Relationships Genetic Comparison

Transcription

1 Relationships Genetic Comparison May minutes 73 marks Page of 5

2 Q. Hummingbirds belong to the order Apodiformes. One genus in this order is Topaza. (a) (i) Name one other taxonomic group to which all members of the Apodiformes belong... () Name the taxonomic group between order and genus... () The crimson topaz and the fiery topaz are hummingbirds. Biologists investigated whether the crimson topaz and the fiery topaz are different species of hummingbird, or different forms of the same species. They caught large numbers of each type of hummingbird. For each bird they recorded its sex recorded its mass recorded the colour of its throat feathers took a sample of a blood protein. The table shows some of their results. Crimson topaz Fiery topaz Male Female Male Female Mean mass / g (± standard deviation) 3.6 (±.9) 0.8 (±.3) 4. (±.6).6 (±0.63) Colour of throat feathers Green Grey edges Yellowish green No grey edges (i) Explain how the standard deviation helps in the interpretation of these data Page of 5

3 In hummingbirds throat colour is important in courtship. Explain the evidence in the table that shows that the crimson topaz and the fiery topaz may be different species of hummingbird The biologists analysed the amino acid sequences of the blood protein samples from these hummingbirds. Explain how these sequences could provide evidence as to whether the crimson topaz and the fiery topaz are different species (Total 8 marks) Q. (a) An order is a taxonomic group. Fruit flies and mosquitoes belong to the same order of insects. Name the other three taxonomic groups to which fruit flies and mosquitoes both belong Page 3 of 5

4 The diagram shows the phylogenetic relationship between five species of fruit fly that belong to the genus Drosophila. (i) Explain what is meant by a phylogenetic relationship. () How many million years ago did D. melanogaster and D. pseudoobscura last share a common ancestor? () Scientists used DNA hybridisation to confirm the relationship between D. mauritania, D. sechellia and D. yakuba. (i) They made samples of hybrid DNA using a gene that was found in all three species. Explain why it was important that they made samples of hybrid DNA from the same gene. Page 4 of 5

5 The hybrid DNA formed between D. mauritania and D. sechellia separated at a higher temperature than the hybrid DNA formed between D. mauritania and D. yakuba. Explain what caused the DNA to separate at a higher temperature. (Total 8 marks) Q3. (a) Explain the principles which biologists use to classify organisms into groups (3) Page 5 of 5

6 Cytochrome c is a protein with about 00 amino acids and is present in all eukaryotic organisms. It has the same three-dimensional shape in all species, but only 30 of the amino acids are the same in all species. The amino acid sequence of cytochrome c has been used to construct the phylogenetic tree shown below. Name the kingdoms represented in this phylogenetic tree.... () What does the phylogenetic tree show about the evolutionary relationship between fungi and insects? Page 6 of 5

7 (d) Suggest how information on amino acid sequences is used to construct a phylogenetic tree (e) Suggest one advantage and one disadvantage of using cytochrome c to construct a phylogenetic tree. Advantage Disadvantage (Total 0 marks) Page 7 of 5

8 Q4. Cytochrome c is a protein found in all eukaryotes. In humans it consists of 0 amino acids. Biologists have compared the amino acid sequence in some other species with that in humans. The table shows amino acids 9 to 3 in the amino acid sequences of cytochrome c from four species. Amino acid in this position in cytochrome c Species Human Ile Phe Ile Met Lys Chicken Ile Phe Val Gln Lys Dogfish Val Phe Val Gln Lys Chimpanzee Ile Phe Ile Met Lys (a) What do the results suggest about the relationship between humans and the other three species? Suggest one advantage of using cytochrome c to determine relationships between species () Comparing the base sequence of a gene provides more information than comparing the amino acid sequence for which the gene codes. Explain why (Total 5 marks) Page 8 of 5

