Evolution & Speciation (HL IB Biology)

The apple maggot fly (Rhagoletis pomonella) is a species of fruit fly that lays eggs on apples. As a result of this they are often found in apple orchards, where they can cause damage to apple yields.

Scientists studied two populations of apple maggot flies from orchards that were separated by a busy road. They found that flies from the two populations were unable to interbreed when they were kept together in the same container.

Suggest a reason for this observation.

The size of one of the orchards that was studied by the scientists had been systematically reduced by the farmer to make way for grazing cattle. The table below shows the size of the apple orchard and the estimated population of apple maggot flies over time.

Calculate the percentage decrease in the population of apple maggot flies from 1995 to 2015.

The scientists estimated the apple maggot fly population size in part b) by sampling four trees from five randomly selected areas of the orchard between May and July. They concluded that the reduction in orchard size caused a significant decrease in apple maggot flies between 1995 and 2015.

Using the data from part b) and your own knowledge, evaluate the scientist's conclusion.

Wisdom teeth are thought to serve very little purpose in modern humans. These teeth are third molars that human ancestors (such as Homo habilis) used to grind down large volumes of raw plant material. These early humans had larger jaws that could accommodate a third pair of molars.

The diagram below compares the lower jaw of Homo habilis and Homo sapiens according to scale.

Suggest why modern humans still have wisdom teeth.

Wisdom teeth can cause a range of oral health problems, including gum infections, damage to other teeth and problems with eating due to teeth being pushed out of position as wisdom teeth grow. Some scientists believe that this may affect their persistence in future generations.

The graph below shows ploidy levels of 1 719 plant species that were studied in different regions of Svalbard in Norway, ranging from warmer forested regions to the northern Arctic desert.

Describe the results shown in the graph.

The scientists concluded from this study that polyploidy was more common in species of plants adapted for extreme cold environments because it helps to "buffer against inbreeding". 

Suggest why inbreeding is so common with these groups of plants

[1]

(ii)

Explain how polyploidy could buffer the effects of inbreeding

[2]

The Pyrenean desman (Galemys pyrenaicus) is a small, semi-aquatic, globally threatened mammal related to moles and shrews. It lives in the Pyrenees, a mountain range between France and Spain, and can be seen in the image below.

Suggest two adaptive features of the Pyrenean desman.

The scientists found that there were two populations of desman living in the Pyrenees; a northern and southern population. Analysis showed that there was variation between the two populations. Some of the variation could be accounted for by environmental factors such as food availability, but some could not.

Outline a source of variation other than environmental factors.

During a study that lasted many years, scientists found that the number of desman travelling from the northern population to the southern side of the mountain range was extremely low. The scientists suspect that the original desman species may have split into two different species.

Explain how the original desman species may have split into two separate species.

Explain the importance of heritable variation in evolution.

Researchers collected fish from a water source inside a cave and from the same water source in the open air.

They measured the diameter of the eyes of each fish as well as the length of its body. From these measurements they calculated the mean values for each site. Their results are shown in the table below.

An article published by a researcher several years before this study suggested that animals living in caves had similar adaptations; smaller eyes and a smaller body for decreased energy expenditure.

Evaluate this suggestion in the light of the data in the table above. 

The researcher decided to continue their investigation and calculate the genetic diversity of the fish. Their results are shown in the table below.

State, with a reason, what can be concluded about the genetic diversity of fish in the open air in comparison to fish in the cave.

The percentage of fish with allele C in the open is different from the percentage of fish with allele C in the cave. Suggest a reason for this difference.

Suggest how the researcher could find out if the fish living in the open are still the same species as those living in the cave.

Explain how polyploidy can lead to the formation of new plant species.