NCERT Class 10 Science — Chapter 1: Life Processes

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Assertion (A): The rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Reason (R): The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air.

Official previous-year question

Verified 1 Aug 2026.

Options

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is NOT the correct explanation of A
CA is true but R is false
DA is false but R is true

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Solution

The correct option is

Both A and R are true and R is the correct explanation of A

Explanation

Respiration involves the intake of oxygen from the environment for cellular metabolism. The rate of breathing in an organism is primarily determined by the metabolic requirement for oxygen and the concentration of oxygen available in the surrounding medium (air or water).

Analysis of Assertion and Reason:

Assertion (A): Correct. Aquatic organisms, such as fish, exhibit a significantly faster rate of breathing compared to terrestrial organisms. They must constantly pump water over their respiratory surfaces (gills) to maintain adequate oxygen uptake.
Reason (R): Correct. The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air. While air contains approximately 21% oxygen, the concentration of oxygen dissolved in water is much lower.
Justification: Because the oxygen concentration in water is low, aquatic organisms must process a larger volume of the medium (water) in a shorter time to extract the necessary amount of oxygen. This necessitates a faster breathing rate. Therefore, the low availability of oxygen (Reason) is the direct cause of the faster breathing rate (Assertion).

Key Takeaway:
Aquatic organisms have a faster breathing rate than terrestrial organisms as a physiological adaptation to compensate for the low concentration of dissolved oxygen in water compared to the high oxygen content in air.

Your note

More from Chapter 1: Life Processes

Which enzyme, present in saliva and pancreatic juice, is primarily responsible for the breakdown of starch into simpler sugars?

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The accumulation of which compound in muscle cells leads to cramps during sudden physical activity or anaerobic respiration?

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Which hair-like structures lining the upper respiratory tract help in filtering air by trapping dust and particles?

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In the circulatory system of fishes, the heart is characteristically composed of how many chambers?

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With reference to maintenance functions in organisms, consider the following statements: 1. The transfer of energy source from outside to inside is referred to as respiration. 2. These processes require energy sourced from outside the body. 3. All organisms obtain energy directly from sunlight. Which of the statements given above is/are correct?

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The correct option is

Both A and R are true and R is the correct explanation of A

Explanation

Analysis of Assertion and Reason:

Assertion (A): Correct. Aquatic organisms, such as fish, exhibit a significantly faster rate of breathing compared to terrestrial organisms. They must constantly pump water over their respiratory surfaces (gills) to maintain adequate oxygen uptake.
Reason (R): Correct. The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air. While air contains approximately 21% oxygen, the concentration of oxygen dissolved in water is much lower.
Justification: Because the oxygen concentration in water is low, aquatic organisms must process a larger volume of the medium (water) in a shorter time to extract the necessary amount of oxygen. This necessitates a faster breathing rate. Therefore, the low availability of oxygen (Reason) is the direct cause of the faster breathing rate (Assertion).