Topic 5: Ecology & Evolution

Communities and ecosystems

5.1.1 Define species, habitat, population, community, ecosystem and ecology.

Species	Group of genetically identical organisms that can interbreed to produce fertile offspring.
Habitat	Normal living place of an organism
Population	Groups of organisms of the same species living in the same area at the same time.
Community	Groups of populations of organisms living and interacting with the abiotic environment
Ecology	Study of the interaction between living organisms and between living organisms and their environment
Ecosystem	A community and its abiotic factors

Background info

Abiotic means non-living. Abiotic factors include light, temperature, atmospheric gases and precipitation. Thus an ecosystem is different groups of organisms living together and interacting with the non-living environment.

What is a community?
A. A group of organisms living and interacting in the same trophic level
B. A group of populations living and interacting in a food chain
C. A group of organisms of the same species living and interacting in an ecosystem
D. A group of populations living and interacting in an area

Which of the following ecological units includes abiotic factors?

A. A community
B. An ecosystem
C. A population
D. A trophic level

5.1.2 Distinguish between autotroph and heterotroph

An autotroph synthesizes its own organic molecules whereas heterotrophs acquire these organic molecules from other organisms by consuming them. An autotroph is the producer in a food web/chain whereas heterotrophs are consumers.

Autotrophs obtain carbon from inorganic substances (CO₂) whereas heterotrophs obtain carbon from organic sources (fatty acids, carbohydrates, amino acids).

5.1.3 Distinguish between consumers, detritivores and saprotrophs.

Consumers	Detritivores	Saprotrophs
Consumes living organic matter	Ingests dead organic matter	Secretes digestive enzymes onto dead organic matter, because it is unable to ingest the macromolecules of organic matter
Mainly animals	Mainly decomposers	Mainly fungi and bacteria

Which group of organisms in the carbon cycle converts carbon into a form that is available to primary consumers?
A. Decomposers
B. Saprotrophs
C. Detritus feeders
D. Producers

5.1.4 - Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms).

The easiest to remember in my opinion are shown below:

Diatom --> Freshwater shrimp --> Leech --> Trout

European White waterlily --> Brown China Mark moth --> Common Roach --> Common Moorhen

5.1.5 Describe what is meant by a food web.

A food web are interconnected food chains that show complex feeding relationships between living organisms in an ecosystem.

It shows the following:

·         That there may be more than one producer.

·         Producers may be prey to more than one consumer

·         Consumers may have more than one food source and these food sources can exist at different trophic levels, e.g. a tertiary consumer could feed on both primary and secondary consumers.

·         Arrows showing direction of energy flow from producers to upper level consumers.

b

5.1.6 Define trophic level.

Trophic level – Position of an organism in a food chain or food web.

5.1.7 Deduce the trophic level of organisms in a food chain and a food web.

Trophic level 1	Producer	Oak tree
Trophic level 2	Primary consumer	Oak beauty caterpillar
Trophic level 3	Secondary consumer	Caterpillar-hunting beetle
Trophic level 4	Tertiary consumer	Common shrew
Trophic level 5	Quaternary consumer	Red fox

The food web below shows some of the feeding relationships found between the organisms living in or near a river in England.

                                                  

(a)                    Identify an organism in the food web that is

(i)                     an autotroph.

...........................................................................................................................

(1)

(ii)                   both a secondary and tertiary consumer.

...........................................................................................................................

5.1.8 Construct a food web containing up to 10 organisms, using appropriate information.

Like above. I'll find a question from a past paper that addresses this assessment statement.

5.1.9 State that light is the initial energy source for almost all communities.

5.1.10 Explain the energy flow in a food chain.

Light is the initial energy source for almost all communities, and is absorbed by producers and used in photosynthesis to produce chemical energy. This energy is transferred to primary consumers when they consume the producer. However only 10% of this energy is available at each trophic level. Therefore 90% of energy is lost at each trophic level as heat due to cell respiration & metabolism as well as through undigested/uneaten matter that is not consumed and defecation. For this reason, there are less consumers as there are producers because energy transfers between trophic levels are not 100% efficient.

5.1.11 State that energy transformations are never 100% efficient

5.1.12 Explain reasons for the shape of pyramids of energy.

• Pyramids of energy shows inflow of energy at each trophic level, in kJ m-2 per year.
• Pyramids of energy are pyramid-shaped because energy transformations between trophic levels is never 100 percent efficient.
• 90 percent of energy lost at each trophic level due to cell respiration and undigested matter of organisms.
• Pyramids of energy cannot be inverted because matter (organic compounds) cannot be created nor destroyed.
• Thus organic compounds would have to be created for there to be more energy available at higher trophic levels than lower trophic levels.

