• Write your index number in the space at the top right-hand corner of this page.

• Answer ALL questions. Write all your answers in the spaces provided in this booklet.

2. A bean was soaked in water for 24 hours and subsequently pinned horizontally on to a piece of cardboard, and allowed to germinate. After two days, when a plumule and radicle had emerged through the micropyle, measurements of the angle of curvature of the plumule and the angle of curvature of the radicle were made. Measurements were taken every hour over a period of ten hours. The results are shown in the table below.

1. Using the same scale and axes, plot graphs of plumule curvature against time and radicle curvature against time. Use the squared paper at the end of this answer booklet.

[ten marks]

 

2. Which part of the seedling emerges first through the micropyle? Indicate the significance of this.

[two marks]

 

3. Compare and contrast the patterns of emergence of the radicle and plumule during this ten-hour period.

[five marks]

4. What stimulus brings about the responses observed?

[two marks]

 

5. Describe the mechanism through which this stimulus generates the observed response of the radicle.

[three marks]

 

The experiment was repeated with minor changes. In the modified procedure, the root cap was removed from the radicle as soon as it emerged through the micropyle. The meristematic tissue was left intact. Following treatment, the seed was allowed to germinate under the same experimental conditions as before. Curvature of the radicle did not occur during the modified procedure.

 

6. What can you conclude from this observation?

[three marks] [Total: twenty-five marks]

2. Mitosis may be observed in cells from the root tip of plants.

1. Why should cells from the root tip be considered particularly suitable for observing mitosis?

[five marks]

 

2. Give a detailed description (in point form) of the procedure involved in preparing root tip squashes in order to observe the different stages of mitosis.

[twelve marks]

4. Mitosis preserves the diploid state in the organism. Which particular events in mitosis ensure that this is so?

[three marks]

 

5. In some cases, no dividing cells are visible in a root squash preparation. Suggest possible reasons for this.

[five marks] [Total: twenty-five marks]

4. The diagram below represents a transverse view of a lumbar vertebrum from a mammal.



1. Identify the structures labelled A through D.

Structure A:

Structure B;

Structure C:

Structure D:

[eight marks]

2. What is the general function of the long projections arising from the vertebrum?

[three marks]

3. In what way is the three-dimensional shape of these projections adapted to their function?

[three marks]

4. Suggest a reason as to why structure C is particularly large in lumbar vertebrae.

[three marks]

5. Why is structure A particularly long in lumbar vertebrae when compared with most cervical vertebrae?

[three marks]

6. Draw a diagram showing a lumbar vertebrum as it would be expected to appear in longitudinal view. Use the space provided below for your drawing.

[five marks] [Total: twenty-five marks]

 

 

6. The response of woodlice to different levels of environmental humidity was investigated by placing 100 adult woodlice in an elongated chamber characterised by a constantly maintained gradient of humidity along its length. The chamber was kept under constant conditions of temperature and illumination for forty-eight hours during which time the distribution of the woodlice was noted at intervals. The results are listed in the table below:

	number of woodlice
Relative Humidity (%)	3 hours after start	14 hours after start	24 hours after start	48 hours after start
0-10	0	2	0	8
10-20	0	15	0	12
20-30	0	16	0	9
30-40	2	6	0	11
40-50	0	20	1	7
50-60	3	17	5	14
60-70	10	8	9	8
70-80	25	6	35	10
80-90	35	4	30	11
90-100	25	6	20	10

 

 

1. Suggest a suitable null hypothesis for this investigation.

[three marks]

 

2. What general patterns are evident in the data?

[five marks]

4. The researcher intends to determine whether the final distribution of woodlice (at 48 hours) is significantly different from the distribution at 14 hours and the distribution at 24 hours. Name a statistical test that may be used to carry out these two comparisons. Justify your answer.

Statistical test:

Justification:

[six marks]

 

5. Suggest a way of summarising the data in useful graphical form. You are NOT required to draw any figures.

[three marks]

 

6. What conclusions can you draw, if any, about the response of woodlice to environmental humidity?

[four marks]

8. Suggest ONE precaution that should be taken before starting the experiment.

[two marks]

 

9. Suggest ONE possible source of error that may be influencing the result obtained.

[two marks] [Total: twenty-five marks]