Cell Structure & Size of Specimens (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

A student investigated the number of petals on the flowers of two species of daisy, species A and species B.

Fig.1 shows one daisy flower of species A.

Fig. 1

The actual length of petal XY of the daisy in Fig.1 was measured by the student as 5 mm.

Measure the length of petal XY in the photograph in Fig.1. A cm-ruler has been included for your use. Include the units.

Use the formula to calculate the magnification of the photograph.

Show your working.

The student collected 10 flowers from species A and 10 flowers from species B. They counted the number of petals on each flower.

Fig. 2 shows some of the daisy flowers of species A.

Fig. 2

Count the number of petals on flowers 9 and 10 in Fig. 2 and record the number of petals in Table 1.

Table 1

[1]

Calculate the average number of petals for species B.

Give your answer to the nearest whole number.

[1]

Suggest one method that could be used to ensure that the counting of the number of petals is accurate.

[1]

Plot a bar chart on the grid of the average number of petals for species A and species B from Table 1.

State two reasons why the student should have repeated the investigation.

The student noticed that insects fed on the nectar produced by the flowers.

Describe the test that the student would use to find out if the nectar contains reducing sugars.

[3]

State one safety precaution that should be taken when carrying out the test for reducing sugars.

[1]

Fig.1 shows a photomicrograph of a bronchus, surrounded by alveoli and other tissues, in the lung.

Fig.1

(i)

Make a large drawing of the bronchus shown in Fig.1

Do not include any of the alveoli or other tissues in your drawing. Do not label your drawing.

[4]

The diameter of the bronchus in Fig.1 is shown by the line AB.

The actual diameter of the bronchus in Fig.1 is 1.5mm.

The magnification of the bronchus in Fig.1 can be calculated using the following equation:

The length of AB on the original photomicrograph, represented in Fig.1 is 55 mm.

Calculate the magnification of the bronchus in Fig.1

Give your answer to the nearest whole number.

[2]

Fig. 1 shows a cross section through a beetroot.

Image courtesy of Joergens.mi. Original image located at: //commons.wikimedia.org/wiki/File:Beetroot_jm27958.jpg. Licenced under CC-BY-SA-3.0 under conditions found at: https://creativecommons.org/licenses/by-sa/3.0/deed.en. 

Fig. 1

Draw a large diagram of the beetroot in Fig. 1. Do not label your drawing or include line AB.

[4]

The magnification of the beetroot in Fig. 1 is x2.

The length of line AB is 10 cm.

Calculate the actual width of the beetroot using the formula and the measurement of line AB.

Show your working.

[2]

Students conducted an experiment to investigate the effect of temperature on plant cell membranes. They followed the experimental procedure described below.

• Beetroot cores were cut using a cork borer.
• They used a scalpel to cut each core into 2 cm sections.
• Students used six beakers to set up water baths at different temperatures (0°C, 20°C, 40°C, 60°C, 80°C and 100°C).
• The temperature of each water bath was monitored using a thermometer and manually adjusted using cold or hot water.
• 5 cm³ of distilled water was added to each of six test tubes and one test tube was placed in each water bath and left for 5 minutes.
• After 5 minutes, one 2 cm beetroot section was added to each test tube and left for 30 minutes.
• After 30 minutes, the contents of each test tube was placed in a colorimeter and the percentage transmission of light was measured at each temperature.
• The experiment was repeated two more times.

Table 1 shows the results of the investigation.

Table 1

Identify the independent and dependent variable for this investigation.

[2]

State two safety precautions that should be followed during the experimental procedure.

[2]

Use the data in Table 1 to calculate the mean percentage of light transmitted at a temperature of 60°C.

Give your answer to three significant figures.

[1]

Use the grid below to plot a line graph of temperature against the mean percentage of light transmitted from Table 1.

[4]

Explain the importance of repeating the experiment several times.