CS计算机代考程序代写 scheme DNA flex IMPERIAL COLLEGE LONDON

IMPERIAL COLLEGE LONDON

BSc Examination 2020

This paper is also taken for the relevant examination for the Associateship of the Royal College of Science

Evolution and Diversity 2021 (Practice paper)

Noday 0th Unvember 2020 10:00 – 13:00

For first year students in Biological Sciences

Answer ALL questions from SECTION 1, the ONE data interpretation question in SECTION 2, and ONE essay question

from SECTION 3.

Use a SEPARATE answer book for each answer in sections 2 and 3. Sections are weighted at 40% (section 1), 20%

(section 2) and 40% (section 3). Unless otherwise specified, all parts of a question carry equal weighting.

SECTION 1

Attempt ALL OF THE MULTIPLE CHOICE QUESTIONS below.

Record your answers on the separate, machine-readable answer sheet provided. Make sure you complete the parts

at the top of the sheet, including your CID number in the box at top right and in the machine-readable columns

below that.

Complete the answer sheet using an HB PENCIL, following the instructions at the top of the sheet. Correct any

mistakes using the CANCEL ROW for each question. Use a clean eraser only if you wish to cancel a cancel mark.

SOME QUESTIONS IN THIS SECTION MAY HAVE MORE THAN ONE CORRECT ANSWER; SELECT ALL THAT APPLY.

Credit will be given for all correct answers, but you will be penalised with a negative mark for incorrect choices. You

will not be penalised if you do not select an answer.

MCQ questions from past exam papers have been used to construct three 10-question formative quizzes (one for

each of the main EDE themes). These quizzes can be taken as many times as you like and provide a new sample of

questions each time. Please use them too.

1. In the image below, TWO phylogenetic tree diagrams are the same topology. Which TWO are they?

A. 1
B. 2
C. 3
D. 4
E. 5

1

Mac

2. Consider the phylogenetic tree and six-character data table below.

Which TWO of the following characters are synapomorphies of C and A?

A. 1
B. 2
C. 3
D. 4
E. 5

3. Which ONE of the following statements about phylogenetics is true?

A. The term ‘clade’ means ‘paraphyletic’
B. Paraphyletic groups are united by synapomorphies
C. Polyphyletic groups are united by symplesiomorphies
D. The term ‘clade’ means ‘monophyletic’
E. Autapomorphies provide evidence of sister group relationships

4. Which ONE of the following statements is true?

A. Humans are the apex of evolutionary perfection
A. To properly classify living things, we only need three groups: land, sea, and air
B. Homology is similarity shared due to convergent evolutionary histories
C. The genealogical relationships of species are called their phylogeny
D. Homoplasy is similarity due to common evolutionary heritage

5. Which TWO of the following represent evidence for the universal common ancestry of life?

A. Fossils of ancestors to which we can trace all living things
B. Common metabolic molecules like ATP
C. A reducing environment for the earliest stages of Earth history
D. A universal genetic code
E. The presence of common organelles, such as a nucleus

6. Which ONE of the following is a type of evidence of life in the Precambrian?

A. Flowering plant fossils
B. Nektonic (‘swimming’) animals such as fishes
C. Stromatolites
D. Terrestrial arthropod tracks
E. Chalk deposits

2

7. Examine the following diagram:

In what order were the rocks laid down or formed (from first to last)? Select ONE answer.

A. E, C, B, D A
B. D, E, C, B, A
C. A, B, C, E, D
D. A, D, B, C, E
E. A, B, C, D, E

8. Xenoturbella, the enigmatic worm-like creature, has which TWO of the following features?

A. Neurons
B. A brain
C. A separate mouth and anus
D. Muscle cells
E. A gonad

9. The Ediacara fossils have been variously interpreted as which THREE of the following?

A. Diploblasts and a few triploblast animals
B. An extinct multicellular clade, the Vendobiota
C. Lichens
D. Algae
E. Metazoans with hard parts such as shells

10. Which THREE of the following do ctenophores have?

A. Radial symmetry
B. Bilateral symmetry
C. Striated muscles
D. Three germ layers
E. Nematocysts

11. Which TWO of the following broad, high-level statements about living things are accurate?

A. Most living species that have been described are animals

B. The eukaryotes are paraphyletic with respect to the prokaryotes

C. All living things (excluding viruses, etc.) contain ribosomes

D. All eukaryotes arise from a common ancestor that formed a symbiosis with a cyanobacterium

E. The earliest evidence we have of eukaryotic life is from the Cambrian period

3

12. Which major eukaryotic group can be described as: “A diverse group of mostly heterotrophic unicellular

organisms that possess mitochondria. They ancestrally lack plastids and have only rarely acquired them

secondarily. In their cell structure, they are mostly amoebae with filose (pointed) pseudopods, and some

lineages secrete small shells for themselves made of silica or calcium carbonate”. Select ONE answer.

