Tag: cell theory

X-ray crystallography is a technique to study the structural details of crystallizable proteins and nucleic acids. X-ray microscope developed by Kirkpatrick is useful in studying detailed structures of chemicals present in solid state, e.g., haemoglobin, insulin, DNA, RNA etc. due to diffraction of X rays by different atoms of the substance. 

Phase contrast microscope has a phase plate and an annular diaphragm. They bring about changes in light rays passing through the specimen producing differences in light intensity. Denser parts alter path of light more than the thinner parts. This produces varying contrast for different regions. 

Fluorescent microscope is useful in detecting those components which show autofluorescence, e.g., chlorophylls, collagen fibrils, vitamin A. Others can be made fluorescent by coating with fluorochrome dyes like acridine orange and coriphosphine. This is called as secondary fluorescence and is useful in detecting specific biomolecules.

Robert Brown, a Scottish botanist, is credited with the discovery and naming of the cell nucleus in 1831 while studying orchid cells.

The most powerful lens of the light microscope is the 100X oil immersion objective because light is refracted every time it passes through a medium with a different refractive index, the quality of the image is reduced with each passage. Thus, by reducing the number of such passages to a minimum, the clarity, brilliance and resolving power is preserved. Immersion oil has been formulated so that it has a refractive index identical to that of glass. Thus, two changes in refractive index can be eliminated by placing a drop of immersion oil on the specimen, and immersing the 100X oil immersion objective directly into the drop. 

Nucleus, Golgi bodies and chloroplasts are the organelles of the cell and hence can easily be visible under the compound microscope. The nuclear membrane is the membrane which separates the nucleus with the cytoplasm. It is a double lipid bilayer membrane which can only be visible under the electron microscope.
Thus, the correct answer is option (D), 'membrane separating the nucleus from the cytoplasm'.

Stethoscope is a medical instrument used to hear internal sounds of an animal body. Generally used to hear lung and heart sounds.
Microscope is an instrument which is used for observing very small objects. It uses lens or combination of lenses to produce a magnified image of tiny objects which are not visible to the naked eye. Microorganisms are not visible to naked eyes. Hence, microscope is used to observe them. 

Robert Hooke discovered cell in the year 1665. He observed cork cell in the bark of Spanish oak tree under a simple microscope and was able to see the empty structures surrounded by walls and named it a cell. He elucidated his observation in a book called "Micrographia".

Average diameter of microorganisms, like bacteria, is 0.2 to 2 micrometer. They cannot be seen with the naked eye. Microscope is used to observe such small microorganisms. It uses lens or combination of lenses to produce a magnified image of tiny objects which are not visible to the naked eye.

• Robert Hooke observed “honeycomb-like structures” in cork cells under the self-designed microscope. He called the hollow shells. A German biologist Rudolph Virchow observed that all living cells arise from pre-existing cells ('omnis-cellula e cellula') which were added to the cell theory as a doctrine. The term “cell nucleus” was used the first time by Robert Brown. Leeuwenhoek formed a single lensed microscope to observe the tiny organisms which were then named as microorganisms. Thus, the correct answer is option A.