R3101 PLANT TAXONOMY, STRUCTURE & FUNCTION

Transcription

1 INCLUDING EXAMINERS COMMENTS R3101 PLANT TAXONOMY, STRUCTURE & FUNCTION Level 3 Wednesday 7 February :30 11:10 Written Examination Candidate Number:. Candidate Name:.. Centre Number/Name: IMPORTANT Please read carefully before commencing: i) The duration of this paper is 100 minutes; ii) iii) iv) ALL questions should be attempted; EACH question carries 10 marks; Write your answers legibly in the spaces provided. It is NOT necessary that all lined space is used in answering the questions; v) Use METRIC measurements only; vi) vii) viii) ix) Use black or blue ink only. Pencil may be used for drawing purposes only; Where plant names are required, they should include genus, species and where appropriate, cultivar; Where a question requires a specific number of answers; only the first answers given that meet the question requirement will be accepted, regardless of the number of answers offered; Please note, when the word distinct is used within a question, it means that the items have different characteristics or features. Ofqual Unit Code H/505/2966 Please turn over/..

2 ANSWER ALL QUESTIONS Q1 Describe FIVE characteristics of angiosperms that have enabled them to adapt to life on land..... Please see over/.. MARKS 10 2

3 Please turn over/.. 3 Total Mark

4 Q2 a) Explain the meaning of the following terms giving ONE NAMED example for EACH: i) cultivar; ii) trade designation. 3 3 i) ii) Please see over/..

5 Describe the significance of the International Code of Nomenclature for Cultivated Plants (ICNCP) for horticulturists. Total Mark Please turn over/.. 5

6 Q3 a) Compare aerobic and anaerobic respiration by completing the table below: Aerobic respiration Anaerobic respiration Location in cell 2 Products 2 Energy yield per glucose molecule respired 2 Please see over/.. 6

7 State TWO advantages and TWO disadvantages of anaerobic respiration in plants. 7 Please turn over/.. Total Mark

8 Q a) Describe how heterostyly favours cross pollination in plants. Please see over/.. MARKS 6 8

9 Describe how the flowers of a NAMED plant example are adapted for pollination by moths. Please turn over/.. MARKS Total Mark 9

10 Q5 a) Describe the process of carbon dioxide fixation in photosynthesis. Please see over/.. MARKS 10

11 Describe how levels of carbon dioxide can be manipulated in intensive glasshouse production. Please turn over/.. MARKS 6 Total Mark 11

12 Q6 a) Name ONE plant of horticultural importance which produces pomes. Describe the structure of a pome with the aid of a clearly labelled diagram. MARKS 1 5 Please see over/.. 12

13 c) Identify TWO succulent fruit categories, other than a pome, giving a NAMED plant example for EACH. Please turn over/.. MARKS Total Mark 13

14 Q7 a) State ONE function for EACH of the following secondary tissues; i) phelloderm (secondary cortex); ii) secondary phloem (inner bark). i) ii) Describe the structure of the cells in the phelloderm. 1 Please see over/

15 c) Describe the structure of cells in the secondary phloem under the following headings; i) sieve tube cells; ii) companion cells. 3 2 i) ii) Please turn over/.. Total Mark 15

16 Q8 Describe the uptake of mineral nutrients in the plant from the soil to the stem. Please see over/

17 .. Please turn over/.. Total Mark 17

18 Q9 a) Pinus sylvestris is a xerophyte. State TWO environmental conditions to which it is adapted. 2 Label FOUR xeromorphic features on the diagram below. TS Pinus sylvestris leaf Please see over/.. 18

19 c) Explain how EACH labelled feature in enables the plant to survive xerophytic conditions. Please turn over/.. Total Mark 19

20 Q10 Describe the role of endogenous plant growth regulators in EACH of the following: i) seed dormancy; ii) seed germination; iii) leaf abscission. MARKS 3 3 i) ii). Please see over/.. 20

21 iii) ******* Total Mark 21

22 These questions are the property of the Royal Horticultural Society. They must not be reproduced or sold. The Royal Horticultural Society, Wisley, Woking, Surrey GU23 6QB. Charity Registration Number: /SC

