5.1 Communities and ecosystems
5.1.1 Define species, habitat, population, community, ecosystem and ecology.
● Species: a group of organisms that can interbreed and produce fertile offspring.
● Habitat: the environment in which a species normally lives or the location of a living organism.
● Population: a group of organisms of the same species who live in the same area at the same time.
● Community: a group of populations living and interacting with each other in an area.
● Ecosystem: a community and its abiotic environment.
● Ecology: the study of relationships between living organisms and between organisms and their environment.
5.1.2 Distinguish between autotroph and heterotroph.
● Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances.
○ Examples: cyanobacteria, algae, grass.
● Heterotroph: an organism that obtains organic molecules from other organisms.
○ Examples: zooplankton, fish, sheep.
5.1.3 Distinguish between consumers, detritivores and saprotrophs.
● These are the three types of heterotrophs.
● Consumer: an organism that ingests other organic matter that is living or recently killed.
● Detritivore: an organism that ingests non-living organic matter.
○ earthworms, dung beetles
● Saprotroph: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.
○ fungi and bacteria
5.1.4 Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms).
Only real examples should be used from natural ecosystems. AB → indicates that A is being “eaten” by B (that is, the arrow indicates the direction of energy flow). Each food chain should include a producer and consumers, but not decomposers. Named organisms at either species or genus level should be used. Common species names can be used instead of binomial names. General names such as “tree” or “fish” should not be used.
● A sequence of trophic levels in which each organism is the prey/food for the next, and the first organism is photosynthetic/a producer.
● Grassland ecosystem in Europe
○ carrot plant → carrot fly → flycatcher → sparrowhawk → goshawk
● Galapagos ecosystem
○ sea lettuce → marine iguana → Galapagos snake → Galapagos hawk
● Marine ecosystem
○ Diatoms → copepods → herring → seal → great white shark
5.1.5 Describe what is meant by a food web.
● A food web is an interconnecting series of food chains.
● It shows all the feeding relationships in a community.
● The arrows indicate the direction of energy flow.
● Useful representation since one organism often eats more than one type of food
5.1.6 Define trophic level.
● The tropic level of an organism is its position in the food chain.
● producer, primary consumer, secondary consumer, tertiary consumer, quaternary consumer, quinary consumer, etc.
5.1.7 Deduce the trophic level of organisms in a food chain and a food web.
5.1.8 Construct a food web containing up to 10 organisms, using appropriate information.
5.1.9 State that light is the initial energy source for almost all communities.
No reference to communities where food chains start with chemical energy is required.
5.1.10 Explain the energy flow in a food chain.
● A food chain includes a producer and consumers.
○ Producers convert solar energy into chemical energy in the form of organic molecules.
○ Consumers obtain necessary energy from eating organisms of the previous trophic level.
● Food chains represent the direction of energy flow.
● Energy is lost between trophic levels because:
○ materials are not consumed or assimilated
○ and heat loss through cell respiration.
● About 10-20% of energy is passed on from one trophic level to the next, and this factor limits the length of food chains.
5.1.11 State that energy transformations are never 100% efficient.
Reference to the second law of thermodynamics is not expected.
5.1.12 Explain reasons for the shape of pyramids of energy.
● A pyramid of energy shows the flow of energy from one trophic level to the next in a community.
● The units of pyramids of energy are, therefore, energy per unit area per unit time, for example, kJ m–2 yr–1
● Each level is smaller than the one below it because energy is lost at each trophic level.
○ Some organisms die before an organism in the next level eats them (energy is not transferred).
○ Some parts of organisms, such as hair and bones, are not eaten.
○ Much energy is released as heat from cellular respiration.
● Approximately 10% of energy is passed on to each successive trophic level, and this limits the length of a food chain.
a food chain includes a producer and consumers;
represents the direction of energy flow;
energy loss occurs between trophic levels;
due to material not consumed/assimilated;
and from heat loss due to cell respiration;
energy passed on from one level to next is 10-20% ;
which limits length of food chain;
photosynthesis / producers convert solar energy to chemical energy (in organic
molecules);
consumers obtain necessary energy from eating organisms of previous trophic level;
an energy pyramid shows the flow of energy from one tropic level to the next
(in a community);
units are energy per unit area per unit time /
21
Jmyr
−−
;
Pyramid of energy – properly drawn, each level no more than one fifth the width of
the level below it, with three correctly labelled trophic levels
e.g. producer, primary consumer; [8 max]
5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
● Energy is not recycled -- it is supplied to ecosystems in the form of light, is converted into chemical energy and flows through food chains and then is lost as heat.
