IGCSE Biology Extended 19.4.7—Factors that lead to each phase Topic Practice

• Explain the factors that lead to each phase in the sigmoid curve of population growth, making reference, where appropriate, to the role of limiting factors

[Maximum number: 3]

Bacteria are used in many biotechnological processes.

Genetically engineered bacteria that are used to make insulin were grown in a fermenter for five days.

Samples were taken from the fermenter every six hours and the number of bacteria in $1.0 \mathrm{~mm}^{3}$ of the nutrient solution were counted.

Changes in the numbers of living bacteria in the samples taken from the fermenter are shown in Fig. 3.1.

Fig. 3.1

Explain, with reference to Fig. 3.1, why the bacteria did not grow in the fermenter for longer than five days.

[Maximum number: 3]

Genetically modified bacteria were grown in a fermenter. The number of bacteria was measured, and the data are shown in Fig. 5.1.

Fig. 5.1

Describe and explain the change in bacterial population size from 24 hours to 50 hours shown in Fig. 5.1.

[Maximum number: 1]

During the exponential (log) phase of a sigmoid growth curve, which factor limits population growth?

availability of food

build-up of wastes

presence of disease

rate of reproduction

0 selected

Question 3(c)(iii)

Question 5(c)(iv)

Question 37