Chapter 5 - Ecology and Evolution

Chapter 5 IB biology Ecology and Evolution

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5.1.1 Define species, habitat, population, communi

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.

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5.1.2 Distinguish between autotroph and heterotrop

Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances. Produce their own food. PRODUCERS

From the sun --> photosynthesis --> glucose.

Heterotroph: an organism that obtains organic molecules from other organisms. Cannot make their own food. CONSUMERS

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5.1.3 Distinguish between consumers, detritivores

Consumer: an organism that ingests other organic matter that is living or recently killed.

Detritivore: an organism that ingests non-living organic matter.

Saprotroph: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

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5.1.4 Describe what is meant by a food chain

Sequence of relationship between trophic levels. First organism synthesizes organic molecules from inorganic substances = PRODUCERS --> Primary consumer --> Secondary consumer etc

A food chain shows the sequence of feeding relationships and energy flow between species.

  • grass--> grasshopper --> toad --> hognose snake --> hawk
  • algae --> mayfly larva --> juvenile trout --> kingfisher
  • grass--> grasshopper--> frog--> rat
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5.1.5 Describe what is meant by a food web

Diagrams that show the feeding relationships in a community. A food web is an interconnecting series of food chains. The arrows in a food web indicates the direction of energy flow.

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5.1.6 Define trophic level

A trophic level is where an organism is positioned on a food web or food chain.

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5.1.7 Deduce the trophic level of organisms in a f

Producer (light --> chemical energy)

Primary consumer

Secondary consumer

Tertiary consumer


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5.1.8 Construct a food web


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5.1.9 State that light is the initial energy sourc

light is the initial energy source for almost all communities

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5.1.10 Explain the energy flow in a food chain

Energy transformations are not 100 % efficient. --> loss of energy, less energy for next trophic level.

  • Some organisms die before consumed
  • some parts are not eaten
  • energy released in cell respiration or converted into heat
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5.1.11 State that energy transformations are never

energy transformations are never 100% efficient

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5.1.12 Explain reasons for the shape of pyramids o

Pyramids of energy are always pyramid shaped where each level is smaller than the one below it. This is because less energy flows through each successive trophic level.

Energy is lost --> less energy for next trophic level.


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5.1.13 Explain that energy enters and leaves ecosy

Energy can enter and leave an ecosystem but nutrients must be recycled. Sun is the main source of energy on this planet. It is absorbed by photosynthesizing organisms, which convert light to chemical energy. Nutrients must be recycled by obtaining them from other organisms or products of organisms.

(see carbon cyle..)

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5.1.14 State that saprotrophic bacteria and fungi

saprotrophic bacteria and fungi (decomposers) recycle nutrients

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5.2.1 Draw and label a diagram of the carbon cycle



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5.2.2 Analyse the changes in concentration of atmo


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5.2.3 " Green house effect"

Five major greenhouse gases:

  • CO2
  • Methane
  • Oxides of Nitrogen (NOX)
  • Sulphur dioxide
  • CFCs (Chloroflourocarbons)

Human activities have increased the production of greenhouse gases, though these are naturally occuring from the beginning. --> Concentration in atmosphere and contribution to greenhouse effect is rising.

The light from the sun arriving to the Earth has short wavelengths and can mostly pass through the atmosphere. This sunlight warms up the surface of Earth which emits long wave radiation. The greenhouse gases trap this heat and make the Earth's temperature warmer than it would have been if this heat escaped.

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5.2.4 Outline the precautionary principle

The Precautionary Principle holds that, if the effects of a human-induced change have the potential to be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm to the environment or its inhabitants, before proceeding. That is the reverse of the the normal situation, were those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

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5.2.5. The precautionary principle and the greenho

There is strong evidence that states that global warming is caused due to the increasing amounts of greenhouse gases. However, this theory is not proved. Some argue against taking measures of combat global warming, since it is not absolutely certain that greenhouse gases are causing it. Oil companies and airlines in particular have voiced opposition since their business depends on the extraction, sale or buring of fossil fuels which is a major contributior of greenhouse gases. On the other hand, many scientists argue that if we wait for the proof of the harmful nature of excess greenhouse gases before reacting, the consequences would probably have reached a catastrophic level. Global warming is not only harmful for humans, but also on the the other species of the planet. It is our ethical and moral responsibility to ensure that we do not, knowingly, destroy their habitat or lead to the extinction of their species. The risks concerning global warming are so great that the precautionary principle should be employed and all activities that can possibly enhance the green the level of greenhouse gases should prove that it does not enhance the greenhouse gas levels, before it is allowed to be carried out.

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5.2.6 Outline the consequences of a global tempera

The effects of a global temperature increases on the Arctic ecosystems 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.

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5.3.1 Outline how population size is affected by n

Natality: offspring are produced and added to the population

Mortality: individuals die and are lost from the population

Immigration: individuals move into the area from elsewhere and are added to the population.

Emmigration: Individuals move out of an area to live elsewhere.

If (natality + immigration) > (mortality + emmigration) then population is increasing.

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5.3.2 Draw and label a graph showing a sigmoid (S-


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5.3.2 continued...

1. Exponential growth phase, individuals increase at a faster and faster rate

2. transitional phase, growth rate slows down considerably - still increasing but slowly

3. plateau phase, number of individuals has stabilized - no more growth

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5.3.3 Explain the reasons for the exponential grow

Exponential Phase: natality rate is higher than mortality rate. The resources needed by the population such as food are abundant, and diseases and predators are rare.

