Exam-style Questions

Question 1

Explain the evidence that led to the 3-domain model of classification, replacing the 5-kingdom model

Answer 1

Using techniques such as molecular phylogeny, both similarities and differences were found between archaea and bacteria. Such as, both have 70S ribosomes, but bacteria have a peptidoglycan cell wall, whilst archaea don’t.

Question 2

Give a method that a scientist, with a new theory based upon experimental results, could use to share with others in the scientific community

Answer 2

scientific conference

Question 3

Explain why gel electrophoresis produces individual DNA profiles

Answer 3

because of the differences in each individual’s DNA, fragments of different lengths are produced. Under UV light, the different lengths of DNA are separated out

Question 4

Give 2 reasons why scientists used to classify African elephants as a single species

Answer 4

• both species have a similar appearance
• were not able to observe if they could breed together to produce fertile offspring

Question 5

Explain why fragments of DNA can be separated by gel electrophoresis

Answer 5

The DNA fragments are negatively charged due to their phosphate group. So, the DNA fragments move towards the positive electrode when a current is applied. The smaller fragments move faster and further than larger fragments

Question 6

Describe the information scientists can use to classify an organism as a new species

Answer 6

• compare physical features
• observe their behaviour and their ecological niches in an ecosystem
• use gel electrophoresis or DNA profiling
• if they produce infertile offspring when they are bred with another species

Question 7

Explain why it may be difficult to classify a newly discovered organism as a separate species

Answer 7

• they may interbreed to produce fertile offspring
• there may be variation within the species, e.g. sexual dimorphism

Question 8

Describe how scientists can use gel electrophoresis to show that these plants belong to the same species

Answer 8

Obtain the DNA from the 2 different plants. Use restriction enzymes to cut the DNA into smaller fragments. The DNA fragments are then placed in a gel, and a current is applied through it, separating the different DNA fragment by length. Identical patterns show that they are from the same species

Question 9

Describe evidence, other than the gel electrophoresis of DNA, that a scientist could use to establish the evolutionary relationships between species

Answer 9

by using information about similar physical features and molecular phylogeny. By using information about the fertility systems, such as mating behaviour, and looking at information about which ecological niches the species occupy in an ecosystem

Question 10

Which organism causes the symptoms of malaria

Answer 10

Plasmodium Falciparum

Question 11

Which molecules are separated using gel electrophoresis when classifying organisms

Answer 11

DNA

Question 12

The ‘Priscoculex burmanicus’ mosquito species became extinct about 100 million years ago.
State why it was difficult for scientists to decide if this insect belonged to a different species from modern mosquitos

Answer 12

Because they are all dead, scientists can’t breed them together with modern mosquitos to see if they produce fertile offspring

Question 13

Protein molecules in the solution do not separate as easily as DNA fragments.
Explain how protein molecules in the solution must be treated so that they can be separated by gel electrophoresis

Answer 13

The proteins must be digested by digestive enzymes, so that they become smaller lengthed fragments. A buffer is needed to prevent changes in pH, to avoid denaturing the digestive enzymes

Question 14

Stat what the thickness of the bands in gel electrophoresis indicates FOR PROTEINS

Answer 14

a difference in amount of protein

Question 15

Suggest how DNA profiles are compared

Answer 15

• compare size of the bands
• compare total number of bands
• compare position of bands

Question 16

Explain how organisms can be classified into taxonomy groups

Answer 16

• by comparing their physical features
• organisms with common features are placed in the same group

Question 17

Describe how the scientific community would have evaluated Woese’s theory.

Answer 17

doing peer review, by repeating his experiments to validate his data

Question 18

Woese suggested that organisms could be placed in taxonomic groups, based on molecular phylogeny. Explain what is meant by his statement

Answer 18

• organisms with common features are placed in the same group
• all taxonomic groups are different
• phylogeny means the detection of shared evolution between two groups of organisms. It is based on DNA evidence

Question 19

Chiffchaffs and willow warblers are often found at the same time in the same woodlands, they do not interbreed.
Suggest reasons why the two species do not interbreed

Answer 19

• they have different mating calls
• reproductive isolation
• breed at different times of the year

Question 20

Chiffchaffs and willow warblers are often found at the same time in the same woodlands. Records show little change in their appearance during the last two hundred years.
Suggest why the rate of change in the appearance of these two species is relatively slow

Answer 20

• they live in the same habitat, so live in the same environmental conditions. Thus, have the same selective pressures
• there may be little change in the environment, so the gene pools stay stable

Question 21

Explain what is meant by the sentence ‘Once his scientific paper was published in a journal, this allowed critical evaluation of his data by the scientific community’

Answer 21

• scientists repeat the experiments to test the scientists results, and checking if they are reliable or not