Tag: bacteria - introduction, shape and structure

Viruses play an important role in horizontal gene transfer and genetic diversity. The evolution history showcases the origin of viruses as to have evolved from plasmids when pieces of DNA moved between cells. As
big bits of cellular DNA became independent and some DNA stuck with cell genomes. Thus, the correct answer is option D.

• A virus is an organism that can be considered both living and non-living. 
• It can be considered as living when it is inside any host (bacterium) as the virus infects the host cell and replicates inside it making several copies of it. 
• When it is outside the host cell, it is non- living as it can not carry out its life- processes of either reproducing or digestion etc.
• Thus, option A is correct here.

Viruses are non-cellular organisms and replicate only when they infect the host cell. 

Reproducing is one of the characteristics of the living organisms. Viruses definitely multiply. Viruses must use host cells to create more virions. Since viruses don’t have organelles, nuclei or even ribosomes, they don’t have the tools they need to copy their genes and create whole new virions. Instead, viruses enter living cells and then hijack the host’s cellular equipment to copy viral genetic information, build new capsids and assemble everything together. So, the correct answer is 'They can reproduce'.

The algae posses the chlorophyll pigments in the cells which allow these organisms to prepare the food by the process of photosynthesis. They are autotrophic because they can prepare the food on their own. The fungi are the heterotrophic or saprophytic organisms as they do not possess the chlorophyll pigments. They cannot prepare the food and depend on the other sources for food. 

An organism that is capable of synthesizing its own food from inorganic substances using light or chemical energy is called as autotrophic organism. It includes green plants, algae and certain bacteria. Algae are photoautotrophs meanings they use light as the source of energy to prepare their food.

Viruses are obligate filterable parasites capable of independent existence and when they enter inside the body of the host they start utilising the host machinery for its own reproduction.