic/non-polar annotation ✔

c. cholesterol between phospholipid tails ✔

d. glycoprotein ✔

e. integral proteins/channel proteins ✔

f. peripheral proteins ✔ Allow this if it does not extend across the membrane

Elements should be clearly drawn, correctly positioned and annotated.

a. use of the binomial system ✔

b. agreed/developed by scientists / OWTTE ✔

c. hierarchy of taxa used ✔ Names of the seven taxa not required. 

d. three domains used/three domain names ✔ OWTTE

e. genome/DNA sequence similarities
OR
amino acid sequence of specific proteins ✔

f. species from a common ancestor are grouped together
OR
included in the same clade/branch in cladogram ✔

g. use evidence of evolutionary origin ✔ Allow example e.g. fossil record comparison

h. shared characteristics within a group
OR
similar embryonic development ✔

a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔

b. energy provided «mainly» by sunlight ✔

c. light energy converted «to chemical energy» through photosynthesis ✔

d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔

e. «these» carbon compounds/foods contain/are a source of «useable» energy «for life» ✔

f. carbon compounds/energy are transferred along food chains when eaten by consumers/heterotrophs ✔ Allow OWTTE for mpf for passed up trophic levels.

g. respiration returns carbon «dioxide» to the environment ✔

h. respiration releases stored/chemical energy as ATP/heat ✔

i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔

j. energy is lost/not recycled ✔

k. nutrients are recycled / example of recycled nutrient e.g. carbon ✔

l. decomposers recycle minerals/inorganic nutrients ✔

Draw a diagram of a palisade mesophyll cell labelling only the structures that would not be present in a pancreatic cell.

Explain the process of photosynthesis.

Describe the process of peat formation.

a. cell wall

Must be shown as a double line

b. large vacuole

Labelled either inside or on the membrane

c. chloroplast/plastid

d. starch grain

e. tonoplast

Allow [2 max] if any features common to both plant cells and animal cells are labelled

[Max 3 Marks]

a. autotrophs perform photosynthesis

b. carbon dioxide and water are the reactants/raw materials required for «photosynthesis»

c. light splits water molecules/causes photolysis

d. «photolysis» releases oxygen as a «waste» product

e. light energy is converted into chemical energy

f. «photosynthesis» produces organic compounds/glucose/carbohydrates

g. photosynthesis occurs in chloroplasts

h. chlorophyll «photosynthetic pigment» absorbs light

i. different pigments absorb different wavelengths «of light»

j. chlorophyll absorbs red and blue light/ends of the spectrum

k. carbon dioxide concentration/temperature/light intensity are limiting factors

Award only [1] for correct display of equation unless further annotated or explained

Allow up to [2] for correct use of understandings specified as AHL topic 8

[Max 8 Marks]

a. formed from dead plant material/leaves/mosses/Sphagnum

b. formed in waterlogged sites/bogs/mires/swamps

c. where bacteria/fungi/saprotrophs are not active/are inhibited

d. organic matter not fully decomposed

e. «occurs» in acidic conditions

f. «occurs» in anaerobic conditions

Reject anaerobic respiration

g. «very» slow process/takes a long time

[Max 4 Marks]

State the genus of this organism.

State the domain in which it is classified.

Outline the method of nutrition carried out by P. caudatum.

Outline one aspect of how P. caudatum carries out homeostasis.

Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.

Paramecium

eukaryotes

heterotroph/consumer as it feeds on bacteria/algae/yeast/smaller single celled organisms
OR
heterotroph/consumer as it does not have chloroplasts

Heterotrophic must be qualified.

a. lives in fresh water so water enters cell (by osmosis);

b. contractile vacuoles collect and expel water;

c. homeostasis is keeping internal conditions within limit/constant / involves osmoregulation/regulating water content/potential;

a. mitochondria/chloroplasts show features in common with prokaryotes/similar size;

b. multiply by binary fission/in same manner;

c. have naked loop of DNA/circular DNA/own DNA;

d. surrounded by a double membrane;

In a about half of the candidates named the genus correctly (Paramaecium), but significantly fewer could state the correct domain (eukaryota). The most common wrong answers were prokaryote and eubacteria. Only the better candidates were able to outline the method of nutrition (heterotrophy) in b and describe how homeostasis is carried out, in spite of being specifically stated in the syllabus. The endosymbiotic theory was quite well known.

Draw a molecular diagram of alpha-D-glucose.

Outline how carbon compounds are produced in cells using light energy.

