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ISC Board Exam 2014 : Biology Paper 2 (Practical) with Model Answers

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ISC 12th
Indian School Certificate Examination (ISC), New Delhi

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BIOLOGY PAPER 2 (PRACTICAL) Question 1 [5] (a) You are provided with two flower specimens D-41 and D-42. Describe the floral characteristics of each in semi-technical terms. (The details of individual whorls are not required.) (b) With a sharp razor blade, cut a longitudinal section of flower specimen D-41. Place one of the cut surfaces on a moist filter paper. Show it to the Visiting Examiner. Draw a neat and labelled diagram of the cut surface. (c) Cut a longitudinal section of flower specimen D-42 with a sharp razor blade. Arrange one cut surface on a moist filter paper and draw a neat and labelled diagram of this cut surface. (d) Observe the cut surfaces of the flower specimens D-41 and D-42 with the hand-lens provided and record your observations of the following features in a tabular form as follows: D-41 (i) D-42 Corolla Shape (ii) Androecium: (1) Relation of stamens to each other (2) Relation of stamens to petals Gynoecium (1) Number of locule(s) (2) Type of placentation (e) Take a fresh specimen D-42. Isolate its pistil. Cut a transverse section of its ovary. Draw a neat labelled diagram of the transverse section. (f) Name the families to which each specimen D-41 and D-42 respectively belong. (g) Write two characteristic features of each family you have mentioned in (f) above. (h) Draw a floral diagram of specimen D-42. (i) Write the floral formulae of D-41 and D-42. (j) Mention the botanical name of one economically important plant belonging to each family that you have named in (f) above. 91 Comments of Examiners (a) Several candidates wrote in details on all the floral whorls instead of describing the floral characteristics in semi-technical terms. Spelling errors were common. (b) & (c) D-41 and D-42 Some common mistakes made by candidates are as follows: (i) Gamopetalous/gamosepalous conditions were not shown correctly; (ii) Epipetalous condition was not represented; (iii) Shape of the flower was incorrect; (iv) Fixation not clear; (v) Bifid stigma was not clear; (vi) Ovules were not attached to the placenta; (vii) Labelling was incorrect. (d) (i) Specific terms for the shape was not mentioned by some candidates. Most of the candidates explained in detail. (ii) Candidates were not sure about the term polyandrous . Several candidates made spelling mistakes while writing the type of placentation. (e) A few candidates drew the L.S. of the ovary instead of the T.S. In some cases, the placenta and marginal placentation were wrongly drawn. Guidelines were not connected properly in several cases. The elongated and narrow locule was not shown in some diagrams. (f) A number of candidates spelt the family names incorrectly. In place of family name, many mentioned the sub-family name. (g) The characteristic features of each family were given correctly by most candidates. (h) The Mother axis was not shown by many candidates. Orientation of the whorls was incorrect in several cases. (i) Incomplete floral formulae were written by many candidates. A few candidates used commas. (j) The rules for binomial nomenclature were not followed while writing the scientific names. In several cases, spelling mistakes were made by candidates. 92 Suggestions for teachers Advise students to read the questions repeatedly. Stress upon the correct spelling. Explain the meaning of semitechnical term. Emphasize on the use of correct semi-technical terms with correct spelling. Emphasize on the importance of neat labelled diagram. Students should be taught to draw by observing the specimen during practical period and not from the book later. Laboratory manuals should be regularly corrected and mistakes should be pointed out before the next practical class. Difference between L.S. and T.S. must be clearly explained. Candidates should be encouraged to prepare both the types of slides and observe them under the microscope. The concept of the mother axis must be clearly explained. Orientation of the various whorls in relation to the mother axis must be understood. Teacher should write the floral formula on the board and should explain the use of the various signs and symbols. Teach students the rules for Binomial nomenclature. MARKING SCHEME Question 1. (a) D-41 (Petunia): Ebracteate, pedicellate, actinomorphic/regular, complete, bisexual / hermaphrodite, pentamerous, hypogynous, cyclic. D-41 (Dhatura): Ebracteate, pedicellate, cyclic, hypogynous, bisexual/hermaphrodite, infundibuliform/campanulate, complete. actinomorphic/regular, D-42 Complete, Ebracteate/bracteate, pedicellate, hermaphrodite, zygomorphic, hypogynous, papillionaceous, pentamerous. (b) Drawing: Drawing points: 1. 