A. Fungi

B. Brown algae

C. Excavates

D. Diatoms

E. Rhizaria

13. Which TWO of the following are true about the fungi?

A. They have one disproportionately diverse clade
B. They have left a nearly complete fossil record
C. They are widely agreed to have evolved nine million different species
D. They harbour abundant cryptic species
E. They are the dominant plant mutualists, pathogens and recyclers

14. Which ONE of the following is true of most fungi?

A. They are free-living
B. They have determinate growth, aging and senescence
C. They are aquatic flagellated unicells or yeasts
D. They have absorptive, or osmotrophic, nutrition using hydrolytic exoenzymes
E. They are strictly asexual

15. Which TWO of the following are true about filamentous fungi?

A. Unicells with flagella evolved into hyphal species that then evolved yeast unicells
B. Dimorphic species have flagellated and non-flagellated unicells
C. Budding yeasts gave rise to fission yeasts
D. Hyphae form mycelia that can form networks and may form tissues
E. Budding yeasts gave rise to unicells with flagella

16. Keeping stomata open under hot, dry conditions is (select ONE answer):

A. Good because it refills xylem cavities
B. Good because it prevents photorespiration
C. Good because it allows reactive oxygen species to escape
D. Bad because excess water is lost
E. Bad because excess O2 is lost

17. Which ONE of the following phenotypes would you expect in a mutant plant unable to synthesise the
phytochrome chromophore?

A. Absence of phototropism
B. Reduced photosynthetic electron transport
C. Highly elongated seedling hypocotyl even in light
D. Increased heat sensitivity
E. Lethality

4

18. In flowering time regulation, which ONE of the following statements correctly describes the function of the
CONSTANS (CO) gene?

A. It allows plants to detect winter cold
B. It suppresses expression of the FT flowering hormone
C. It enables synchronisation with pollinator activity
D. It is only expressed in short days
E. It allows plants to respond to photoperiod

19. Using the equations below, estimate the approximate water potential (ψ) at equilibrium for the depicted
plant cell, with total solute content of cell and bathing solution shown. Select ONE answer.

ψ = ψπ + ψP

ψπ = −CRT

where C is concentration (in molar); R is the gas constant (0.008134 MPa L K−1 mol−1); T is temperature, 298 K;

ψπ is osmotic potential; and ψP is pressure potential.

A. −1.5 MPa
B. −0.5 MPa
C. 0 MPa
D. +1.5 MPa
E. +0.5 MPa

20. Which ONE of the following structures would you expect to be missing in C-function mutant flowers?

A. Petals
B. Stamens and sepals
C. Sepals
D. Carpels and petals
E. Carpel and stamens

21. Fish live in water – do they need to drink? Select ONE answer.

A. Only marine fish do
B. Only freshwater fish do
C. Only when migrating back into rivers from the sea
D. Only during metamorphosis
E. Only in low oxygen conditions

22. The remnant of the molluscan shell found in squid is called the (select ONE answer):

A. Radula
B. Beak
C. Hectocotylus
D. Mantle
E. Pen

5

23. What is the purpose of Kohler illumination? Select ONE answer.

A. To enhance fine details by rotating the light path by 90o

B. To match the numerical aperture to the length of the ocular
C. To increase the size of the numerical aperture
D. To align and centre the illumination path
E. To properly focus the occular graticule

24. What easily observable feature distinguishes carnivores from herbivores? Select ONE answer.

A. Bifocal orbits
B. Dentition
C. Efficient metabolism
D. Nostril position
E. Neural crest

25. Which ONE of the following statements about physiological conformers and physiological regulators is true?

A. A conformer is always limited to a very narrow range of environmental conditions
B. A regulator always has complex anatomical modifications to maintain system integrity
C. Only vertebrates are regulators
D. Only animals are regulators
E. The internal conditions of a regulator are stable across a range of environmental conditions
F.

6

SECTION 2

Attempt the SINGLE DATA INTERPRETATION QUESTION below. If you make an error in the earlier parts of the

question, you can still receive credit for a correct and logical analysis in the later parts of the question.