9 Q5. (a) The cheetah, Acinonyx jubatus, and other cat species belong to the family Felidae. Complete the table to show the classification of the cheetah. Kingdom Animalia Chordata Mammalia Carnivora Family Felidae Genus This system of classification is described as hierarchical. Explain what is meant by a hierarchical classification () Despite differences in form, leopards, tigers and lions are classified as different species of the same genus. Cheetahs, although similar in form to leopards, are classified in a different genus. (i) Describe one way by which different species may be distinguished. () Suggest two other sources of evidence which scientists may have used to classify cheetahs and leopards in different genera (Total 6 marks) Page 9 of 5

10 Q6. (a) Class, family, genus and kingdom are terms used in classifying organisms. Write the terms in the correct sequence. Largest number of species Smallest number of species () Cytochrome c is a protein. The table shows the sequence of the last six amino acids in cytochrome c in humans and three other animals. Animal Human Sequence of amino acids in cytochrome c lys ile phe ile met lys lys th rphe va lglu lys lys ile phe ile met lys lys ile phe val glu lys The three other animals are a monkey, a fish and a horse. One of the three is in the same order as humans. Two are in the same class. (i) Complete the table to show the animal from which each sample of cytochrome c was taken. Explain your answer. () () DNA hybridisation shows similarities between DNA samples. Explain why (3) (Total 6 marks) Page 0 of 5

11 Q7. Read the following passage. Soon a single drop of blood might be enough to reveal, at a very early stage, if a patient has cancer. It could also tell us what type of cancer it is and whether it is treatable. Fragments of DNA from body cells are present in blood plasma. Some of these fragments may be from cancer cells. The fragments can be detected by a new test in which a test strip containing 5 nucleic acid binds to sections of altered DNA. Other cancer-detecting techniques involve removing a tissue sample from a patient. The tissue sample is used to obtain mrna. By examining the mrna, scientists can discover whether cancer is present. Use information from the passage and your own knowledge to answer the questions. (a) Describe how altered DNA may lead to cancer (6) Explain why fragments of DNA from cancer cells may be present in blood plasma (lines 3-4) Page of 5

12 Explain why the nucleic acid on the test strip will only bind to altered DNA (lines 4-5) (d) This test strip will allow cancers to be detected at a very early stage. Explain why cancer is more likely to be treated successfully if the disease is detected at a very early stage (e) Explain how examining mrna (line 7) enables scientists to discover whether cancer is present (3) (Total 5 marks) Page of 5

13 Q8. (a) A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange (6) Mackerel live in the surface waters of the sea. Toadfish live on the seabed in deep water. The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why Page 3 of 5

14 The graph shows oxygen dissociation curves for toadfish haemoglobin and for mackerel haemoglobin. Explain how the shape of the curve for toadfish haemoglobin is related to where the toadfish is normally found Page 4 of 5

15 (d) Scientists analysed the sequence of amino acids in one polypeptide chain in the haemoglobin of four different species of ape. The only difference they found affected the amino acids at three positions in the polypeptide chain. Their results are shown in the table. The letters are abbreviations for particular amino acids. Species Position 87 Position 04 Position 5 Chimpanzee T R P Bonobo T R P Gorilla T K P Orang utan K R Q (i) What information do the data in the table suggest about the relationships between the chimpanzee, the bonobo and the gorilla? Explain your answer. Hybrid DNA was made from the gene for chimpanzee haemoglobin and the genes for the haemoglobin of the other three species of ape. Which of the three samples of hybrid DNA would separate into two strands at the lowest temperature? Explain your answer. (3) (Total 5 marks) Page 5 of 5

