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SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Ecosystems Learning objectives: Define the term ecosystem; State that ecosystems are dynamic systems; Define the terms biotic factor and abiotic factor, using named examples; Define the terms producer, consumer, decomposer and trophic level; Describe how energy is transferred through ecosystems; Outline how energy transfers between trophic levels can be measured; Discuss the efficiency of energy transfers between trophic levels; Explain how human activities can manipulate the flow of energy through ecosystems; Describe one example of primary succession resulting in a climax community; Describe how the distribution and abundance of organisms can be measured, using line transects, belt transects, quadrats and point quadrats; Describe the role of decomposers in the decomposition of organic material; Describe how microorganisms recycle nitrogen within ecosystems (only Nitrosomonas, Nitrobacter and Rhizobium need to be identified by name); Key definitions: Compile a glossary by writing your own definitions for the following key terms related to the learning objectives above. Key term ecosystem habitat population community biotic factors abiotic factors producer Definition SACKVILLE SCIENCE DEPARTMENT Key term consumer decomposer trophic level food web pyramid of biomass pyramid of energy productivity megajoule (MJ) primary productivity net primary productivity succession pioneer community climax community saprotrophs nitrogen-fixing bacteria mutualistic Definition A2 BIOLOGY SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Ecosystems The concept of the ecosystem was developed to describe the way groups of organisms are predictably found together in their physical environment. A community comprises all the organisms within an ecosystem. Both physical (abiotic) and biotic factors affect the organisms in a community, influencing their distribution and their survival, growth and reproduction. The biosphere The biosphere containing all the Earth’s living organisms amounts to a narrow belt around the Earth extending from the bottom of the oceans to the upper atmosphere. Broad scale life-zones or biomes are evident within the biosphere, characterised according to the predominant vegetation. Within these biomes, ecosystems form natural units comprising the non-living, physical environment (the soil, atmosphere, and water) and the community (all the populations of different species living and interacting in a particular area). Community biotic factors producers consumers detritivores decomposers Interact in the community as: competitors, parasites, pathogens, symbionts, predators, herbivores. Physical environment Atmosphere wind speed and direction humidity light intensity and quality precipitation air temperature Soil nutrient availability soil moisture and pH composition temperature Water dissolved nutrients pH and salinity dissolved oxygen temperature Physical factors and gradients Gradients in abiotic factors are found in almost every environment; they influence habitats and microclimates, and determine patterns of species distribution. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Energy in ecosystems An ecosystem is a natural unit of living (biotic) components, together with all the non-living (abiotic) components with which they interact. Two processes central to ecosystem function are energy flow and chemical cycling. The mitochondria of eukaryotic cells use the organic products of photosynthesis as fuel for cellular respiration. Respiration generates ATP; an energy currency for cellular work: static biomass locks up some chemical energy growth and repair of tissues muscle contraction and flagella movement active transport processes e.g. ion pumps production of macromolecules e.g. proteins Cellular work generates heat which is lost from the system. The waste products of cellular respiration are used as the raw materials for photosynthesis. Chemical elements such as nitrogen, phosphorus, and carbon are cycled between the biotic and abiotic components of the ecosystem. Energy, unlike matter, cannot be recycled. Ecosystems must receive a constant input of new energy from an outside source. In most cases, this is the Sun. Food chains and food webs Every ecosystem has a trophic structure: a hierarchy of feeding relationships that determines the pathways for energy flow and nutrient cycling. Species are divided into trophic levels on the basis of SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY their sources of nutrition. The first trophic level (producers), ultimately supports all other levels. The consumers are those that rely on producers for their energy. Consumers are ranked according to the trophic level they occupy (first order, second order, etc.). the sequence of organisms, each of which is a source of food for the next, is called a food chain. Food chains commonly have four links but seldom more than six. Those organisms whose food is obtained through the same number of links belong to the same trophic level. Note that some consumers (particularly ‘top’ carnivores and omnivores) may feed at several different trophic levels, and many primary consumers eat many plant species. The different food chains in an ecosystem therefore tend to form complex webs of interactions (food webs). The way living things obtain their energy can be classified into two categories. The group upon which all others depend is called producers or autotrophs. They are organisms able to manufacture their food from simple inorganic substances. The consumers or heterotrophs (comprising the herbivores, carnivores, omnivores, decomposers and detritivores), feed on the autotrophs or other heterotrophs to obtain their energy. The energy flow into and out of each trophic level in a food chain can be identified and represented diagrammatically using arrows of different sizes. The sizes of the arrows represent different amounts of energy lost from that particular trophic level. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Primary productivity The energy entering ecosystems is fixed by producers in photosynthesis. The rate of photosynthesis is dependent on factors such as temperature and the amount of light, water, and nutrients. The total energy fixed by producers in photosynthesis is referred to as the gross primary production (GPP) and is usually expressed as Joules (or kJ)m-2. However, a portion of this energy is required by the plant for respiration. Subtracting respiration from GPP gives the net primary production (NPP). The rate of biomass production, or net primary productivity, is the biomass produced per area per unit time. Measuring productivity Primary productivity of an ecosystem depends on a number of interrelated factors (light intensity, nutrients, temperature, water and mineral supplies), making its calculation extremely difficult. Globally, the least productive ecosystems are those that are limited by heat energy and water. The most productive ecosystems are systems with high temperatures, plenty of water and non-limiting supplies of soil nitrogen. The primary productivity of oceans is lower than that of terrestrial ecosystems because the water reflects (or absorbs) much of the light energy before it reaches and is utilised by producers. Leaf area index (LAI) – a measure of the total leaf area of a given plant; Harvestable dry biomass – used for commercial purposes, it is the dry mass of crop available for sale or use; Relative growth rate (R) – the gain in mass of plant tissue per unit time; R= increase in dry mass in unit time original dry mass of the plant Net assimilation rate (NAR) – the increase in plant mass per unit of leaf area per unit time; essentially it is the balance between carbon gain from photosynthesis and carbon loss from respiration. NAR = increase in dry mass in unit time leaf area The flow of energy through an ecosystem can be measured and analysed. It provides some idea as to the energy trapped and passed on at each trophic level. Each trophic level in a food chain or web contains a certain amount of biomass: the dry mass of all organic matter contained in its organisms. Energy stored in biomass is transferred from one trophic level to another (by eating, defaecation etc.), with some being lost as low-grade heat energy to the environment in each transfer. Three definitions are useful: Gross primary production: the total of organic material produced by plants (including that lost to respiration). Net primary production: the amount of biomass that is available to consumers at subsequent trophic levels. Secondary production: the amount of biomass at higher trophic levels (consumer production). Production figures are sometimes expressed as rates (productivity). SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY The percentage of energy transferred from one trophic level to the next varies between 5% and 20% and is called the ecological efficiency (efficiency of energy transfer). An average figure of 10% is often used. The path of energy flow in an ecosystem depends on its characteristics. In a tropical forest ecosystem, most of the primary production enters the detrital and decomposer food chains. However, in an ocean ecosystem or an intensively grazed pasture more than half the primary production may enter the grazing food chain. Ecological succession Ecological succession is the process by which communities in a particular area change over time. Succession takes place as a result of complex interactions of biotic and abiotic factors. Early communities modify the physical environment causing it to change. This in turn alters the biotic community, which further alters the physical environment and so on. Each successive community makes the environment more favourable for the establishment of new species. A succession (or sere) proceeds in seral stage, until the formation of a climax community, which is stable until further disturbance. Early successional communities are characterised by a lower species diversity, a simple structure, and broad niches. In contrast, climax communities are complex, with a large number of species interactions, narrow niches, and high species diversity. Past community – some species in the past community were outcompeted, and/or did not tolerate altered abiotic conditions. Present community – the present community modifies such abiotic factors as: light intensity, wind speed, air temperature, soil composition, light quality, wind direction, soil water, and humidity. Future community – changing conditions in the present community will allow new species to become established. These will make up the future community. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Primary succession Primary succession refers to colonisation of regions where there is no pre-existing community. Examples include regions where the previous community has been extinguished by a volcanic eruption (such as the Indonesian island of Krakatau which erupted in 1883), newly formed glacial moraines, or newly formed volcanic islands (as when Surtsey appeared off Iceland in 1963). The sequence of colonisation described below is typical of a Northern hemisphere lithosere; a succession on bare rock. This sequence is not necessarily the same as that occurring on another substrate, such as volcanic ash, which allows the earlier establishment of grasses. Bare rock → lichens, bryophytes, and annual herbs → grasses and small shrubs → fast growing trees e.g. rowan → slower growing broadleaf species (ash and oak) [climax community] after 100-200 years Secondary succession in cleared land (150+ years for mature woodland to develop again) A secondary succession takes place after a land clearance e.g. from fire or landslide. Such events do not involve loss of the soil and so tend to be more rapid than primary succession, although the time scale depends on the species involved and on climatic and edaphic (soil) factors. Humans may deflect the natural course of succession e.g. by mowing, and the climax community that results will differ from the natural community. A climax community arising from a deflected succession is called a plagioclimax. Primarily bare earth → open pioneer community (annual grasses) [1-2 years] → grasses and low growing perennials [3-5 years] → scrub: shrubs and small trees [16-30 years] → young broad-leaved woodland [31-150 years] → mature woodland mainly oak [150+ years] Gap regeneration cycle in a rainforest (500-700 years) Large canopy trees have a profound effect on the make-up a rainforest community, reducing light penetration and impeding the growth of saplings. When a large tree falls, it opens a hole in the canopy that lets in sunlight. Saplings then compete to fill the gap. Canopy tree removed → gap created by fall of large tree is colonised by tree ferns → growth of subcanopy trees suppresses tree ferns; seedlings of canopy trees grow beneath the subcanopy → rapid growth of young canopy species to occupy the gap → mature trees develop to form climax community of rainforest Wetland succession Wetland areas present a special case of ecological succession. Wetlands are constantly changing as plant invasion of open water leads to siltation and infilling. This process is accelerated by eutrophication. In well drained areas, pasture or heath may develop as a result of succession from freshwater to dry land. When the soil conditions remain non-acid and poorly drained, a swamp will eventually develop into a seasonally dry fen. In special circumstances an acid peat bog may develop. The domes of peat that develop produce a hummocky landscape with a unique biota. Wetland peat ecosystems may take more than 5000 years to form but are easily destroyed by excavation and lowering of the water table. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY An open body of water, with time, becomes silted up and is invaded by aquatic plants. Emergent macrophyte species colonise the accumulating sediments, driving floating plants towards the remaining deeper water. The increasing density of rooted emergent, submerged, and floating macrophytes encourages further sedimentation by slowing water flows and adding organic matter to the accumulating silt. The resulting swamp is characterised by dense growths of emergent macrophytes and permanent (although not necessarily deep) standing water. As sediment continues to accumulate the swamp surface may, in some cases, dry off in summer. In colder climates, low evaporation rates, high rainfall, and invasion by Sphagnum moss leads to development of a peat bog; a low pH, nutrient poor environment where acidtolerant plants such as sundew replace swamp species. Shoreline zonation Zonation refers to the division of an ecosystem into distinct zones that experience similar abiotic conditions. In a more global sense, differences in latitude and altitude create distinctive zones of vegetation type, or biomes. Zonation is particularly clear on a rocky seashore, where assemblages of different species form a banding pattern approximately parallel to the waterline. This effect is marked in temperate regions where the prevailing weather comes from the same general direction. Exposed shores show the clearest zonation. On sheltered rocky shores there is considerable species overlap and it is only on the upper shore that distinct zones are evident. Rocky shores exist where wave action prevents the deposition of much sediment. The rock forms a stable platform for the secure attachment of organisms such as large seaweeds and barnacles. Sandy shores are less stable than rocky shores and the organisms found there are adapted to the more mobile substrate. The zonation of species distribution according to an environmental gradient is well shown on rocky shorelines. In Britain, exposed rocky shores occur along much of the western coasts. Variations in low and high tide affect zonation, and in areas with little tidal variation, zonation is restricted. High on the shore, some organisms may be submerged only at spring high tide. Low on the shore, others may be exposed only at spring low tide. There is a gradation in extent of exposure and the physical conditions associated with this. Zonation patterns generally reflect the vertical movement of seawater. Sheer rocks can show marked zonation as a result of tidal changes with little or no horizontal shift in species distribution. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Decomposers and recycling Living things need nitrogen to make proteins and nucleic acids. The diagram above shows how nitrogen atoms are cycled between the biotic and abiotic components of an ecosystem. Bacteria are involved in ammonification, nitrogen fixation, nitrification and denitrification. Nitrogen fixation – can occur when lightning strikes or through the Haber process. However, these processes only account for about 10% of nitrogen fixation around the world. Nitrogenfixing bacteria account for the rest. Many of these live freely in the soil and fix nitrogen gas, which is in the air within soil, using it to manufacture amino acids. Nitrification – happens when chemoautotrophic bacteria in the soil absorb ammonium ions and oxidise them to nitrites or by oxidising nitrites to nitrates. Denitrification – other bacteria convert nitrates back to nitrogen gas. When the bacteria involved are growing under anaerobic conditions such as in waterlogged soils, they use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 1. Total plant growth within an ecosystem depends on the light intensity, temperature and the supply of water and inorganic minerals to the ecosystem. Table 3.1 shows the net primary production by plants in four different ecosystems. (a) Discuss possible reasons for the differences in net primary production in these ecosystems. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [4] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (b) To calculate the net primary production figures in Table 3.1 in kJm-2year-1, it is necessary to measure the energy content of the primary producers. Outline how the energy content, in kJ, of a primary producer such as grass can be measured in the laboratory. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (c) The efficiency with which consumers convert the food they eat into their own biomass is generally low. Table 3.2 compares the energy egested, absorbed and respired in four types of animals. Complete Table 3.2 to show the percentage of energy consumed that is converted into biomass in the perch and the cow. You may use the space below for your working. [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (d) Describe and explain, using the data from table 3.2, how the trophic level of a mammal affects the percentage of its food energy that it is able to convert to biomass. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] (e) Using the data from Table 3.2 and your knowledge of energy flow through food chains, suggest which of these four animals could be farmed to provide the maximum amount of food energy in kJm-2year-1 for humans. Explain the reasons for your choice. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 2. Knowledge of the nitrogen cycle can be used to make decisions about management of farmland. A farmer uses her grass meadow to raise sheep. In a separate field she grows cabbages. Fig. 1.1 shows part of the nitrogen cycle. The four boxes on the bottom line of the diagram refer to substances in the soil. (a) Briefly describe the steps that must occur for plant protein to be converted to animal protein in the farmer’s sheep, as shown by arrow A on Fig. 1.1. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (b) List the processes which contribute to B in the meadow where sheep are raised. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (c) Name the bacteria that carry out processes C and D, and explain the significance of these bacteria for the growth of plants. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] (d) Use the letters on Fig. 1.1 to explain why the soil nitrate concentration will decrease in the cabbage field if it is used to grow repeated crops of cabbages year after year. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (e) The farmer does not wish to use inorganic fertiliser to replace the nitrate in the soil of the cabbage field. She wishes to make use of process F. Suggest a crop she could plant that would allow process F to occur and explain how this would add nitrate to the soil. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] 3. Two-spot ladybirds, Adalia bipunctata, show a colour polymorphism. They are normally red with two black spots. However, melanic individuals occur which are black with two red spots. A student investigated the proportion of these colour forms in the ladybird population along a transect going up a hill near his school. (i) Suggest a suitable technique by which the student might have collected his samples of ladybirds along this transect. ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [1] (ii) The student’s teacher suggested he should make several transects up the hill rather than just one transect. Explain why this is good experimental design. ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [1] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (iii) The student’s results are shown in Table 7.1. Suggest a method of processing this data to make comparisons between the frequency of the red form and black form of ladybird at the different altitudes more valid. Explain why your method is an improvement. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (iv) Evaluate whether the student was correct to conclude as follows: “My data showed a positive correlation between increasing altitude and the frequency of the black form of the ladybird. I therefore concluded that high altitude causes the black form to survive better.” ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (v) The black, melanic, form of the ladybird is caused by an allele (B) that is dominant. The red form of the ladybird is therefore homozygous recessive at this locus (bb). State what is meant by the term recessive. ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [1] (vi) The data in Table 7.1 give the total number of the red form of ladybird found as 296, and the total number of the black form of ladybird as 50. The Hardy-Weinberg principle states that: p+q=1 p2 + 2pq + q2 = 1 Use the Hardy-Weinberg principle and the figures given above to calculate the frequency of the dominant allele, p, and the recessive allele, q, in the two-spot ladybird population. Show each step in your working. Give your answers to 2 decimal places. p = ____________________ q = ____________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 4. Organisms do not live in isolation, but interact with other organisms and with their physical environment. (a) State the word used to describe: the study of the interactions between organisms and their environment ___________________________________________________________ [1] the physical (non-living) factors in the environment ___________________________________________________________ [1] a physical area that includes all the organisms present and their interactions with each other and with the physical environment ___________________________________________________________ [1] (b) State and describe two types of ecological interaction that can occur between different species in a habitat. As part of each description, you should name the two species involved in your chosen example. 1. ___________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 2. ___________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [6] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 5. The distribution and abundance of plants in a habitat can show how a physical factor varies across the habitat. Describe how you would measure the distribution and abundance of plants over a distance of 100 metres. In your answer, you should make clear the sequence of procedures you would follow ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ _____________________________________________________________ [6] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 6. Peat bogs are large areas of waterlogged land that support a specialised community of plants. Peat bogs take thousands of years to form. Fig. 5.1 lists the main stages in the formation of a peat bog. (a) Name the process summarised in Fig. 5.1 that changes a lake community into a peat bog community. ___________________________________________________________ [1] (b) Using Fig. 5.1, list two abiotic factors that play a role in determining what species of plant can grow in an area. 1 ____________________________________________________________ 2 _________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (c) Most of the minerals in a peat bog are held within the living plants at all times, not in the soil. Plants like bog cotton and bog asphodel recycle the minerals they contain. The leaves of these plants turn orange as the chlorophyll within them is broken down. Minerals such as magnesium ions are transported from the leaves to the plants’ roots for storage. Describe one similarity and two differences in mineral recycling in a peat bog and in a deciduous forest. similarity ______________________________________________________ ______________________________________________________________ differences ____________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] (d) In Ireland in 2002, two well preserved Iron Age human bodies were found in peat bogs. Despite having been dead for over two thousand years, the bodies had not decomposed. They still had skin, hair and muscle. Suggest why these bodies had not decomposed. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (e) Suggest two reasons why the large scale removal of peat from bogs for use in gardens is discouraged by conservation groups. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] 7. Great tits, Parus major, are birds that form male-female pairs. The male of each pair then establishes an area of territory, which he defends against other great tits by singing and threat displays. The birds build a nest within the territory in which the eggs are laid and young chicks are reared. Weasels, Mustela rivalis, are predators which eat eggs and young chicks. Fig. 6.1. shows how the territory size of great tits affects the risk of nest predation by weasels. (a) Describe the relationship shown in Fig. 6.1. ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [1] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (b) Suggest and explain what effect weasels may have on the population size of the great tit. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] 8. The ochre starfish, Pisaster ochraceus, is a starfish that lives on rocky intertidal shores. It is the top predator in its habitat. Fig. 6.2 shows part of the food web for this starfish. An experiment was carried out in which all the starfish were removed from am 8m x 2m area of the shore. In an equivalent area of the same size, the starfish were not removed. The population sizes of the other organisms in the food web were monitored at intervals. It was found that in the area in which starfish were removed: chitons and limpets disappeared anemones, sponges and nudibranchs decreased in abundance SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (a) explain why two areas of the same size were monitored. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (b) Using Fig. 6.2., explain why the chitons and limpets disappeared in the area from which starfish were removed. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (c) Using Fig. 6.2., suggest the sequence of events that led to the decrease in abundance in nudibranchs in the area from which starfish were removed. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 9. Earthworms are abundant in fertile soil where they play an important role in the transfer of energy in the ecosystem. An example of a food chain involving earthworms is shown in Fig. 8.1. (a) Define the following terms: producer ______________________________________________________ ______________________________________________________________ ______________________________________________________________ consumer _____________________________________________________ ______________________________________________________________ ______________________________________________________________ SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY trophic level ___________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] (b) One way of measuring the abundance of earthworms is as follows: place quadrat frames of known area onto the ground pour a chemical solution onto the soil to cause the earthworms to come up to the surface wait and then count the earthworms Researchers used this technique in 2004 and 2006 to compare the abundance of earth worms in four areas of soil: soil underneath buckthorn plants soil underneath honeysuckle plants bare soil after the removal of buckthorn plants bare soil after the removal of honeysuckle plants The results are shown in Fig. 8.2. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Suggest two variables which the researchers should have controlled in order to make the results comparable. 1 ____________________________________________________________ _____________________________________________________________ 2 ____________________________________________________________ ___________________________________________________________ [2] (c) Evaluate, with reference to the error bars in Fig. 8.2, whether the data show a valid difference in the abundance of earthworms between the ‘soil underneath honeysuckle’ and ‘soil with honeysuckle removed’ sites for July 2004. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (d) Ecosystems can be described as dynamic. State two pieces of evidence from Fig. 8.2. that show that the ecosystem is dynamic. 1 ____________________________________________________________ _____________________________________________________________ 2 ____________________________________________________________ ___________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Populations and sustainability Learning objectives: Explain the significance of limiting factors in determining the final size of a population; Explain the meaning of the term carrying capacity; Describe predator-prey relationships and their possible effects on the population sizes of both the predator and the prey; Explain, with examples, the terms interspecific and intraspecific competition; Distinguish between the terms conservation and preservation; Explain how the management of an ecosystem can provide resources in a sustainable way, with reference to timber production in a temperate country; Explain that conservation is a dynamic process involving management and reclamation; Discuss the economic, social and ethical reasons for conservation of biological resources; Outline, with examples, the effects of human activities on the animal and plant populations in the Galapagos Islands; Key definitions: Compile a glossary by writing your own definitions for the following key terms related to the learning objectives above. Key term carrying capacity competition intraspecific interspecific coppicing conservation biodiversity Definition SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Populations Populations have a number of attributes that may be of interest. Usually, biologists wish to determine population size (the total number of organisms in the population). It is also useful to know the population density (the number of organisms per unit area). The density of a population is often a reflection of the carrying capacity of the environment, i.e. how many organisms a particular environment can support. Populations also have structure; particular ratios of different ages and sexes. These data enable us to determine whether the population is declining or increasing in size. We can also look at the distribution of organisms within their environment and so determine what particular aspects of the habitat are favoured over others. One way to retrieve information from populations is to sample them. Sampling involves collecting data about features of the population from samples of that population (since populations are usually too large to examine in total). Sampling can be done directly through a number of sampling methods or indirectly e.g. monitoring calls, looking for droppings or other signs. Density and distribution Distribution and density are two interrelated properties of populations. Population density is the number of individuals per unit area (for land organisms) or volume (for aquatic organisms). Careful observation and precise mapping can determine the distribution patterns for a species. The three basic distribution patterns are: random, clumped and uniform. Random distributions: occur when the spacing between individuals is irregular. The presence of one individual does not directly affect the location of any other individual. Random distributions are uncommon in animals but are often seen in plants. Clumped distribution: occur when individuals are grouped in patches (sometimes around a resource). The presence of one individual increases the probability of finding another close by. Such distributions occur in herding and highly social species. Uniform distribution: occur when individuals are evenly spaced within the area. The presence of one individual decreases the probability of finding another individual very close by. Predator-prey interactions SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Some mammals, particularly in highly seasonal environments, exhibit regular cycles in their population numbers. Snowshoe