23 R3101 PLANT TAXONOMY, STRUCTURE & FUNCTION Level 3 Wednesday 7 February 2018 Candidates Registered 11 Total Candidates Passed 6% Candidates Entered 119 Passed with Commendation 31% Candidates Absent/Withdrawn 20 Passed 33% Candidates Deferred 2 Failed 36% Senior Examiner s Comments On the whole this paper was well answered with the majority of candidates attempting and completing all the questions. The following guidelines should be of help to future candidates. 1. Where named plant examples are asked for, full botanical names (genus and species) are required to achieve full marks. Common names will not be given a mark. 2. Use the command statements e.g. list or name (single words only), state (a few sentences), describe or explain (a fuller answer) together with the mark allocation, to judge the depth of the answer. Half marks are often allocated where the basic information given is correct but needs further qualification to gain the full mark. 3. Where a number of answers are specified in the question, the examiner will not select correct answers from a list e.g. if the question states State TWO plant names, only the first two names given will be marked.. Labels on diagrams should be correctly positioned to avoid ambiguity and diagrams should be clearly drawn and annotated. No marks will be awarded for artistic merit. 5. Candidates should use unambiguous plant examples as reference sources from, for example, the RHS Find a Plant Service available on the RHS Website. 23

24 ANSWER ALL QUESTIONS Q1 Describe FIVE characteristics of angiosperms that have enabled them to adapt to life on land MARKS 10 Q1 Many candidates mentioned characteristics without explaining how these adapted angiosperms to life on land or if they did, there was a lack of detail. For example, mention of a vascular system needed to be accompanied by description of its role in enabling water and minerals to be taken up by the roots and circulated around the aerial parts of the plant. Similarly, pollen enables a wide range of transfer mechanisms for the male gamete other than just water. Both of these give plants the opportunity to occupy drier habitats. Comparison was often made with conifers or lower plants which are also land dwelling. Such comparisons were not asked for in the question and could not be credited. Better candidates described five clear characteristics rather than a long list, only the first five characteristics could be credited. There were many possibilities here. For example, some candidates chose roots, stems, leaves, flowers and seeds as the characteristics and went on to discuss how these supported life on land in terms of allowing plants to live in a wide range of environments and/or compete with other plants. Mention of adaptations such as perennating organs or xeromorphic features such as sunken stomata were also credited as were more specific features and processes such as stomata, a cuticle, pollen, secondary thickening, double fertilisation or a range of life cycles. Some examples of good answers are: The seed has a food supply e.g. starch in cotyledons or endosperm, to initiate growth of the embryo until it is able to photosynthesise and it may also have dormancy mechanisms to delay germination until suitable conditions arrive Stomata can open and close for gas exchange due to their guard cells, therefore allowing photosynthesis to take place but minimising water loss from transpiration A range of life cycles e.g. ephemeral, annual, perennial enable plants to colonise a wide range of habitats and withstand adverse conditions Stems support the aerial parts of the plant enabling it to grow higher so leaves can access light and flowers can disperse pollen and seeds more efficiently, thereby competing with other plants and enabling occupation of a wide range of habitats. Double fertilisation gives rise to an endosperm food store in some angiosperms providing storage products e.g. starch for growth of embryo until it is able to photosynthesise General comments made by candidates which also apply to non-angiosperm plants that live in water could not be credited, e.g. they possess chloroplasts to create their own food by photosynthesis as this statement does not specifically relate to the presence of leaves or adaptations for photosynthesis by angiosperm plants that have adapted to life on land. 2