16 M. (a) (i) Kingdom / phylum / class; Accept Animalia / animal kingdom / Chordata / Chordates / Aves Allow phonetic spelling Family; (i). Shows the spread of the data / how data varies;. Reject range. Accept varies from the mean. Overlap = no difference / due to chance / not significant;. Allow converse 3. Low SD means results more reliable / repeatable; 3. Ignore accurate / valid max. Different colour / different feathers / different throat;. Birds don t mate / pair bond with / recognise other species;. Reference to courtship alone is not sufficient. Different species would have different amino acid sequences; Accept more closely related = more similar sequence. Amino acid sequence is the result of DNA / alleles / base sequence; References to incorrect statements about coding negates second mark [8] M. (a) Kingdom, phylum and class;; Lose mark for each error (i.e. omission or incorrect response). Sequence not essential. (i) Shows evolutionary relationship; 6; (i). Base sequence will be similar/some bases in common;. These bases will bind together/hydrogen bonds/complementary pairs; Do not accept same here. Accept converse providing that it is clear that the converse argument is being made. Page 6 of 5

17 . Relationship is closer/more complementary bases/more base pairs;. More hydrogen bonds; 3. More heat energy needed (to separate bonds); Do not allow stronger hydrogen bonds. Not higher temperature as this is in question. max [8] M3. (a) large groups are divided into smaller groups; (not just hierarchical ) members of a group have features in common; based on anatomy/fossils/embryology/dna/specific aspect of cell biology /homologous structures;; (any two for marks) reflects evolutionary history; 3 max fungi and animals; (insects and fungi) have common ancestor; they diverged a long time ago / before others referred to in phylogenetic tree; (d) those with similar sequences put in same groups/ are more closely related; the greater difference in amino acid sequence the longer ago the groups diverged; (e) A - present in all (eukaryotic) species or organisms / quantifiable; D - extinct species not considered/no timing of events available /only limited number of amino acid sequences /can t include prokaryotic species [0] M4. (a) Most closely (related) to chimpanzee/most recent common ancestor; Least (related) to dogfish/least recent common ancestor; Allow chicken is second to chimpanzee as equivalent to second mark point. Allow answers which compare similarity in DNA/genetic material. Marks should not be awarded for answers which only compare amino acid sequences without any indication of relationships. Allow monkey for chimpanzee and fish for dogfish Page 7 of 5

18 Is present in all eukaryotes; Reference to base triplet/triplet code/more bases than amino acids/longer base sequence than amino acid sequence; Introns/non-coding DNA; Same amino acid may be coded for/dna code is degenerate; Different (base) triplets code for same amino acid = marks Reject different amino acids are formed/produced. Ignore reference to codon. max [5] M5. (a) phylum, class, order; species, Acinonyx jubatus; larger groups containing smaller groups; (i) do not interbreed to produce fertile offspring / different DNA / different niches; fossil record; evolutionary history/phylogeny; biochemical differences e.g. DNA/proteins/cytochromes; homologous features / named feature; karyotype / number and form of chromosomes; (discount any example credited in (i)) [6] M6. (a) Kingdom, class, family, genus; (i) (Human) Fish Rhesus monkey Horse; As aminals closely related, more amino acids in sequence; Page 8 of 5

19 The more similar the DNA, the more similar the base sequences; The greater the number of hydrogen bonds/bonds between base pairs; More energy/heat needed to separate strands; Q Correct terminology of base, base pair and hydrogen bond must be used as specified in scheme. 3 [6] M7. (a) (DNA altered by) mutation; (mutation) changes base sequence; 3 of gene controlling cell growth / oncogene / that monitors cell division; 4 of tumour suppressor gene; 5 change protein structure / non-functional protein / protein not formed; 6 (tumour suppressor genes) produce proteins that inhibit cell division; 7 mitosis; 8 uncontrolled / rapid / abnormal (cell division); 9 malignant tumour; max 6 cancer cells die / break open; releasing DNA; normal DNA and changed DNA have different sequences; DNA only binds to complementary sequence; (d) fewer abnormal / cancerous cells / smaller tumours; less cell damage; less spread / fewer locations to treat; max (e) mrna base sequence has changed; gene / DNA structure is different / has mutated; cancer gene active / tumour suppressor gene inactive; 3 [5] Page 9 of 5