Eight data interpretation questions from past exams have been provided on Blackboard, along with detailed

answers. This is every DI question we have ever set in ED: no more exist! Please use them too.

1. The evolutionary relationships of turtles have been one of the great mysteries in the study of amniote
phylogeny. Although we never discussed turtles specifically in the lectures, we have the tools at our disposal to
solve this conundrum! For each of the relevant parts below, you must re-draw each tree required in your exam
answer booklet.

There are four commonly debated hypotheses on the placement of turtles within amniote phylogeny. They are:

1. The sister group of all other amniotes
2. The sister group of diapsids
3. The sister group of archosaurs
4. The sister group of lepidosaurs

A. Using the phylogenetic tree above as a ‘backbone’, draw each of these four alternative hypotheses. You
must re-draw the tree in your exam answer booklet. (20%)

B. Turtle skulls have long been considered to exhibit an anapsid condition (see diagram below). Based on this
information, which of the above four hypotheses in part A would you consider most consistent with this
information? Briefly explain why. (20%)

7

C. Recently, the skull of a very early stem-group turtle, Pappochelys, was described. This skull is illustrated
below. What is anatomically significant about this skull and how might it impact your answer to part B
above? (30%)

D. The skull illustrated below belongs to an extinct reptile-like animal called Captorhinus, which has an anapsid-
type skull. This taxon is considered a stem-group amniote. Illustrate its place in the phylogenetic tree of
amniotes using the backbone tree given in part A (re-draw the tree in your exam answer booklet; you can
leave out turtles). Illustrate your reasoning by showing the relevant evidence on the tree (hint: you just need
to consider one character at this point). (10%)

E. If Pappochelys is in fact a stem-group turtle, what does this say about the evolution of the anapsid condition
in turtles? How does it relate to the skulls of “true” anapsids like Captorhinus? (20%)

8

SECTION 3

Attempt ONE essay from the choices below.

In the exam, there will be a choice of ONE ESSAY FROM FOUR OPTIONS. We provide here eight essay titles along

with the mark schemes (‘model answers’) that were approved by the external examiners, to give you a better idea of

the range of essay questions we might set.

2. Describe the evolutionary history leading to the origin of jawed vertebrates. Detail the sequence of character

acquisition using a phylogenetic tree, together with examples from living and extinct vertebrates.

3. Give an overview of the fungi, explaining their key morphological features, reproduction, nutrition, and ecology.

4. In the context of the conquest of land by plants, discuss the key innovations involved in plant terrestrialisation

and/or diversification.

5. Cephalopods retain most of the basic molluscan elements, but have diverged along paths that show similarities

to several other groups. Squid are similar to schooling fish, octopus are similar to conger/moray eels, and

cuttlefish are similar to coral reef fish. Choose one of these examples/pairs and explain the adaptations found in

the cephalopod. Are cephalopods better at being fish than fish are?

…and another four…

1. A recently published paper claims that lungfishes evolved the ability to breathe air in response to an oxygen

minimum during the Late Devonian period. Critically evaluate this scenario in light of the fact that the oldest

known sarcopterygian (lobe-finned) fish is a fossil from the late Silurian of China.

2. Are all animal eyes homologous? Give the evidence to support your answer.

3. How do plants cope with stressful environments? Compare and contrast evolutionary adaptations with

adjustments that can be made within a plant’s lifetime.

4. Counter gradient (countercurrent) systems have evolved several times in different lineages. Illustrate and discuss

what the system does and how it works by giving two examples from different lineages.

9

Answers

SECTION 1

1. AB
2. B, E
3. D
4. D
5. B, D
6. C
7. A
8. A, D
9. A, B, C
10. B, C, D
11. A, C
12. E
13. D, E
14. D
15. A, D
16. D
17. C
18. E
19. C
20. E
21. A
22. E
23. D
24. B
25. E

10

SECTION 2

1. Turtle data interpretation question

A. The correct answer should look as follows:

B. The most plausible hypothesis to explain this evidence would be to place turtles in position 1 in the
phylogenetic tree. The reasoning for this should be the absence of any (evident) temporal fenestrae (the
openings in the skull behind the eye/orbit).

C. The skull is significant in a number of ways: it possesses teeth, a laterally open nostril, but most significantly,
it appears to have two temporal fenestrae (openings on the side of the skull). Noticing this will be significant
in separating first from second-class answers! The significance lies in the fact that it doesn’t look very turtle-
like. The condition is reflective of diapsid reptiles and thus implies that hypotheses 2, 3, and 4 might, in fact,
be true.

