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In some countries, certain plants have seasonal growth. During the summer plants transport sucrose from the leaves to store it as starch in the roots.
Table 1.1 summarises the changes in the leaves and roots during the year.
Table 1.1
[Table_1]
season | leaves | roots
-------|--------|-------
summer | leaves synthesize sucrose | sucrose stored as starch
winter | no leaves | starch stored
spring | leaves growing | starch converted to glucose
You are required to identify the source of four plant extracts. These have been taken from
- a root in winter
- a root in spring
- phloem sap in summer
- phloem sap in winter
(a) (i) Use the information in Table 1.1 to predict which substances you would expect to be present in each of the four plant extracts, then complete Table 1.2.
Key: ✔ (tick) substance present in plant extract
✗ (cross) substance absent from plant extract
Table 1.2
[Table_2]
source of plant extract | substances present in each of the plant extracts
------------------------|---------------------------------------------
| starch | sucrose | glucose
root in winter | | |
root in spring | | |
phloem sap in summer | | |
phloem sap in winter | | | [2]
One sample was taken from each of the four plant extracts shown in Table 1.2.
You are required to identify from which plant extract each of the four samples S1, S2, S3 and S4 was taken.
You are provided with:
Table 1.3
[Table_3]
labelled | contents | hazard | volume / cm3
--------|----------|--------|--------------
Benedict’s solution | Benedict’s solution | harmful | If you require more
| | irritant | of any of these
| | | reagents, please ask
| | | the Invigilator.
Biuret | copper sulfate | harmful |
| sodium hydroxide | irritant |
iodine | iodine in | irritant |
| potassium iodide | |
hydrochloric acid | hydrochloric acid | irritant |
sodium hydrogen carbonate | sodium hydrogen carbonate | none |
(ii) Describe the tests that show that sucrose is present in a plant extract.
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...................................................................................................................................................................[2]
Select the appropriate reagents from those provided in Table 1.3 and carry out tests to identify the samples S1, S2, S3 and S4.
(iii) Prepare the space below and record your results.
(iv) Complete Table 1.4 to match the samples, S1, S2, S3 and S4, with each plant extract.
Table 1.4
[Table_4]
source of plant extract | sample
------------------------|-------
a root in winter |
a root in spring |
phloem sap in summer |
phloem sap in winter | [4]
A student investigated the effect of different concentrations of sodium chloride solution on root tissues. A separate sample of root tissue was put into a starting volume of each concentration of sodium chloride solution. After a set time the root tissue was removed and the final volume of each solution was recorded. The change in volume for each concentration was calculated.
(b) (i) State three variables which the student should keep the same in this investigation. Describe how the student would keep each of these variables the same.
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..................................................................................................................................................................................[4]
The results of the student’s investigation are shown in Table 1.5.
Table 1.5
[Table_5]
concentration of sodium chloride / mol dm−3 | change in volume of solution / cm3
----------------------------------------------|-----------------------------------
0.00 | –6.0
0.25 | +1.0
0.50 | +4.5
0.80 | +5.2
1.00 | +5.2
(ii) Plot a graph of the data shown in Table 1.5.
[Graph]
[4]
(iii) Show on your graph the sodium chloride concentration where there is no change in volume of solution. [1]
Use this information to estimate the sodium chloride concentration where there is no change in volume of solution. ........................... mol dm−3 [1]
(iv) Use your graph to explain the effect of the different concentrations of sodium chloride solution on the root cells.
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..................................................................................................................................................................................[3]
591
578
517
Fig. 2.1 is a photomicrograph of a transverse section through part of a stem.
Fig. 2.1
(a) Draw a large plan diagram of the specimen shown in Fig. 2.1.
Label the epidermis.
[6]
Fig. 2.2 is a photomicrograph of a transverse section through part of a different plant organ from a different plant species.
Fig. 2.2
(b) (i) Prepare the space below so that it is suitable for you to record three observable differences between the specimens in Fig. 2.1 and in Fig. 2.2.
Record your observations in the space you have prepared. [4]
(ii) The actual length of line Y is 495 µm. Use this measurement to calculate the magnification of Fig. 2.2.
You may lose marks if you do not show your working or if you do not use appropriate units.
magnification × ............................................... [4]
(c) You are provided with a sample of plant material, labelled P.
You are required to prepare a slide of the xylem vessels from this plant material.
Proceed as follows:
1. Using forceps extract long thin strands of P containing xylem vessels as shown in Fig. 2.3.
Fig. 2.3
2. Put the strands onto a microscope slide.
3. Add two drops of water and carefully lower a cover slip onto the strands.
4. Put the paper towel over the cover slip and gently press to separate the xylem vessels from surrounding tissue.
5. Look carefully under high power to find two xylem vessels which show different patterns of thickening in the walls.
Make large drawings of two different patterns of thickening in the walls of the xylem vessels.
Label the part of the vessel where lignin is found. [4]
548
503
581