Explain the transformations of carbon compounds in the carbon cycle.

a. hexagonal ring structure with O at one point (between C1 and C5);

b. correct orientation of OH groups (on carbons 1 to 4); Hydrogens not required

c. CH₂OH group shown on fifth carbon with correct orientation;
OR
d. 6 carbon chain with oxygen on first C;

e. H and OH groups correctly orientated;

Carbons do not need to be numbered.

Allow boat or chair diagrams.

Allow [2 max] if linear structure drawn.

a. occurs by the process of photosynthesis;

b. occurs in chloroplasts of plant cells/using chlorophyll;

c. chlorophyll absorbs red/blue light AND reflects green light; Both needed for marking point.

d. raw materials/starting products are carbon dioxide and water/shown in an equation;

e. water is split by photolysis;

f. oxygen is produced as waste/by-product/lost;

g. glucose formed/shown in an equation;

h. glucose molecules combine to form starch for storage;

i. light energy transformed to chemical;

a. autotrophs/producers convert carbon dioxide into carbohydrates/carbon compounds in photosynthesis;

b. carbon dioxide diffuses/moves from the atmosphere /water into autotrophs/plants;

c. carbon compounds are transferred through food chains/OWTTE;

d. carbon dioxide produced by respiration diffuses out of organisms into water/atmosphere;

e. decomposers release carbon dioxide during decay/putrefaction;

f. methane is produced from organic matter in anaerobic conditions (by methanogens);

g. some methane diffuses into the atmosphere/accumulates in the ground;

h. methane is oxidized to carbon dioxide (and water) in the atmosphere;

i. peat forms when organic matter is not fully decomposed because of acidic/anaerobic conditions in waterlogged soils;

j. partially decomposed organic matter from past geological eras/fossils was converted into coal/oil/gas that accumulated in rocks;

k. carbon dioxide is produced by the combustion of biomass/fossilized organic matter/fuels;

i. hard parts of some animals/corals/molluscs are composed of calcium carbonate

m. can become fossilized in limestone;

As this is an “explain” question, simply drawing a labelled diagram is not enough for [7]. Diagram would need sufficient annotations to meet the command term.

If carbon compounds are referred to instead of carbon dioxide, penalise once then ecf.

This was the less favourite option question, generally attempted by the better candidates. In part (a) the candidates tended to gain either 3 for a correct structure or zero. A G2 comment asked whether the different forms of glucose were needed; knowledge of the structure of alpha-glucose is stated in the syllabus.

Most gained some marks for what was really a description of photosynthesis in part (b), and the transformations of carbon compounds in the carbon cycle was quite well known. Some students lost marks by continuing to use the term ‘carbon compounds’ instead of carbon dioxide and the specific compounds. Many went off on a tangent to write about carbon dioxide and climate change etc. Many drew some quite detailed flow charts of the carbon cycle from which some marks could be gleaned or ambiguous statements clarified.

Pictured below are Louis Pasteur’s original drawings of swan-necked flasks.

Describe how Pasteur’s experiments provided convincing evidence to falsify the concept of spontaneous generation.

State the function of life in Paramecium that is carried out by:

cilia.

State the function of life in Paramecium that is carried out by:

the contractile vacuole. 

Discuss the advantages and disadvantages of the use of adult stem cells.

Explain the role of decomposers in an ecosystem.

a. spontaneous generation is life appearing from nothing / from non-living / cells only come from pre-existing cells/life 

b. broth/culture medium (for bacteria) (used/placed) in flasks 

c. broth boiled/sterilized «in some flasks» to kill microbes 

d. no clouding/signs of bacterial growth/reproduction / microbes did not appear «in flasks of boiled broth» 

Allow bacteria or organisms instead of microbes.

e. after necks of flasks were snapped boiled broth became cloudy/growth of microbes 

f. because microbes from the air contaminated the «boiled» broth 

g. curved necks allowed indirect exposure to air but prevented entry of microbes

movement/locomotion
OR
feeding/nutrition

homeostasis
OR
maintain osmotic balance / expels «excess» water / maintains «cell» water content

