Exceptions to the cell theory, Biology

Exceptions to the Cell Theory

Viruses, however, are not the only exception to the Cell Theory as formulated earlier. This has led scientists to take a much broader view of the problem. some organisms like a bacterium, blue-green alga, mycoplasma, amoeba, Chlamydomonas and Mucor are composed basically of a single cell.-In such cases we face another problem. You have so far learnt that the cell is the basic structural unit of an organism, something like bricks in a building.

But in the examples cited above just a single cell constitutes the whole animal, which amazingly performs all the body functions like respiration, digestion, excretion, etc. The problem is further complicated by the occurrence of many multinucleate protozoans, multinucleate animal tissues etc.For example a species of amoeba, Chaos as well as also many other protists like the ciliate Opalina have many nuclei in their body. The common. pond plant Nitella has giant cells with many nuclei in the cytoplasm. There are also tissues and cells in our body which have many nuclei.

Such cells are called syncytial. For example, the striated muscle fibres of our body are syncytial in nature. The problems listed above arose due to the fact that Cell Theory was proposed on the basis of observations on multicellular organism. This created a wrong notion that single celled organisms were totally comparable to a cell of multicellular organisms. It is however, now established beyond any doubt that as it stands today, the present unified Cell Theory given below, is universally applicable with equal force from bacteria to protozoa to humans except for viruses.

Posted Date: 1/12/2013 2:58:29 AM | Location : United States







Related Discussions:- Exceptions to the cell theory, Assignment Help, Ask Question on Exceptions to the cell theory, Get Answer, Expert's Help, Exceptions to the cell theory Discussions

Write discussion on Exceptions to the cell theory
Your posts are moderated
Related Questions
Determine the Food Sources of Pyridoxine? Raw foods contain more of this vitamin than cooked foods. The food sources include: 1. Rich sources: Rice polishing s, wheat bran,

Explain about the Microcolony DEFT? It allows determination of viable cells. Food homogenate is filtered through a DEFT membrane and then placed on the surface of appropriate c

A species has a diploid chromosome number of 56. Is it true or false that of the 28 chromosomes in an ovum, 14 are always paternal? Ignore the effects of crossing over. Justify you

Food Chain The land mass, water bodies and atmosphere are the three endowments of nature on which the living beings have to depend for their nourishment and sustenance. The

Describe how a phagocyte destroys bacteria. The phagocyte forms a pouch in its cell membrane and engulfs bacteria in the pouch. It then pinches off the pouch to produce a vesi

Q. Investigation of aortic regurgitation by Chest X–Ray? Left ventricular dilatation produces cardiomegaly on chest radiograph. Ascending aorta is often prominent. Egg shell ca

why do ecological models commonly have limited applications?

Q. How to investigate aortic stenosis by Roentgenogram? Cardiac enlargement does not occur in pure compensated aortic stenosis. Post stenotic dilatation of aorta may be seen. F

Determine some assessment measures of Zinc? Measurement of zinc in plasma: This is the most common method. Fasting concentrations of less than 70 μg/litre suggests deficie

Define Tips that should be followed before an event Start? Before the event, following tips should be followed:   As the glycogen stores may be used up during night, a h