B4.1 Adaptation to environment

1. The place in which a community, species, population or single organism lives. — This is the definition used in the guide. A habitat is a place, and it can be the place where a whole community lives or where one organism lives; it is described by geographical location, physical location and ecosystem type.
2. The role that a species plays in its ecosystem, including what it feeds on. — A student who merges an organism's way of life with where it lives picks this. The role a species plays is a different idea from its habitat, which is the place in which it lives.
3. A large region of the Earth that shares one type of climate, such as tundra. — A student who has met 'the tundra habitat' in general reading picks this. A region of shared climate is a biome; a habitat is the place where a particular organism, population or community lives and can be very small.
4. The set of organisms of different species that live together in one area. — A student who attaches the word to the organisms rather than the place picks this. The organisms of different species living together are the community; the habitat is the place in which that community lives.

Syllabus statement B4.1.1 · Read this in Learn

1. Salt glands on the leaves of Avicennia secrete excess salt, and the roots of Rhizophora exclude most salt by ultrafiltration. — These are the two main strategies of mangrove trees: preventing most salt from entering at the roots (Rhizophora) and removing salt that does enter by secreting it from glands on the leaf surface (Avicennia). Together with a low water potential in their cells, this allows water uptake from seawater.
2. The roots take up seawater freely because mangroves require large amounts of sodium chloride for their metabolism. — A student who assumes that a plant found only in salty places must need salt picks this. Mangroves tolerate salt rather than requiring it; their adaptations limit and remove salt because it is a stress, not a nutrient they need in quantity.
3. Pneumatophores pump salt out of the roots and back into the mud, keeping the sap of the tree free of salt. — A student who thinks excess salt leaves through the roots picks this. Pneumatophores are aerial roots for gas exchange; salt is excluded at the root surface or secreted from the leaves, and the sap of mangroves does contain salt.
4. The leaves absorb rainwater directly, so the tree does not need to take up any water through its roots from the sea. — A student who thinks leaves absorb water picks this. Mangroves take up water through their roots from seawater, which is possible because their cells maintain a water potential lower than that of the sea.

Syllabus statement B4.1.2 · Read this in Learn

1. Only the distribution of plants is limited by abiotic variables, because animals are able to move away from unfavourable conditions. — A student who thinks of animals as escaping rather than being limited picks this. Animals have ranges of tolerance for temperature, salinity, pH and dissolved oxygen, and moving away from unsuitable conditions is how those limits shape distribution.
2. A species with a wide range of tolerance for temperature is found everywhere that the temperature lies within that range. — A student who considers one abiotic variable at a time picks this. Every abiotic variable must be within the range of tolerance; a place with a suitable temperature may still be too dry, too dark or too saline for the species.
3. Adaptations give a species a range of tolerance for each abiotic variable, and it is absent where a variable is outside that range. — This is the relationship the guide sets out: adaptations determine the range of tolerance, and distribution is limited to places where every abiotic variable lies within the species' range.
4. An abiotic variable is any feature of the environment, whether it is living or non-living, that differs between one place and another. — A student who has lost the meaning of the prefix 'a-' picks this. Abiotic variables are non-living factors such as temperature, water, light, pH and salinity; predators, competitors and food are biotic factors.

Syllabus statement B4.1.3 · Read this in Learn

1. A hay meadow that is cut once each year but is dominated by wild grasses and wildflowers. — A semi-natural habitat has been influenced by humans but is dominated by wild rather than cultivated species. Annual cutting is human influence; the wild grasses and flowers that dominate make the meadow semi-natural.
2. A field of wheat grown from sown seed, with wild poppies growing along its margins. — A student who takes the presence of any wild species as the test picks this. The field is dominated by a cultivated crop; a few wild poppies at the edge do not make it semi-natural.
3. A garden lawn sown with a bought seed mixture and mown every week through the summer. — A student who counts any green outdoor site as semi-natural picks this. A sown lawn is dominated by cultivated grass varieties, so it is not semi-natural.
4. A peat bog in a remote upland with no history of drainage, grazing or other management. — A student who thinks semi-natural means untouched picks this. A bog with no human influence is a natural habitat, which is also acceptable for fieldwork, but the question asks which site is semi-natural: influenced by humans yet dominated by wild species.