Advantages:

a. «adult stem cells» can divide «endlessly» / can differentiate 

b. «adult stem cells» can be used to repair/regenerate «tissues» 

c. fewer ethical objections «than with embryonic stem cells» 

d. adults can give «informed» consent for use of their stem cells 

e. adult source is not killed / «source» would not have grown into new human / no death of embryos used to provide stem cells 

f. no rejection problems / patient’s own cells used 

g. less chance of cancer/«malignant» tumor development «than from embryonic stem cells» 

h. most tissues in adults contain some stem cells

Disadvantages:

i. difficult to obtain/collect/find in adult body/very few available 

j. some «adult» tissues contain few/no stem cells 

k. «adult stem cells» differentiate into fewer cell types «than embryonic cells» /OWTTE

a. saprotrophs/decomposers feed on/break down dead «organic» matter 

b. saprotrophs/decomposers release energy «heat» accelerating decomposition/warming soil 

c. saprotrophs/decomposers recycle nutrients / make nutrients available (to producers)
OR
improves soil fertility / returns nutrients (minerals/nitrates/phosphates/carbon)to soil/water/environment 

d. saprotrophs/decomposers detoxify waste

Explain the processes by which energy enters and flows through ecosystems.

Producers extract phosphates and nitrates from soil. Outline how these ions are used in the synthesis of organic molecules.

Draw a labelled diagram of a pyramid of energy.

a. light energy is the initial energy source for (all) organisms

b. producers/autotrophs change light/radiant energy into chemical energy
OR
producers/autotrophs convert/trap light/radiant energy by photosynthesis

c. producing C₆H₁₂O₆ /sugars/carbohydrates

d. carbon/organic compounds used for energy/growth/repair/storage

e. compounds/energy pass as food along food chains/trophic levels WTTE

f. cellular respiration releases energy as ATP from food

g. energy is lost as heat (during cellular respiration)

h. loss of energy at each trophic level
OR
only approximately 10% of energy is passed to the next trophic level / 90% is lost at each trophic level

i. energy lost in bones/hair when they die/not fully eaten by the next trophic level

j. energy lost in feces/urine

k. decomposers/saprotrophs remove energy from wastes/bodies

l. energy is not recycled

a. by photosynthesis / using energy from light

b. attached to carbon compounds

c. phosphates used to make phospholipids/nucleotides/nucleic acids/DNA/RNA/ATP

Other phosphorus-containing metabolites are acceptable if verified.

d. nitrates are used to make amino acids/proteins/nucleotides/nucleic acids/DNA/RNA/ATP

Other nitrogen-containing metabolites are acceptable if verified.

e. transported from roots to leaves (in xylem)

a. drawn in steps rather than triangle

b. drawn to scale (should be at least 1/5 of the box below it)
OR
annotated with appropriate numeric values

c. producer

d. primary consumer

e. secondary consumer

Award no marks if a drawing has not been made.

“Appropriate numeric values” should indicate scale so accept percentage or numbers.

Outline the process of inhalation.

Explain the process of gas exchange taking place in the alveoli.

Discuss the relationship between atmospheric carbon dioxide concentration and global temperatures.

a. diaphragm contracts / moves downwards/flattens ✔

b. external intercostal muscles contract ✔

c. (muscle contraction) moves the rib cage upwards and outwards ✔

d. increases volume of the thorax / lungs ✔

e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔

a. O₂ diffuses into blood and CO₂ diffuses out from blood ✔

b. blood entering the alveoli is high in CO₂/low in O₂ ✔
OR
air in alveolus is high in O₂/low in CO₂ ✔

c. diffusion (in either direction) take place due to concentration gradients ✔

d. concentration gradients maintained by ventilation/blood flow ✔

e. large surface area created by many alveoli/spherical shape of alveoli for more efficient diffusion ✔

f. rich supply of capillaries (around alveoli) allows efficient exchange ✔

g. type I pneumocytes are thin to allow easy diffusion/short distances ✔

h. gases must dissolve in liquid lining of alveolus in order to be exchanged ✔

i. type II pneumocytes secrete surfactants to reduce surface tension/prevent lungs sticking together ✔

j. type II pneumocytes create moist conditions in alveoli ✔

a. greenhouse effect keeps Earth warm ✔

b. (over-time) earth’s temperature has fluctuated naturally ✔

c. changes in human activities have led to increases in CO₂ concentration ✔

d. CO₂ absorbs infrared/long wave radiation / trapping heat ✔

e. increase in atmospheric CO₂ (concentration) correlates with/causes increased global average temperature ✔

f. use of fossil fuels increases atmospheric CO₂ ✔

g. deforestation removes a carbon sink / less CO₂ absorbed ✔

h. loss of polar ice causes less reflection of surface light/ more reradiation as heat contributing to (global) warming ✔

i. CO₂ is not the only greenhouse gas/ there are other greenhouse gases ✔

This question was attempted by approximately 56 % of candidates.

