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Populations and Communities · Paper 2 — Free Biology HL Practice Questions

1MasterySAQ-SPopulation dynamics: Growth models, carrying capacity5 marksPaper 2~8 min

A population of Daphnia (water fleas) in a small pond grows according to a logistic model. The carrying capacity of the pond is

K = 800

individuals. The graph below shows population size (

N

) against time (

t

) in weeks.

(a)

Identify the population size at which the rate of population growth is greatest. [1 mark]

(b)

Describe the relationship between population growth rate and carrying capacity when

N = 400

individuals, with reference to available resources. [2 marks]

(c)

A pollution event suddenly reduces the population from

N = 750

N = 400

individuals. The pond subsequently recovers fully. Evaluate how the population growth rate immediately after the pollution event compares to the growth rate that existed just before the event, and predict the long-term trajectory of the population. [2 marks]

Solutions

2MasterySAQ-SPopulation dynamics: Growth models, carrying capacity5 marksPaper 2~8 min

An ecologist studies a population of algae (Chlorella vulgaris) in a laboratory culture flask. The population grows according to the logistic growth model. The carrying capacity of the flask is

5.0 \times 10^{6}

cells

\text{mL}^{-1}

. The graph below shows the population size over time.

(a)

State the biological significance of Point B on the logistic growth curve. [1 mark]

(b)

Explain why the per capita growth rate at Point A is greater than at Point C. [2 marks]

(c)

The ecologist adds a chemical that kills 60 percent of the algae, reducing the population to

2.0 \times 10^{6}

cells

\text{mL}^{-1}

(Point D). Evaluate whether the population at Point D will recover to carrying capacity more rapidly than a population starting from Point B, and identify one factor that could prevent full recovery. [2 marks]

Solutions

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