Syllabus statement B4.1.4 · Read this in Learn

1. The water must be deep, so that the coral polyps are shielded from the damaging effects of bright sunlight. — A student who pictures corals as deep-sea animals picks this. The polyps' zooxanthellae need light for photosynthesis, so reef-building corals are confined to shallow water where light penetrates.
2. The water should be turbid and rich in suspended sediment, which supplies food to the polyps. — A student who reasons that more particles means more food for polyps picks this. Suspended sediment cuts off light from the zooxanthellae and can smother the polyps; clarity is one of the conditions required.
3. The water must be shallow and clear enough for light to reach the zooxanthellae in the coral tissue. — Reef-building corals depend on photosynthetic zooxanthellae in their tissues. Depth and clarity are conditions for reef formation because both determine whether enough light reaches the algae; reefs form in clear water generally less than about 50 m deep.
4. The water should be as warm as possible, because calcification speeds up with every rise in temperature. — A student who extrapolates 'corals need warm water' without an upper limit picks this. Corals have a range of tolerance for temperature, typically about 23 to 29 °C; water that is too warm causes stress and bleaching.

Syllabus statement B4.1.5 · Read this in Learn

1. Hot desert is likely to develop in region X and tropical forest in region Y, because rainfall separates them at this temperature. — For any combination of temperature and rainfall pattern one natural ecosystem type is likely to develop. At 26 °C, precipitation below about 250 mm a year gives hot desert, while precipitation above about 2000 mm a year gives tropical forest.
2. Tropical forest is likely in both regions, because it is the temperature of 26 °C that determines which biome forms. — A student who thinks temperature alone sets the biome picks this. The graph has two axes because both variables matter: 150 mm of rain a year cannot support forest at any temperature.
3. Grassland is likely in region X and tropical forest in region Y, because grassland forms wherever it is too dry for trees. — A student who extends grassland down to zero rainfall picks this. Grassland occupies an intermediate band of precipitation; below about 250 mm a year the graph shows desert.
4. No prediction is possible without knowing the latitude of each region, because latitude rather than climate sets the biome. — A student who has memorized biomes as latitude bands picks this. Latitude matters only through its effect on climate; the graph predicts the biome from temperature and precipitation wherever on Earth the region is.

Syllabus statement B4.1.6 · Read this in Learn

1. Taiga, as in northern Canada — A student who treats the two cold northern biomes as interchangeable picks this. Taiga has long cold winters, but its short, mild summers give a growing season long enough, and its precipitation is sufficient, for coniferous forest to grow; a growing season of only a few weeks and permafrost are features of tundra.
2. Hot desert, as in Arabia — A student who identifies a desert by low precipitation alone picks this. Precipitation below 250 mm is shared by hot desert and tundra; the very cold temperatures and frozen subsoil identify tundra.
3. Tundra, as in Arctic Canada — Very cold temperatures, a growing season of a few weeks, very low precipitation and permafrost are the climate conditions that characterize tundra, which supports low-growing plants but no trees.
4. Grassland, as on the prairies — A student who assigns any dry, treeless landscape to grassland picks this. Grassland has warmer growing seasons and, in temperate regions, more precipitation than 250 mm; the frozen subsoil and very short growing season are features of tundra.

Syllabus statement B4.1.7 · Read this in Learn

1. The spines are a defence against herbivores and play no part in reducing the water that the plant loses. — A student who remembers only that spines are sharp picks this. Deterring herbivores is a real benefit, but the primary advantage of leaves reduced to spines is the reduction in transpiring surface area.
2. The waxy cuticle absorbs dew that condenses on the stem at night, and this is the plant's main source of water. — A student who thinks plants absorb water through their surfaces picks this. The cuticle is waterproof and reduces water loss; the saguaro obtains water through its wide, shallow roots when rain falls.
3. The stomata open during the day so that transpiration can cool the stem in the heat of the afternoon. — A student who believes transpiration is for cooling picks this. The saguaro opens its stomata at night, when it is cooler and less water is lost, and stores the carbon dioxide taken in; daytime transpiration would waste the scarce water.
4. Spines in place of leaves reduce the surface area from which water is lost by transpiration. — Spines are modified leaves. Replacing broad leaves with spines leaves the green stem, protected by a thick cuticle, as the photosynthetic surface, and greatly reduces the area from which water can be lost; the spines also shade the stem and deter herbivores.

Syllabus statement B4.1.8 · Read this in Learn

1. All of the marram grass plants that grow on one particular dune system on the coast of Wales. — A student who confuses the population with the place picks this. All the marram plants on one dune system are a population of marram grass; the habitat is the place in which that population lives.
2. The seaward slopes of foredunes in the coastal sand dune ecosystems of western Europe. — A habitat description gives the geographical location (western Europe), the physical location (seaward slopes of foredunes) and the type of ecosystem (coastal sand dune). This option gives all three.
3. The marram grass, sea holly, sand lizards and dune beetles living together on a dune. — A student who treats the habitat as the organisms found there picks this. The species living together on the foredune make up the community; the habitat is the foredune itself.
4. The temperate grassland biome, in which rainfall is too low for forest to develop. — A student who equates habitat with biome picks this because marram is a grass. A biome is a group of ecosystems with similar climate; sand dunes are a coastal ecosystem shaped by sand and salt spray, not temperate grassland, and a habitat is a place, not a biome.