● Nutrients like carbon, nitrogen, and other elements are usually not resupplied to an ecosystem, and therefore must be recycled.
● Nutrients are taken from the environment to make up the biochemical molecules of cells and organisms. Eventually they are returned to the environment once the organism dies and decomposes by saprotrophic bacteria and fungi.
5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
5.2 The greenhouse effect
5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved.
The details of the carbon cycle should include the interaction of living organisms and the biosphere through the processes of photosynthesis, cell respiration, fossilization and combustion. Recall of specific quantitative data is not required.
5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide using historical records.
Data from the Mauna Loa, Hawaii, or Cape Grim, Tasmania, monitoring stations may be used.
DBQS :o
5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.
Students should be aware that the greenhouse effect is a natural phenomenon. Reference should be made to transmission of incoming shorter-wave radiation and re-radiated longer-wave radiation. Knowledge that other gases, including methane and oxides of nitrogen, are greenhouse gases is expected.
● Heat retention by gases is called the greenhouse effect.
● Light from the sun enters the atmosphere as short wave radiation. Sunlight warms the Earth’s surface and this re-emits long wave radiation back towards the atmosphere. Greenhouse gases in the atmosphere trap some of the long-wave radiation, causing the Earth to be warmer than if the radiation escaped.
● The rise in atmospheric concentration of greenhouse gases therefore correlate with the rising temperatures on Earth.
● Greenhouse gases include: carbon dioxide, methane, oxides of nitrogen, and sulfur dioxide.
5.2.4 Outline the precautionary principle.
The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.
5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.
● Although there is strong evidence that greenhouse gas emissions are causing global warming, there is no proof.
● Many scientists advocate the precautionary principle by arguing that if we wait for proof of the effects of greenhouse gases before reacting, the consequences would already have reached a catastrophic level.
● The risks are so great that the precautionary principle must be followed: anyone advocating continuing to emit greenhouse gases at current levels, or even to increase emissions, should be required to prove that this will not cause a damaging increase in the greenhouse effect.
● The issue of global warming is, by definition, a genuinely global one in terms of causes, consequences and remedies.
● Only through international cooperation will a solution be found.
● There is an inequality between those in the world who are contributing most to the problem and those who will be most harmed.
5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems.
Effects include increased rates of decomposition of detritus previously trapped in permafrost, expansion of the range of habitats available to temperate species, loss of ice habitat, changes in distribution of prey species affecting higher trophic levels, and increased success of pest species, including pathogens.
● Increased rates of decomposition of detritus previously trapped in permafrost due to thawing polar sheets. This will result in the release of carbon dioxide, further increasing atmospheric concentrations.
● Expansion of the range of habitats available to temperate species/change in the distribution of prey species, altering food chains and affecting animals in higher trophic levels.
● Marine species of animal in Arctic waters may become extinct, since some are extremely sensitive to temperature changes in seawater.
● Loss of ice habitat used for feeding and breeding, areas that will be lost to polar bears and other animals.
● Sea levels will rise in low-lying areas of land and will be flooded.
● Extreme weather events, such as storms, will become more frequent, with harmful effects on species that are not adapted.
5.3 Populations
5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration.
● Natality and immigration cause a population to increase.
● Mortality and emigration cause a population to increase.
● The overall change in a population is modelled by the equation:
○ Population change = (natality+immigration) - (mortality+emigration)
● A population is stable when (natality+immigration)=(mortality+emigration)
● If (natality+immigration)>(mortality+emigration), then the population is growing
● If (natality+immigration)<(mortality+emigration), then the population is decreasing
5.3.2 Draw and label a graph showing a sigmoid (S-shaped) population growth curve.
5.3.3 Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.
● 1. Exponential growth phase - Natality rate is higher than mortality rate
○ Plentiful resources such as food, space, and light
○ Little or no competition from other inhabitants
○ Favourable abiotic factors such as temperature or dissolved oxygen
○ Little or no predation or disease
● 2. Transitional phase - Natality rate begins to fall and mortality rate begins to rise
○ There is increasing competition for resources because there are more individuals in the population
○ There are more predators, which are attracted by the growing food supply
○ The spread of disease is an increased risk because a large number of individuals are living together in a limited space.
