Why should scientists control variables in an experiment?
To get accurate results
To make it unfair
To finish faster
Which gas is released when fuels like petrol are burned?
Carbon dioxide
Oxygen
Nitrogen
Cigarette smoke is harmful because it ____
Contains clean gases
Has oxygen
Contains toxic chemicals
Which of these helps reduce air pollution?
More cars
Burning rubbish
Planting trees
What happens when we breathe out?
Carbon dioxide leaves the body
Oxygen enters the body
Nitrogen is used by lungs
What happens when we breathe in?
Carbon dioxide enters the lungs
Oxygen leaves the body
Oxygen enters the lungs
Which gas helps plants make food during photosynthesis?
Carbon dioxide
Oxygen
Nitrogen