Syllabus statement B4.1.1 · Read this in Learn

1. Sea spray and dew collect inside the rolled leaf and are absorbed through the stomata, supplying the plant with water. — A student who thinks leaves take in water through their stomata picks this. Marram grass absorbs water through its deep roots and rhizomes; stomata are pores for gas exchange, and the rolled leaf is an adaptation for reducing the water lost through them.
2. The hairs increase the surface area from which water evaporates, so that the leaf is cooled more effectively in the sun. — A student who believes transpiration exists to cool the plant picks this. On a dune, water is the scarce resource, so the adaptation works by reducing evaporation, not increasing it; the hairs trap humid air rather than providing an evaporating surface.
3. Humid air is trapped around the stomata, lowering the water vapour concentration gradient and slowing transpiration. — Water vapour diffuses out of stomata down a concentration gradient. Inside the rolled leaf the hairs hold a layer of still, humid air, so the gradient between the leaf interior and the air outside the stomata is small and the rate of transpiration is reduced. This conserves water in a habitat where sand holds little.
4. The stomata inside the roll are held permanently closed, so the plant loses no water while the leaf is rolled. — A student who thinks dry-habitat plants shut their stomata for good picks this. Stomata must open to admit carbon dioxide for photosynthesis; the rolled leaf reduces the water lost while they are open rather than abolishing it.

Syllabus statement B4.1.2 · Read this in Learn

1. They absorb water vapour from the humid air above the mud to supplement the uptake by the roots. — A student who thinks plants absorb water through above-ground surfaces picks this. Water is taken up in liquid form by the roots; the problem the pneumatophores solve is the lack of oxygen in the mud, not a lack of water.
2. They anchor the tree against the tidal currents by spreading its weight across the soft mud. — A student who has seen the arching stilt roots of Rhizophora and assumes all aerial roots give support picks this. Avicennia's pneumatophores are thin, pencil-like roots that give little support; their function is gas exchange.
3. They secrete excess salt taken up from seawater onto their surfaces, where the tide washes it away. — A student who reasons that salt must leave by the route it entered picks this. Avicennia secretes excess salt from salt glands on its leaves, not from its roots; pneumatophores are for gas exchange.
4. They let oxygen diffuse from the air into the root tissues buried in anaerobic mud. — Roots need oxygen for aerobic respiration, and waterlogged mud contains almost none. Pneumatophores carry lenticels above the mud surface through which oxygen enters and diffuses down to the buried root system.

Syllabus statement B4.1.2 · Read this in Learn

1. 22 °C is outside the trout's range of tolerance, so the population in the river will die out before the end of summer. — A student who takes the optimum range to be the whole range of tolerance picks this. The upper limit of tolerance given is 25 °C; 22 °C lies in the zone of stress, where trout survive with reduced growth.
2. 22 °C is inside the trout's range of tolerance but outside its optimum, so the fish survive but are under stress. — The range of tolerance (0 to 25 °C) is wider than the optimum range (10 to 16 °C). At 22 °C the trout are in a zone of stress: they survive, but growth and reproduction are reduced. Only above 25 °C would the limit of tolerance be exceeded.
3. The trout will adapt during their lifetime, widening their range of tolerance to include the new temperature. — A student who uses 'adapt' in its everyday sense picks this. A range of tolerance is set by inherited adaptations; individuals cannot extend it, and in any case 22 °C is already within the range.
4. Temperature cannot limit where trout live, because unlike plants they can swim away from unfavourable water. — A student who thinks abiotic variables affect only plants picks this. Swimming away from warm water is precisely how temperature limits the distribution of trout: they are absent from water outside their range of tolerance.

