BA, BSc, and MSc Degree Examinations

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1 Examination Candidate Number: Desk Number: BA, BSc, and MSc Degree Examinations Department : BIOLOGY Title of Exam: Animal and Plant Biology Part I Time Allowed: 1 hour and 30 minutes Marking Scheme: Total marks available for this paper: 50 Instructions: Answer all ques ons in the spaces provided on the examina on paper The marks available for each ques on are indicated on the paper For marker use only: Office use only: Total as % DO NOT WRITE ON THIS BOOKLET BEFORE THE EXAM BEGINS DO NOT TURN OVER THIS PAGE UNTIL INSTRUCTED TO DO SO BY AN INVIGILATOR page 1 of 9

2 Answer all questions in the spaces provided 1. a) What was Darwin s abominable mystery? (1 mark) Darwin was apparently baffled by what he thought was the rapid diversification and evolution of angiosperms / flowering plants NB Students have been warned with a couple of learning outcomes: 1) Define and explain Darwin s abominable mystery AND 2) Evaluate the evidence and different theories that might explain the abominable mystery. A will be is very easy to remember. B and C are the important questions. No further marks for a What was this is recall and the bottom of Bloom s taxonomy; more credit for knowledgeable answers that apply, or arguably, evaluate evidence. These are a couple more rungs up the taxonomy. b) Describe a piece of scientific evidence that could help explain the abominable mystery. (2 marks) Several possible answers 1) Evidence that dramatic increases in the numbers of both insects and flowering plants have been determined from the fossil record 2) An ancient genome duplication predated the early angiosperm lineage (Amborella) 3) Evidence from models that predict that due to the density of veins in the leaves of angiosperms allows more water for photosynthesis, and more nutrients, compared to non-flowering plants c) Provide an alternative view that does not support this evidence as an explanation. (3 marks) 1) Angiosperms were probably already diverse before they evolved flowers that attracted insects 2) Although proteins have been identified that interact to pattern flowers in the earliest know angiosperms, this doesn t explain fully the diversity in form and function in flowers. 3) Although angiosperms might be more efficient than gymnosperms, needles in conifers, for example, have a much greater surface area than most angiosperms MLO: Describe the major events in the evolutionary history of plants and animals with an appreciation of the characteristics of major animal and page 2 of 9

3 plant phyla. 2. Describe a pollination strategy and explain why it promotes outbreeding. Marks are not awarded for naming a specific plant, although this knowledge may be helpful when describing the strategy or providing an explanation. A good example is Antirrhinum which has an inflorescence - a stem that produces lots of flowers sequentially (1 mark). The flowers are relatively large and can be only opened by bees. The flowers have a landing platform, bee guides and nectar. Antirrhinum also emits scent that is attractive to bees and is most intense when bees are most active (1 mark). The scent is produced from petal tissue closest to the opening of the flower. This strategy is successful because it targets a single pollinator (1 mark). This strategy also has selected a pollinator that will make many visits to a different Antirrhinum plants transferring pollen between different individuals and this promotes outbreeding (1 mark). MLOs: Review the adaptive significance, organisation and function of the principal Describe the major events in the evolutionary history of plants and animals with an appreciation of the characteristics of major animal and plant phyla. page 3 of 9