20 M8. (a) Large surface area provided by lamellae/filaments; Q Candidates are required to refer to lamellae or filaments. Do not penalise for confusion between two Increases diffusion/makes diffusion efficient; 3 Thin epithelium/distance between water and blood; 4 Water and blood flow in opposite directions/countercurrent; 5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached; 5 Not enough to say gives steep concentration gradient 6 As water always next to blood with lower concentration of oxygen; 7 Circulation replaces blood saturated with oxygen; 8 Ventilation replaces water (as oxygen removed); 6-8 Accept answers relating to carbon dioxide 6 max Mixing of air and water (at surface); Air has higher concentration of oxygen than water; Diffusion into water; Plants/seaweeds near surface/in light; Produce oxygen by photosynthesis; max Not much oxygen near sea bed; Toadfish haemoglobin (nearly) saturated/loads readily at /has higher affinity for oxygen at low partial pressure (of oxygen); (d) (i) The chimpanzee and the bonobo are more closely related (than to the gorilla); They have identical amino acids/one of the amino acids is different in the gorilla; (Chimpanzee) orang-utan; Amino acids different so bases different; Few hydrogen bonds; 3 [5] Page 0 of 5

21 E. (a) (i) Almost all students gained this mark. Again, almost all gained this mark, with many writing a mnemonic of one form or another in the margin. (i) Most students gained the first mark for a simple definition of standard deviation in terms of the spread of the data. A few failed to gain the mark by using the word range as an alternative to spread. The interpretation of standard deviation in terms of overlap was less well understood, and very few students suggested that a low standard deviation was related to closely grouped and therefore reliable data. This question was mostly answered successfully. However some students used up all the space describing the differences in colours, and did not link the different colours of the two types of hummingbird to successful mating or to species recognition. They referred only to courtship which, as the term appeared in the stem, did not gain credit. The majority of low marks gained in this question resulted from students failing to respond to the question these sequences (i.e. the amino acid sequences) could provide evidence and going on to describe how different DNA base sequences would give different proteins. Although students seemed to appreciate that different species have different amino acid sequences in the same protein, few could link this to differences in the DNA base sequence. Students seemed unclear about the relationships between the DNA base sequences and the amino acid sequence, and the use of incorrect terminology made their answers even more opaque. E. (a) The majority of candidates gained full credit here, although it was not uncommon, to see references to genera and species. In spite of the example given some candidates suggested other organisms that might be considered as insects or attempted to identify the taxa concerned. Candidates who explained a phylogenetic relationship in terms of evolution gained credit for part (i). The answers to part suggested that many candidates were able to interpret the diagram successfully. Much misunderstanding was in evidence in the answers to part (i). Only the better candidates appeared to understand the underlying principle. Using the same gene from each of the three species would mean that there would be a similarity between the base sequences which would allow the formation of hydrogen bonds. Most candidates appeared of the opinion that bases sequences would be identical. Part was answered rather better. E3. (a) Often not well done and answers were generally poorly expressed. Many candidates did not answer the question set and just described the classification system involving Kingdom, Phylum, etc. or gave the definition of a species. Often there was no mention of putting organisms into groups with similar characteristics. Those who did mention characteristics often did not mention the standard methods and chose any characteristic which could be different such as method of feeding. References to cell or anatomical differences were often vague. Page of 5

