4.5 Species and Taxonomy

Question 1

What is a species?

Answer 1

A group of organisms that can (interbreed to) produce fertile offspring

Question 2

Suggest why 2 different species are unable to produce fertile offspring

Answer 2

● Different species have different chromosome numbers → offspring may have odd chromosome number
● So homologous pairs cannot form → meiosis cannot occur to produce gametes

Question 3

Explain why courtship behaviour is a necessary precursor to successful
mating

Answer 3

● Allows recognition of members of same species → so fertile offspring produced
● Allows recognition / attraction of opposite sex
● Stimulates / synchronises mating / production / release of gametes
● Indicates sexual maturity / fertility
● Establishes a pair bond to raise young

Question 4

Describe a phylogenetic classification system

Answer 4

● Species (attempted to be) arranged into groups, called taxa, based
on their evolutionary origins (common ancestors) and relationships
● Uses a hierarchy:
○ Smaller groups are placed within larger groups
○ No overlap between groups

Question 5

Name the taxa in the hierarchy of classification

Answer 5

1. Domain (largest / broadest)
2. Kingdom
3. Phylum
4. Class
5. Order
6. Family
7. Genus
8. Species (smallest)

Question 6

How is each species universally identified?

Answer 6

A binomial consisting of the name of its genus and species, eg. Homo sapiens

Question 7

Suggest an advantage of binomial naming

Answer 7

Universal so no confusion as many organisms have more than one common name

Question 8

How can phylogenetic trees be interpreted?

Answer 8

● Branch point = common ancestor
● Branch = evolutionary path
● If two species have a more recent common
ancestor, they are more closely related (eg. C & D)

Question 9

Describe two advances that have helped to clarify evolutionary
relationships between organisms

Answer 9

1. Advances in genome
   sequencing → allowing
   comparison of DNA
   base sequences

● More differences in DNA base sequences → more distantly related /
earlier common ancestor
● As mutations (change in DNA base sequences) build up over time

2. Advances in
   immunology → allowing
   comparison of protein
   tertiary structure (eg.
   albumin)

● Higher amount of protein from one species binds to antibody against
the same protein from another species → more closely related / more
recent common ancestor
● As indicates a similar amino acid sequence and tertiary structure
● So less time for mutations to build up