Syllabus statement B4.1.3 · Read this in Learn

1. Salinity has no effect on sea lavender, because cover is zero at both the highest and the lowest salinity recorded. — A student who expects a correlation to be a straight-line trend picks this. Absence at both extremes with a peak between them is exactly the pattern a limiting abiotic variable produces, so it is evidence for an effect, not against one.
2. The transect proves that salinity is the cause of the distribution, because cover changes wherever salinity changes. — A student who treats a matching pattern as proof picks this. Up a salt marsh, salinity, time submerged, soil moisture and competition all change together, so the transect shows a correlation but cannot prove which variable is the cause.
3. Individual sea lavender plants adjust their salt tolerance to match the salinity of the quadrat in which they are growing. — A student who thinks individuals adapt to wherever they find themselves picks this. The tolerance range is an inherited property of the species; the data show where the species can and cannot survive, not plants changing their tolerance.
4. Cover peaks at intermediate salinity, consistent with a range of tolerance whose optimum lies near 20 to 24 ppt. — Cover is zero at 35 ppt and at 12 ppt, rises to a maximum of 60% at 24 and 55% at 20, and falls on either side. This hump-shaped pattern is what a range of tolerance predicts: limits at the extremes and an optimum between them. The data show a correlation; they do not by themselves prove causation.

Syllabus statement B4.1.4 · Read this in Learn

1. Place quadrats at random coordinates within the wood only, because the field contains no dog's mercury and so gives no useful data. — A student who sees empty quadrats as wasted picks this. Quadrats with zero cover at high light intensity are essential data: they mark the limit of the species' range and provide the contrast without which no correlation can be shown.
2. Place quadrats at regular intervals along a transect from the field into the wood, recording percentage cover and a light-sensor reading at each quadrat. — A transect samples the gradient of light from open field to shaded wood at many points, and pairing a cover value with a sensor reading at each quadrat gives the data needed to test for a correlation.
3. Record the species present in one large quadrat in the field and one large quadrat in the wood, since two contrasting sites are enough to show a correlation. — A student who carries a two-treatment experimental design into fieldwork picks this. Two sites can show a difference, but a correlation needs many sampling points across the gradient of the variable.
4. Count the plants in quadrats along the transect but take one light reading at the wood edge, because light does not vary within a habitat. — A student who thinks an abiotic variable has one value for a whole habitat picks this. Light intensity falls steeply from the field into the wood, and it must be measured at every quadrat so that each cover value is paired with the light there.

Syllabus statement B4.1.4 · Read this in Learn

1. Seawater at pH 8.1 is acidic, so it dissolves the calcium carbonate of existing coral skeletons directly. — A student who takes the word 'acidification' literally picks this. A pH of 8.1 is still alkaline; the water has become less alkaline, and the harm comes from reduced carbonate ion availability slowing calcification, not from acid dissolving reefs.
2. The extra dissolved carbon dioxide is toxic to the coral polyps, which die before they can deposit any skeleton. — A student who treats carbon dioxide as a poison picks this. Carbon dioxide at these concentrations does not poison the polyps; its effect is chemical, reducing the carbonate ion concentration on which calcification depends.
3. A fall of only 0.1 pH units is far too small to affect any organism, so the threat to reefs has been greatly overstated. — A student who reads the pH scale as linear picks this. pH is logarithmic: a fall of 0.1 units is an increase of about 26% in hydrogen ion concentration, enough to reduce carbonate ions measurably.
4. Fewer carbonate ions are available, so calcification slows and may not keep pace with reef erosion. — Corals build skeleton by combining calcium ions with carbonate ions. Dissolved carbon dioxide releases hydrogen ions that combine with carbonate ions, lowering their concentration, so deposition of calcium carbonate slows. A reef persists only if deposition outpaces the constant erosion by waves and boring organisms.

Syllabus statement B4.1.5 · Read this in Learn

1. The similar appearance shows that cacti and euphorbias share a recent common ancestor that spread to both continents. — A student who equates similarity with close relationship picks this. The question states that they belong to different families; the similarity arose independently and is not inherited from a shared recent ancestor.
2. Similar abiotic conditions selected for similar adaptations in unrelated lineages, an example of convergent evolution. — Natural selection in similar hot desert conditions favoured water storage and reduced leaf area in both families independently. Convergent evolution of this kind is one reason the ecosystems of a biome have similar communities even though their species differ.
3. Hot desert is one biome, so its community is the same on every continent and each plant in it has the desert form. — A student who expects a biome to contain the same community of species everywhere picks this. The ecosystems of a biome have similar communities, not identical ones: cacti and euphorbias are different families with their own species, and their shared form arose separately by convergent evolution, not from belonging to one community.
4. Individual plants of any family develop spines and swollen stems when they grow in dry conditions during their lifetime. — A student who uses 'adapt' in its everyday sense picks this. Adaptations are inherited features produced by natural selection over generations; a plant does not grow spines because it finds itself in a dry place.