25 Q2 Explain the meaning of the following terms giving ONE NAMED example for EACH: a) i) cultivar; ii) trade designation. 3 3 Describe the significance of the International Code of Nomenclature for Cultivated Plants (ICNCP) for horticulturists. Q2 a) i) Many candidates could not name and correctly spell the two plant examples. Most candidates were able to explain what is meant by the term cultivar. Cultivar is an abbreviation of cultivated variety and cultivars need to be maintained by human intervention, few stated that cultivars have to be uniform, stable and distinct. Cultivar names always begin with an uppercase letter and the name enclosed in single quotation marks. Care should be taken with choice of a cultivar example. Many candidates gave trade designations instead, especially where a rose was chosen as the named plant example. ii) Trade designations were widely understood to be alternative selling names used for commercial purposes but few candidates explained that they are often given when the cultivar name is unsuitable, e.g. in a foreign language, or is often applied whilst a plant being registered for Plant Breeders Rights. A trade designation is usually written in small block capitals, or a different font, and the name is not enclosed by commas. (Although this is difficult to do in a handwritten examination answer this should be mentioned in the text). Better candidates were aware that the International Code of Nomenclature for Cultivated Plants (ICNCP) is an international rulebook for regulation of the naming of cultivars and includes description of how cultivar names should be written (also for Groups, grexes and graft hybrids). Many confused the ICNCP with Plant Breeders Rights (it is not the ICNCP which tests uniqueness, uniformity and stability or chooses names). Similarly it is International Registration Authorities which register cultivar names not the ICNCP. Sometimes ICNCP rules were confused with International Code of Nomenclature (ICN) rules for algae, fungi and plants, such as the Rule of Priority. Candidates said very little about the significance to horticulturists. Correct cultivar names reduce confusion in planting schemes or when ordering plants and enable plant names to be registered, for example. The ICNCP also gives rules for how cultivar names should be published. Marks were awarded for examples of nomenclatural rules e.g. cultivar names must not be in Latin. 25

26 Q3 a) Compare aerobic and anaerobic respiration by completing the table below: Aerobic respiration Anaerobic respiration Location in cell Products Energy yield per glucose molecule respired State TWO advantages and TWO disadvantages of anaerobic respiration in plants. Q3 This question was generally well answered a) Whilst most candidates were clear that aerobic respiration takes place in the mitochondrion and were credited for this, some could also state that the first part of the process (glycolysis) occurs in the cytoplasm. Fewer candidates knew that anaerobic respiration occurs solely within the cell cytoplasm. Concise, single word answers were accepted such as products of aerobic respiration being water and carbon dioxide. Equations were accepted as long as the products were clearly indicated. For anaerobic respiration some candidates misnamed ethanol giving ethane or ethylene instead. A number of candidates did not mention units of energy of ATP in their answer for energy yield so could not be credited, some gave the correct numbers for energy yield (3-38 ATP for aerobic vs 2 ATP for anaerobic) but others gave energy yield in kj for which any reasonable figure was accepted. Few candidates provided two advantages of this process to plants, which include the ability to withstand periods without oxygen, for example in waterlogged or compacted soil, and enables seeds to survive when dormant. Almost all candidates knew that the disadvantages of aerobic respiration are that ethanol is toxic to plant cells and that the amount of energy produced is not enough for growth. Many mentioned rice plants taking advantage of anaerobic respiration but they just have mechanisms which enable them to withstand ethanol and access oxygen more effectively. 26

27 Q a) Describe how heterostyly favours cross pollination in plants. 6 Describe how the flowers of a NAMED plant example are adapted for pollination by moths. Q a) Candidates who understood heterostyly answered this well, giving Primula vulgaris as an example. Many however confused heterostyly with protandry/protogyny or monoecy/dioecy. Better answers made it clear that the lengths of style and filament varied in the two types of flower placing the stigma /style at the top or bottom of the corolla in the two different arrangements. Candidates found it difficult to explain how this aided cross pollination due to pollen being collected and picked up from different parts of the bee s body. Better candidates were aware that a single plant contains only one of the flower types. Better candidates chose a well recognised plant example with flowers adapted for pollination specifically by moths such as Nicotiana alata, Lonicera periclymenum or Matthiola longipetala. and characteristics included the pale colour of petals, night-scented, and features of the flower structure that allow moths to either hover or perch, depending on the type of moth. Often the named plant example did not match the description although generalised features of moth- pollinated flowers such a strong scent, flowers opening or scent production at dusk, length of corollas matching the moth s proboscis, were still credited. 27