Transitional phase: Natality rate starts to fall and/or the mortality rate starts to rise. Natality is still higher than mortality so the population still rises, but less and less rapidly.

Plateau Phase: Natality and mortality are equal so the population size is constant. Population is limited by shortage of resources (such as food), more predators, more diseases or parasites. All of these factors limits population increase because they become more intense as population rises and becomes more crowded. They either reduce the natality rate or increase the mortality rate. If the population is limited by shortage of natural resources, it has reached the carrying capacity of the environment. The carrying capacity is the maximum population size that can be supported by the environment.

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5.3.4 List three factors that set limits to popula

The 3 factors that set limits to population increase are food availability, predation and disease

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5.4.1 Define evolution

Evolution is the accumulation of changes in the heritable characteristics of a population.

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5.4.2 Outline the evidence for evolution

Homologous anatomical structures

Remarkable similarities between some groups of organisms in their structure. Bones in the limbs of vertebrates --> pentadactyl limb --> evolved from common ancestor = homologous structures

The Fossil Record

Hard to explain without evolution --> as change over time. Acanthostega fossils show that vertebrates could have evolved from fish via an aquatic animal with legs.

Selective breeding of domesticated animals

The breeding of animals that are reared for human use are clearly related to wild species and in many cases can still interbreed with them. These domesticated breeds have been developed from wild species, by selecting individuals with desirable traits, and breeding from them. The striking differences in the heritable characteristics of domesticated breeds give us evidence that species can evolve rapidly.

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5.4.3 State that populations tend to produce more

Population growth produces more offspring than the carrying capacity of an environment can support.

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5.4.4 Explain that the consequence of the potentia

  • The population produces more offspring than the carrying capacity of the environment can support.
  • Offspring/population compete fro limited resources.
  • Some individuals are consequently "fitter" in terms of freedom from disease, food availability.
  • These individuals are more likely to successfully reproduce.
  • Through inheritance of the genes for these advantageous characteristics the frequency of these characteristics become greater in the next generation.
  • The alleles for the advantageous characteristic become more frequent in the population. 
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5.4.5 State that the members of a species show var

members of a species show variation

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5.4.6 Explain how sexual reproduction promotes var

Variation is essential for natural selection and therefore for evolution. Although mutation is the original source of new genes or alleles, sexual reproduction promotes variation by allowing the formation of new combinations of alleles. 2 stages in sexual reproduction promotes variation:

1. Meiosis allows a huge variety of genetically different gametes to be produced by each individual.

2. Fertilization allows alleles from two different individuals to be brought together in one new individual.

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5.4.7 Explain how natural selection leads to evolu

The much better-adapted individuals pass on their characteristics to more offspring than the less well-adapted individuals. The results of natural selection therefore accumulate. As one generation follows another, the characteristics of the species gradually change, the species evolve.

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5.4.8 Explain two examples of evolution in respons

Before Penecillin was invented, bacteria was leading cause of death. However, once it began to be used, since it's an antibiotic, some individuals of bacteria may carry the gene Penillinase, which codes for an enzymes that deactivates Penicillin, making them resistant to an antibiotic such as Penicillin. Thus, when it is indeed used, they will be the only ones left to reproduce and new bacteria will also be resistant to the antibiotic.

The peppered moth is another example of evolution in response to environmental change. When Britain began industrialising, soot would come from factories and land on trees. A species of peppered moth with lighter colour vanished and those with darker colour flourished because they could hide themselves easily.

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5.5.1 Outline the binomial system of nomenclature

Called "binomial" because two names are used.

1. First name is Genus, with first letter being a capital.

2. Second name is species, no capital.

3. Italics are used when the name is printed.

4. The name is underlined if it is handwritten.

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5.5.2 List seven levels in the hierarchy of taxa u

taxa  (

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5.5.3 Distinguish between the following phyla of p


Have no roots, only structures similar to root hairs called rhizoids. Mosses have simple leaves and stems. Liverworths consists of a flattened thallus. Height up to O.5 metres. Spores produced in a capsule. The capsule develops at the end of a stalk.


Ferns have roots, leaves, non-woody stems. Divided leaves. Height up to 20 m. Reproduction: sporangia – contain reproductive spores.


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5.5.3 continued...


Trees (100 m), shrubs, woody (lignin) stems, waxy narrow needlelike leaves. Vascular system (tracheids). Reproduction: seeds are produced. The seeds develop from ovules on the surface of the scales of female cones. Male produce pollen.


Roots, stems, leaves, vascular bundles waxy cuticle, annual or perennial up to 100 m. Reproduction: seeds are produced. The seeds develop from ovules inside ovaries. The ovaries are part of flowers. Fruit develop from the ovaries, to disperse the seed.

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5.5.4 Distinguish between the following phyla of a

Porifera:  No clear symmetry, attached to a surface, pores through body,  no mouth or anus, eg. spores

Platyhelminthes: bilaterally symmetric , flat bodies, unsegmented,  mouth but no anus, eg. planaria, tapeworms.

Mollusca: Muscular foot and mantle, Shell usually present, Segmentation not visible, Mouth and anus. eg. slugs, snails, squids.

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5.5.4 Distinguish between the following phyla of a

Cnidaria Radially symmetric, Tentacles, Stinging cells, Mouth but no anus, Eg, jellyfish, corals

 Annelida, Bilaterally symmetric,  Bristles often present, Segmented, Mouth and anus, Eg, earthworms

 Anthropoda, Bilaterally symmetric, Exoskeleton, Segmented, Jointed appendages, Eg, insects, spiders


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5.5.5 Apply and design a key for a group of up to

See text book p.149

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