iGCSE Biology (0610)-19.4 Populations - iGCSE Style Questions Paper 3

Question

(a) The boxes on the left show two terms.
The boxes on the right show the descriptions of some terms.
Draw one line to link each term to its description.
Draw two lines.

(b) The growth of bacteria in a flask containing nutrients was monitored for six hours.
The number of live bacteria per \(cm^{3}\) was estimated every 30 minutes.
Fig. 6.1 shows the results.

(i) The data in the graph has been divided into four phases: A, B, C and D.
The list shows the names of the four phases.
death exponential lag stationary
Use the words from the list to identify phases A, B, C and D shown in Fig. 6.1.

(ii) Complete the sentences using the data shown in Fig. 6.1 and your knowledge.
The number of live bacteria in phase A remained at ………………………………………. per \(cm^{3}\).
In phase B the number of live bacteria doubled between 2.0 hours and ………………………………………. hours.
The maximum number of live bacteria occurred in phase ………………………………………. .
In phase ………………………………………. the number of live bacteria decreased because the bacteria did not have enough ………………………………………. .

▶️ Answer/Explanation

Solution

(a)

Explanation: The term “population” is linked to “all the organisms of one species in a habitat” because a population refers to a group of individuals of the same species in a given area. “Community” is linked to “all the organisms of different species in a habitat” as it includes multiple interacting populations.

(b)(i) A) lag
B) exponential
C) stationary
D) death

Explanation: Phase A is the lag phase where bacteria adapt to the environment. Phase B is the exponential phase with rapid growth. Phase C is the stationary phase where growth stabilizes, and Phase D is the death phase due to resource depletion.

(b)(ii) 1000 ;
2.5 ;
C ;
D ;
(named) nutrients / oxygen ;

Explanation: In Phase A, bacteria count remains at 1000 per \(cm^{3}\). The doubling time in Phase B is from 2.0 to 2.5 hours. The peak population occurs in Phase C (stationary), and the decline in Phase D (death) is due to insufficient nutrients/oxygen.

Question

A population of a species of fish was accidentally introduced into a lake.

(a) State two features that can be used to classify this introduced species as a fish.

(b) Describe what is meant by the term population.

(c) Fig. 4.1 shows the changes in the population size of the introduced fish species in the lake between 2004 and 2010.

(i) The boxes on the left show the letters identifying the sections of the graph in Fig. 4.1.
The boxes on the right show the phases of population growth.
Draw lines to link each letter with the correct phase.
Draw three lines.

(ii) Describe possible reasons for the change in population size between 2009 and 2010 in Fig. 4.1.

▶️ Answer/Explanation

Solution

(a) Any two from:
• Scales
• Gills
• Swim bladder
• Fins
• Lateral line
(These are defining features of fish, distinguishing them from other aquatic organisms.)

(b) A population refers to a group of organisms of the same species living in the same area at the same time. (This definition highlights the ecological context of the term.)

(c)(i)

(The graph sections are matched with phases: exponential growth, stationary phase, and decline.)

(c)(ii) Possible reasons for the population decline between 2009 and 2010 include:
• Increased predation or overfishing
• Disease or pollution
• Competition for limited resources
(These factors explain the observed decrease in population size during the specified period.)

iGCSE Biology (0610)-19.4 Populations – iGCSE Style Questions Paper 3

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