Energy & Feeding Relationships (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

A student wanted to investigate a garden ecosystem.

She counted the number of insects caught in spider webs in one small section of the garden.

She found six spider webs in the small section of the garden sampled.

Diagrams of the spider webs are shown in Fig. 1 Each black dot represents one insect caught in a spider web.

Fig. 1

Use Fig. 1 to complete Table 1

Table 1

Spider web	Number of insects caught in each web
A
B
C
D
E
F
Total

[2]

Calculate the average number of insects per web in the small section of the garden, using the information in Fig.1 and Table 1.

The student counted the total number of spider webs in the whole garden and found that there were a total of 102 spider webs.

Use this information and your answer to part (a)(ii) to estimate the total number of insects caught in webs in the whole garden. 

Suggest one reason why the estimated total number of insects caught in webs in the whole garden may not be accurate.

Fig. 2 is a photograph of a spider.

A spider’s body has two main parts. The legs are all attached to the cephalothorax which is the upper part of the body and starts at label X on Fig. 2. The lower part of the body is called the abdomen and is nearest to label Y on Fig. 2. 

Fig. 2

Make a large drawing of the spider in Fig. 2 to show its outline, including its legs.

Label the abdomen.

[5]

Measure the length of the spider between points X and Y in Fig. 2 Include the units. A ruler, graduated in cm, has been added to Fig. 2 for this purpose. 

Draw a line in the same position on your drawing and measure the length of your drawing.

Calculate the magnification of your drawing using your measurements and the following equation:

Table 2 contains some other data collected by the student from the garden ecosystem.

Table 2

Type of organism	Number found in the garden ecosystem
Trees	2
Bushes	5
Other plants	37
Herbivores	118
Carnivores	14

Plot a bar chart of the data in Table 2.

[3]

Herbivores and carnivores are animals.

Use the data in Table 2 to calculate the ratio of animals to plants.

Show your working and give your answer in its simplest form.