NEET-XI-Biology
02: Biological Classification
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- Qstn #10What are the characteristic features of Euglenoids?
Ans : Some characteristic features of Euglenoids are as follows.
- Euglenoids (such as Euglena) are unicellular protists commonly found in fresh water.
- Instead of cell wall, a protein-rich cell membrane known as pellicle is present.
- They bear two flagella on the anterior end of the body.
- A small light sensitive eye spot is present.
- They contain photosynthetic pigments such as chlorophyll and can thus prepare their own food. However, in absence of light, they behave similar to heterotrophs by capturing other small aquatic organisms.
- They have both plant and animal-like features, which makes them difficult to classify.
- Qstn #11Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
Ans : Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.
Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.
Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.
A.I.D.S, small pox, mumps, and influenza are some common examples of viral diseases.
- Qstn #12Organise a discussion in your class on the topic- Are viruses living or non-living?
Ans : Viruses are microscopic organisms that have characteristics of both living and non-living. A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) suggests that viruses are alive. In addition, they can also respond to their environment (inside the host cell) in a limited manner.
However, some other characters, such as their inability to reproduce without using the host cell machinery and their acellular nature, indicate that viruses are non-living. Therefore, classifying viruses has remained a mystery for modern systematics.