● 3. Plateau phase - Natality and mortality are equal, the population has hit the carrying capacity.
○ Shortages of resources, eg. food.
○ More predation
○ More disease or parasites
5.3.4 List three factors that set limits to population increase.
● Availability of resources
● Predation
● Disease
5.4 Evolution
5.4.1 Define evolution.
● Evolution is the cumulative change in the heritable characteristics of a population.
If we accept not only that species can evolve, but also that new species arise by evolution from pre-existing ones, then the whole of life can be seen as unified by its common origins.
Variation within our species is the result of different selection pressures operating in different parts of the world, yet this variation is not so vast to justify a construct such as race having a biological or scientific basis.
5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.
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Fossil record
● A fossil is the ancient preserved remains of an organism. The existence of fossils is difficult to explain without evolution. The fossil can be dated from the age of the rock formation. Sequences of fossil can show the gradual change of an organism over geological time. Continuous fossil records are rare with most containing large time gaps until subsequent discoveries are made. One conclusion that can be drawn from observing fossils is that life on Earth is constantly changing.
Selective breeding
● The breeds of animal that are reared for human use are clearly related to wild species
● In many cases domesticated animals can still interbreed with their wild relative
● Domesticated breeds have been developed by selecting desirable traits, and breeding from them
● The striking differences in the heritable characteristics of domesticated breeds provides a strong record of recent changes in heritable characteristics and evidence that species can evolve rapidly
Homologous structures
● There are remarkable similarities between some groups of organisms and their structures.
● For example. bones in the limbs of vertebrates are strikingly similar. The structure is called the pentadactyl limb and is present in species like: humans, porpoise, moles, bats, and horses.
● The most likely explanation for these structural similarities is that the organisms have evolved from a common ancestor. Structures developed from a common ancestor are called homologous structures.
5.4.3 State that populations tend to produce more offspring than the environment can support.
5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.
● Populations of living organisms tend to increase exponentially, yet, on the whole the number of individuals in populations remains nearly constant.
○ This is because more offspring are produced than the environment can support--there is a struggle for existence in which some individuals survive and some die.
● Living organisms vary and the members of a species are different from each other in many ways. Some individuals have characteristics that make them well adapted to their environment and others have characteristics that make them less well adapted.
○ The better adapted individuals tend to survive and reproduce more successfully than the less adapted individuals. This is natural selection.
● The better adapted individuals pass on their characteristics to more offspring than the less adapted individuals. The results of natural selection therefore accumulate. As one generation follows another, the characteristics of species gradually change --the species evolves.
5.4.5 State that the members of a species show variation.
5.4.6 Explain how sexual reproduction promotes variation in a species.
meiosis results in four haploid cells/gametes;
random assortment of chromosomes;
in metaphase I;
gives rise to variety of haploid gametes;
2n
possible gametes where n is the haploid number;
crossover may occur between homologous chromosomes;
in prophase I;
causes new combinations of genetic material/alleles;
non-disjunction causes changes in chromosome numbers;
infinite variety in gametes;
random process of fertilization;
random process of mating;
new combinations even with same parents;
mutation can occur in prophase I e.g. deletion / inversion / translocation;
5.4.7 Explain how natural selection leads to evolution.
Greater survival and reproductive success of individuals with favourable heritable variations can lead to change in the characteristics of a population.
● Populations of living organisms tend to increase exponentially, yet, on the whole the number of individuals in populations remains nearly constant.
○ This is because more offspring are produced than the environment can support--there is a struggle for existence in which some individuals survive and some die.
● Living organisms vary and the members of a species are different from each other in many ways. Some individuals have characteristics that make them well adapted to their environment and others have characteristics that make them less well adapted.
○ The better adapted individuals tend to survive and reproduce more successfully than the less adapted individuals. This is natural selection.
● Some variation has to be inherited and passed on to offspring.
○ The better adapted individuals pass on their characteristics to more offspring than the less adapted individuals. The results of natural selection therefore accumulate. As one generation follows another, the characteristics of species gradually change --the species evolves.