28 Q5 a) Describe the process of carbon dioxide fixation in photosynthesis. Describe how levels of carbon dioxide can be manipulated in intensive glasshouse production. 6 Q5 a) This question was generally answered well. Better candidates recognised that carbon dioxide fixation takes place in the light independent stage of photosynthesis so did not give a description of the whole process. Having said that, this section was generally well answered with mention of the cyclic process, catalysed by enzymes (including RuBisCo), uptake of H and energy supplied by the light dependent reactions in the form of NADPH and ATP and conversion of CO 2 into glucose. Some candidates described differences between carbon fixation in C3, C and CAM plants where correct statements regarding carbon fixation were rewarded. In this section the answer needed to relate to practices in intensive glasshouse production systems. Statements such as carbon dioxide is pumped in required further qualification as the question asks how this is achieved in intensive glasshouse production systems. Supplementation of carbon dioxide levels using dry ice for example, is not common commercial practice. Candidates who described the various methods for replacing or supplementing scored well. Examples were the use of CO 2 gas from canisters, exhaust from heating systems, propane burners. Additional marks were awarded for description of ventilation to replace CO 2 used, the use of fans to circulate air in the glasshouse, the levels of CO 2 used in enrichment (around 1000ppm) and automated monitoring of levels. Several candidates discussed the relationship between respiration and photosynthesis which was not asked for, and a number said that ventilation was necessary to reduce O 2 levels as it inhibits photosynthesis which is incorrect in this setting. Changing the spacing of plants will not affect levels of CO 2 overall. Note that atmospheric levels now stand at around 00ppm not 300ppm. 28

29 Q6 a) Name ONE plant of horticultural importance which produces pomes. 1 Describe the structure of a pome with the aid of a clearly labelled diagram. 5 c) Identify TWO succulent fruit categories, other than a pome, giving a NAMED plant example for EACH. Q6 a) Almost all candidates were able to name one plant which produces pomes such as Malus sylvestris or Pyrus communis Most candidates were able to draw a cross section of a pome and label the fleshy receptacle/hypanthium correctly. The positions of the epicarp and mesocarp (which are virtually indistinguishable) were less well known but the hard endocarp, the central cartilaginous core enclosing the seed, was generally correctly indicated. Other marks could be gained from labelling the seed, the epidermis and the withered remains of the sepals and other flower parts at one end and the pedicel at the other. It is difficult to label the pericarp accurately. On the whole the diagrams were well executed but labels should touch the part indicated to be credited. c) No marks could be awarded for stating the plant example alone or where the fruit type was incorrectly named. The two succulent fruit categories most widely chosen were drupe (e.g. Prunus domestica) and berry (e.g. Solanum lycopersicum) although pseudocarp (e.g. Fragaria x ananassa) was also accepted, as were drupelets (e.g. Rubus fruticosus). Sorbus spp. have pomes and so could not be credited in this section. Candidates should give full botanical names rather than just a genus. 29

30 Q7 a) State ONE function for EACH of the following secondary tissues; i) phelloderm (secondary cortex); ii) secondary phloem (inner bark). 1 1 c) Describe the structure of the cells in the phelloderm. Describe the structure of cells in the secondary phloem under the following headings; i) sieve tube cells; ii) companion cells Q7 a) This question was very badly answered and the structure of the individual cells was not well known. Many candidates failed to identify function or structure as asked and some described the position of the tissues. If recognised correctly most candidates were able to give one function for each tissue. Fuller answers gained most marks; for function of phelloderm, these included mention of starch or water storage, adding to girth in secondary woody stems or the ability to become meristematic in response to wounding. These were fully credited rather than stating packing or support. For function of secondary phloem, transport of sucrose, mineral and hormones was the most popular answer. Many candidates confused phelloderm with phellogen (cork cambium) or phellum (cork) and so were unable to answer this section successfully. Phelloderm is parenchyma tissue, any structural characteristic of this tissue e.g. air spaces between cells or thin cell walls was credited. Whether a cell is living or dead is not a structural feature but inclusion of cell contents such as a membrane and cell organelles is. c) In answer to this part many candidates described the structure of the tissues rather than the cells. Marks were awarded for sieve tube cells having sieve plates, no nucleus, a thin cytoplasm with few organelles and a large lumen for example. Companion cells have a nucleus, dense cytoplasm with many mitochondria and both are elongated and connected via plasmodesmata. Candidates are reminded to differentiate between function and structure, with many repeating comments about the function of the phloem cells in part c) rather than describing their structure. 30

