Classification & Cladistics (HL IB Biology)

The common dogwood, Cornus sanguinea, is a broadleaved shrub of the family Cornaceae native to Europe and Western Asia. Some of the classification of the common dogwood is shown in the table below. 

Identify taxa (i)-(vii) from the table above. Note that one box has been left intentionally blank; you do not need to identify the taxon from the blank box.

Cornus canadensis and Cornus nuttallii are similar in appearance and are both found across North America.

With the exception of breeding them together, state two ways in which scientists could determine that these dogwood varieties are two separate species.

Dogwood species are identified by the use of binomial names such as Cornus canadensis and Cornus nuttallii.

State the purpose of the binomial system of naming organisms.

Specimen A and specimen B are similar species of invertebrate. 

Scientists wanted to determine whether specimen A and B are different species of invertebrate, or different forms of the same species.

In order to do this they caught large numbers of each specimen type and measured the body mass and length of each individual before calculating the means and standard deviations (SD). Their results are shown in the table below.

Explain how the standard deviation can help with the interpretation of this data.

The scientists hypothesised that the two specimens were different forms of the same invertebrate species.

Evaluate this hypothesis using the data in the table part (a).

The appearance of specimen A is shown in the image below.

 Use the dichotomous key below to deduce the order to which specimen A belongs.

Cytochrome c is a respiratory protein consisting of roughly 100 amino acids while haemoglobin is a quaternary protein found in red blood cells consisting of over 400 amino acids.

Suggest, with a reason, which of these two proteins is a better choice for use in identifying evolutionary relationships across plantae, fungi and animalia.

Explain how biochemical sequence analysis, as opposed to other methods of classification, ensures that natural classification is carried out.

Scientists studied the amino acid sequence of cytochrome c in five different animals. The amino acid sequence was compared with human cytochrome c and the number of differences to the human sequence were recorded.  The results are shown in the table below.                                                                            

State, with a reason, one conclusion that can be reached from the data in the table above about the relationship of humans to other animals.

An assistant who looked at the results in the table in part (c) suggested that dogs were more closely related to ducks than to any of the other animals.

State, with a reason, whether or not the student’s suggestion is valid.

The image below shows the classification of some animals with antlers and horns.

State the number of different orders that are present in the image above.

Compare and contrast the sciences of taxonomy and cladistics.

Deer are members of the suborder (a smaller division within an order) ruminantia, which are themselves members of the order artiodactyla. The relationships between the artiodactyla are shown on the cladogram below.  * denotes a now extinct taxon. 

Identify, with a reason, an example of the closest evolutionary relationship shown in the cladogram.

A student reading the cladogram in part (c) identified the ruminantia as a clade.

Explain why the student was incorrect in their identification of the ruminantia as a clade.

Describe the features of archaea that mean they are classified as a distinct domain in the three domains system of classification.  

Outline the reclassification of the scrophulariaceae, or figwort family.

Ailuropoda melanoleuca, the giant panda, and Ailurus fulgens, the red panda, are both native to China. They share the following similarities:

• They live in similar environments
• They both digest bamboo as a primary source of food
• They both have a pseudo-thumb (a sixth digit) used to grip and shred food such as bamboo

The following table shows the differences between a comparable sequence of mitochondrial DNA of the giant panda and the red panda.

A group of students concluded that the giant panda and the red panda are closely related.

Use the information provided to evaluate this conclusion.

After careful deliberation, the group of students decided that the giant panda and red panda were, in fact, not closely related.

Suggest an explanation for the existence of a pseudo-thumb in both species.

The base sequence of a different section of mitochondrial DNA (mtDNA) were analysed to determine the differences between giant panda and red panda DNA. In total, there were eight differences between the mtDNA of the two species.

Mitochondrial DNA is estimated to mutate at a rate of 1.87 x 10^-7 mutations site^-1 year^-1. Use the information given to calculate how long ago the giant panda and the red panda evolved from a common ancestor. Show your working and round your answer to three significant figures.

Explain the difference between a taxon and a clade.

Cetaceans is an order of carnivorous aquatic mammals which include dolphins, whales and porpoises. The following diagram shows two proposals that have been put forward regarding the closest living relative of the cetaceans, represented by diagrams R and S.

Compare and contrast the information in diagrams R and S.

Casein is a protein found in the milk of most mammals. Scientists investigated the differences in the DNA base sequence of the gene coding for casein in the mammals shown in diagrams R and S. The following table shows their results.

Scientists concluded that diagram S best represents the currently accepted theory regarding the evolutionary origin of cetacean.

Based on the information provided, evaluate this conclusion.

More recently, scientists decided to merge the order Cetacea and Artiodactyla into a single order called Cetartiodactyla based on new sequencing results.

Explain the importance of classifying organisms correctly according to their clade.

Based on the information provided in part a), deduce four other taxonomic groupings/levels of classification that would be similar for dolphins and whales.

DNA hybridisation is a technique used to determine the genetic similarity between species. The double stranded DNA of two different species is mixed and then heated until the strands separate. This provides an opportunity for hybridisation between the different DNA strands to occur. The mixture is then cooled in order to allow new hybrid double stranded DNA molecules to form. The greater the degree of hybridisation, the more genetically similar the two species are.

Scientists investigated the genetic similarity between four species of bacteria (A to D) by allowing their DNA to hybridise with each other. The results of this investigation are shown in the table below.

Identify the species of bacteria that is most closely related to the other bacterial species.

[1]

Explain your answer at part i).

[1]

Scientists concluded that species D was the first to branch off from the common ancestor that they all share.

Based on the information provided, comment on this conclusion.

The group of scientists also investigated the similarity of the protein molecules that make up peptidoglycan in the cell walls of the bacterial species. The amino acid sequence of species A was compared to those of species B to D.

The results are shown in the table below:

Based on the information provided and your knowledge of protein synthesis, explain the reason why the bacterial species show such a high level of similarity between the protein molecules, even though there are differences in their DNA.

The following diagram shows a cladogram that indicates the evolutionary relationship of plants. Note that different taxonomic groups are represented in the cladogram.

Identify the plant phyla which are the most closely related

The common names of some plant genera and species were given in this cladogram.

Using the information given in part a), explain how using the common names could cause confusion when studying this cladogram.

Gemniferous spikemoss, tooth-leaved clubmoss, spikemoss and the resurrection plant can all be considered members of the same clade.

Explain this statement.

Compare and contrast the domain Eubacteria with the domain Eukaryotes.

Constructing the evolutionary relationship between organisms based on morphology alone will not always deliver accurate results.

Outline the advancements that have been made in constructing cladograms in the field of cladistics.