Done well by many. Diaphragm contraction and external intercostal muscle contraction was commonly known along with the idea that the rib cage moves upwards and outwards. Further understanding of the consequent pressure changes in the thorax was not clear.

This question was attempted by approximately 56 % of candidates.

Some coherent, clear answers were given earning the maximum marks. However, commonly, valid ideas were given but were jumbled. Coherent writing was usually missing. The term diffusion was missing in many answers. The idea that alveoli are surrounded by capillaries to enable exchange of gases between the air in alveolus and the blood did not seem to be a mental picture for many. Concentration gradients as a reason for diffusion of oxygen or carbon dioxide between the alveoli and the blood was rarely explained. However, it seemed that everyone knew about surfactants from type II pneumocytes.

This question was attempted by approximately 56 % of candidates.

This question was actually quite narrow as reflected in the number of marks it could earn. Some candidates understood which part of the global warming topic was being asked of them and stuck to the topic. Good applications to the carbon cycle were given. Strong responses avoided deviations into consequences and how humans should behave. Several misunderstandings surfaced. For example that CO₂ was responsible for the breakdown of the ozone layer. Many seemed to tie ozone layer destruction and global warming information together in their explanation. Atmospheric carbon dioxide and the ozone layer were confused. Some thought that the ozone layer traps heat.

Outline the roles bacteria play in the carbon cycle.

Describe the evolution of antibiotic resistance in bacteria.

Explain the process of genetically modifying bacteria.

a. decomposition of dead organic material «by saprotrophic bacteria» 

b. «decomposition» leads to CO₂ formation/regeneration due to respiration 

c. «saprotrophic bacteria only» partially decompose dead organic matter in acidic/anaerobic conditions in waterlogged soil 

d. results in peat formation in bogs/swamps 

e. photosynthetic bacteria/cyanobacteria fix CO₂ in photosynthesis

a. problem results from excessive use of antibiotics by doctors/veterinarians/in livestock
OR
low antibiotic doses taken by patients (not finishing treatment) 

b. natural variation exists in any population of bacteria making some resistant to a specific antibiotic 

c. variation arises from mutation
OR
antibiotic resistance can be transferred between bacteria by plasmids 

d. antibiotic kills all bacteria except those that are resistant 

e. resistant bacteria survive, reproduce and pass on resistance to offspring 

f. soon population is made of mainly antibiotic resistant bacteria 

g. this is an example of natural selection «increasing frequency of characteristics that make individuals better adapted to environment»

a. genetic modification carried out by gene transfer between species 

b. genes transferred from one organism to another produce the same protein/amino acid sequence 

c. due to universality of genetic code
OR
organisms use same codons of mRNA to code for specific amino acids 

d. mRNA for required gene extracted/identified 

e. DNA copies of mRNA made using reverse transcriptase 

f. PCR used (to amplify DNA to be transferred) 

g. genes/DNA transferred from one species to another using a vector 

h. plasmid acts as vector to transfer genes to bacteria/E. coli 

i. plasmid cut open at specific base sequences using restriction endonuclease
OR
plasmid cut to produce blunt ends then extra cytosine/C nucleotides added
OR
sticky ends made by adding extra guanine/G nucleotides
OR
mention of sticky ends if not gained already 

j. cut plasmids mixed with DNA copies stick together (due to complementary base pairing) 

k. DNA ligase makes sugar-phosphate bonds to link nucleotides of gene with those of plasmid 

l. bacteria that take up plasmid are identified 

m. (genetically modified) bacteria will reproduce carrying the transferred gene 

n. example – eg: as production of human insulin using E. coli bacteria

Accept any of the points clearly explained in an annotated diagram.

State two causes of the decrease of biomass along food chains in terrestrial ecosystems.

The table shows the global carbon budget over two decades; the years 1990 to 1999 and 2000 to 2009.

[Source: © International Baccalaureate Organization 2019]

Using the table, explain causes of the changes in carbon flux over the two decades.

