2010 Biology Paper 3- Question 2

Organisms in an environment compete with each other for the same basic needs in their survival. Competition between individuals of different species is called interspecific competition and competition between individuals of the same species is called intraspecific competition. The effect of the competition is shown in their growth such as the height, size and dry mass.

Based on the above information, plan a laboratory experiment to study the effect of interspecific competition between maize and paddy plants on their growth.

The planning of your experiment must include the following aspects:

• Problem statement
• Hypothesis
• Variables
• List of apparatus and materials
• Experimental procedure
• Presentation of data

Sample answer

Problem statement (3 marks)	What is the effect of interspecific competition between maize and paddy plants on their growth?
Hypothesis (3 marks)	Maize plant grow taller than paddy plant// The growth of maize plant is less when it is grown with paddy plant than when it is grown alone.
Variables (3 marks)	Manipulated variable : Type of plant// Maize and paddy plants (only one) Responding variable : Growth of plant//dry mass//height//size (only one) Constant variable : Distance between each seedling//amount of water//intensity of sunlight//nutrient//temperature//duration (only one)
List of apparatus and materials (3 marks)	Apparatus : Tray, oven, balance and ruler Material : Paddy, maize, soil, water
Experimental procedure (3 marks)	1. 3 trays : X is planted with paddy, Y planted with maize and Z with maize and paddy. 2. The seedling trays are filled with equal amount of garden soil. 3. Initial dry mass/any other growth parameter of the seedlings are measured. 4. 5-30 paddy/maize seedlings are planted at 5 cm apart. 5. The seedlings are watered everyday. 6. The trays are weeded. (precaution) 7. After 7-30 days, 5-10 paddy seedlings are removed from tray X and the roots are cleaned (precaution) and then heated/dried in an oven at 105oC. 8. The average dry mass of seedlings is measured using a balance and recorded. 9. Steps 7-8 are repeated with maize seedlings in tray Y and maize and paddy seedlings in tray Z. 10.All data are recorded in a table.
Presentation of data (2 marks)	Types of plants(Tray) Initial dry mass (g) Final dry mass (g) Difference in dry mass (g) Paddy (X) Maize (Y) Paddy (Z) Maize (Z)