CSEC Biology Paper 3 January 2020 - Free CXC Past Paper with Answers

A farmer obtains some broccoli seeds and wants to find out which of three temperature conditions is best for germination, so that she can decide where to plant the seeds. The three temperature conditions are field temperature ($32–34 \ ^\circ C$), room temperature ($25 \ ^\circ C$) and greenhouse temperature ($15 \ ^\circ C$).

Plan and design an experiment which will allow you to advise the farmer of the best temperature for planting the broccoli seeds. Use the following sections to guide you.

Hypothesis

State TWO possible sources of error in the experiment designed in (a).

Suggest THREE reasons why water is essential for seeds to germinate.

State THREE visible characteristics that can be used to classify these organisms into two groups.

Using one of the characteristics identified in (a), complete Table 2 below to show how the organisms may be classified into two groups.

TABLE 2: CLASSIFYING OF ORGANISMS

Name an instrument that the biologist could have used to collect the organisms, in Figure 1 on page 8.

Briefly describe how the instrument named in (c) (i) is used.

State TWO precautions that the biologist should have taken when collecting the organisms in Figure 1 on page 8.

A biologist wants to estimate the size of the butterfly population. On his first visit to the garden he captured 15 butterflies, then marked each of them with paint on its wings. A week later, he returned to the garden and captured 20 butterflies. Five of these butterflies had paint on their wings.

Calculate the number of butterflies in the population using the following formula:

Number of organisms in the population = $\frac{\text{Number of organisms captured on second visit} \times \text{Number of organisms marked on the first visit}}{\text{Number of recaptured animals that were marked}}$

Of the 15 butterflies captured on his first visit, the biologist noticed that those of the same species had either blue wings only, red wings with blue stripes only or red wings only. He concluded that the colour of the butterflies' wings is determined by codominant alleles.

Using the symbols R for red and B for blue, use a genetic diagram to explain why the biologist would conclude that the alleles are codominant.

Predict the phenotypic ratio of the population if two of the butterflies with striped wings are crossed.