5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
Energy enters ecosystems via sunlight and exits ecosystems via heat energy. However nutrients are recycled when organisms die because saprotrophs and detritivores break down the dead organic matter and the nutrients within it, resulting in nutrients becoming part of the soil solution. These nutrients are absorbed by producers and are then passed on to the primary consumers when the plant material is digested, and the nutrient cycle continues.

nutrient cycles within ecosystem / nutrients are recycled;
example of nutrient cycle with three or more links;
nutrients absorbed by producers / plants / roots;
nutrients move through (food chain) by digestion of other organisms;
nutrients recycled from decomposition of dead organisms;
nutrients from weathering of rocks enter ecosystem;
nutrients lost by leaching / sedimentation (eg shells sinking to sea bed);    

5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.

The greenhouse effect

5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved.

5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide using historical records.

Carbon dioxide levels in the atmosphere are rising due to increased use of fossils fuels in power station and cars.
Data from the Mauna Loa monitoring station in Hawaii shows that CO2 levels in the air have risen from 315 ppm (parts per million) in 1958 to 386 ppm (parts per million) in 2008, which is 22.5% increase in CO2 concentration.

5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.

Increased usage of fossil fuels to generate electricity and to power cars has caused an increase in the concentrations of greenhouse gases, including water vapour, nitrogen oxides, carbon dioxide and methane, in the atmosphere. 

During the greenhouse effect, shorter-wave radiation hits the earth from the sun and is reflected back into space mainly as heat. A proportion of the outgoing radiation is longer-wave radiation which is trapped by the atmosphere, increasing atmospheric temperatures to allow life to exist on earth. However, increased greenhouse gases cause what is known as the enhanced greenhouse effect. More longer-wave radiation is trapped by greenhouse gases and is reflected back to the earth, increasing ocean and atmospheric temperatures at a high rate than normal, which can disrupt climatic and ocean patterns, thereby threatening ecosystems.

Conversely, some scientists are skeptical about whether humans are causing the enhanced greenhouse effect because throughout the Earth's history there have been many fluctuations in greenhouse gas levels and global temperatures.

Explain how the emission of gases, both naturally and through human activity, can alter the surface temperature of the Earth. 8 marks

The greenhouse effect is a natural phenomenon that has occurred over millions of years. Shorter-wave radiation travels through the atmosphere and reaches the Earth’s surface, increasing its temperature. This radiation is reflected back to the atmosphere as longer-wave radiation. A large proportion of this trapped by the atmospheric greenhouse gases, causing the lower atmosphere to heat up. This process is essential to ensure livable temperatures for living organisms on Earth.

However due to industrialization and our increased use of fossil fuels, emissions of greenhouse gases including carbon dioxide, methane and nitrogen oxide have significantly increased so that more longer-wave radiation is trapped in the earth’s atmosphere, causing it to heat up. This is the basis of global warming. However humans are not the only source of greenhouse gases; cows are significant emitters of the greenhouse gas methane, and a significant amount of greenhouse gases are produced by volcanic activity.

5.2.4 Outline the precautionary principle.

Precautionary principle states that when a human-induced change could be potentially harmful, those responsible for the change must prove that it will not do harm before proceeding, instead of those against the change having to prove that it will do harm.

5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect. 

According to the precautionary principle, when an activity such as the burning of fossil fuels can raise the threat of harm, measures should be taken, even if a cause-and-effect relationship has not scientifically been established.

5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems (Perfect essay question).

Key ideas to discuss:

·         Global warming increases global temperatures of Earth

·         May result in climate change and greater ranges in temperature

·         Ice melting causes sea levels to rise

·         Disturbs ocean current systems delivering warm water from tropical regions northwards to temperate regions, disrupting food production.

·         Uncovers permafrost, causing increased rate of decomposition of detritus, increasing carbon dioxide levels in atmosphere

·         Loss of habitat for arctic foxes and polar bears, causing them to migrate northwards to colder environments.

Arctic ecosystems consist of ice deserts and lower lying regions with vegetation described as tundra. An average rise in global temperatures caused by global warming would cause the glaciers and snow in the ice deserts to melt. This freshwater would flow down to the lower lying regions and flood the tundra, at least temporarily. Eventually, the high temperatures warm up the arctic soils, allowing bacteria and fungi to decompose the accumulated detritus, releasing CO2 and methane into the atmosphere, further contributing to the enhanced greenhouse effect.

