Across
- 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.
Down
- 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.