Biology 3 Nov/Dec 2009

Biology Paper 3,Nov/Dec 2009

Questions:		1	2	3		Main

General Comments
Weakness/Remedies
Strength

Question 1
The diagram below is an experiment set-up to show that photosynthesis takes place in the leaf. Study it carefully and use it to answer questions 1(a) to 1(e). Name the parts labeled I to VIII. Name of parts: I…………………………………………… V…………………………………… II. ………………………………………… VI.………………………………… III. ………………………………………… VII.………………………………… IV. ………………………………………… VIII. ……………………………….. [ 4 marks] (i) State two reasons why the part labelled IV is boiled in III. ………………………………………………………………………………… … …………………………………………………………………………………… [2 marks] (ii) State two reasons why the part labeled IV is boiled in V. ………………………………………………………………………………… ………………………………………………………………………………………………………………………………….[2 marks] (iii) What is the effect of the part labeled V on IV? ………………………………………………………………………… ……. [ 1 mark] Outline the steps to be taken after the stage of the experiment illustrated to arrive at the conclusion. …………………………………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………………………………….. [ 8 marks] State one important precaution to be taken during the experiment. …………………………………………………………………………………………………………………………………………. [ 1 mark] State two factors which must be available to a plant for its leaf to give a positive result at the end of this experiment. …………………………………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………………………………. [2 marks]
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OBSERVATION
This question was the most popular question in this section and most candidates performed fairly well. Most candidates could correctly name the labeled parts except the tripod stand which a large number of candidates named as retort stand. Many candidates also lost marks due to wrong spellings. Most candidates could say why the leaf was boiled in water and alcohol but omitted to say that the immersion in alcohol in addition to decolourizing was to also detect the presence of starch. Most candidates could not outline the steps necessary to bring the experiment to a conclusion and could not state the precaution to be taken during the experiment. Expected answers include: Steps to conclude experiment - remove the leaf from the alcohol; - and dip it in boiling water; - to soften it; - and remove the traces of alcohol; - put the leaf on a white tile; - and add a few drops of iodine solution to it; - a blue black colour; - indicates the presence of starch; - showing that photosynthesis has taken place in the leaf. Precaution - Avoid exposing alcohol to naked flame (because it is inflammable) Most candidates correctly stated factors needed by the plant for the experiment to yield a positive result and scored the full marks here.