The humus-rich soils as well as warmer temperatures would promote the establishment of conifer forests that would entice other animals to inhabit the region for hibernation. This would also encourage predators to follow these animals, and these predators would carry parasites with them, causing an increased presence of pathogens in the region.

ALTERNATIVE RESPONSE

Arctic ecosystems consist of ice deserts and lower-lying vegetation called tundra. The enhanced greenhouse effect causes the temperature on Earth to increase, which would result in the melting of ice and glaciers. This would have a multitude of outcomes, but the immediate outcome would result in more freshwater entering the oceans, causing sea levels to rise, threatening low-lying inhabited regions. In addition, this cold water would disrupt ocean current systems that deliver warm water from tropical regions northwards to colder regions. This would disrupt agricultural production of food, which would affect many people in those countries.

The melting of the ice deserts in arctic ecosystems would also allow detritivores and saprotrophic bacteria and fungi to decompose the accumulated detritus in the soil, which would lead to further releases of carbon dioxide in the atmosphere and thereby accelerating the enhanced greenhouse effect even further.

However, the major impacts of the removal of much of the ice in arctic ecosystems would provide an increased range of habitats for temperate species such as the alpine marmot but also lead to the loss of a habitat for some species such as the polar bear.

The increased plants and animals in this changed habitat would inevitably attract predators, which in turn would increase the presence of pathogens that parasite the expanded range of animals and plants.

• The enhanced greenhouse effect causes atmospheric temperatures to increase due to the longer-wave radiation being trapped in the atmosphere
• This results ice in arctic ecosystems to melt, which has numerous consequences.
• One effect is a change in the salinity of the oceans, affecting global ocean currents which in turn has an impact on the climates of different countries.
• The melting of ice also raises sea levels, which can cause flooding of low-lying regions, potentially interfering with agricultural production in poorer countries and effecting food distribution.
• In addition, the loss of the ice increases the absorption of solar radiation, thus further increasing atmospheric temperatures.
• After the melting of the ice, the detrititus underneath is subject to decomposition by saprotrophic bacteria and fungi, which produce carbon dioxide that further adds to the enhanced greenhouse effect.
• Increased temperatures in arctic ecosystems would also result in some species becoming extinct and/or other species moving to colder regions to survive.
• On the other hand, there would be an increase in the population of pest species and species adapted to warmer conditions due to the expanding range of new habitat available.

May 2012 markscheme

increasing rates of decomposition of detritus previously trapped in permafrost;

expansion of the range of habitats available to temperate species;

loss of ice habitat;

loss  of  ice  increases  absorption  of  solar  radiation resulting in increased warming  of atmosphere;

changes in water salinity;

changes in distribution of prey species affecting higher trophic levels;

increased success of pest species;

extinction of species adapted to arctic/cold conditions;

humans can/should take steps to reduce/slow losses in habitat / given example of measure taken;

statement applying the precautionary principle to this issue;


May 2010 markscheme
global warming is an increase in temperature of the atmosphere/
oceans/Earth;
may result in climate change / changes in amount of precipitation /
greater ranges in temperature;
melting ice leads to rising of sea level;
leading to loss of habitat / example of organism that would lose
habitat;changes in salinity / changes in ocean currents change distribution
of nutrients;
changes in predator-prey relationships (due to ecosystem disruption);
increased success of pest species;
temperate species with bigger range of habitats as ice melts;
increased rate of decomposition of detritus;           

Classification

5.5.1 Outline the binomial system of nomenclature.

• Internationally recognized nomenclature
• First name indicates genus and second name indicates species, e.g. Elodea canadensis
• Nomenclature helps scientist around the world to identify organisms and enables them to communicate about the same species.
• All members of the same genus share special features

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 kingdoms for each level.

"Common oak"                                                        

Plantae                                                                      Animalia        

Angiospermophyta                                                 Chordata

Dicotyledonae                                                          Mammalia

Fagales                                                                     Primates

Fagaceae                                                                  Hominidae

Quercus                                                                   Homo

Robur                                                                       sapiens

5.5.3 Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta.

