Q1.
Do plants only take in substances from their surroundings, or do they also release something?
Answer
Plants both take in and give out. During photosynthesis they take in carbon dioxide and water, and they release oxygen into the air.
Carbon dioxide + Water → Glucose + Oxygen
Water vapour also escapes from the leaves. Separately, plants respire all the time — taking in oxygen and giving out carbon dioxide.
Activity 10.5 is the experiment that shows the release of oxygen: bubbles of gas collect in an inverted test tube above a water plant kept in sunlight.