Chandani wanted to investigate the effects of substances (lime, urea fertilizer, common salt, and compost manure) mixed with soil on plant growth. She used 12 uniform pots (3 pots per substance), the same soil, same seeds, equal watering, and a sunny location, then measured plant height daily. (i) Identify the independent variable, dependent variable, and controlled variable in Chandani's experiment. (ii) Why did Chandani use 3 pots for each substance?

Question

Accepted Answer

(i) Independent variable: The type of substance mixed with the soil (lime, urea, salt, or compost). Dependent variable: The height/growth of the plant. Controlled variable: The type and amount of soil, size of the pots, type of seeds, amount of water given, and sunlight exposure — all kept the same across every pot. (ii) She used 3 pots for each substance to repeat the trial (replication). Using only one pot could give an unreliable or accidental result; testing with 3 pots for each condition helps confirm that the observed effect is consistent and not due to chance, making the conclusion more reliable and valid.