5.4b Natural Selection

13/05/2013 § 1 Comment

I want to talk about natural selection. And the simplest way to do it is to describe its observations and deductions. For every observation, there is a deduction, or an explanation.

The first observation notes that all populations tend to produce more than necessary, and more than the carrying capacity of their environment. But if every individual were actually surviving, the populations of ecosystems would increase exponentially 100% of the time, which is not what happens as we know from the sigmoid population curve. The deduction for this observation is that all populations struggle to survive, but some individuals live while others die. There is a struggle for existence.

The next observation is that all organisms are different from one another, despite being in the same species. The differences they hold affect how well suited they are to their environment and either help them or hurt them. This is called adaptation and certain individuals are better adapted than others. The deduction for this observation is basically natural selection: the more well adapted individuals normally survive while the less well adapted die. This makes sense, right?

The final observation is that variation is passed onto the offspring of individuals so that it becomes heritable. The deduction of this observation is that those better adapted individuals who do survive pass on their traits (the ones that helped them to survive) to their offspring, which will increase the proportion of individuals who can survive in the environment. After a few generations, the characteristics of the population will change to suit the environment.


Essay Questions

  1. Outline what is meant by the trophic level of an organism with three examples from one named habitat. (4 max)
  2. Compare the ways in which autotrophic, heterotrophic and saprotrophic organisms obtain energy. (6 max)
  3. Draw a labelled sigmoid population growth curve. 4 marks
  4. Explain the factors that cause a population to follow the sigmoid ( S-shaped) growth curve. (8 max)
  5. Apply the concept of carrying capacity to the struggle for survival resulting from overproduction of offspring. (5 max)
  6. Outline the international system used for naming species of living organisms. (4 max)
  7. Discuss the definition of the term species. (8 max)
  8. Name the levels and the specific taxa in the hierachy of classification using humans as an example. (2 max)
  9. Describe the relationship between the rise in the concentration of atmospheric carbon dioxide and the enhanced greenhouse effect. 5 marks
  10. Outline the consequences of a global temperature rise on arctic ecosystems. 6 marks
  11. Outline the precautionary principle. 5 marks
  12. Outline the structural differences which characterize bryophytes, filicinophytes, coniferophytes and angiospermophytes. 9 marks
  13. List the structural differences between bryophytes and angiospermophytes. 5 marks
  14. Briefly explain Darwin`s theory of evolution. 4 marks
  15. Outline five types of evidence which support the theory of evolution by natural selection. 6 marks
  16. Outline one modern example of observed evolution by natural selection. 2 marks
  17. Explain the evidence from homologous anatomical structures that supports the theory of evolution. 6 marks
  18. Outline how antibiotic resistance in bacteria can arise in response to environmental change. 5 marks
  19. Antibiotic resistance in bacteria is an example of evolution in response to environmental change. Using another example, explain how an environmental change can lead to evolution. 8 marks

A bit more?



Page 196, missing links

1. Calculate the length of Dilong paradoxus, from its head to the tip of its tail. —> 110mm ÷ 4.9mm * 100(mm) = 2244.9mm or 224.5cm

2. Deduce three similarities between Dilong paradoxus and reptiles that live on Earth today. —> Long neck and tail, same shape of skull, sharp teeth

3. Suggest a function for the protofeatheres for Dilong paradoxus. —> It could have kept the dinosaur from water or could have increased its speed because it looks like one of the dinosaurs that rely on running.

4. Suggest two features which Dilong paradoxus would had had to evolve, to become capable of flight. —> 1) Longer feathers more suited to flight, 2) bigger bone structure in the arms for wings

5. Explain why it is not possible to be certain whether the protofeathers of Dilong paradoxus are homologous with the feathers of birds. —> It isn’t possible because we are unsure of whether or not birds existed at the same time of the Dilong paradoxus and even if we did, we wouldn’t have enough evidence currently to determine if the feathers are homologous with each other.

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§ One Response to 5.4b Natural Selection

  • Dave Ferguson says:

    Great use of several approaches to learning!

    Grade 6 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them in a wide variety of situations.

    Data-based questions: missing links
    page 196
    1 1600 mm/ 1.6 m
    2 Answer should refer to:
    • Similar skull bones.
    • Similar dentition.
    • Similar tail vertebrae.
    3 Maintenance of a stable body temperature/
    4 Modified forelimbs; smaller body size.
    5 Direct observation not possible; DNA/molecular
    evidence not available.

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