2 sepals (long) shown 2. 2-3 gamopetalous, bell shaped petals shown 3. 2-3 epipetalous stamens shown 4. Long basifixed anther shown 5. Prominent style with bifid stigma shown 6. Style shorter than petals 7. 2 locules visible in the ovary 8. 2 rows of ovules attached to the placenta 93 (c) Drawing: D 42 D-42 V S Drawing points: 2 sepals shown Standard, wing and keel shown At least three stamens shown Bent style shown One chambered ovary shown 4-5 ovules shown attached to the upper margin Pedicel shown (d) D-41 D-42 Corolla (i) Shape Bell shaped/ Infundibuliform/ papillionaceous campanulate Androecium i) Relation of stamens to each other Polyandrous/ free Diadelphous/ 2 bundles ii) Relation of stamens to petals Epipetalous Free i) Number of locules in the ovary Two One ii) Type of placentation Axile Marginal Gynoecium 94 (e) Diagram: T.S. of ovary of D-42 Drawing Points Narrow, elongated locule shown Locule One locule drawn Ovary wall Marginal placentation shown Placenta One ovule connected with the placenta (f) Labelling Points Ovule D-41 Solanaceae D-42 Leguminosae / Fabaceae (g) D-41 obliquely placed ovary, swollen placenta, bifid stigma, epipetalous stamen with long prominent anther. D-42 Papilionaceous corolla Diadelphous stamens Marginal placentation Vexillary aestivation (any two) 95 (h) F.D. D-42 5 joined sepals with correct orientation 5 petals in vexillary aestivation 10, diadelphous stamens, (9) + 1 unilocular ovary with one ovule attached (j) One bract shown (according to flower) (i) Mother axis showing marginal placentation Br O K(5) C(5)A5 G(2) --- Floral formula of D-41 + --- Floral formula of D-42 Br % K(5) , C1 + 2 +(2) A1 + (9) G 1 D-41: Solanum tuberosum, Capsicum annuum, Lycopersicum esculentum, Datura stramonium, Bombax malabaricum D-42: Arachis hypogaea, Pisum sativum, Glycine max, Phaseolus vulgaris 96 Question 2 [5] (a) You are provided with glassware and twigs of plant D-43 to set up an experiment to demonstrate photosynthesis. Set up the experiment using tap water and one or two twigs of plant D-43. (b) Keep the set-up at a distance of 5 cm, from the source of light. When gas bubbles start emerging from the cut end of the twig(s), show the experimental set-up to the Visiting Examiner. Draw a neat and fully labelled diagram of the experimental set-up. (c) Count the number of bubbles evolved in one minute and record it. Repeat your observations for two more readings in this set-up. Tabulate the readings as shown in the table in (f). Calculate the average number of bubbles (x) evolved in one minute. (d) Now, place the experimental set-up at a distance of 15 cm. from the source of light. Wait for two minutes. Count the number of gas bubbles evolved in one minute. Take three readings. Calculate and record the average number of bubbles (y) evolved in one minute. (e) Shift the set-up at a distance of 25 cm. from the source of light. Wait for two minutes. Count the number of gas bubbles evolved in one minute. Again take three readings. Calculate and record the average value (z). (f) Tabulate your observations as follows: Distance of set-up from light source Number of gas bubbles evolved per minute I II III Average value (c) 5 cm (x) (d) 15 cm (y) (e) 25 cm (z) (g) Explain your observations with reference to each average value, (x), (y) and (z), recorded by you in the table above. (h) Name the plant specimen D-43. (i) Mention two precautions taken by you while setting up this experiment. (j) What is concluded from this experiment? 97 Comments of Examiners (a) A number of candidates did not follow the instructions Suggestions for teachers given. Some common errors made by candidates were as Each student must set up all follows: physiological set ups individually The stem of Hydrilla was not placed pointing and not in groups. towards the neck of the funnel; Teachers must monitor each Too many twigs were used in the funnel. student individually. (b) Candidates made the following errors while drawing the Students must be encouraged to experimental setup: draw diagrams by observing the Light source was not shown; physiological set up and not from The test tube did not touch the funnel; any book. The stem of the funnel was drawn above the level of Students must be trained to take water in the beaker; the readings carefully. They must Bubbles were drawn in blank spaces. also be told to write observation (d) In a number of cases, the number of bubbles evolved in and explanation separately. one minute was either too less or too many. The relationships