Evolution (Edexcel A (SNAB) A Level Biology)

The image below shows a series of fossils in varying states of completeness.  
Eusthenopteron is an extinct genus of fish while Ichthyostega is an extinct genus of partially aquatic tetrapod (four-legged vertebrates). 

Compare and contrast the fossil Ichthyostega with Acanthostega.

Use the information in the diagram at part (a) to explain how these fossils provide evidence for the process of evolution.

The theory of evolution by natural selection is widely accepted by the modern scientific community due to several different sources of evidence that support it.

Other than the fossil record, state two sources that provide evidence for evolution.

Scientists collected specimens of Southern cave crayfish (Orconectes australis - pictured below) living in different parts of a system of caves.

Some of the specimens were collected close by the mouth of the cave, while others were taken from parts that were deeper in the cave system.

They measured the diameter of the eyes of each crayfish, as well as the length of the antennae. From these measurements, they calculated the mean values for each site.

Their results are shown in the table below.

An article that the scientists studied during a literature review suggested that cave dwelling crayfish living deeper in cave systems had smaller eyes to decrease their energy expenditure and longer antennae to better explore their environment for food and predators, compared to their counterparts living close to the mouth of caves.

Use the data in the table to evaluate this suggestion.

Calculate the percentage decrease in the mean eye diameter between the crayfish living close to the cave mouth and those living deeper in the cave system.

The scientists predict that over time the different populations of crayfish in the cave system may form different species.i)

Which of the following events must occur for this to happen? 

1. There must be a geographical barrier that form between the different populations
2. The phenotypes of the individuals in both populations must change
3. There must be no gene flow between the populations

Before publishing the research done by the scientists on the Southern cave crayfish, it was peer reviewed by a panel of experts.

Explain the importance of the peer review process in the scientific community.

The Cape dwarf chameleon (Bradypodion pumilum) is a species of chameleon that is endemic to the southwestern Cape region of South Africa. They are mainly found in the typical fynbos and renosterveld vegetation of the area which are characterised by woody shrubs and reeds, but have experienced significant habitat loss due to urbanisation. They have been shown to be partially adaptable to this by establishing themselves within gardens, overgrowth along the roadside or undeveloped urban areas.

Explain how urbanisation could result in speciation within a population of Cape dwarf chameleons over time.

Male Cape dwarf chameleons are not usually territorial, but regular confrontations between males may escalate and result in fighting on occasion. Studies have shown that males with larger casques and pink flank patches were more successful during fights. 

The diagram below shows an image of a Cape dwarf chameleon.

Vegetation was removed from part of a garden where a population of chameleons lived. This decrease in habitat size led to more confrontations between the male chameleons.

Predict what may happen to the size of the casque and pink flank patch in the male chameleons of this population over time.

(1)

Explain your answer from part (i).

(2)

Which of the following provides the most accurate description of natural selection? 

Mutations are an important source of variation that enables natural selection to occur.

Explain how a mutation could lead to a change in a characteristic of an organism.

Explain the importance of heritable variation in evolution.

Research was carried out on beak size in the island-living finch species Geospiza fortis.

G. fortis feeds on seeds, which are plentiful, small, and soft in the years when the weather is normal, but the seeds become larger and tougher in drought years. Some of the research results are shown in the graph below.

Which of the following statements explains the results in the graph? 

Compare and contrast allopatric and sympatric speciation.