hares in Canada exhibit such a cycle of population fluctuation that has a periodicity of 9-11 years. Populations of lynx in the area show a similar periodicity. Contrary to early suggestions that the lynx controlled the size of the hare population, it is now known that the fluctuations in the hare population are governed by other factors, most probably the availability of palatable grasses. The fluctuations in the lynx numbers however, do appear to be the result of fluctuations in the numbers of hares (their principal food item). This is true of most vertebrate predator-prey systems: predators do not usually control prey populations, which tend to be regulated by other factors such as food availability and climatic factors. Most predators have more than one prey species, although one species may be preferred. Characteristically, when one prey species becomes scarce, a predator will ‘switch’ to another available prey item. Where one prey species is the principle food item and there is limited opportunity for prey switching, fluctuations in the prey population may closely govern predator cycles. Competition and niche size Niche size is affected by competition. The effect on niche size will vary depending on whether the competition is weak, moderate or intense, and whether it is between members of the same species (intraspecific) or between different species (interspecific). Moderate interspecific competition: the tolerance range represents the potential (fundamental) niche a species could exploit. The actual or realised niche of a species is narrower than this because of competition. Niches of closely related species may overlap at the extremes, resulting in competition for resources in the zones of overlap. Intense interspecific competition: when the competition from one or more closely related species becomes intense, there is selection for a more limited niche. This severe competition prevents a species from exploiting potential resources in the more extreme parts of its tolerance range. As a result, niche breadth decreases (the niche becomes narrower). Intense intraspecific competition: competition is most severe between individuals of the same species, because their resource requirements are usually identical. When intraspecific competition is intense, individuals are forced to exploit resources in the extremes of their tolerance range. This leads to expansion of the realised niche to less preferred areas. Overlap in resource use between competing species From the concept of the niche arose the idea that two species with the same niche requirements could not coexist, because they would compete for the same resources, and one would exclude the other. This is known as Gause’s ‘competitive exclusion principle’. If two species compete for some of the same resources e.g. food items of a particular size, their resource use curves will overlap. Within the zone of overlap competition between the two species will be intense. Interspecific competition In naturally occurring populations, direct competition between different species (interspecific competition) is usually less intense than intraspecific competition because coexisting species have evolved slight differences in their realised niches, even though their fundamental niches may overlap (a phenomenon termed niche differentiation). However, when two species with very similar niche requirements are brought into direct competition through the introduction of a foreign species, one usually benefits at the expense of the other. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY The inability of two species with the same described niche to coexist is referred to as the competitive exclusion principle. In Britain, introduction of the larger, more aggressive, grey squirrel in 1876 has contributed to a contraction in range of the native red squirrel, and on the Scottish coast, this phenomenon has been well documented in barnacle species. The introduction of ecologically aggressive species is often implicated in the displacement or decline of native species, although there may be more than one contributing factor. Displacement of native species by introduced ones is more likely if the introduced competitor is also adaptable and hardy. It can be difficult to provide evidence of decline in a species as a direct result of competition, but it is often inferred if the range of the native species contracts and that of the introduced competitor shows a corresponding increase. The European red squirrel, Sciurus vulgaris, was the only squirrel species in Britain until the introduction of the American grey squirrel, Sciurus carolinesis, in 1876. In 44 years since the 1940 distribution survey, the more adaptable grey squirrel has displaced populations of the native red squirrels over much of the British Isles, particularly in the South. Whereas the red squirrels once occupied both coniferous and broad-leafed woodland, they are now almost solely restricted to coniferous forest and are completely absent from much of their former range. Intraspecific competition Some of the most intense competition occurs between individuals of the same species (intraspecific competition). Most populations have the capacity to grow rapidly, but their numbers cannot increase indefinitely because environmental resources are finite. Every ecosystem has a carrying capacity (K), defined as the number of individuals in a population that the environment can support. Intraspecific competition for resources increases with increasing population size and, at carrying capacity, it reduces the per capita growth rate to zero. When the demand for a particular resource e.g. food, water, nesting sites, nutrients or light exceeds supply, that resource becomes a limiting factor. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Populations respond to resource limitation by reducing their population growth rate e.g. through lower birth rates or higher mortality. The response of individuals to limited resources varies depending on the organism. In many invertebrates and some vertebrates such as frogs, individuals reduce their growth rate and mature at a smaller size. In some vertebrates, territoriality spaces individuals apart so that only those with adequate resources can breed. When resources are very limited, the number of available territories will decline. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY Humans and the Galapagos Charles Darwin’s visit to the Galapagos Islands in 1835 provided the stimulus for his theory of natural selection. The island’s isolation and small population sizes provide optimal conditions for rapid evolutionary change. The Galapagos form part of one of the best-conserved tropical archipelagos and have high numbers of native species. These include the famous Darwin’s finches, giant tortoises and land iguanas. For these reasons, the United Nations allocated them World Heritage Site status in 1978. Unfortunately, 50% of vertebrate species and 25% of plant species on the islands are recognised as endangered, and conservation issues on the Galapagos reflect similar issues in the rest of the world. The population of the Galapagos has grown in response to a developing tourist trade, an expanding demand for marine products like sea cucumbers and lobster, and economic problems in mainland Ecuador in the 1990s. in 1980, the population was about 5000, and 4000 tourists visited the islands each year. In 2005, the population was 28 000 and 100 000 tourists visited the islands. This dramatic increase in population size has placed huge demands on water, energy and sanitation services, which the authorities are struggling to meet. More waste and pollution have been produced, and the demand for oil has increased. An oil spill in 2001 had an adverse effect on marine and coastal ecosystems. Increased pollution, building, and conversion of land for agriculture have caused destruction and fragmentation of habitats. Forests of Scalesia trees and shrubs (a genus unique to the islands) have been almost eradicated on Santa Cruz and San Cristobal to make way for agricultural land. Any conservation plan for the Galapagos Islands has to take the concerns of local people seriously, and plan for their economic livelihood. Finding a balance between environmental, economic and social concerns is essential for conservation to be successful. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 1. Sarawak is an area of tropical rainforest in south-east Asia. Logging has been allowed in 60% of the forest. A study was carried out into the effects of logging on the diversity of mammal species living in the forest. An area of rainforest was sampled before logging, immediately after logging and then again two years and four years after logging. Before logging began, there were 29 mammal species and four years after logging there were 26 mammal species. Table 5.1 shows the population densities of six groups of mammals before and after logging. Where numbers were too small to measure the density, the species was recorded as ‘present’. (a) Marbled cats and otters are carnivores, while squirrels, shrews and deer are herbivores. Use the information provided to choose the best word(s) or terms to complete the following passage: The rainforest ____________________ is a dynamic set of interactions between populations of organisms and the abiotic environment. Energy flows from ____________________, such as trees, to ____________________ consumers, such as squirrels, and on to consumers such as cats and otters and higher ____________________. The activities of decomposers contribute to the energy lost from the ____________________ component of the rainforest but decomposers allow ____________________ to be recycled. [6] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (b) Table 5.1 shows that the number of small squirrels increases initially, but then decreases. Explain, using your knowledge of factors affecting population growth, why the small squirrel population in this rainforest does not increase in size indefinitely. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [4] (c) Describe, using the information provided, how species richness and species evenness change in the rainforest by comparing the situation before logging and four years after logging. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (d) Suggest why marbled cats and oriental small-clawed otters became extinct in this area but other mammals did not. ______________________________________________________________ ___________________________________________________________ [1] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (e) Outline three reasons for conserving biological resources, such as the rainforest in Sarawak. 1 ____________________________________________________________ _____________________________________________________________ 2 ____________________________________________________________ _____________________________________________________________ 3 ____________________________________________________________ ___________________________________________________________ [3] (f) Timber is produced sustainably in the United Kingdom. Describe and explain the benefits of two management practices used in sustainable timber production in a temperate country. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [4] 2. The sheep on a farm belong to a rare breed called Greyface Dartmoor. The Rare Breeds Survival Trust (RBST) gives advice on looking after these sheep and keep records to monitor the breeding of these sheep, in order to maintain a healthy population. (a) Why is the continued existence of rare breeds of farm animals desirable? ______________________________________________________________ ______________________________________________________________ SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [4] (b) North Ronaldsay sheep are listed as ‘endangered’ by the Rare Breeds Survival Trust. These sheep were raised on a small Scottish Island where they were kept along the seashore for most of the year. The sheep developed an unusual metabolism that allowed them to survive by eating seaweed. They are, however, susceptible to copper poisoning when fed on grass. State the two essential steps that must have occurred for a breed to develop a distinctive metabolism, such as the ability to eat mainly seaweed. ______________________________________________________________ ___________________________________________________________ [2] (c) Suggest what particular problems make the North Ronaldsay breed one of the most endangered sheep breeds in the United Kingdom. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] 3. Wading birds (waders) are birds that feed in shallow water. Table 4.1 shows changes in the population size of four species of wader in two areas of the Western Isles off the coast of Scotland. Area 1 is an area that has remained free of hedgehogs. Area 2 is an area where four hedgehogs were introduced from the mainland in 1974. Since then, they have established a large population. Hedgehogs eat the eggs of ground-nesting birds like waders. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (a) Calculate the percentage decrease in the number of breeding pairs of snipe in area 2 between 1983 and 2000. Show your working. Answer = ____________________ % [2] (b) Use the data in Table 4.1 to describe and explain the effect of the introduction of hedgehogs on the number of breeding pairs of waders in area 2. