P3 Answering Technique

Question 1
Observation
In 0.2M of sucrose solution, the final diameter of potato disc is 1.90 cm.
In 0.6M of sucrose solution, the final diameter of potato disc is 1.40 cm.
Your answer must be specific. Where do u get it?? From the title in the given table.

Inference
(At 0.2M of sucrose solution) water molecule diffuses into the potato disc by osmosis.
(At 0.6M of sucrose solution) water molecule diffuses out of the potato disc by osmosis.
You give reasons (why) based on your observation. But remember, inference 1 for observation 1 and inference 2 for observation 2. Jgn. silap, rugi....potong markah

Variables
Manipulated variable
Concentration of sucrose solution : Use five different concentrations of sucrose solutions

Responding variable
Final diameter of the potato disc : Measure and record the final diameter of potato disc by using a metre rule
The word record and the instrument used are important.
//
Percentage change in diameter of potato disc : Calculate the percentage change in diameter of potato disc
by using the formula :
(Final – Initial) diameter of potato disc x 100%
Initial diameter of potato disc
If you choose to write about the formula, must state clearly

Constant variable
Time taken to immerse the potato discs : Fix the time (to immerse the potato discs) at 20 minutes.
If the exact time or units are stated in the question, students must write them down. If not, telor ayam la....

Hypothesis
As the concentration of sucrose solution increases, the final diameter of potato disc / the percentage change in diameter decreases.
Just the MV + RV and the relationship(higher, lower); no need to explain further.
Majority of the students like to write `depends on', `affects', `influences'....style PMR.....1 mark only

Table
1. Title and units (must be correct)
No units will be given in the question. Students must refer the earlier page.
2. Apply readings from the table given earlier.(salin jer)
3. Some calculation.

Graph
1. Both axes with correct units and title
2. All points plotted correctly (don't simply add any readings on you own; eg. connect it to 0 ka...)
3. Smooth curve touching all points.

Relationship
The concentration of sucrose solution which is isotonic to the cell sap of potato disc is *0.49M. The percentage change in diameter is zero because
the rate of water that diffuses in and out of the cell is equal.
Must explain.

Prediction
Diameter (of potato disc) is more than 1.9 cm
Distilled water is hypotonic to the cell sap of potato disc
so more water diffuses into the potato (disc) by osmosis.
We predict more or less by referring to the data from the earlier page. Don't simply guess.

Operational definition (Give explanation based on the experiment; not theoretically. Normally combine CV,MV & RV)
Osmosis is the movement of water to / from potato disc through the plasma membrane (of potato) due to the difference concentration between sucrose solution and cell sap of potato cell that will result in changes / decrease / increase in diameter of potato disc.

We don't write osmosis is the movement of water molecules from the region of `high water concentration/low solute concentration' to the region of `low water concentration/high solute concentration' through the semi permeable membrane....as in the book (theory)

Classifying
Salin balik je...dlm kotak....kacang

Total : 33 marks

Question 2 (Latest format)
Eg.
Plan a laboratory experiment to investigate the percentage of vitamin C content in each fruit. DCPIP (dichlorophenolindophenol) 0.1% solution is used to test the presence of vitamin C in the fruit juices.
[Apple, Orange, Watermelon]

Problem statement (3 marks)
1. What is the percentage of vitamin C content in watermelon, orange and apple?/ fruits? //
2. Does apple/orange/watermelon contain more vitamin C than orange/watermelon/apple? //
3. Which fruit has more percentage of vitamin C?
(Remember, all must be in question form. Change the aim into a question form. (kacang). No question mark, deduce 1 mark)

Hypothesis (MV+RV+R) (3 marks)
Watermelon has highest content of vitamin C compare to other fruits.


Materials & Apparatus (3 marks)
DCPIP solution, Standard Ascorbic Acid, Fruit juices / watermelon juice/orange juice/apple juice, Conical flask /beaker, Syringe with needle, Specimen tube

Procedure (3 marks)
K1 : Steps to set up the apparatus & materials
K2 : Steps to handle the fixed variable
K3 : Steps to handle the manipulated variable
K4 : Steps to handle the responding variable
K5 : Precautionary steps / steps taken to get accurate results / readings
(Examiners will be looking for all these 5Ks to get 3 marks )

Eg.
K1 1. Three specimen tubes is labelled as A1, A2 and A3.
K2 2. Fill each specimen tubes with 1 ml of 0.1% DCPIP solution
K1 3 . Use a syringe to take 10 ml of standard ascorbic acid
K1 4 . Place the syringe needle into the DCPIP solution and release the ascorbic acid slowly into the DCPIP solution in A1
K4 5 Observe the change of DCPIP colour and stop releasing the ascorbic acid when the DCPIP become colourless/ no more blue traces
K4 6 Record the volume of ascorbic acid used to dicolourise the DCPIP solution.
K1/K5 7 Repeat steps 3 – 6 for A2 and A3 and calculate the average volume.
K1/K5 8 Juices from each of the fruits is obtained and kept fresh before used
K1/K2 9 Three specimen tubes is labelled as (B1, B2, B3, C1, C2, C3, D1, D2 and D3), and fill each specimen tubes with 1 ml of 0.1% DCPIP
K3 10 Repeat steps 2 – 7 by using fruit juices to replace the standard ascorbic acid.
K5 11 Do not shake the bottle to prevent from DCPIP is oxidated.
K4 12 Record the volume of watermelon juice, apple juice and orange juice that discolourise the DCPIP in the table and calculate the average volume
K4 13 Calculate the percentage of vitamin C in each of the fruit juice using the formula below:

Percentage of vitamin C in fruit juice =
volume of 0.1% ascorbic acid X 1.0 mgcm-1
volume of fruit juice

Tak payah tulis all the Ks in front. For reference only.

Presentation of Data (2 marks)

No data is required. Just the title and the correct units.
Total : 17 marks