Contoh:
Soalan tentang "the effect of enzyme concentration on the rate of hydrolysis of starch". Diberi bacaan dalam jadual;
Test tube Concentration of Time taken for
amylase (%) complete hydrolysis
of starch (minute)
A 0.17 24
B 0.33 12
C 0.5 8
D 0.67 6
Observations:
i) Time taken for complete hydrolysis of starch in test tube A (amylase 0.17%) is 24 minutes
ii) Time taken for complete hydrolysis of starch in test tube D (amylase 0.67%) is 6 minutes
Manipulated variable (MV)
Responding variable (RV)
Tujuannya ialah untuk memudahkan membuat inferens (inference):
i) At 0.17% of enzyme concentration, the mixture contains the lowest amount of enzyme molecules/active sites took the longest time to hydrolyse the starch
ii) At 0.67% of enzyme concentration, the mixture contains the highest amount of enzyme molecules/active sites took the shortest time to hydrolyse the starch
Peringatan:
- Inferens (i) adalah untuk observation (i),
- manakala inferens (ii) pula untuk observation (ii).
- Kesilapan di sini akan membuat pelajar kehilangan terus markah untuk inferens!
Kesilapan pelajar - mengulang observation ketika menjawab soalan inferens
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Hypothesis
Situasi A:
Berdasarkan soalan yang sama, bagaimana pula nak buat hypothesis?
Contoh jawapan:
1 - The higher the enzyme concentration, the higher the rate of enzyme reaction.
2 - The higher the enzyme concentration, the faster the time taken for complete hydrolysis of starch
MV RV the higher (relation)
1 + 1 + 1 = 3 marks
Peringatan:
Tolong jangan guna - directly propotional / is affected by / affects untuk hubungkait MV dengan RV.
Seperti;
The rate of reaction is directly propotional to the enzyme concentration. (X) Cuma dapat markah MV & RV sahaja = 2, silap-silap tak di terima langsung (terutamanya directly propotional) untuk jawapan Bio.
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Situasi B:
Kalau soalan tidak melibatkan nilai menaik atau menurun.
Contoh:
1 - Nilai tenaga beberapa sampel makanan (Bread, banana, peanut)
2 - Nilai BOD beberapa ekosistem akuatik (tasik Chini, Sg. Pinang, Sg. Seget)
Bagaimana pula hendak membuat Hypothesisnya?
Contoh hypothesis:
1 - Peanut contains the highest energy value compared to bread and banana.(or vise versa)
2 - Sg. Seget has the highest BOD value compared to Sg. Pinang and Tasik Chini. (or vise versa)
MV RV highest....compared to
1 + 1 + 1 = 3 marks
Perhatian:
Anda boleh lihat, MV yang paling ekstrim terus diambil untuk dibandingkan dengan MV yang lain. Nilai ekstrim boleh diambil dari bacaan yang paling tinggi atau paling rendah.
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Handling Variables
Masih merujuk soalan yang sama pada post 14 Nov. Bagai mana nak buat 'method to handle variables?
Variable Method to handle the
variable
i) Manipulated variable:
Concentration of By diluting the
enzyme (%) 1% amylase with
distilled water using
measuring cylinder
ii) Responding variable:
Time taken for By recording the time
complete hydrolysis taken when the colour
of starch (min) // of iodine stops changing /
stays brown using
stopwatch
Rate of enzyme By calculating using
reaction min-1 formula : 1/min
iii) Constant variable:
Volume By measuring 4cm3
of starch cm 3 // of 1% starch solution
using measuring
cylinder
Temperature of By fixing &
waterbath oC // monitoring the waterbath
temperature at 37oC
using thermometer
Concentration of By fixing the concentration
starch (%) of starch at 1%
Peringatan:
1) Pada variables, unit mesti dinyatakan (oC, min-1, cm3, ml.... etc)
2) Kata kunci pada method to handle mesti tepat.
3) Penggunaan apparatus dengan menggunakan perkataan "using" dan dinyatakan apparatusnya, kecuali pada fixing concentration kerana larutan telah disediakan.
4) Diringkaskan cerita, anda bayangkan macam mana anda pegang alatan, tuang, cairkan atau gunakan alatan untuk dapatkan variable tersebut dalam makmal, ITU YANG ANDA JADIKAN METHOD TO HANDLE...
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Relationship from graph
Merujuk eksperimen dalam soalan tempohari, cuba lihat soalan ini pula:-.
"Based on the graph, describe the relationship between the concentration of enzyme and the rate of reaction."
Sering kali pelajar hanya mampu mendapat 1 markah sahaja kerana menjawab;
--> As the enzyme concentration increases, the rate of reaction increases. (1)
Sepatutnya huraian kena kaitkan juga dengan "amount of active sites" pada enzyme dan bagaimana kesan active sites ini mempengaruhi tindakbalas.
Jawapan yang betul,
--> As the enzyme concentration increases, the rate of reaction increases (1) because the quantity of active sites also increases (1). Therefore, more substrate can be hydrolise simultaneously/at the same time (1)
--> 3 marks!
Peringatan:
Ketika nak jawab soalan ini, perlu ambil kira observation pada graf dan inference yang telah di buat..
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Prediction & Operational DefinitionNext question...
--> "Predict what would happen if Experiment D is repeated using 10% of starch solution. Explain your answer."
Students will tend to answer,
--> "The rate of reaction will increase because more substrates are present".... (2 marks).
Students seldom get full marks in this questions, why? Because they neglect the effects of the "more substrate" point.
The best answer is:-
--> "The rate of reaction will increase (1) because more substrates are present (1) and more enzyme-substrate complexes can be formed simultaneously/at the same time (1)" ---> (3 marks)
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--> "Based on the experiment, what is the operational definition of amylase?"
Warning! ---> Students usually leave this question BLANK!!
To answer this question, you'll have to look back on the observations of the experiment..
1) Look at the function of amylase ie: to hydrolise starch (you'll find it at The Aim of exp)
2) Look also at how you determine the result.. in this case, the colour change of iodine.
3) Look at the rate of reaction
Using the above points,
--> Amylase is a substance that hydrolise the starch (1) shown by the colour change of iodine from brown to dark blue (1). As the enzyme concentration increases, the rate of reaction also increases. (1) --> (3 marks)
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--> "State the conclusion on the results of the experiment."
This one is "piece of cake"!
--> The higher the enzyme concentration, the faster the time taken for complete hydrolysis of starch. Hypothesis accepted. --> (3 marks)
Do you notice the answer highlighted in blue?? Yes, that is taken from the hypothesis! What you have to do is.... just re-write the hypothesis and add the statement "Hypothesis accepted" That's all... (full marks!) Labels: Kertas 3 1 comments
