Biology 1992 Paper I Marking Scheme

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Biology 1992 Paper I Marking Scheme

CE BIO 1992 Alex Lam

    1. (a) (i) (1)

     N . B. No mark for separate food chains

     Award 1 mark for each correct feeding relationship ( x 10 = 2;) --------------2;

     Award an additional ; mark for a correct and complete food web ---------------- ;

     Deduct ; mark for each incorrect feeding relationship / incorrect

    representation in the food web. (No deduction below zero.)

     (ii) food chain A -----------------------------------------------------------------------------------------------------1

     more trophic levels involved / longer food chain -------------------------------------------------------1

     more energy will be lose during the transfer between successive trophic levels ---------------1

     due to respiration, metabolic activities , death. etc. ----------------------------------------------------1

     (ii) bees ---------------------------------------------------------------------------------------------------------------1

     they help in pollinating the flowers -------------------------------------------------------------------------1

     (iv) * reptiles ----------------------------------------------------------------------------------------------------------1

     possession of dry scales -------------------------------------------------------------------------------------1

    Total : 11 marks

    1. (a) (i) When asked to construct a food web showing the feeding relations most candidates could

    draw the connecting lines linking the organisms. Some, however, forgot to put in the

    relevant arrows. A number of candidates put the higher level consumers at the bottom of the

    food web which is not the conventional representation of a food web.

     (ii) Many candidates tailed to stress that the longer the food chain, the more energy lost

    during the transfer between successive trophic levels.

     (iv) Many candidates mentioned the presence of scales as a noticeable external feature of

    snakes but failed to point out that they are "dry".

    Paper I Marking Scheme & Year Report P.1

CE BIO 1992 Alex Lam

    1. (b) (i) vessel Y ------------------------------------------------------------------------------------------------------------1

     Its thick / elastic wall ----------------------------------------------------------------------------------------- 1+

     helps resisting the high blood pressure -------------------------------------------------------------------1

     (ii) vessel X (renal vein) * vena cava * heart * pulmonary artery * lungs

     * pulmonary vein * heart * aorta* vessel Y (renal artery) ----------------------------------4

     N.B. ; mark for each correct spelling of the organs in the correct sequence

     ; mark for the flow chart / direction of blood flow

     vessel X vessel Y (iii)

    carbon dioxide less more ---------------------------------------------1


    glucose concentration less more ---------------------------------------------1

    Total : 9 marks

    1. (b) (i) Many candidates’ descriptions of the function of an artery did not match with the structural

    feature stated in the answer. Some candidates thought that the thick and elastic wall of the

    artery was to pump or to create a high blood pressure rather than to withstand or resist it.

     (ii) Many candidates did not read the question carefully and so drew diagrams of the kidney

    and its related blood capillaries instead of a flowchart showing a double circulation of blood

    in relation to the kidney. It seems that they had no idea of what a flowchart is.

     (iii) A number of candidates were confused about the relative concentrations of carbon dioxide

    and glucose in the pulmonary artery when compared with those in the pulmonary vein. Paper I Marking Scheme & Year Report P.2

CE BIO 1992 Alex Lam

    1. (c) (i) correct axes with labels ---------------------------------------------------------------------------------------1

     correct key -------------------------------------------------------------------------------------------------------1

     correct plotting of 8 points for each curve (N.B. overall shape must be correct) --------- 1,1

     N.B. Accept alternative presentations of graph

     (ii) Due to its small leaf area (0% to 20% maximum size) / rapid growth of leaf, -------------------1

     the leaf has insufficient photosynthetic product for growth ------------------------------------------1

     Therefore, it requires an external supply of sucrose --------------------------------------------------1

     (iii) between 20 ; 2% to 60 ; 2% of maximum leaf size ---------------------------------------------------1

     (iv) Copy the outline of the leaf on a piece of graph paper -----------------------------------------------1

     Count the grids / squares and estimate the total area that the leaf covers ----------------------1

    Total : 10 marks

    1. (c) (i) Most candidates failed to plot all the points for the import of sucrose into the leaf as given in

    the question, in particular for those points which lie along the horizontal axis (X-axis). Many

    even failed to label the axes or mark the origins of both axes.

     (ii) Many candidates did not read the questions thoroughly, only indicating the difference

    between the import and export of sucrose rather than explaining it. Others failed to point out

    that while the leaf size changed from 0% to 20% there was little photosynthesis (but not no

    photosynthesis) due to the small leaf area and hence insufficient chlorophyll.

     (iv) Candidates were not used to suggesting simple workable methods to extend a given

    investigation. When asked to estimate the leaf area, many simply suggested measuring

    both the length and width of the leaf. Others suggested a weighing method which in fact Paper I Marking Scheme & Year Report P.3

CE BIO 1992 Alex Lam

would not lead to any estimate of the leaf area.

