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(a) (i) Decide which three further concentrations of triglycerides to make, then complete Table 1.1.
• The difference between each concentration should be 1%.
• You will need to make up 20 cm³ of each concentration.
[Table_1] with columns: volume of milk solution / cm³, volume of distilled water / cm³, percentage concentration of triglycerides in milk
20, 0, 5
(a) (ii) State the concentration of triglycerides which you would expect to reach the end-point (pink to white) in the shortest time.
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(a) (iii) Prepare all the concentrations of triglycerides as in Table 1.1 in the containers provided.
(a) (iv) Process your raw data to find the time taken to reach the end-point for each concentration (these are your processed results).
If you have time check your results.
(iii) Prepare the space below to record your processed results.
(a) (iv) Calculate the rate of lipase activity for the 5% concentration of triglycerides.
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(a) (v) Describe how you could set up a control for this investigation using the apparatus provided.
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(a) (vi) Identify one significant source of error in this investigation.
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(b) (i) Plot a chart of the data shown in Table 1.2.
(b) (ii) Suggest one reason for the difference in the time taken to reach the end-point between evaporated milk (V) and dried milk (D).
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(c) Identify two variables that the student would need to standardise to compare the activity of different concentrations of lipase immobilised in alginate beads.
Describe how one of these variables would be standardised.
525
580
509
K1 is a slide of a transverse section through a plant leaf. This plant grows in the Mediterranean region.
(a) (i) Draw a large plan diagram of the part of the leaf indicated by the shaded sector in Fig. 2.1.
[Image_1: Fig. 2.1, draw this sector]
On your diagram, use a ruled label line and label to show an epidermis. [4]
(ii) Find an area on the specimen in K1 showing a group of four xylem vessels. Choose one group of four whole xylem vessels.
Make a drawing of this group, as observed on the specimen on K1.
On your drawing, use a label line and label to show one lumen. [5]
Fig. 2.2 shows a photomicrograph of a stage micrometer viewed through a microscope.
The smallest measurement on this stage micrometer is 0.1 mm.
[Image_2: Fig. 2.2]
You are required to:
• find the area of the field of view, using Fig. 2.2
• count the number of chloroplasts in a quarter of the field of view, using Fig. 2.3 (on page 14)
• calculate the number of chloroplasts per mm2.
(b) (i) Calculate the area of the field of view, using:
• the formula for the area of a circle $\pi r^2$
• $\pi = 3.14$
• $r =$ radius of the field of view.
You will lose marks if you do not show your working or if you do not use appropriate units.
area of field of view $\text{......................}$ mm2 [2]
[Image_3: Fig. 2.3]
(ii) Count and record the sample number of chloroplasts in the quarter of the field of view.
• Mark clearly on Fig. 2.3 each of the chloroplasts counted.
• Estimate the total number in the whole field of view.
Calculate the number of chloroplasts per mm2.
You will lose marks if you do not show your working.
number of chloroplasts $\text{......................}$ mm–2 [4]
Fig. 2.4 is a photomicrograph of a one-celled organism which lives in fresh-water. You are not expected to have studied this organism. The organism has engulfed some green algae (R) which it uses for food.
[Image_4: Fig. 2.4]
(c) (i) Prepare the space below so that it is suitable for you to record the observable differences between Fig. 2.3 and Fig. 2.4.
To help you some of the structures on Fig. 2.4 have been labelled with letters.
Record your observations in the space you have prepared. [5]
The organism you have observed in Fig. 2.4 is part of a food web.
(ii) State the trophic level of the organism in Fig. 2.4.
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Describe one observable feature of the specimen in Fig. 2.4 which supports this conclusion.
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............................................................................................................................. [2]
598
571
528
