The oxygen cycle illustrates the oxygen flow occurring in several parts of our vast ecosystem. It helps maintain the concentration of oxygen in the atmosphere. It takes place in three stages. During photosynthesis, the green plants release oxygen into the atmosphere in the first stage. Later in the second and third stages, aerobic organisms use the oxygen released by green plants and release carbon dioxide back into the air, which the plants in the first stage use during photosynthesis.
| Definition: The oxygen cycle is the movement of oxygen from the atmosphere through a series of intricate processes. |
Oxygen Cycle Chemistry Questions with Solutions
Q1. The atmosphere contains ________ of oxygen.
(a) 21 per cent
(b) 13 per cent
(c ) 75 per cent
(d) None of the above
Answer: (a) The atmosphere contains 21 per cent of oxygen.
Q2. Oxygen from the atmosphere is used up in processes, namely
(a) Combustion
(b) Respiration
(c ) In the form of oxides of nitrogen
(d) All of the above
Answer: (d) Oxygen from the atmosphere is used up in combustion, respiration and the form of oxides of nitrogen.
Q3. The two forms of oxygen formed in the atmosphere are
(a) Water and ozone
(b) Ozone and oxygen
(c ) Water and oxygen
(d) All of the above
Answer: (b) The two forms of oxygen formed in the atmosphere are ozone and oxygen.
Q4. In the oxygen cycle, the movement of oxygen takes place within
(a) Atmosphere
(b) Biosphere
(c ) Lithosphere
(d) All of the above
Answer: (d) In the oxygen cycle, the movement of oxygen takes place within the atmosphere, biosphere and lithosphere.
Q5. The oxygen cycle is an example of the _______ cycle.
(a) Chemical
(b) Photosynthesis
(c ) Biogeochemical
(d) None of the above
Answer: (c ) The oxygen cycle is an example of the biogeochemical cycle.
Q6. What is the oxygen cycle?
Answer: The oxygen cycle is the movement of oxygen from the atmosphere through a series of intricate processes. It helps maintain the oxygen level of the atmosphere.
Q7. What are the different stages of the oxygen cycle?
Answer: The oxygen cycle is the movement of oxygen from the atmosphere through a series of intricate processes. It takes place in three stages.
Stage 1: In the first stage, during photosynthesis, the green plants release oxygen into the atmosphere.
Step 2: In the second stage, all the aerobic organisms use the oxygen released by the green plants.
Step 3: In the third stage, the aerobic organisms release the carbon dioxide back into the air, which the plants in the first stage use during photosynthesis.
Thus, oxygen is balanced in the atmosphere.
Q8. Name any four processes in which atmospheric oxygen is used?
Answer: The processes in which atmospheric oxygen is used are mentioned below.
1. Breathing
2. Decomposition
3. Combustion
4. Rusting
Q9. Answer the following questions.
(a) Name the process which returns oxygen to the atmosphere.
(b) What are the various forms of oxygen in the earth’s crust?
Answer: (a) Photosynthesis returns oxygen to the atmosphere.
(b) Organic molecules and water are the forms of oxygen in the earth’s crust.
Q10. Draw a diagram to show the oxygen cycle in nature.
Answer:
Q11. What is a biogeochemical cycle?
Answer: Biogeochemical cycle refers to the movement of matter from the atmosphere through a series of intricate processes.
Q12. What are the primary reservoirs of oxygen?
Answer: The primary reservoirs of oxygen are mentioned below.
1. Atmosphere
2. Hydrosphere
3. Biosphere
4. Lithosphere
Q13. What is photosynthesis?
Answer: Photosynthesis is the process in which plants use water, sunlight and carbon dioxide to form oxygen and energy in the form of sugar. It helps maintain the oxygen level of the atmosphere.
Q14. Match the following.
| Column A | Column B |
|---|---|
| Nitrogen | 97 per cent of the water on earth |
| Oxygen | 3 per cent of the water on earth |
| Carbon dioxide | 0.04 per cent in air |
| Freshwater | 21 per cent in air |
| Salt Water | 78 per cent in air |
Answer:
| Column A | Column B |
|---|---|
| Nitrogen | 78 per cent in air |
| Oxygen | 21 per cent in air |
| Carbon dioxide | 0.04 per cent in air |
| Freshwater | 3 per cent of the water on earth |
| Salt Water | 97 per cent of the water on earth |
Q15. Name two processes responsible for producing oxygen in nature.
Answer: The two methods responsible for producing oxygen in nature are mentioned below.
1. Photosynthesis
2. Photodissociation
Practise Questions on Oxygen Cycle
Q1. Explain the significance of the oxygen cycle.
Q2. What is photodissociation?
Q3. What would happen if all the oxygen present in the environment is converted to ozone?
Q4. What is the ozone layer? What is responsible for the depletion of the ozone layer?
Q5. What is the role of respiration in the oxygen cycle?
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