7. (a) Diagram 15 shows a series of experiments conducted by a student. All the experiment set-ups are placed near sunlight. Observations are made after two days.
Diagram 15
(a) (i) What are the objectives of this experiment? [2 marks]
Diagram 15
(a) (i) What are the objectives of this experiment? [2 marks]
· 1(a) and 1(b) aimed at studying the parts of the coleoptile that is sensitive to light stimulus
· 1(c) and 1(d) aimed at studying the diffusion of auxin from the tip to the elongating region to cause a growth response
(ii) Two days have lapsed after the experiment. Draw the expected observations. Explain your observations and finally draw a conclusion for each of the above experiments. [9 marks]
· Each drawing with explanation is worth 1 mark
· 1(a) - the coleoptile bends towards unilateral light stimulus to cause a growth response [1] because auxin that is produced at the shoot tip diffuses to the shaded side to cause a more rapid growth in that region [1]
· 1(b) – when the tip is removed, auxin is absent to cause any growth response [1]. Therefore, there is no response observed [1]
· Conclusion: Auxin is produced at the tip which makes the shoot tip sensitive to light stimulus [1]
· 1(c) - There is no growth response observed [1] because auxin that is produced at the tip cannot diffuse down to the elongating region to cause a growth response [1]
· 1(d) - the coleoptile bends towards unilateral light stimulus to cause a growth response [1] because auxin that is produced at the shoot tip diffuses through the agar block [1] to the shaded side of the coleoptile to cause a more rapid growth in that region [1]
· Conclusion: Auxin has diffused down the coleoptile through the agar block, but not the mica plate, to stimulate growth response towards unilateral light [1]
Any 9
(b) Diagram 16 shows an experiment to test the action of a detergent with enzymes on oil residue on clothes. Three similar shirts P, Q and R with the same oil residue of equal size were washed at three different temperatures which are 15 °C, 65 °C and 35 °C, respectively.
Diagram 16 - Clothes
Explain your observations. ` [9 marks]
· At 15C – the low temperature did not promote rapid enzymatic reaction to break down the oil residue on clothes P [1]
· This is because the enzymes were inactive which caused low frequency of effective collision between the enzyme and its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was low [1]
· At 35C – the optimal temperature allowed rapid enzymatic reaction to break down the oil residue on clothes R [1]
· This is because the enzymes were actively moving to collide with its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was at optimal level [1]
· At 65C – the high temperature has denatured the enzymes [1]
· This caused the enzymatic reaction to stop and the oil residue on clothes Q was not greatly removed [1]
· Therefore, the rate of reaction was very low [1]
· 1(c) and 1(d) aimed at studying the diffusion of auxin from the tip to the elongating region to cause a growth response
(ii) Two days have lapsed after the experiment. Draw the expected observations. Explain your observations and finally draw a conclusion for each of the above experiments. [9 marks]
· Each drawing with explanation is worth 1 mark
· 1(a) - the coleoptile bends towards unilateral light stimulus to cause a growth response [1] because auxin that is produced at the shoot tip diffuses to the shaded side to cause a more rapid growth in that region [1]
· 1(b) – when the tip is removed, auxin is absent to cause any growth response [1]. Therefore, there is no response observed [1]
· Conclusion: Auxin is produced at the tip which makes the shoot tip sensitive to light stimulus [1]
· 1(c) - There is no growth response observed [1] because auxin that is produced at the tip cannot diffuse down to the elongating region to cause a growth response [1]
· 1(d) - the coleoptile bends towards unilateral light stimulus to cause a growth response [1] because auxin that is produced at the shoot tip diffuses through the agar block [1] to the shaded side of the coleoptile to cause a more rapid growth in that region [1]
· Conclusion: Auxin has diffused down the coleoptile through the agar block, but not the mica plate, to stimulate growth response towards unilateral light [1]
Any 9
(b) Diagram 16 shows an experiment to test the action of a detergent with enzymes on oil residue on clothes. Three similar shirts P, Q and R with the same oil residue of equal size were washed at three different temperatures which are 15 °C, 65 °C and 35 °C, respectively.
Diagram 16 - Clothes
Explain your observations. ` [9 marks]
· At 15C – the low temperature did not promote rapid enzymatic reaction to break down the oil residue on clothes P [1]
· This is because the enzymes were inactive which caused low frequency of effective collision between the enzyme and its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was low [1]
· At 35C – the optimal temperature allowed rapid enzymatic reaction to break down the oil residue on clothes R [1]
· This is because the enzymes were actively moving to collide with its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was at optimal level [1]
· At 65C – the high temperature has denatured the enzymes [1]
· This caused the enzymatic reaction to stop and the oil residue on clothes Q was not greatly removed [1]
· Therefore, the rate of reaction was very low [1]
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