31 Q8 Describe the uptake of mineral nutrients in the plant from the soil to the stem. MARKS 10 Q8 This question was generally well answered although many candidates described the uptake of water rather than minerals. Most candidates described how minerals are taken up from the soil as ions dissolved in soil water and travel through the apoplast in cell walls and the symplast via plasmodesmata across the cortex. A common mistake was stating incorrectly that minerals enter cells by osmosis rather than by active transport. The structure of the endodermis and its Casparian strip was often poorly described. The Casparian strip is a band of wax in the wall of the endodermal cell which prevents water and minerals passing between adjacent cells, forcing them to cross the endodermal membrane and enter the symplast. A description of active transport, movement of ions against a concentration gradient which uses ATP/energy and facilitated diffusion down a concentration gradient (which involves carriers in membranes) also gained marks. Many candidates went on to describe movement in the stem and leaf which was not asked for. Mention of the mechanisms of transpiration pull and root pressure were credited where these were related specifically to mineral uptake rather than just general descriptions of the processes. 31

32 Q9 a) Pinus sylvestris is a xerophyte. 2 State TWO environmental conditions to which it is adapted. Label FOUR xeromorphic features on the diagram below. TS Pinus sylvestris leaf c) Explain how EACH labelled feature in enables the plant to survive xerophytic conditions. Q9 a) A number of candidates failed to demonstrate an understanding of xerophytic conditions which lead to drought due to lack of available soil water or physiological drought conditions such as frozen soil and high wind. Xerophytic plants are adapted to environmental conditions relating to lack of water availability. Full marks were given for the statements low humidity, high windspeeds or low soil water availability for example rather than just temperature, wind, drought, humidity, dryness, freezing etc. Most candidates were able to label some xeromorphic features on the leaf such as sunken stomata, a thick cuticle, endodermis, hypodermis, needle shape or xylem in centre. Pinus leaves are not rolled and have a thickened cuticle compared with nonxerophytes. c) An explanation how each labelled feature reduces transpiration water loss rather than just a description, gained full marks. For example, sunken stomata increase the boundary layer/increase humidity so reduce the rate of diffusion from the leaf OR the endodermis has a Casparian strip which reduces water loss from the xylem OR the thick cuticle also contains waxes which are waterproof which in turn will reduce water loss by transpiration OR the needle shape reduces leaf area so reducing the number of stomata and the amount of water loss through transpiration. Pinus sylvestris does not carry out CAM or C photosynthesis. 32

33 Q10 Describe the role of endogenous plant growth regulators in EACH of the following: i) seed dormancy; ii) seed germination; iii) leaf abscission. 3 3 Q10 i) Most candidates were able to name abscisic acid which promotes dormancy and gibberellic acid which breaks dormancy. Full marks were given for a description of how the levels of each plant growth regulator rise and fall in the dormant period and the factors such as temperature/stratification which bring this about. ii) Candidates had to elaborate on their answer in i) to gain marks here and describe the actual role of GA in triggering breakdown of storage substrates to provide energy for the developing embryo. Better candidates described the role of the aleurone layer in grasses producing the enzymes which breakdown storage products in response to GA. The role of auxin in the tropic response of the radicle in germinating seeds was also mentioned by some and credited. iii) Most candidates were aware that it is ethene (ethylene) which triggers leaf abscission, not abscisic acid. Further marks were gained by describing the development of the abscission layer and mentioning that cytokinin and auxin act antagonistically to ethene so preventing abscission. Candidates stating that a plant growth regulator influences a process, for example ethylene influences leaf abscission without saying how, could not be fully rewarded. 33