Biology Module 3

3.1 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Selection Pressures 

→ The biotic and abiotic factors of an ecosystem that affect an organism’s behaviour, survival, and reproduction. 

→ Significant changes in biotic or abiotic conditions create selection pressures.

Population : All of the organisms from the same species living in a particular area.

Community : A group of populations in a particular area.

Ecosystem : A community of living organisms that interact with each other and their surrounding environment.

Ecosystem = Biotic factors + Abiotic factors



Effects of Selection Pressures 

→ Organisms best suited to selection pressures will tend to be more abundant because they have a better chance of survival, and reproduce more. 

     → Changes in population sizes may affect other species living in the ecosystem too. 

→ Selection pressures make some characteristics favourable and others unfavourable, driving the evolution of the species towards the favourable trait. 

→ Individuals with traits that are better suited to an environment are more likely to : Reproduce → Pass favourable trait to offspring → Favourable trait common in population. 




3.2 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Invasive Species 

→ An invasive species is an organism that is not native to a specific location.

→ The introduction of an invasive species can act as a selection pressure on native organisms, therefore influencing its population dynamics.



Predation : One animal killing another for food

Parasitism : One organism benefits at the expense of another, usually without killing them.

Commensalism : One organism benefits while the other is neither harmed or benefited.

Mutualism : Both organisms benefited from the relationship. 

Competition : Both organisms, often of the same species, competing over the same resource / space / mate etc, are harmed. 



Darwin in the Galapagos Islands 

→ Darwin observed small ground finches on the Galapagos Islands

→ The shape of their beak was observed - size of beaks differed 

→ Naturally occurring changes in colour, beak size, and leg length

→ Depending on which island they lived on, and the conditions they found themselves in, some birds would thrive and reproduce. 






3.3 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Adaptations

→ The development of specific features of an organism that enable them to survive and reproduce in a specific environment. 

Adaptations allow organisms to : Access resources, Attract mates, Avoid predation, Communicate → Increasing their chances of survival. 

→ Adaptations arise in response to specific biotic and abiotic factors in the environment. 

→ Adaptation is an evolutionary response driven by natural selection. 

Structural Adaptations : the physical features of an organism that allow it to be better suited to its environment. 

Physiological Adaptations : the internal bodily functions of an organism that help it to be better suited to its environment. 

Behavioural Adaptations : the actions that an organism makes to improve its ability to survive in its environment. 



Biological diversity : 

→ Diversity allows for adaptations. 

Generic → Genetic makeup in a species

Species → Measure of diversity of species

Ecosystem → Variation of different ecosystems. 



Genetic diversity : 

→ Important for the population to be able to adapt 

→ Environments are constantly changing and pose selective pressures that enable some organisms with favourable characteristics to survive and reproduce. 

→ No variation in the population will be more detrimental for an invasive organism or pressure 

→ More genetic diversity = more chance of survival 



Convergent vs Divergent evolution : 

Convergent 

→ Distantly related species which have moved to similar environments and are exposed to similar selection pressures to evolve similar habits, similar variation would be favoured by natural selection to enable them to survive. 



Divergent 

→ Ancestral species radiates into a number of descendant species with both similar and different traits. 

→ Usually influenced by various selection pressures. 

→ An example is Darwin’s finches. 



Gradual natural selection vs punctuated 

Gradualism 

→ Populations slowly diverge by accumulating changes in characteristics due to selection pressures

→ Suggest that transitional forms should exist.

→ Common ancestor

→ Small variation 



Punctuated equilibrium

→ Occurs in short bursts of rapid change, followed by long period of stability within populations

→ Mutations are passed on



The theory of evolution by natural selection : 

→ Diversity allows adaptations to change in an environment

→ Species have been developing for billions of years

→ All theories of evolution share a common basic premise. 

     → Living organisms arose from common ancestors or a common life form and have changed over time. 

     → Differences that occur among groups of living organisms imply that living things change over time

     → Similarities occur in living things and suggest a common ancestry ; the basic chemistry, inherited from a common life form, has remained relatively unchanged and has been passed down through generations. 



3.4 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Adaptations 

  • Darwin in the Galapagos Islands

    • He collected specimens of finches living on each of the islands.

    • They were classified as 14 different species (all similar to those in South America).

    • He reasoned that all finches came from a common ancestor, and the differences in beak shape and size was due to the different selection pressures.

Theory of natural selection

  • The theory has five main tenets:

  1. Variation exists within populations

  2. More offspring produced than can survive

  3. Those offspring that are better adapted to their environment will survive and reproduce

  4. The favourable adaptations are passed onto the next generation

Over time, the favourable adaptations will increase in the population (as long as the environment does not change) 



Biogeography evidence : 

→ For a new species to arise, it must be genetically isolated. 

→ Predictions based on biogeography provide evidence to support this feature of the theory of evolution. 

→ If isolation is a criterion necessary for a new species to arise from an original species, the new species should resemble species with which they shared a habitat. 



Fossil evidence : 

→ The sequence in which fossils are laid down in a rock reflects the order in which they were formed

→ Law of Superposition 

     → Further down in a rock represent an older fossil

→ Relative dating relies on the assumption that the fossils higher up in the rock are younger than the lower fossils → Fossils are dated relative to each other. 

→ Absolute dating enables the actual age of the specimen to be determined by using radioactive elements that are present. 



3.5 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Speciation : the formation of a new and distinct species during evolution.

Macroevolution : takes place over millions of years and results in new species arising.

Microevolution : involves small-scale changes within a population over shorter periods, but does not generally produce new species.

→ An accumulation of microevolutionary changes within a population can lead to speciation.

Mutation : a change in the sequence of an organism's DNA.

Migration : the movement of genetic diversity, usually within a species.

Genetic drift : the change in the frequency of an existing gene variant in a population due to random chance.

Natural selection : the process through which populations of living organisms adapt and change.

Concept of evolution → Every organism shares a common ancestor




3.6 - Describes biological diversity by explaining the relationships between a range of organisms in terms of specialisation for selected habitats and evolution of species



Gradualism Theory (Charles Darwin) : Evolution is a continual process of change where over a long time period, individuals possess small changes until they split into a number of different species. 

→ Not much evidence to back up this theory 



Punctuated Equilibrium : The evolution of species proceeds in a pattern of long periods of stability followed by rapid periods during which many new species emerge and some become extinct. 

→ Relies on Darwin’s theory of natural selection

→ Suggests that evolution is not as gradual or continual as originally proposed. 



Divergent evolution : the process whereby one species branches out into different environments, producing organisms that possess different characteristics. 



Convergent evolution : the process whereby organisms that are not closely related evolve similar structures in response to similar environmental conditions. 





3.7 - biochemical evidence, comparative anatomy, comparative embryology and biogeography (ACSBL089) – techniques used to date fossils and the evidence produced



Fossils : Remains, impressions, or traces of life forms that have been preserved in material such as ice, sediment, or amber. 



Relative dating

→ Involves arranging fossils in chronological order

→ Does not give fossils a numerical age

→ Qualitative (focuses on description rather than numbers) 

Stratigraphy : A process involving the comparison of the position of rock strata that contain fossils to determine the comparative time scale of their occurrence. 



Absolute dating

→ Provides a precise estimate of a fossil’s age.

→ Provides a fossil’s specific numerical age 

→ Quantitative method of dating

Radiometric dating : The process of determining the age of rocks or fossils from the decay of radioisotopes. 

Radioisotopes : Unstable atoms that are taken up by rocks or living matter in proportions equal to the environment. 

→ Once an organism dies, its radioisotopes levels decrease.