Byrophyta –

·         No true roots, stems or leaves/ rhizoids are present

·         nonvascular/ no true xylem or phloem tubes

·         Not woody

·         Produce spores in capsules

Filicinophyta-

·         no true xylem or phloem tubes

·         Produce spores in sporangia

·         Not woody

·         Pinnate leaves

Coniferophyta-

·         Woody stems and roots

·         Needle-like leaves

·         Produce seeds in cones not fruit

Angiospermophyta

·         Produce flowers

·         Seeds enclosed in fruit

·         Can form woody tissue

·         Have ovules in ovaries.

bryophyta have no roots / only have rhizoids;
bryophyta have simple leaves/stems / only a thallus;
bryophyta produce spores in capsule;
byrophyta are nonvascular;
bryophyte exhibit (pronounced) alternation of generations / a
significant gametophyte generation;

                   filicinophyta have roots, stems and leaves;
filicinophyta (often) have divided/pinnate leaves;
filicinophyta produce spores in sporangia/spores on the undersides of leaves;
filicinophyta exhibit alternation of generations;
filicinophyta have primitive vascular tissue / no true xylem and phloem;

                   coniferophyta have woody stems;
coniferophyta (often) have narrow leaves/needles/scales;
coniferophyta produce seeds in cones/unenclosed seeds;

                   angiospermophyta have flowers;
angiospermophyta have ovules in ovaries;
angiospermophyta produce seeds (with hard coats) in fruits;                                             9 max

Byrophyta (mosses, liverworts)	Filicinophyta (ferns)	Coniferophyta (conifers, pine trees)	Angiospermophyta (flowering plants)
Not woody	Not woody	Woody stems and roots	Can form woody tissue
No roots, cuticle, stems or leaves (rhizoids present)	Leaves in fronds with cuticle	Needle-like leaves	Waxy cuticle on leaves
Spores produced in capsules on end of stalk	Spores produced in sporangia on underside of leaf	Produce seeds not enclosed in fruit	Produce seeds enclosed in fruit. Produce flowers
No true xylem or phloem tubes	No true xylem or phloem tubes		Have ovules in ovaries

5.5.4 Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca and arthropoda.

Annelid –

• Segmented
• Bilaterally segmented
• Bristles present
• Mouth and anus

Porifera –

·        No special shape

·        No organs or tissues

·        No symmetry

·        No mouth or anus

·        Cells organized in canals, chambers and pores

Mollusca –

·        Unsegmented

·        Bilaterally symmetric

·        Mouth and anus

·        Double or single shell

·        Soft-bodied

·        Radula used for feeding

Platyhelminthes – 

• Unsegmented
• Bilaterally symmetric
• Mouth but no anus
• Soft with no skeleton
• Rudimentary head

Arthropod – 

·        Hard chitinous exoskeleton

·        Segmented

·        Bilaterally symmetric

·        Jointed appendages

Cnidaria

• Tentacles with stinging cells
• Radial symmetry
• Two cell layers
• Two forms - medusa and polyp

5.5.5 Apply and design a dichotomous key for a group of up to eight organisms.

Animal phyla

(1) Mouth and anus                 go to 3 

      No mouth or no anus        go to 2

(2) No mouth or anus             Porifera

      Mouth but no anus            Platyhelminthes

(3)  Bilateral symmetry          go to 4

       Radial symmetry             Cnidaria

(4)  Segmented                     go to 5

       Unsegmented                Mollusca

(5) Bristles present              Annelida

      Hard exoskeleton          Arthropoda

Plant phyla

(1) Roots, stems and leaves present           go to 2

      Roots stems and leaves absent            Byrophyta

(2) Can form woody tissue                           go to 3
      Cannot form woody tissue                      Filicinophyta

(3) Seeds enclosed in fruit                            Angiospermophyta

      Seeds not enclosed in fruit                      Coniferophyta


Evolution (this topic is mostly about writing long paragraphs, like below)
5.4.1 Define evolution
Evolution is the cumulative change in the heritable characteristics of a population. (Heritable meaning able to be inherited).
5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.
Fossil record:
The fossil record is a collection of preserved parts or traces of dead organisms. Examples of fossils include hard body parts such as bones, imprints left behind fossils buried in mud, petrified specimens, frozen parts or whole organisms and casts and moulds made from fossil imprints.Fossilisation however is a rare event because it requires certain conditions such as environments where sediments are likely to cover organisms, protecting them from saprotrophs and detritivores. The rarity of fossilisation occurring decreases the likelihood of fossils being found, which has resulted in missing links in the fossil record of many species, including humans. Despite these drawbacks, the study of fossils allows scientists to deduce the age, habitat, locomotion, diet and other features and characteristics of species. Despite the incompleteness of the fossil record, it does show a process of gradual change in the heritable characteristics of a population over time.