D. The correct answer should look as follows

E. The implication of Pappochelys is that turtles may have primitively possessed two temporal openings—giving
credibility to the diapsid hypotheses of relationships (as discussed above). The consequence of this would be
that the anapsid condition of turtles is convergent or a reversal.

11

SECTION 3

First batch of four:

2. Jawed vertebrates

 2B answers will cover some of the key anatomical facts, and likely mapped on a mostly accurate

phylogenetic tree. The phylogenetic tree will be mostly a restricted view of the jawed vertebrate crown,

showing jawless fishes as successive sister taxa. However, some anatomical details might be lacking from

internal node. However, the answers may lack detail or explanation of sequential evolutionary events.

 2A answers will cover all of the key anatomical traits discussed in lectures and accurately map them on the

phylogenetic tree. A minimal taxon set in the tree will be modern cyclostomes (hagfish, lampreys) and

gnathostomes; ‘unnamed’ jawless fishes, osteostracans, and placoderms indicated as the sister group of

crown-gnathostomes.

 First class: answers will show examples of outside reading and might include examples of fossil jawless fish

groups not explicitly discussed in the lectures. Additional character traits, such as the evolution of tail

morphology might be considered. They will discuss the characters in terms of adaptive/functional value.

3. Fungi

 2B answers will explain that fungi are largely multicellular, with a mycelium composed of tubular

multinucleate hyphae. They will note that most fungi are heterotrophic and take up their nutrition from the

extracellular environment by absorption rather than phagocytosis. They will give at least one example of

their ecological importance, e.g. in recycling of wood. They will discuss spores as the main reproductive

strategy, and list some of the main clades.

 2A answers will give clear and well-chosen examples to illustrate the points noted in 2B above. They will

additionally note that most fungi are biotrophic, and many use extracellular digestive enzymes. They will

discuss the involvement of fungi in mutualistic symbioses such as mycorrhizae or lichens, and give an

account of the asexual and sexual reproductive strategies of some of the major groups.

 First class answers will additionally bring in material from the biodiversity challenge: e.g. explaining the

continuum from parasitism to mutualism, giving a good overview of the relationships of the main fungal

clades (glomeromycetes, basidiomycetes, ascomycetes, etc.) within the larger eukaryotic tree, discussing the

difference between sexual and asexual spores, describing the difference between mycelial and yeast growth

forms, etc.

12

4. Plant terrestrialisation

 2B answers will explain some of the main challenges to living on land (e.g. drought, mineral nutrition,

dispersal, fire, UV). Some of the many innovations that could be discussed include vasculature, dominant

sporophytes (diploidy as a genetic back-up for DNA repair), wind- and animal-pollination, roots, leaves,

wood, seeds, flowers and fruits.

 2A answers will explain clearly the morphological structures and functions, and be explicit about the group(s)

in which innovations arose, the evolution of the innovation (e.g. what was the ancestral condition, what

further evolution the innovation underwent, etc.)

 First class answers should compare relevant information across different groups (e.g. thallus structure in

green algae, leaves in mosses, needles in conifers, and flat leaves in angiosperms) and include outside

reading, giving examples not covered in class (e.g. pollen, mycorrhizae) and relevant complementary

information from the fossil record and molecular phylogenetics.

5. Cephalopods as fish analogues

 2B answers will list most of the adaptations and mention convergent evolution. Better than fish because of

better prey handling with arms/tentacles.

1. Eyes with lenses, retina and large optic nerves

2. Modification of feeding siphon for locomotion

3. Reduction of shell for flexibility and buoyancy

4. Nervous system control of melanophores for communication and camouflage

5. Modification of foot to arms for feeding and locomotion

6. Modification of radula to form beak

7. Modification of mantle to form bellows and fins

8. Modification of statocysts to statoliths for orientation, pressure, sound

 2A answers will list all adaptations (except probably 7 & 8), and better than fish in terms of better prey

handling with arms, eyes (no blind spot), faster and better control of colouration for camouflage and

communication.

 First class answers will list all the adaptations, or include others such as internal fertilization (modification of

arm-tip in males). May include comparison of age of groups. Better than fish: added detail about eye

structure that optic nerve does not pass through the retina as in vertebrates, lack of bony skeleton gives

advantage in buoyancy and posture flexibility. Should give some balance by e.g. pointing out the lack of

adaptation to freshwater, and the fact that the retina is metabolically highly active, so there are some

metabolic advantages of having photoreceptors ‘backwards’ even if anatomically it seems maladaptive.

