Biology · Interaction and interdependence

C4.1 — Populations and communities

Biology · SL / HL · syllabus-mapped notes

1. C4.1.1

   Populations as interacting groups of organisms of the same species living in an area

   Define population, and explain the interactions between its members.

2. C4.1.2

   Estimation of population size by random sampling

   Explain random sampling and sampling error, and interpret standard deviation.

3. C4.1.3

   Random quadrat sampling to estimate population size for sessile organisms

   Estimate population size for sessile organisms using randomly placed quadrats.

4. C4.1.4

   Capture–mark–release–recapture and the Lincoln index to estimate population size for motile organisms

   Estimate population size for motile organisms using the Lincoln index, and state its assumptions.

5. C4.1.5

   Carrying capacity and competition for limited resources

   Explain carrying capacity, and name the resources that limit it in plants and animals.

6. C4.1.6

   Negative feedback control of population size by density-dependent factors

   Contrast density-dependent and density-independent factors, and give the three dependent groups.

7. C4.1.7

   Population growth curves

   Explain the three phases of the sigmoid growth curve, and why exponential growth stops.

8. C4.1.8

   Modelling of the sigmoid population growth curve

   Model sigmoid growth experimentally, and evaluate the strengths and limits of the model.

9. C4.1.9

   Competition versus cooperation in intraspecific relationships

   Contrast competition and cooperation within a species, with examples of each.

10. C4.1.10

    A community as all of the interacting organisms in an ecosystem

    Define community, and explain why no population lives in isolation.

11. C4.1.11

    Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationship within communities

    Define the six categories of interspecific relationship, with examples.

12. C4.1.12

    Mutualism as an interspecific relationship that benefits both species

    Explain mutualism using root nodules, mycorrhizae and zooxanthellae.

13. C4.1.13

    Resource competition between endemic and invasive species

    Explain how alien species become invasive and displace endemic species.

14. C4.1.14

    Tests for interspecific competition

    Test for association between species, and explain why association is not proof of competition.

15. C4.1.15

    Use of the chi-squared test for association between two species

    Carry out a chi-squared test of association, and state its validity conditions.

16. C4.1.16

    Predator–prey relationships as an example of density-dependent control of animal populations

    Explain the four-step predator-prey cycle and the time lag that makes it oscillate.

17. C4.1.17

    Top-down and bottom-up control of populations in communities

    Contrast top-down and bottom-up control, using the Shropshire meres.

18. C4.1.18

    Allelopathy and secretion of antibiotics

    Explain antibiotics and allelopathic agents as secondary metabolites.