With reference to aquatic animals, consider the following statements: 1. All sea animals have a streamlined shape to move easily in water. 2. Squids and octopuses make their body shapes streamlined when they move in water. 3. Gills are the primary respiratory organs in most fish. Which of the statements given above are correct?

The correct option is (c) 2 and 3 only. Explanation Aquatic animals exhibit various adaptations to survive in water, including body shape modifications for movement and specialized organs for respiration. While streamlining is a common adaptation to reduce friction, it is not universal among all aquatic species. Statement-wise Analysis: - Statement 1 is Incorrect: Not all sea animals possess a streamlined shape. Organisms such as squids and octopuses, which typically inhabit deeper ocean levels near the seabed, do not naturally have a streamlined body shape while at rest. Other bottom-dwellers like starfish also lack this shape. - Statement 2 is Correct: Although squids and octopuses are not permanently streamlined, they possess the physiological ability to alter their body shape. When they need to move through the water, they make their bodies streamlined to reduce resistance and swim efficiently. - Statement 3 is Correct: Gills are the primary respiratory organs in most fish. They are specialized projections of the skin that allow fish to extract oxygen dissolved in water. Aquatic mammals like whales and dolphins do not possess gills; they breathe air through blowholes or nostrils. Key Takeaway: While a streamlined body is a prevalent adaptation for reducing water resistance, some deep-sea animals like squids adopt this shape only during movement. Gills are the standard respiratory organ for fish, whereas aquatic mammals utilize lungs.

With reference to aquatic animals, consider the fo... - NCERT Class 6 Science MCQ

Solution

The correct option is (c) 2 and 3 only.

Explanation

Aquatic animals exhibit various adaptations to survive in water, including body shape modifications for movement and specialized organs for respiration. While streamlining is a common adaptation to reduce friction, it is not universal among all aquatic species.

Statement-wise Analysis:

Statement 1 is Incorrect: Not all sea animals possess a streamlined shape. Organisms such as squids and octopuses, which typically inhabit deeper ocean levels near the seabed, do not naturally have a streamlined body shape while at rest. Other bottom-dwellers like starfish also lack this shape.
Statement 2 is Correct: Although squids and octopuses are not permanently streamlined, they possess the physiological ability to alter their body shape. When they need to move through the water, they make their bodies streamlined to reduce resistance and swim efficiently.
Statement 3 is Correct: Gills are the primary respiratory organs in most fish. They are specialized projections of the skin that allow fish to extract oxygen dissolved in water. Aquatic mammals like whales and dolphins do not possess gills; they breathe air through blowholes or nostrils.

Key Takeaway: While a streamlined body is a prevalent adaptation for reducing water resistance, some deep-sea animals like squids adopt this shape only during movement. Gills are the standard respiratory organ for fish, whereas aquatic mammals utilize lungs.

NCERT Class 6 Science — Chapter 4: The living organisms - characteristics and habitats

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