between the (f) A few candidates calculated the average value of rate of photosynthesis and the number of bubbles and wrote the answer in fraction. nature of light intensity must be (g) Some candidates did not explain each observation explained. separately. Most candidates gave a general report. Some candidates simply copied the chart. (j) A number of candidates did not write Rate of photosynthesis and failed to explain its relationship with the intensity of light. MARKING SCHEME Question 2. (b) 98 Drawing points: Labelling points: Stem of the twigs pointed towards the neck Light of the funnel Water Test tube rests on the funnel Test tube Stem of the funnel under water Gas bubbles / air bubbles Light source shown Beaker Bubbles shown in the test tube in water Funnel Hydrilla/aquatic plant (f) Distance of set-up from light source Number of gas bubbles evolved per minute I II III Average value (c) Observation Observation Observation (X) Maximum (d) 15 cm Observation Observation Observation (Y) Medium (e) (g) 5 cm 25 cm Observation Observation Observation (Z) Minimum (X) Shows maximum value as set-up was close to light source; more photosynthesis; more gas bubbles evolved. (Y) Average value decreased, as light intensity has decreased due to increase in the distance; photosynthesis decreased; less gas bubbles evolved. (Z) Minimum average value as light intensity decreased further; rate of photosynthesis less; few gas bubbles evolved. (two each) (h) Hydrilla / Elodea (i) (i) Stem of funnel should be completely under water (ii) Cut end of the twig(s) should be in the mouth of the stem of the funnel. (iii) Test tube should be completely filled with water for inverting over the funnel. (iv) Light source should be present. (v) Fresh twigs should be used. (j) (any two) The rate of photosynthesis depends on the intensity of light. 99 Question 3 (a) [5] With the sharp razor/blade provided, cut thin transverse sections of specimen D-44. Select a good transverse section and stain with safranin. Mount the section in glycerine. Observe it under low power of the microscope and show it to the Visiting Examiner. (b) Draw a neat labelled outline of the mount as observed under the microscope. (Cellular details are not required.) (c) Answer the following questions: (i) Identify the given specimen. (ii) Give two reasons to support your answer in (c)(i) above. Comments of Examiners (a) Candidates of a few centres were unable to prepare Suggestions for teachers slides properly. Common mistakes made by Students must be trained to draw candidates were: an outline diagram and to show Overstaining or understaining; the structure of vascular bundles Oblique/thick section; clearly. Improper mounting. Students must be trained to (b) Some errors made by candidates in the drawing were observe the most distinctive as follows: features under the microscope. Indistinct pith not clear; Many candidates were not sure of the endodermis and pericycle. In some cases, epiblema was labelled as epidermis. Thick cortex was not shown. (c) Many candidates were unaware of the difference between general features and identifying features . Some failed to mention the nature of vascular bundles and the exact number. 100 MARKING SCHEME Question 3. (b) Drawing points: Labelling points: Root hair shown Root hair Epiblema shown Epiblema Thick cortex shown Cortex Endodermis shown Endodermis Pericycle shown Pericycle 4-5 radial vascular bundle shown 4-5 radial vascular bundle Pith poorly developed/absent Pith Xylem, Phloem (c) (i) Identification of T.S. of dicotyledonous root : (ii) Reasons: Vascular bundles are radial Number of vascular bundles between 2 6 Xylem is exarch Pith is poorly developed. Epidermal hair are unicellular (any two) 101 Question 4 [5] Identify the given specimens A to E. Give two reasons to support your answer in each case. Draw a neat labelled diagram of each specimen. You are not allowed to spend more than three minutes for each spot. Note: Hand over your continuation booklet to the Supervising Examiner after you finish answering this question. Comments of Examiners Specimen A Common errors made by candidates were as follows: Incomplete identification was done by a number of candidates. Many did not mention T.S. or Mammalian . In several cases, candidates did not label the diagram completely. A few candidates did not mention seminiferous tubules . In some cases, the labelling and the reason for identification did not match. Specimen B A number of candidates did not mention T.S. in the identification. In some cases, the gap between the inner mass of cells and zona pellucida was not drawn distinctly. Many did not label zona pellucida and also did not mention it in the reason. Suggestions