Question

Which one of the following categories of animals is correctly described with no single exception in it?

• A. All bony fishes have four pairs of gills and an operculum on each side.
• B. All mammals are viviparous and possess diaphragm for breathing
• C. All sponges are marine and have collared cells.
• D. All reptiles possess scales, have a three-chambered heart and are cold-blooded (poikilothermic)

Answer 1

The correct option is A

All bony fishes have four pairs of gills and an operculum on each side.

The correct option is option A.

Explanation of correct option:

1. Osteichthyes, commonly known as bony fish, have an ossified (bony) endoskeleton with a hard matrix of calcium phosphate.
2. It includes both marine and freshwater fishes with a bony endoskeleton.
3. They have four pairs of gills which are covered by an operculum on each side.
4. An operculum is a hard, bony flap that resembles a plate and protects a bony fish's gills.

Explanation of incorrect options:

Option B:

1. In mammals, breathing is done by the lungs and is enhanced by the muscular diaphragm.
2. Mammals are viviparous, with few exceptions.
3. Prototheria ( example - monotremes) is oviparous.
4. Animals classified as oviparous are those that lay eggs with little to no other embryonic development occurring inside the mother.

Option C:

1. Members of the phylum Porifera are commonly referred to as sponges.
2. They are mostly marine, but all sponges are not marine.
3. For example - Spongilla is a freshwater sponge.
4. The spongocoel (body cavity) and canals are lined with choanocytes, also known as collar cells in the sponges.

Option D:

1. Reptiles are mostly terrestrial animals.
2. Their skin is covered with scutes or scales.
3. They are cold-blooded animals. The body temperature of reptiles varies with the surrounding atmosphere.
4. All reptiles have three-chambered hearts, except crocodiles, which have four-chambered hearts.

Final Answer: All bony fishes have four pairs of gills, and an operculum on each side is correctly described with no single exception in it.