SL Content Statements

• A3.1.1

  Variation between organisms as a defining feature of life

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  Students should understand that no two individuals are identical in all their traits. The patterns of variation are complex and are the basis for naming and classifying organisms.
  

• A3.1.2

  Species as groups of organisms with shared traits

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  This is the original morphological concept of the species as used by Linnaeus.
  

• A3.1.3

  Binomial system for naming organisms

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  Students should know that the first part of the name identifies the genus, with the second part of the name distinguishing the species. Species in the same genus have similar traits. The genus name is given an initial capital letter but the species name is lowercase.

• A3.1.4

  Biological species concept

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  According to the biological species concept, a species is a group of organisms that can breed and produce fertile offspring. Include possible challenges associated with this definition of a species and that competing species definitions exist.

• A3.1.5

  Difficulties distinguishing between populations and species due to divergence of non- interbreeding populations during speciation

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  Students should understand that speciation is the splitting of one species into two or more. It usually happens gradually rather than by a single act, with populations becoming more and more different in their traits. It can therefore be an arbitrary decision whether two populations are regarded as the same or different species.
  

• A3.1.6

  Diversity in chromosome numbers of plant and animal species
  

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  Students should know in general that diversity exists. As an example, students should know that humans have 46 chromosomes and chimpanzees have 48. Students are not required to know other specific chromosome numbers but should appreciate that diploid cells have an even number of chromosomes.
  

• A3.1.7

  Karyotyping and karyograms

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  AOS: Students should be able to classify chromosomes by banding patterns, length and centromere position. Students should evaluate the evidence for the hypothesis that chromosome 2 in humans arose from the fusion of chromosomes 12 and 13 with a shared primate ancestor.
  NOS: Students should be able to distinguish between testable hypotheses such as the origin of chromosome 2 and non-testable statements.
  

• A3.1.8

  Unity and diversity of genomes within species

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  Students should understand that the genome is all the genetic information of an organism. Organisms in the same species share most of their genome but variations such as single-nucleotide polymorphisms give some diversity.
  

• A3.1.9

  Diversity of eukaryote genomes

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  Genomes vary in overall size, which is determined by the total amount of DNA. Genomes also vary in base sequence. Variation between species is much larger than variation within a species.
  

• A3.1.10

  Comparison of genome sizes

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  AOS: Students should extract information about genome size for different taxonomic groups from a database to compare genome size to organism complexity.
  

• A3.1.11

  Current and potential future uses of whole genome sequencing

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  Include the increasing speed and decreasing costs. For current uses, include research into evolutionary relationships and for potential future uses, include personalized medicine.
  

AHL Content Statements

• A3.1.12

  Difficulties applying the biological species concept to asexually reproducing species and to bacteria that have horizontal gene transfer

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  The biological species concept does not work well with groups of organisms that do not breed sexually or where genes can be transferred from one species to another.
  

• A3.1.13

  Chromosome number as a shared trait within a species

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  Cross-breeding between closely related species is unlikely to produce fertile offspring if parent chromosome numbers are different.
  

• A3.1.14

  Engagement with local plant or animal species to develop a dichotomous key

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  AOS: Students should engage with local plant or animal species to develop a dichotomous key.
  

• A3.1.15

  Identification of species from environmental DNA in a habitat using barcodes

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  Using barcodes and environmental DNA allows the biodiversity of habitats to be investigated rapidly.