Paper I Marking Scheme & Year Report P.4

CE BIO 1992 Alex Lam

    2. (a) (i) Tube 3 ------------------------------------------------------------------------------------------------------------1

     is a passage for sperms / semen and urine -------------------------------------------------------------1

     (ii) * testis -------------------------------------------------------------------------------------------------------------1

     (iii) D is for reproduction / production of sperms ------------------------------------------------------------1

     A is for excretion / osmoregulation -------------------------------------------------------------------------1

     which is essential for the maintenance of a constant

     internal environment / prevents accumulation of toxic materials -----------------------------------1

     (iv) B ----------------------------------------------------------------------------------------------------------------1

     The elasticity of B enables the temporary storage of urine ------------------------------------------1

     C ----------------------------------------------------------------------------------------------------------------1

     Erection of C facilitates the transfer of sperms /

     semen into the female reproduction tract ----------------------------------------------------------------1

    Total : 10 marks

    2. (a) (i) Many candidates were confused about the meaning of the terms "urea" and "urine".

     (iii) Some candidates were uncertain about the function of the kidney and wrongly thought that

    it could produce urea (a function of the liver).

    Paper I Marking Scheme & Year Report P.5

CE BIO 1992 Alex Lam

    2. (b) (i) At 1300 hour the transpiration rate is high because

     the stomatal pores are widely open -----------------------------------------------------------------------1

     The resulting high transpiration pull increases the rate of water absorption ---------------------1

     At 2100 hour, the transpiration rate is low because

     the stomatal pores are small / closed ---------------------------------------------------------------------1

     This leads to a decrease in the rate of water absorption ---------------------------------------------1


     The stomata are more wide open at 1300 hour than that at 2100 hour --------------------------1

     Transpiration therefore occurs at a faster rate ----------------------------------------------------------1

     The resulting larger transpiration pull ---------------------------------------------------------------------1

     leads to a higher absorption rate ---------------------------------------------------------------------------1

     (ii) Areas A and B represent either the net amount of water

     lost or gained during the specified period of time ------------------------------------------------------1

     Area B larger than Area A means that there is a net

     gain of water over the 24-hour period ---------------------------------------------------------------------1

     The net gain of water is essential for various life

     processes e.g. formation of new cells, photosynthesis, etc. -----------------------------------------1

     (iii) thicker inner cell wall and thinner outer wall / kidney-shaped ---------------------------------------1

     (iv) sweat pores / glands / blood capillaries ------------------------------------------------------------------1

     prevent overheating -------------------------------------------------------------------------------------------1

    Total : 10 marks

    2. (b) (i) Many candidates misunderstood the question, giving only the changes in amount of water

    in the plant from 1300 hours to 2100 hours instead of relating how such changes could be

    linked to the relative size of the stomatal pores. Many candidates misread the question as

    requiring them to explain changes in transpiration rate with respect to changes in

    temperature and light intensity. Only a few candidates correctly pointed out the relationship

    between transpiration pull and water absorption. In this regard candidates* concept of

    transpiration pull was very vague.

     (ii) Many candidates wrongly interpreted areas A and B as the amount of water transpired or

    absorbed respectively. These are actually the net gain and net loss of water in the plant


     (iv) Many candidates gave the function of the sweat pore in the human skin as only one of

    temperature regulation without specifying that it is mainly for preventing over heating. Many

    incorrectly cited the hair / hair follicle / hair pore / hair gland (rather than the sweat pore or

    sweat gland) as the ‘counterpart’ (in human skin) of the plant stoma.

    Paper I Marking Scheme & Year Report P.6

CE BIO 1992 Alex Lam

    2. (c) (i) the non-green offspring must be homozygous recessive (gg) --------------------------------------1

     therefore, they must receive one recessive gene (g) from each parent --------------------------1

     since both of the parents should have a dominant gene for being green in colour ------------1

     their genotypes must be heterozygous (Gg) ------------------------------------------------------------1


     According to Mendel’s Law / Law of Inheritance -------------------------------------------------------1

     If a cross between two green parents gives rise to

     green and non-green offspring in a 3 : 1 ratio -----------------------------------------------------------1

     (Working of the 3 : 1 ratio) -----------------------------------------------------------------------------------1

     Then both parents must be heterozygous (Gg) ---------------------------------------------------------1



     ------------------------------------- 1 ggGG

    FGGGgGggg ------------------------------------- 1 1

     Genotypic 1 : 2 : 1 --------------------------------------------1

     ratio (green) (green) (non-green)

     That is, about of the green seedlings have a

     heterozygous genotype (Gg) for chlorophyll production i.e. 705 x ------------------------------1

     = 470 --------------------------------------------------------------------------------------------------------------1

     (iii) seeds make use of their food reserve for germination ------------------------------------------------1

    Total : 10 marks

    2. (c) (i) Many candidates lacked the competence to deduce the genotypes of parent plants without

    using a genetic diagram. This inability was clearly aggravated by the poor standard of

    expression in English.