22 (d) (e) About half the candidates gave the correct two answers. Many candidates just listed the groups at the top of the tree and many included Protoctists in their answer. Most candidates stated that fungi and insects had a common ancestor, but only a few were able to give a full answer. Many stated that insects had evolved from fungi, or were closely related. There were many unclear answers which used poor language. Although many put organisms with similar sequences in the same branch, they did not develop their answer any further. There were many references to protein or DNA structure instead of amino acid sequences. This was often poorly answered, although many scored the marks relating to eukaryotes/prokaryotes. E4. (a) Most candidates obtained at least one mark for stating that humans are most closely related to chimpanzees. Approximately half the candidates also gained the second marking point by indicating that humans are least closely related to dogfish. Many candidates used the stem of the question to state correctly that cytochrome is found in all eukaryotes. Incorrect responses usually referred to cytochrome being present in all species. Many candidates did refer to the base triplet code and gained a single mark point. Better candidates referred to introns or to different base triplets coding for the same amino acid. However, a significant number of candidates failed to gain any marks, often describing a base triplet as a gene. E5. Although only a few candidates obtained maximum marks on this question, most candidates were able to gain between two and four marks. (a) Most candidates correctly filled in phylum, class and order, however, weaker candidates often put common names such as cat or cheetah in the species box. Approximately half the candidates gained this mark. Most candidates who did not, either provided definitions which were too vague or referred to different sizes of organisms. (i) Most candidates obtained this mark by referring to the breeding of organisms to produce fertile offspring. Very few candidates gained two marks with the majority simply referring to different diets, colours or behaviour. Correct answers usually referred to fossils, evolutionary history or biochemical differences. Page of 5

23 E7. (a) Many candidates gave a good account of the changes a mutation could produce and those with clear expression achieved full marks; many scored three or four marks. Uncontrolled cell division and malignant tumors were frequently referred to and some appreciated that genes which controlled cell division could have changed. References to benign tumours or cell mutations were irrelevant in the context of this question. (d) (e) Very few candidates achieved marks here, mainly because they did not read the question. Whole cells in the blood were not required, but the understanding that cancer cells could burst or die and release their DNA was. Few seemed to understand this and restated the question without reference to the changed base sequences to which the strip would bind. This was generally well known. The main reason for failing to gain marks was a reference to an undefined it which would be growing, dividing or spreading, causing undefined damage. Here too some candidates who understood the problem found it hard to explain that changes in the mrna would reflect mutations in the DNA and would show that a cancer gene was active. E8. (a) Candidates showed a good understanding of the adaptations of gills for efficient gas exchange. Although there were some who wrote in very general terms about gills, most candidates linked surface area to the possession of gill filaments or lamellae and to diffusion. The principle of counter-current flow was frequently mentioned and it was clear that most candidates had an excellent understanding of this concept. Some illustrated their answers with diagrams and these were occasionally very helpful. Candidates should be aware, however, that marks can only be awarded for diagrams that are properly labelled. There were numerous sketches on which were written figures that might have represented anything. Some points were made less frequently or less convincingly. There was relatively little mention of the roles of ventilation and circulation in maintaining the concentration gradient and many struggled to describe the short diffusion path in sufficient detail to gain credit. There were also a number of frequent misconceptions. These included references to air passing over the gills; to diffusion only being able to take place in water, and to the presence of carbon dioxide being essential for the diffusion of oxygen. Successful responses to this part of the question usually referred to photosynthesis or to the diffusion of oxygen from the higher concentration in the air. There were many answers, however, that involved fanciful ideas about generation of oxygen at depth and this bubbling to the surface, or incorporated the concept of need, such as that there was less oxygen at depth because the toadfish did not need it. This answer illustrated a common failing among less able candidates in answering questions that involve application of knowledge. They were often inclined to rely on recall and, while most were able to indicate that the toadfish environment was low in oxygen, they not infrequently related this to high altitude. There was also a tendency to give answers that were too brief, omitting reference to the context of low partial pressure when describing the high affinity of toadfish haemoglobin for oxygen. Page 3 of 5

24 (d) Answers to part (i) tended to fall into two categories. Either candidates gave very good answers that made the points in the mark scheme succinctly, or they wrote at length about the three organisms without ever quite answering the question. However, it was encouraging to see many excellent answers to a question set in a context which is new to the specification. Part discriminated effectively across the full mark range. Where a single mark was obtained, it usually came from the correct identification of the hybrid DNA from the chimpanzee and the orang-utan separating at the lowest temperature. Some candidates then unfortunately suggested that weaker rather than fewer hydrogen bonds were formed. It was only in the best answers that differences in amino acid sequence were successfully linked to differences in base sequence. Page 4 of 5

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