Homologous structures
The fossil record is a collection of preserved parts/traces of dead organisms. These fossils show changes in the characteristics of a population. It also shows that groups of animals have similar structures called homologous structures that are similar in shape in different types of organisms. This suggests that all organisms evolved from a common ancestor. For example the similar basic structure of the pentadactyl limb found in vertebrates. In different organisms the pentadactyl limb is adapted to different methods of locomotion in particular environments. For instance, a bat's wing is similar in structure to a human hand, except the bat's wing is adapted for flying whereas the human hand was evolutionarily adapted for lifting objects.



comparative anatomy of groups of animals or plants shows certain
structural features are basically similar;
homologous structures are those that are similar in shape in different types
of organisms;
structural similarities imply a common ancestry;
(homologous structures) used in different ways;
example is pentadactyl limb in vertebrates / modification of ovary wall or
pericarp to aid seed dispersal / other suitable example;
adapted to different mode of locomotion in particular environment / 
example of two differences such as bat’s wing and human hand;
illustrates adaptive radiation since basic plan adapted to different niches;
the more exclusive the shared homologies the closer two organisms are related;
certain homologous structures in some species with no apparent function such as
human appendix (homologous with functional appendix in herbivores);

Selective breeding of domesticated animals
Evolution is a cumulative change in the heritable characteristics of a population. Artificial selection by selective breeding of domesticated animals provides a good example of natural selection.
When domesticated animals are bred, individuals are selected that show the most desirable characteristics, and these individuals are interbred. This is exemplified in the breeding of racehorses. The fastest racehorses are selected and interbred. In this way, a cumulative change in the heritable characteristics of a population is brought about. Unlike natural selection, artificial selection may not always lead to the survival of the fittest.

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.

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

1. Antibiotics block specific metabolic pathways in bacteria.

2. Exposure of bacteria to antibiotics is environmental change and is factor for natural selection

3. Only bacteria that show natural resistance to antibiotic survive

4. Natural resistance due to gene mutations

5. Antibiotic resistant bacteria transmit resistant genes to other bacteria via conjugation of pili and binary fission.

6. Bacteria reproduce very quickly and have high rate of mutation, causing bacterial population to evolve and become completely resistant to a certain antibiotic within a few generations.

7. Can occur in hospitals when antibiotic not administered properly, creating environment where antibiotic-resistant bacteria are favoured and selected for.

8. Creates multi-resistant strains of bacteria, e.g. bacteria resistant against tuberculosis antibiotics, TB resistant bacteria.

5.3 Populations 
5.3.1 Outline how population size is affected by natality, immigration, mortality, and emigration. 5.3.2 Draw and label a sigmoid curve. 5.3.3 Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.
A sigmoid growth curve represents what happens when a population colonizes a new habitat. The significant increase in population size during the exponential growth phase is due to a lack of limiting factors such as competition for resources, predation or disease. This results in high natality, low mortality, high immigration from other populations and low emigration out of the habitat. 

As population density increases, the limiting factors increase and the natality rate decreases, mortality rate increases, emigration increases and immigration decreases. This results in a phase called the transitional phase where the population growth rate decreases, but the population size still increases. 

The maximum size of a population that the habitat can support is called the carrying capacity. When a population reaches its carrying capacity, the population size does not increase, but remains constant because the combined natality and immigration will be equal to the comvined mortality and emigration.

5.3.4 List three factors that set limits to population increase.
Competition for resources (food), predation and presence of disease/parasites. 

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Explain how natural selection can lead to evolution using antibiotic resistance in bacteria as an example.

• Populations tend to produce more offspring than the environment can support, which causes a  struggle for survival.
• However because members of a population of the same species show variation,
• some organisms are more likely to survive.
• This is because they have characteristics which are better adapted to environment.
• if characteristics are heritable they will most likely be passed on to offspring
• Can cause change of heritable characteristics of the population.
• This is the case for the evolution of bacteria such as MRSA bacteria in hospitals, after overuse and/or misuse of antibiotics.
• Applied antibiotic acts as selection pressure for bacterial population
• Most bacteria killed by antibiotic
• however few bacteria with natural resistance to antibiotic, due to gene mutations, survive.
• if resistance is heritable, it will be passed on to offspring
• or other bacteria via conjugation of pili.
• The bacterial colony will evolve over many generations so all bacteria become resistant to antibiotic

members of a population of the same species show variation;
some organisms are more likely to survive due to selective
advantage
some organisms have a reproductive advantage;
these variations may be genetically controlled/heritable;
these genes are most likely to be passed on to offspring;
this can change the characteristic of the population;
bacteria can normally be killed with antibiotics;
antibiotics impose a selection pressure;
if a few bacteria have natural resistance to the antibiotic
they will survive;
if the resistance is heritable they will pass it on to their offspring;
they will reproduce/evolve to form bacterial colonies resistant
to the antibiotic;
example of organism selected by use of antibiotic;
(e.g. MRSA bacteria / resistant TB bacteria)