for teachers Students must be trained to make correct observation to identify the given specimen. They should be able to match the drawing, labelling and identifying remarks. Explain the importance of making a simple and completely labelled diagram. Tell students that the distinct identifying features should be mentioned and not general features. Tell students that the drawing should match the identifying features and that the guide lines must not cross over; all apparatus must be labelled. Specimen C T.S. was not mentioned by many candidates in the identification. In several cases, spongy and palisade parenchyma could not be distinguished in the diagram. In many cases, the labelling was incomplete. Specimen D A few candidates identified the spot as Hibiscus / self-pollinated flower / L.S. of flower instead of entomophilous flower. In many cases the labelling was incomplete. Specimen E Wrong or incomplete identification was done by candidates. In some cases, the shape of the thistle funnel was not drawn correctly. In a few cases, the thistle funnel was not labelled. The initial and final level was not clearly mentioned by some candidates. 102 MARKING SCHEME Question 4. Spot A: Identification of T.S. Testis of mammal: Drawing points: Labelling points: Seminiferous tubules shown Seminiferous tubules Leydig cells in between seminiferous tubules shown Leydig cells Elongated Sertoli cells shown Sertoli cells Spermatogania/ spermatocyte/ spermatids/ spermatozoa Spermatogania/ spermatocyte/ spermatids/ spermatozoa Connective tissue shown in between tubules Connective tissue Reasons: (i) Seminiferous tubules showing spermatogenesis (ii) Sperms in the centre of the tubules (iii) Leydig cells in the matrix (any two) 103 Spot B: Identification. T.S. of Morula. Drawing points: Labelling points: Spherical mass of cells in the centre shown. Blastomere/ Inner cell Mass. Zona pellucida shown Zona pellucida Gap shown between mass of cells and zona pellucida Reasons: - Spherical mass of cells visible / many blastomeres. - Mass of cells surrounded by a thin layer of tissues Spot C: Identification of T.S. of dicotyledonous leaf/ Dorsiventral leaf: Drawing points: Labelling points: Palisade tissue shown Palisade parenchyma Spongy parenchyma shown Spongy parenchyma 104 (any two) Lower epidermis with stoma shown Epidermis (lower/upper) Vascular bundle shown Stoma/stomata Thick cuticle in the upper epidermis shown Cuticle Vascular bundle Reasons: - Mesophyll is differentiated into Palisade and Spongy parenchyma - Stomata mainly present on the lower epidermis - Thick cuticle in the upper epidermis (any two) SPOT D Identification: Hibiscus rosa sinensis Entomophilous flower/correct explanation. Drawing: - Large flower shown - Large petals shown - Monadelphous stamen shown - Prominent stigma shown Labelling: Bright petal, pollen grain/anthers, stigma, staminal tube Reasons: - Large brightly coloured showy flower. - Many anthers (with pollen grains). - Stigmatic surface sticky. (any two) 105 SPOT E Identification : Experiment to demonstrate osmosis Drawing Points: Labelling Points: Beaker with water shown Beaker with water Mouth of thistle funnel is covered with semi Thistle funnel permeable membrane Thistle funnel filled with hypertonic solution Semi-permeable membrane Initial level of hypertonic solution is less than Hypertonic solution the final level in the stem of the funnel Initial level, final level Reasons: - Mouth of thistle funnel tied with semipermeable membrane - Beaker has water, thistle funnel has hypertonic solution - Final level of solution in the stem of the funnel higher than initial level (any two) 106 Question 5 Show the following to the Visiting Examiner for assessment: (a) Project [7] (b) Biology Practical File. [3] GENERAL COMMENTS: (a) Topics found difficult by candidates in the Question Paper: Question 1 Floral formula, floral diagram and botanical names. Question 2 Interpretation of the Observation. Question 4 Identification of Morula. (b) Concepts in which candidates got confused: Gamosepalous and epipetalous condition. Exarch and endarch xylem, epidermis and epiblema. Leydig cell and Sertoli cell. Anemophily and Entomophily. (c) Suggestions for candidates: Think logically and establish a cause and effort relationship while setting up a physiological experiment. Conceptual understanding is important. Learn the semi-technical terms with correct spellings. Practice drawing all the diagrams through observation. Read each question carefully and then answer. Make a neat presentation. 107

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Additional Info : ISC 2014 : Board Model Answers (Biology Paper 2)
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