Suggest how climate change can influence the natural selection of organisms that live in the Arctic oceans.

a. «cell» respiration/loss of CO₂/biomass consumed to provide/as a source of energy ✔

b. loss of energy «as heat» between trophic levels means less energy available for building biomass ✔

c. waste products «other than CO₂»/loss of urea/feces/egesta ✔

d. material used/CO₂ released by saprotrophs ✔

e. undigested/uneaten material «teeth, bones, etc»/detritus buried/not consumed
OR
formation of peat/fossils/limestone ✔

a. increased CO₂ flux to the atmosphere due to increased burning of fossil fuels by industry/transportation / cement production ✔

b. «land use change leading to» decreased rate of forest burning
OR
better fire suppression leading to decrease in CO₂ release
OR
example of land use changes that uses less fossil fuel
OR
increase in land covered by forests/plants / forests recovering from historical forestry
OR
any other reasonable explanation of land use change that would lead to decreased rate of carbon flow to atmosphere ✔

c. carbon storage in land decreased as less photosynthesis due to fewer forests/more construction
OR
release of methane due to «drying of» wetlands/sealing of land with concrete/buildings/roads ✔

d. carbon storage in ocean increased due to more photosynthesis/algae/greater concentration of CO₂ in the atmosphere
OR
increased diffusion/rate of dissolving of CO₂ into ocean from the atmosphere
OR
limestone/carbonate accumulation «more snails» ✔

a. individuals in a population will show a variation of adaptations to climate change ✔

b. organisms that resist temperature changes
OR
current changes of the ocean/melting ice/more acidity/changes in food chains will survive better ✔

c. reproduce more and pass on their characteristics ✔

d. organisms with less adaptation will disappear with time ✔

e. example «eg polar bears have less ice to be able to catch prey/seals and are starving the ones that manage to find other food sources will survive» OWTTE ✔

f. changes will occur within species
OR
new species may appear «over time» ✔

Accept any valid example of an Arctic ocean organism.

A large proportion of students looked at this question and immediately reeled off an answer in terms of energy (as in many previous years). Few made the connection between biomass and energy, for example in respiration CO₂ is lost from the food chain during respiration, or that urea has mass etc.

3a(ii) was the question most discussed on the G2 comments. The expectation was that the students would address each of the four arrows, with an explanation for each. Good candidates did this. Others just combined everything into a general essay on climate change. Weaker candidates just restated the figures without any explanation of them at all. Whilst it is appreciated that none of the candidates was around between 1990 and 1999, references to the Industrial revolution were out by well over a century. This question would have benefitted from a larger answer box.

In 3b weaker candidates seemed to think that they needed to give a detailed description of climate change and filled up most of the box with it. Better candidates were able to state that animals who could cope with warmer surroundings, would survive to breed and pass on their characteristics, while those who could not would perish, and give an example such as the polar bear. There were some G2 comments that Arctic foodwebs were not on the syllabus. It is doubted that any IB student does not know that it is cold in the Arctic, but because of climate change it is warming up slowly.

Describe the structure and function of starch in plants.

Outline the production of carbohydrates in photosynthesis.

Discuss the processes in the carbon cycle that affect concentrations of carbon dioxide and methane in the atmosphere and the consequences for climate change.

Structure:

a. «starch» is a polysaccharide/is composed of glucose molecules 

b. contains amylose which is a linear/helical molecule 

c. contains amylopectin which is a branched molecule 

Function:

d. storage of glucose/energy in plants 

e. storage form that does not draw water

a. light is absorbed by chlorophyll
OR
chlorophyll absorbs more red and blue light 

b. «absorbed» light energy is converted to chemical energy 

c. some of the energy is used for production of ATP 

d. water molecules are split/photolysis 

e. produces oxygen «as waste product»/hydrogen/NADPH 

f. plants absorb/fix CO₂ «from air or water» 

g. ATP/energy is needed to produce carbohydrates/starch

a. CO₂ is produced from respiration in organisms/combustion of biomass/fossil fuels 

b. CH₄ is produced by anaerobic respiration of biomass/«methanogenic» bacteria 

c. CH₄ is oxidized to CO₂ and water 

d. CO₂ is converted into carbohydrates/organic compounds by autotrophs/producers/photosynthesis 

e. CO₂ can be converted to calcium carbonate/fossilized into limestone 

f. «partially» decomposed organic matter/biomass can be converted into peat/coal/oil/gas/fossil fuels 

g. CO₂ and CH₄ are both greenhouse gases/increase greenhouse effect 

h. both absorb long-wave radiation from the earth and retain the heat in the atmosphere 

i. increased CO₂ concentrations in the atmosphere correlate with increased combustion of fossil fuels 

j. rising average global temperatures correlate with more greenhouse gases in the atmosphere 

k. cattle production/rice paddy/defrosting of tundra increase CH₄ in the atmosphere
OR
increasing CO₂ leads to acidification of marine/aquatic environments 

l. the global temperature increase influences/disrupts climate patterns

OWTTE

Outline energy flow through a community in a natural ecosystem.