13

Second batch of four:

1. Lungfish evolution

 2B answers will note that air-breathing is a general feature of bony vertebrates, and that it is the ancestral

state for both lobe-finned and ray-finned fishes. There are many examples of extant fishes that possess lungs

and breathe air. Air breathing was therefore a feature we infer was present in the last common ancestor of

all bony fishes.

 2A answers will give more technical detail and make an argument along the following lines: the oldest

representative of a crown group sets the minimum age for the clade, and the bony vertebrate crown group

is delimited by ray-finned fishes and lobe-finned vertebrates. The oldest lobe-finned fish is, ipso facto, a

crown-group bony fish. If there is a late Silurian lobe-finned fish, then the last common ancestor of bony

vertebrates must be at least as old as the late Silurian. The Silurian pre-dates the Devonian; therefore, air

breathing must be much-older than the late Devonian.

 First class answers will conclude that it seems doubtful that lungfish air-breathing was an adaptation to low

oxygen levels during the late Devonian, and may have some more to say about the problems of “Just So

Stories” in evolutionary biology.

2. Animal eye evolution

 2B answers will note that many metazoans have eyes, and that that eyes have ‘traditionally’ been thought to

have evolved independently at least 30 times, so are not homologous. They may give a confused explanation

of the material below for a 2A.

 2A answers will be clear why the eye was thought to have evolved independently: they come in many

different forms: compound eyes, lensed eyes etc. They will additionally, and clearly, explain that it has

become clear that they all share a common molecular specification machinery involving, inter alia, Pax-6, a

transcription factor.

 First class answers will carefully nuance their answer. It is clear that complex eyes have evolved many times,

but that they share a common cellular basis. It seems likely that photoreceptor cells are ancient and

homologous, and it is this that Pax-6 homologues specified in the LCA Eumetazoa. Thus it is not complex

eyes that are homologous, but their cellular components

14

3. Plant stress

 2B answers will focus on the taught material centred on plants in desert environments, emphasising that

some taxa have adapted to cope with the several stresses posed, especially drought and temperature

extremes, and high light. Coverage of principle features of xerophytes would be expected, including cacti

and similar succulents: reduced or absent leaves, low SA/V ratios, CAM, sunken stomata, dense trichomes or

silver epidermis for reflection; trichomes also extend boundary layer, reducing transpirational gradient,

drought deciduous and resurrection habits etc Higher marks for extended comparative examples indicating

OR, and for specific details of the mechanistic advantages of the adaptation

 2A answers will additionally explain that all plants will make adjustments (acclimation) to ameliorate

problems of drought, heat and high light: stomatal closure, leaf movements, osmotic adjustment,

chloroplast stacking, photoprotection (also against UV) via xanthophyll cycle, anthocyanin synthesis, etc.

Other cell processes include altered lipid unsaturation levels, heat shock proteins/chaperones etc

 First class answers may include more extensive mechanistic and molecular details, or could focus on other

stresses e.g. cold, salinity, nutrient starvation, heavy metals, atmospheric pollutants from outside reading.

Comparison between water stress and salinity stress would be insightful, as they share some mechanisms.

4. Counter gradient systems

 2B answers will explain that in a counter-current system flows run side-by-side, but in opposite directions,

compared to concurrent where parallel flows run in the same direction. A counter-current system maximizes

the diffusion gradient from one flow to the other and uptake or exchange is optimized. Classic examples are

fish gills (O2 in, CO2 out), penguin feet (reduce heat loss), mammalian kidney (countercurrent multiplier,

reduced water loss), nostrils/nares (reduce water & heat loss).

 2A answers will give detailed descriptions of two different systems, including the structure of system, e.g.

flows running in opposite directions with thin layers between (between capillary walls / between blood

vessel, gill epithelium, and water / etc); the increased efficiency of exchange because of increased distance

over which a diffusion gradient exists. Examples must be from different groups. If giving an example for

thermoregulation or reduced heat loss, this must include the term rete mirabile. If bird lungs are included,

this is a cross-current flow, but is acceptable if this terminology is mentioned and explained.

 First class answers may demonstrate analysis through e.g. including additional material on bird lung to

explain advantages/differences between cross-current vs countercurrent and why this is even more efficient

for gas exchange; however, a simple description of bird respiration is off topic.

15

Answers