Syllabus statement B4.1.7 · Read this in Learn

1. Heat is radiated from blood flowing near the surface of the ears, cooling the fox without any loss of water. — The ears are a large, thin surface richly supplied with blood, so heat is transferred from the blood to the air by radiation. Cooling in this way costs no water, which is the scarce resource in the desert; the ears also give the fox acute hearing.
2. The ears detect prey moving beneath the sand; their size has nothing to do with body temperature. — A student who thinks of ears only as organs of hearing picks this. Hearing is one function, but the large vascular surface is also a heat-radiating organ, which is why desert foxes have far larger ears than Arctic foxes.
3. The ears sweat heavily, and the evaporation of this sweat is the fox's main way of losing heat. — A student who generalizes from human sweating picks this. Sweating would waste water; the fennec cools by radiation from its ears, avoids the daytime heat and shelters in a burrow.
4. The ears store fat that can be broken down to release water when the fox has nothing to drink. — A student who transfers the camel's-hump story picks this. The ears are thin and contain blood vessels, not fat; the fennec obtains water from its food and conserves it by producing concentrated urine.

Syllabus statement B4.1.8 · Read this in Learn

1. Rolled leaves lined with hairs that trap humid air and reduce water lost by transpiration. — A student who expects every adaptation to conserve water picks this. Rolled, hairy leaves belong to marram grass on a dry dune; in rainforest water is abundant, and the pressures are light, support and nutrients.
2. Buttress roots that spread out above the ground and support the tall trunk in the shallow soil. — The soil is too shallow for deep anchorage, so the kapok is held up by buttress roots that flare out from the base of the trunk and spread the load over a wide area, while a shallow root network absorbs nutrients from the surface litter.
3. A deep taproot that reaches the water table far below the shallow layer of nutrient-poor soil. — A student who assumes a tall tree needs a deep root picks this. Rainforest trees have shallow, wide root systems because nutrients are at the surface and water is plentiful; support comes from buttress roots.
4. Drip tips on the leaves that channel rain into the leaf blade, where the water is absorbed directly. — A student who thinks leaves absorb water picks this. Drip tips shed water from the leaf surface so that it dries quickly; water is taken up by the roots, not through the leaf blade.

Syllabus statement B4.1.8 · Read this in Learn

1. Each monkey develops a grasping tail by practice in its life and passes the change to its young. — A student who uses 'adapt' in its everyday sense and thinks acquired features are inherited picks this. Young monkeys do learn to climb, but the structure of the tail (its musculature and friction pad) is an inherited adaptation shaped by natural selection over generations; practice does not alter what is passed on.
2. It was selected for because shortage of water in the canopy is the main pressure on rainforest animals. — A student who applies the desert framework to the rainforest picks this. Water is abundant in rainforest; the pressures on a canopy animal are moving between branches and reaching food, which the tail addresses.
3. It is an inherited adaptation to moving and feeding in the canopy, where it acts as a fifth limb. — The tail has a hairless friction pad and can support the whole body, so the monkey can hang from a branch while both hands reach fruit at the branch tips. It is an inherited feature produced by natural selection in a canopy-dwelling lineage.
4. It shows that spider monkeys are closely related to other animals with grasping tails, such as chameleons. — A student who equates similar features with close relationship picks this. A chameleon is a reptile; grasping tails evolved independently in the two lineages by convergent evolution.

Syllabus statement B4.1.8 · Read this in Learn

1. Salinity is irrelevant because any seawater is salty enough for corals; only the sediment from the river prevents reef formation. — A student who does not see salinity as a variable picks this. Sediment does prevent reef formation by reducing clarity, but corals also have a narrow range of tolerance for salinity, roughly 32 to 42 parts per thousand, and river water dilutes the sea below that range; both conditions fail here.
2. The sediment carried by the river is a benefit, supplying food to the polyps; reefs are absent only because the water is too fresh. — A student who reasons that more particles means more food picks this. Low salinity is a genuine reason for the absence, but suspended sediment is not a benefit: it cuts off light from the zooxanthellae and smothers the polyps, so clarity is a second condition that is not met.
3. Reefs would form here only if the water were deeper, because the bright light in shallow coastal water damages the polyps. — A student who pictures corals as deep-sea animals picks this. Shallow water is a requirement, not a problem, because the zooxanthellae in the coral tissue need light; the absence of reefs here is explained by the low salinity and poor clarity of the river-influenced water.
4. River water lowers the salinity below the range corals tolerate and its sediment reduces the clarity of the water. — Two of the five conditions for reef formation are not met. Fresh water from the river dilutes the sea below the salinity that reef-building corals tolerate, and the suspended sediment reduces the light reaching the zooxanthellae and can smother the polyps. Warmth and shallowness alone are not enough.

Syllabus statement B4.1.5 · Read this in Learn