CHAPTER 2

2. A dark red-coloured compound.
5. The concentration of oxygen in the air is lower at a _____ altitude.
8. At night or on a hot day, the guard cells become _____ and straight.
10. A person who does not smoke but inhales cigarette smoke is known as ____ smoker.
11. A substance in cigarette smoke that can cause addiction.
13. Cancer causing chemical substances.
14. It can cause soil to be less fertile.
16. The structure that opens or closes the trachea.
17. The respiratory system of insects.
18. A condition of damaged alveoli.
20. Pathway of air into the nasal cavity.

1. A colourless gas with a pungent smell.
3. Guard cells contain _______ to carry out photosynthesis.
4. Process of movement of particles from a high concentration region to a low concentration region.
6. The skin of frogs is thin and very ____ to gas.
7. In the breathing mechanism model, the rubber sheet represents the ____.
9. A part of respiratory tract.
12. This happens to the intercostal muscles during inhalation.
15. The exchange of gaseous occurs here.
19. One of the harmful substances in the air.