5.1a Communities, Ecosystems

29/04/2013 § Leave a comment

It’s the end of April, so close to May, and so close to the end of the year. This… is the last unit of HL Bio year one. I bring you – Ecology. We can start off with some key vocabulary that is apparently important but wasn’t mentioned in the reading. Weird.

  • a habitat is the environment in which a species normally lives
  • a species is a group of organisms that can interbreed and produce fertile offspring
  • a population is a group of organisms of the same species who live in the same area at the same time
  • a community is a group of populations living and interacting with each other in an area
  • an ecosystem is a community and its abiotic environment
  • ecology is the study of relationships between living organisms and between organisms and their environment

So, all animals need organic molecules in order to make their food, like glucose and amino acids (to make proteins, whooo). There are two kinds of organisms based on how they obtain their food sources. The autotrophs are self-feeders, so they make their own organic molecules out of inorganic substances, like plants. The heterotrophs eat other organisms. I think that says it all.

Organisms’ positions on the food chain are based according to how they get their food. There are also other ways for organisms to obtain organic matter from other organisms. The consumers ingest the actual organism and digest them. The detritivores ingest and digest the dead organism. The saprotrophs digest dead organic matter externally by secreting digestive enzymes onto the dead matter.

A food chain is what shows the order in which animals eat each other, basically. There are normally two to five organisms in the food chain. The organisms at the bottom are the producers, who are autotrophic because they get their food sources by making it out of inorganic matter. These include terrestrial green plant and phytoplankton – organisms that can do photosynthesis. Afterwards are primary, secondary, tertiary (and so on) consumers, who eat each other. These terms are called trophic levels, which is the organism’s level of consumption (?) in its food chain. Food chains and trophic relationships can also be illustrated by food webs, which are quite complex, look out.

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



Page 176, unexpected diets

1. Which of the organisms is autotrophic? —> The euglena (figure 4) is autotrophic.

2. Which of the organisms is heterotrophic? —> The ghost orchid (figure 3), venus fly trap (figure 2) and dodder (figure 5) are heterotrophic.

3. Of the organisms that are heterotrophic, deduce which is a consumer, which a detritivore, and which a saprotroph? —> The dodder is a saprotroph. The ghost orchid is a detritivore. The venus fly trap is a consumer.

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