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When a person eats food containing starch, the enzyme amylase is released to hydrolyse (break down) the starch into reducing sugar.
As the food passes from the mouth to the stomach and then to the small intestine, amylase is released in the mouth and in the small intestine but is not released in the stomach.
(a) Fig. 1.1 shows a sketch of the changes in the concentration of the biological molecule, starch, as it enters the mouth and passes to the small intestine.
Sketch another line on the graph to show the changes in the concentration of reducing sugar as the starch enters the mouth and passes to the small intestine.
[2]
(b) You are provided with four samples, $S1, S2, S3$ and $S4$.
One of these samples contains starch suspension which a person is about to eat.
The other three represent samples taken from:
• the mouth 2 minutes after being eaten
• the stomach 10 minutes after being eaten
• the small intestine 2 hours (120 minutes) after being eaten.
You are required to identify the samples $S1, S2, S3$ and $S4$ by testing the samples for starch and for reducing sugar, using only the apparatus and reagents provided.
You are provided with:
[Table_1]
If $Benedict's$ or $iodine$ come into contact with your skin, wash off immediately under cold water.
It is recommended that you wear suitable eye protection.
You will need to think about how you will carry out the tests so that you can determine the relative concentrations of the starch and reducing sugar.
(i) Decide how you will test each solution to show the relative concentration of starch present.
State the reagent you will use ........................................... .
Describe how you will carry out the test for starch.
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State what you will record.
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Describe how you will determine which solution has the highest concentration of starch present.
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(ii) Decide how you will test each solution to show the relative concentration of reducing sugar present. You may measure the time taken to the first colour change.
State the reagent you will use ........................................... .
When testing for reducing sugar the volume of the reagent should be equal to or more than the volume of the sample.
Describe how you will carry out the test to measure the reducing sugar concentration.
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State how you will determine which solution has the highest concentration of reducing sugar present.
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1. Carry out the test for starch and the test for reducing sugar on each of the solutions, $S1, S2, S3$ and $S4$.
If the time taken to the first colour change for the reducing sugar test is longer than 180 seconds then record ‘more than 180’.
(iii) Prepare the space below and record your results.
[5]
(iv) Using your results in $(b)(iii)$ and using the information on page 2, complete Table 1.1 to show the identification of the samples, $S1, S2, S3$ and $S4$.
[Table_1.1] [2]
(v) Explain how you decided which sample was taken from the small intestine.
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(c) A student wanted to obtain a quantitative estimate of the reducing sugar concentration in a sample.
Describe how the student could obtain a quantitative estimate of the concentration of reducing sugar in a sample.
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(a) The eyepiece graticule in the microscope can be used to measure different tissues.
(i) Use the eyepiece graticule in the microscope to measure across the diameter of the root as shown in Fig. 2.1:
$$\begin{align*} L \text{ to } Q &= \text{..................} \text{ eyepiece graticule units} \\ L \text{ to } M &= \text{..................} \text{ eyepiece graticule units} \\ M \text{ to } N &= \text{..................} \text{ eyepiece graticule units} \\ N \text{ to } Q &= \text{..................} \text{ eyepiece graticule units.} \end{align*}$$ [3]
(ii) Use the measurements from (a)(i) to state:
the length across the diameter of the root (L to Q) .................. eyepiece graticule units
the length of cortex across the diameter .................. eyepiece graticule units
Calculate the length of cortex as a percentage of the diameter of the root.
You may lose marks if you do not show your working.
answer = ................................................... % [3]
(iii) Use the measurements from (a)(i) to help you draw a large plan diagram of half of the root on K1, shown by the shaded area in Fig. 2.2.
You are expected to draw the correct shape and proportions of the different tissues.
Use one ruled label line and label to identify the xylem. [5]
(iv) Observe the central tissue in the root on K1. These cells are not identical.
Select one group of four adjacent (touching) cells which show some of the differences between these cells. Each cell must touch at least two of the other cells.
Make a large drawing of this group of four cells.
Use one ruled label line and label to identify the cell wall of one cell. [5]
(b) The xylem vessel elements transport water and minerals from the roots to the leaves. This transport depends on the negative pressure in the xylem being greater than the force of gravity.
Scientists measured the xylem pressure at different heights in a tree. This was repeated for a number of trees of the same species.
The scientist's mean results are shown in Table 2.1:
[Table_1]
$$\begin{array}{|c|c|} \hline \text{height/m} & \text{mean xylem pressure /MPa} \\ \hline 50.5 & -0.800 \\ 62.5 & -0.875 \\ 74.0 & -0.950 \\ 82.0 & -1.000 \\ 89.5 & -1.045 \\ \hline \end{array}$$
Use a sharp pencil for graphs.
(i) Complete and plot the graph of the data shown in Table 2.1. [4]
(ii) Explain, using your knowledge of adhesion and cohesion, how water is transported through the xylem vessel elements in a tree with transpiring leaves. [2]
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