Biology Questions

Asterias has bilateral symmetry only at larval stagebut fivefold symmetry (pentamerism, a special type of radial symmetry) as adults.

Nereis do not possess any symmetry elements in their body organisation.

A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template by a process called Reverse Transcription.

In brief its function is that copies all or part of the virus RNA (retroviruses are RNA-only) as DNA which can then be integrated into the DNA of the host organism.

The mammalian heartis called myogenic (myo = muscle, genie = originating from). It means the heart beat or the activities of the heart are auto regulated which originates from a muscle called nodal tissue.In the human heart,heartbeat originates and contraction is initiated by a special modified heart muscle known as sinoatrial node. It is located in the right atrium; while the QRS waves are the depolarisation of the ventricles, which initiates the ventricular contraction.The T-wave represents the repolarisation,that is, the return of the ventricles from excited tonormal state.Hepatic portal system is the unique vascular connection that exists between the digestive tract and liver. This vein carries blood from intestine to the liver.

Euglena move by a flagellum (plural ‚ flagella), which is a long whip-like structure that acts like a little motor.

The paramecium uses its cilia to sweep the food along with some water into the cell mouth after it falls into the oral groove.

The underside of the starfish is covered with hundreds of tube feet, which it uses for walking around, for attaching tightly to rocks, and for holding on to prey.

Nereis possess setae and parapodia for locomotion