4 3. Use an example to define the following terms in the context of plant reproduction and explain the advantages of each strategy: a) Persistence (2 marks) Marram grass is a good example of a plant that reproduces asexually by vegetative reproduction. This is a good example of persistence because Marram occupies the same habitat (sand dunes) over a long period of time (1 mark) and develops a local ecosystem that suits this plant s primary method of reproduction (1 mark) - vegetative reproduction. b) Multiplication (2 marks) Populus tremuloides is a good example of a tree that reproduces by asexual reproduction. This is a good example of multiplication where a single rootstock produces vast numbers of identical offspring or clones to produce entire forest of trees (1 mark). This is a very successful strategy because these trees do not expend energy on sexual reproduction the interconnected network of roots is thought to enhance nutrient acquisition (1 mark). c) Dispersal (2 marks) Dispersal describes how seeds are transported away from the parent plant to a more preferred location. This process may also enhance seed germination. The South American mistletoe Tristerix corymbosus produces green fruit that are eaten by a marsupial, which disperses the seed to a new location. The mistletoe seeds only germinate after they have been through the digestive tract of the marsupial. The seeds are passed whole and with a sticky covering that attaches them to the trunks and branches of trees where they germinate. MLOs : Review the adaptive significance, organisation and function of the principal Describe and appreciate the diverse physiological strategies that allow plant and animal life in different environments. page 4 of 9

5 4. a) Describe the hypersensitive response in plants. (2 marks) This is a mechanism of defence. Uninfected cells surrounding the site of infection rapidly produce large numbers of reactive oxygen species, undergo cell wall strengthening and die (1 marks). This prevents a barrier to biotrophic pathogens and slows the growth of necrotrophic ones (1 marks). b) Explain how systemic acquired resistance differs from the hypersensitive response. (2 marks) Systemic acquired resistance occurs after a plant has acquired immunity to infection, unlike the hypersensitive response which is a response to an infection (2 marks). MLOs : Review the adaptive significance, organisation and function of the principal Describe and appreciate the diverse physiological strategies that allow plant and animal life in different environments. Describe the major regulatory systems that integrate physiological responses in plants and animals. 5. a) Briefly define photorespiration, and how it affects photosynthesis in plants. (3 marks) Photorespiration is the Oxygenation of RUBISCO (1 mark) It competes with Carboxylation to produce a 3C and 2C compound (1 mark). CO2 is a byproduct, and can result in significant losses of Carbon from the plant (1 mark) Students may focus on the photorespiration/water trade off - if they do they will get a mark, for partial relevance, but that isn t what the question asks. b) Rice, one of the major grain crops of the tropics and sub-tropics, is a C3 plant. Many researchers are exploring the possibility of engineering C4 rice plants. Why would this be an advantage? This is a question designed to test how the students put the lecture information together. I mentioned C3 rice in passing during the lecture, so this shouldn t be totally left-field. page 5 of 9

6 In the tropics, with high light, high temperature, and in some cases, low rainfall environments, C4 plants have evolved to be more prevalent (1 mark) Productivity is higher because photorespiration is inhibited (1 mark). As a C3 plant, rice is vulnerable to photorespiration, and needs a lot of water (1 mark). If it was C4, then rice could be grown over a wider area, or in different seasons (1 mark for a sensible deduction) MLOs 3. Review the adaptive significance, organisation and function of the principal 4. Describe and appreciate the diverse physiological strategies that allow plant and animal life in different environments 5. Describe the major regulatory systems that integrate physiological responses in plants and animals 6. a) Briefly compare Carbon assimilation per unit biomass in fast growing and slow growing plants. (3 marks) Carbon assimilation occurs via photosynthesis, which is governed at the whole plant level by the amount of tissue available for photosynthesis, ie the amount of leaf area (1 mark). This rate will be the same in both fast and slow growing plants (1 mark). Fast growing plants allocate more resource to tissue that can photosynthesise, and therefore assimilate Carbon more quickly per unit that slow growing plants that allocate fixed C to more structural (non-photosynthetic) tissue.(1 mark) b) How would low nutrient availability affect growth rate in plants? This question links resource allocation (L7) to nutrient uptake (L8). This is not a trade-off discussed explicitly in the lecture. Nutrient uptake requires energy (1 mark). Where nutrients are limiting, fast growing plants in environments where C assimilation is not limiting will be able to fund either active nutrient uptake systems or by recruiting symbionts (eg mycorrhizas, cluster roots etc.) (1 mark). However, in nutrient poor environments where C assimilation is also limiting (by eg light or temp) (1 mark), then the plant will trade off biomass accumulation with nutrient uptake from poor soils, and growth rates are likely to be correspondingly slow(1 mark). MLOs page 6 of 9

