Explanation

A heterocyclic compound is a ring structure that contains at least one atom other than carbon in the ring.

Pyridine has a nitrogen atom in its ring structure, making it a heterocyclic compound. 

Explanation

Viruses lack organelles like ribosomes, mitochondria, and Golgi apparatus.

They are simple particles composed of genetic material (DNA or RNA) and a protein coat.

They need to infect a host cell to use the host's ribosomes to replicate.

Explanation

The pair that is not isomorphous is Na₂CO₃, CaCO₃. 

While both compounds have similar chemical formulas.

The difference in ionic radii between sodium and calcium leads to different crystal structures, making them not isomorphous.

Explanation

• When light passes through a prism, refraction occurs, leading to the formation of a spectrum.
• Refraction is the bending of light as it passes through a medium with a different optical density.
• It causes the different wavelengths of light to separate and form a spectrum.

Explanation

 The special enzyme used to cut DNA at specific sequences is called a restriction enzyme or restriction endonuclease.

These enzymes are crucial for various molecular biology techniques like genetic engineering and DNA fingerprinting.

They recognize specific sequences within the DNA and cleave the molecule at those sites. 

Explanation

In echinoderms, water enters the water vascular system through a sieve-like structure called the madreporite.

This structure, often a small, light-colored plate, acts as an opening to the internal water-filled canals.

Water then flows through a series of canals, including the stone canal and radial canals, eventually reaching the tube feet.

Explanation

Circinate vernation, a term in botany, describes the arrangement of young leaves in a coiled or spiralled manner, characteristic of fern fronds. This coiled structure, often resembling a crozier or fiddlehead, protects the tender growing tip of the leaf as it matures. 

Explanation

I have never known him for a long time.

میں اسے ایک عرصے سے کبھی نہیں جانتا تھا۔

"Have never known" is the correct present perfect tense.

It indicating that up until now, the speaker has never known the person.

Explanation

Explanation

A basic buffer is made by combining a weak base with its salt formed with a strong acid (e.g., NH₄OH + NH₄Cl).

This mixture resists pH change upon addition of small amounts of acid or base.