     (ii) Some candidates did not use the genetic symbols as given in the question while others

    gave the genotypic ratio of 1:2:1 without referring to the genotypes involved. Many

    candidates failed to give a logical explanation of how they could deduce the parental

    genotypes from what is given in the question.

    Paper I Marking Scheme & Year Report P.7

CE BIO 1992 Alex Lam

    3. (a) (i) * chlorophyll -----------------------------------------------------------------------------------------------------1

     (ii) to remove the residue / green chloroplasts --------------------------------------------------------------1

     so that results / any colour changes of subsequent food

     tests can be easily observed --------------------------------------------------------------------------------1

     (iii) * cellulose --------------------------------------------------------------------------------------------------------1

     - it increases the bull of the indigestible material )

     - and stimulates the muscular movements along )

     the alimentary canal / peristalsis ) any TWO ------------------------------ 1,1

     - to prevent constipation )

     (iv) The presence of reducing sugar is shown by the ------------------------------------------------------1

     formation of orange precipitate in the Benedict’s test -------------------------------------------------1

     The presence of vitamin C is shown by the decolorization of the DCPIP solution --------- 1+1

     N.B. If more than 2 food tests are mentioned, deduct 1 mark for every additional food

    substance wrongly deduced. No deduction below 0.

    Total : 10 marks

    3. (a) (i) The term "chlorophyll" was often misspell. Many candidates mistook "chloroplast" as the

    pigment responsible for the green colour of the green pepper.

     (iii) Some candidates confused excretion with egestion of undigested food substances.

     (iv) Some candidates were not aware that the presence of vitamin C could still be deduced

    although the decolorisation of DCPIP was masked by the pale green colour of the original

    filtrate. A considerable number of candidates wrongly thought that Benedict’s test was a test

    for the presence of glucose. They failed to note that Benedict’s test is only a test for the

    presence of reducing sugar.

    Paper I Marking Scheme & Year Report P.8

CE BIO 1992 Alex Lam

    3. (b) (i) the iris muscle (circular muscle) contracts ---------------------------------------------------------------1

     to reduce the size of the pupil -------------------------------------------------------------------------------1

     to prevent too much light entering the eyeballs ---------------------------------------------------------1

     to over stimulate / damage the retina ---------------------------------------------------------------------1

     (ii) the ciliary muscle relaxed ------------------------------------------------------------------------------------1

     increasing the tension on the suspensory ligaments --------------------------------------------------1

     the lens became less convex -------------------------------------------------------------------------------1

     to enable it to focus on a far away object.



     N.B. ----------------------------------------------------------------------------------------- No lens, no mark

     No arrows, deduct 1 mark

     Light rays not reaching retina, deduct 1 mark

     (iv) voluntary ---------------------------------------------------------------------------------------------------------1

    Total : 10 marks

    3. (b) (i) Some candidates confused the terms "iris" and "pupil". They failed to realize that the pupil

    is an aperture or opening at the centre of the iris which is a circular muscular sheet at the

    front of the eye ball. Also quite a few candidates confused the terms: "eye muscles", "ciliary

    muscles" and "iris muscles" in their descriptions.

     (ii) Many candidates did not realize that in the eye, the relaxation of the ciliary muscles would

    lead to an increase in tension of the suspensory ligament. As a result the suspensory

    ligament would become tightened or taut but it would not contract on its own.

     (iii) Some candidates did not complete the ray diagram fully whilst others forgot to put in the

    arrows to indicate the direction of the light rays all the way onto the retina.

    Paper I Marking Scheme & Year Report P.9

CE BIO 1992 Alex Lam

    3. (c) (i) 40 - 12 = 26 times / minutes (N.B. no unit, no mark) ------------------------------------------------1

     (ii) An increase in breathing rate

     - provides the body with more oxygen )

     - and hence more energy is released )

     - by respiration / oxidation of food ) any THREE ------------------------------1,1,1

     - It also helps the body to get rid of )

     carbon dioxide (product of respiration) )

     more quickly )

     (iii) Intercostal muscle contracts to raise the rib cage ------------------------------------------------------1

     Diaphragm muscle contracts to make the diaphragm flattened ------------------------------------1

     These 2 actions together increase the volume of thoracic cavity ----------------------------------1

     thus decrease the thoracic pressure / pressure inside the lung ------------------------------------1

     The greater atmospheric pressure forces air into the lungs -----------------------------------------1

     (iv) The amplitude / depth of breath is greater ---------------------------------------------------------------1

    Total : 10 marks

    3. (c) This was the most well answered part of the paper indicating that candidates were generally well

    prepared for topics related to fundamental human physiological processes like the breathing

    mechanism in the human body. In contrast, however, questions set in other parts of the paper on

    plant physiological processes like tropism and transpiration led to vague answers which were

    often filled with misconceptions.

    Paper I Marking Scheme & Year Report P.10

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