7 3. Review the adaptive significance, organisation and function of the principal 4. Describe and appreciate the diverse physiological strategies that allow plant and animal life in different environments 5. Describe the major regulatory systems that integrate physiological responses in plants and animals 7. Using the example of wild populations of chilli peppers, explain what is meant by an evolutionary or fitness trade-off. (5 marks) Chilli peppers are adapted to a variety of environments. Not every trait is suited to each in environment that wild populations of chillis occupy (1 mark). Phenotypic variation is important in wild populations of chillies and appears balanced between different environments (1 mark). For example, there is an evolutionary trade-off between the hotness of chillis due to the amount of capsaicin present in the fruit, and the density of stomata in the leaves (1 mark). Pungent plants are much more resilient to fungal attack than non-pungent plants in wet or humid conditions. Even though pungent plants produce fewer seeds, they have a fitness advantage in humid or wetter climates (1 mark). In drier climates a lower stomatal density is much more advantageous because it reduces water loss, in areas where pathogens are much less prevalent. In these conditions non-pungent plants appear to use limited water resources more efficiently than than pungent plants (1 mark). A by product of capsaicin is in determining a preferred disperser for the seeds. MLOs Review the adaptive significance, organisation and function of the principal Describe and appreciate the diverse physiological strategies that allow plant and animal life in different environments. Describe the major regulatory systems that integrate physiological responses in plants and animals. 8. a) Describe how action potentials are propagated along an axon. (3 marks) page 7 of 9

8 The spreading of charges from the membrane depolarization that occurs during an action potential (1) leads to the depolarization of neighbouring axon sections (1). This depolarization triggers an action potential in this section of the axon because voltage-gated sodium ion channels open, allowing for the influx of sodium ions (1). Many answers were awarded full marks. Some students described how action potentials are generated, but not how they propagate along an axon. b) Explain how axon myelination increases the speed of action potential propagation. The electrical insulation of the membrane by myelin (1) enables the spreading of a charge from an action potential over a greater distance along the axon because less charge is lost across the membrane (1). Therefore, the charge from an action potential in a myelinated axon can elicit action potentials further away compared to an action potential in a non-myelinated axon (1). Because the spreading of charge along the axon is much faster compared to the generation of new action potentials, action potential propagation is faster in myelinated axons (1). Many good answers. Most students mentioned electrical insulation by myelin that reduces loss of charge across the membrane. However, often an explanation of why this increases the speed of action potential propagation was either missing or not very clear. Relevant module learning outcomes: 2. An understanding of the adaptive significance, organisation and function of the principal organ systems of animals, including the digestive, circulatory, excretory, thermoregulatory and skeletal systems, and how these organ systems may vary with animal body plan, size and environmental circumstance 5. An understanding of the major regulatory systems that integrate physiological responses in plants and animals. 9. Describe how information about the strength and type of a sensory stimulus is transferred to the brain. The strength is encoded by the firing rate of action potentials, with a page 8 of 9

9 stronger signal leading to a higher firing rate (1). Stronger stimuli also often activate more sensory receptors than weak signals (1). The type of stimulus is clear from where in the brain the signal arrives, because each sensory receptor only responds to one type of stimulus (1), and the information is transferred to a specific location in the brain (1). Many good answers. Some answers were incomplete, and some students described how the location of the stimulus is transferred to the brain. Relevant module learning outcomes: 2. An understanding of the adaptive significance, organisation and function of the principal organ systems of animals, including the digestive, circulatory, excretory, thermoregulatory and skeletal systems, and how these organ systems may vary with animal body plan, size and environmental circumstance 5. An understanding of the major regulatory systems that integrate physiological responses in plants and animals. page 9 of 9