Explain how natural selection can cause traits such as drought resistance to develop in wild plants.

Suggest possible benefits and risks of using genetic modification to develop varieties of crop plant with traits such as drought resistance.

1. communities are made up of populations of different species;
2. plants receive energy from the sun/light;
3. convert it to chemical energy through photosynthesis;
4. chemical energy is stored in organic/C-compounds;
5. the energy is passed to other organisms through feeding / reference to food chain;
6. respiration (of plants and animals) converts the chemical energy (of C-compounds) to other useful forms of energy;
7. eventually the chemical energy is lost as heat energy;
8. energy is non-recyclable/lost from a community/ecosystem;
9. energy losses between trophic levels limit food chains/mass of top trophic levels/only about 10 % of energy is transferred;

1. (natural selection occurs if) there is variation in degree of drought resistance among members of a population/same species;
2. variation is caused by mutations (when changes occur in the DNA/nucleic bases/chromosomes);
3. variation during meiosis occurs (with separation of chromosomes);
4. variation occurs during sexual reproduction (as different alleles combine);
5. some variations make some plants more drought-resistant;
6. example of variations: deeper roots/more storage tissue for water/thicker cuticles/less opening of stomata/other verifiable variations;
7. these variations let some survive and reproduce better/have more offspring
   OR
   (these variations) confer selective advantage;
8. these variations/characteristics are passed onto offspring which survive better;
9. natural selection increases the frequency of these characteristics;
10. eventually leads to changes/evolution in the species / more drought-resistant plants;

      Benefits:

1. increase crop growth/food productivity;
2. with limited water/ less water is used;
3. increase amount of land available for food production in dry areas;
   Risks:
4. these plants may out-compete other species in the community/may cause extinction of some species/affect the food chains in the community;
5. the modified gene/recombinant DNA may pass to other organisms;
6. more grain requires more nutrients from the soil so its quality may diminish/monoculture issues;
7. GMO may have health effects in consumers / OWTTE;

Must include at least one benefit and one risk for [3 max].

This was well attempted with an average score of 3. The question was about energy, but weaker students also tended to include biomass. Fortunately, very few students failed to grasp the idea that the energy is lost from the ecosystem and not recycled.

The inclusion of ‘drought resistance’ in the stem of the question should have been a suggestion to include it, but many answers were far to general with a vague attempt to explain Natural Selection in general without explaining how the initial variation in the population came about. There were quite a few ‘Lamarckian’ answers with claims of individuals adapting to cope with the change. The average for this question was only 2.8, putting it as one of the most poorly answered.

Again, drought resistance was in the stem, but not always used. There were many general ‘rants’ about GMO crops without setting out the facts.

Identify the dominant plant phylum in the boreal forest.

In some areas there are gaps in the boreal forest where trees fail to grow and peat tends to accumulate. Suggest reasons for this.

An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.

The boreal forests are situated close to the north pole and even in summer the intensity of sunlight is lower than at the equator. Sketch a graph showing the effect of light on the rate of photosynthesis, labelling the axes.

coniferophyta/conifer/coniferous/gymnosperms/pinophyta ✔

a. waterlogged soil/poor drainage
OR
acidic soil
OR
anaerobic conditions/soil ✔

b. organic matter is not «fully» decomposed «leading to peat formation»
OR
decomposers/saprotrophs less active/fewer in cold «temperatures» ✔

a. higher temperatures so more transpiration/droughts/dehydration/water shortage ✔

b. more forest fires ✔

c. more/new pests/diseases because of the changed conditions ✔

d. competition from trees/plants «that colonize/spread to boreal forests» ✔

e. trees/«named» organisms «of boreal forests» not adapted to warmer conditions
OR
trees/«named» organisms migrate/extend range due to the warmer conditions ✔

f. trees die so there is loss of habitat for animals ✔

g. faster decomposition/nutrient cycling «so conditions in the ecosystem change» ✔

h. standing water/floods due to more snow/permafrost melting ✔

a. x-axis labelled as light intensity/amount of light AND y-axis labelled as rate of photosynthesis/rate of oxygen release/rate of carbon dioxide uptake ✔

b. curve starting at/slightly to the right of the x-axis origin and rising rapidly and then more slowly and plateauing but never dropping ✔