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (c) Suggest two factors that might have allowed a large population of hedgehogs to increase from just four individuals in area 2. Explain how each factor has led to an increase in the hedgehog population. 1 ____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ 2 ____________________________________________________________ _____________________________________________________________ _____________________________________________________________ ___________________________________________________________ [4] (d) Three suggested methods to reduce the effect of hedgehogs on the numbers of waders in area 2 were considered. These were: trapping and moving hedgehogs to the mainland trapping hedgehogs and keeping them in captivity indefinitely trapping of hedgehogs followed by humane killing The third method was judged to be the most effective and likely to succeed in reducing hedgehog numbers. Comment on the ethical issues involved in making this decision. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [3] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 4. The Hardy-Weinberg principle can be used to predict the expected frequencies of albino and non-albino alleles in a population. However, this principle can only be applied to populations which fulfil all of the following criteria: sexually reproducing organisms diploid organisms large populations randomly-mating populations The tiger, an endangered species of mammal, is undergoing a worldwide captive breeding programme in zoos. Suggest why the Hardy-Weinberg principle cannot be used to predict the expected frequencies of albino and non-albino alleles in the worldwide zoo population of tigers. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ _____________________________________________________________ [2] 5. A change in allele frequencies in a population is described as an evolutionary change. List two factors that might cause allele frequencies to change from generation to generation in a population that meets the Hardy-Weinberg criteria. ________________________________________________________________ _____________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 6. The Galapagos Islands are 600 miles away from the nearest land mass, South America. They consist of 15 main islands, 3 smaller islands, and 107 rocks and islets. This collection of islands is home to many endemic species of animals and plants. This means that these species are found nowhere else in the world. (a) Explain, using scientific terms, why a collection of small islands remote from the mainland provides optimal conditions for speciation. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] (b) In 1978, the United Nations (UN) declared the Galapagos Islands a World Heritage Site. This led to a rise in the resident human population and the number of visitors to the Islands. Table 2.1 shows how the number of people living on and visiting the Galapagos Islands changed between 1980 and 2005. Calculate the percentage increase in the number of visitors to the Galapagos Islands between 1980 and 2005. Show your working. Give your answer to the nearest whole number. Answer = ____________________ % [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (c) Outline the main ways in which increased human presence and activity have put endemic species on the Galapagos Islands, and in the sea around them, at risk of extinction. In your answer, you should link the ecological pressures imposed by human activity to examples of Galapagos Island species that have been affected ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ _____________________________________________________________ [7] (d) In 2007, the United Nations (UN) put the Galapagos Islands on its Red List of endangered sites. The Galapagos government’s response to this action included making new laws and placing restrictions on human activity, issuing eviction orders and culling introduced species of animals. Suggest one economic and one ethical problem that might have arisen from this 2007 UN decision. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ___________________________________________________________ [2] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY 7. Fig. 4.1 shows some notes that a gardener pinned to his notice board to remind him of jobs to do. Each is based on a different biological principle. (a) Match the notes, A to H, with the biological principles on which they are based. Write the correct letter next to the description of each principle. Biological principle Letter artificial selection ______ predator-prey interaction ______ apical dominance ______ nitrogen fixation ______ reproductive cloning ______ positive chemotaxis ______ decomposition ______ use of plant hormones ______ [8] SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (b) Four other procedures associated with growing or storing crops are described in Table 4.1 below. Name a biological process that is slowed down or stopped by each procedure. 8. Many species of insects have evolved resistance to chemical insecticides. Three different patterns of resistance in insect species R, S and T are shown in Fig. 6.1. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY (a) Complete the table below with the letter(s), R, S and T, to indicate which species show a continuous pattern of variation and which species show a discontinuous pattern. (b) A student noted a number of statements on his revision card that referred to the patterns of resistance shown in species R, S and T in Fig. 6.1. Complete Table 6.1 below, by selecting the correct numbered statement(s) that explain the genetic basis of each pattern of resistance for each species. SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY You may select a number more than once. (c) Dog fleas are small parasitic insects that live in the fur of dogs and feed on their blood. Dogs are routinely treated with sprays or powders to kill fleas. A vet believes that dog fleas may have become resistant to a popular fleakiller product. He asks an A-level work experience student to plan an experiment to test this hypothesis. The student needs to sample fleas from dogs visiting the surgery and also fleas from long grass in fields visited by dog-walkers. The fleas then need to be treated for resistance to the flea-killer. Describe the methods the students could use to: collect both samples of fleas find out the proportion of fleas that are resistant process the data In your answer, you should describe the methods for collection, testing and data processing in a logical series of steps ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ SACKVILLE SCIENCE DEPARTMENT A2 BIOLOGY ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ _____________________________________________________________ [7]