A3.1 Diversity of organisms

Question 1

A3.1.2—Species as groups of organisms with shared traits

Answer 1

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

Question 1

A3.1.1—Variation between organisms as a defining feature of life

Answer 1

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.

Question 2

A3.1.3—Binomial system for naming organisms

Answer 2

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.

Question 3

A3.1.4—Biological species concept

Answer 3

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.

Question 4

A3.1.5—Difficulties distinguishing between populations and species due to divergence of noninterbreeding populations during speciation

Answer 4

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

Question 5

A3.1.6—Diversity in chromosome numbers of plant and animal species

Answer 5

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

Question 6

A3.1.7—Karyotyping and karyograms

Answer 6

Application of skills: 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.

Question 7

A3.1.8—Unity and diversity of genomes within species

Answer 7

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.

Question 8

A3.1.9—Diversity of eukaryote genomes

Answer 8

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.

Question 9

A3.1.10—Comparison of genome sizes

Answer 9

Application of skills: Students should extract information about genome size for different taxonomic
groups from a database to compare genome size to organism complexity

Question 10

A3.1.11—Current and potential future uses of whole genome sequencing

Answer 10

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

Question 11

A3.1.12—Difficulties applying the biological species concept to asexually reproducing species and to
bacteria that have horizontal gene transfer

Answer 11

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.

Question 12

A3.1.13—Chromosome number as a shared trait within a species

Answer 12

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

Question 13

A3.1.14—Engagement with local plant or animal species to develop a dichotomous key

Answer 13

Application of skills: Students should engage with local plant or animal species to develop a
dichotomous key

Question 14

A3.1.15—Identification of species from environmental DNA in a habitat using barcodes

Answer 14

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