May 2005 “Discuss theory of evolution”
originally advanced by Darwin/Wallace;
based on observations;
overproduction of offspring leads to struggle for survival;
variation exists;
some varieties better adapted than others;
best adapted survive / reproduce and pass on characteristics;
evolution is change in species / allele frequency with time;
evidence that species have evolved include observed evolution / multiple antibiotic
resistance;
second example of evidence e.g. fossil record;
some claims in the study of evolution (of extinct species) are not testable/cannot be
proven;
competing explanation was inheritance of acquired characteristics/Lamarck’s ideas;
competing idea is that of special creation;
5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.
Other examples could include: the changes in size and shape of the beaks of Galapagos finches; pesticide resistance, industrial melanism or heavy-metal tolerance in plants.
Antibiotic resistance in bacteria
● A gene that gives resistance to an antibiotic is transferred to a bacterium by means of a plasmid or in some other way. There is then variation in this type of bacterium - some of the bacteria are resistant and some are not.
● Antibiotics are used to control the bacteria. Natural selection favours the bacteria that are resistant to it and kills the non-resistant ones.
● The antibiotic-resistant bacteria reproduce and spread, replacing the non-resistant ones. Eventually, most of the bacteria are resistant.
● Different antibiotics are used to control the bacteria. Resistance to this is soon developed, so another antibiotic is used, and so on until multiple resistant bacteria have evolved.
Industrial melanism in lady bugs
● The two-spotted lady bug usually has red wings with two black spots. The red colour serves to warn predators that it tastes unpleasant.
● A melanic form also exists, which has black wing cases. The melanic form absorbs heat more efficiently than the red form. It therefore has a selective advantage when sunlight levels are low and it is difficult for ladybugs to warm up.
● The melanic form became common in industrial areas of Britain, but declined in the 1960s. The decline corresponded with the decrease in smoke in the air.
● When smoke was no longer present in the air, the advantage of the melanic form was lost and warning colouration became more important.
e.g. antibiotic resistance of bacteria;
exposure of bacteria to antibiotics;
survival and reproduction of bacteria with resistant gene;
Defne the term evolution and, using two examples, explain the process of evolution in
response to environmental change.
definition: [3 max]
evolution is the process of cumulative change over time;
some variation has to be inherited;
increased reproduction of individuals with favourable characters over time;
thus, species adapt to the environment;
Award [3 max] for each example.
named example;
environmental change;
evolutionary response;
e.g. antibiotic resistance of bacteria;
exposure of bacteria to antibiotics;
survival and reproduction of bacteria with resistant gene;
e.g. heavy metal tolerance in plants / melanism in ladybugs / pepper moths;
5.5 Classification
5.5.1 Outline the binomial system of nomenclature.
● The binomial system of nomenclature is used for the classification of organisms.
● It is binomial because two names are used.
● The first name is the genus name. A genus is a group of similar organisms. It is given an upper case first letter.
● The second name is the species name. A species is a group of organisms with similar characteristics, which can interbreed to produce fertile offspring. It is given a lower case first letter.
● Italics are used when the name is printed, and the name is underlined if handwritten.
5.5.2 List seven levels in the hierarchy of taxa—kingdom, phylum, class, order family, genus and species—using an example from two different kingdom for each level.
Grey wolf:
Kingdom: | |
Phylum: | |
Class: | |
Order: | |
Family: | |
Genus: | |
Species: | lupus |
Coast redwood:
Kingdom: | Plantae |
Phylum: | Coniferophyta |
Class: | Pinopsida |
Order: | Pinales |
Family: | Taxodiaceae |
Genus: | Sequoia |
Species: | semipervirens |
5.5.3 Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta.
● Bryophyta: short plants with no roots, simple leafs and stems; non-vascular meaning they have no xylem/phloem; reproduce through spores; maximum height 0.5m; eg. mosses, liverworts, hornworts
● Filicinophyta: ferns; vascular plants with roots, leaves, and non-woody stems; reproduce through spores; maximum height 15m
● Coniferophyta: conifers; vascular plants with roots, leaves, and woody stems; leaves in the form of needles or scales; produce seed cones; reproduce using pollination by wind.
● Angiospermophyta: flowering plants; very variable but generally have stems, leaves, roots; flowers are the reproductive organs, and seeds are produced inside the ovaries of the flower --> ovaries develop into fruits to disperse the seed.
5.5.4 Distinguish between the following phyla of animals, using simple external recognition features: porifecnidaria, platyhelminthes, annelida, mollusca and arthropoda.
5.5.5 Apply and design a key for a group of up to eight organisms.
A dichotomous key should be use
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