Historical Discovery of Plasma Membrane — NEET Biology
📚 Practice ConceptThe detailed structure of the membrane was studied only after the advent of the electron microscope in the 1950s. Meanwhile, chemical studies on the cell membrane, especially in human red blood cells (RBCs), enabled the scientists to deduce the possible structure of plasma membrane.
Which of the above statements are NOT correct? S1: Mycoplasmas, representing the smallest known cells, are eukaryotic organisms that lack a cell wall. S2: The irregular shape of human White Blood Cells (WBCs) indicates that cellular shape is always independent of the specific function a cell performs. S3: Nerve cells are among the longest cells, and their elongated structure directly aids in the rapid transmission of nerve impulses across long distances. S4: All living organisms are composed of cells, and a semi-fluid matrix, the cytoplasm, is an essential component present in both prokaryotic and eukaryotic cells. S5: Centrosomes, non-membrane bound organelles, are found in animal cells and are primarily involved in the synthesis of lipids and steroidal hormones.
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Correct answer: A — S1, S2 and S5 are not correct.
Let's evaluate each statement: S1: Mycoplasmas are indeed the smallest known cells and lack a cell wall, but they are prokaryotic, not eukaryotic organisms. Thus, this statement is incorrect. S2: The shape of a cell varies with the function it performs. While WBCs have an irregular (amoeboid) shape, this is related to their function (e.g., phagocytosis), and not all cell shapes are irregular or independent of function (e.g., disc-like RBCs, long nerve cells). Thus, this statement is incorrect. S3: Nerve cells are indeed among the longest cells, and their elongated structure is crucial for efficient signal transmission over long distances. This statement is correct. S4: Cells are the fundamental units of life, composing all organisms, and cytoplasm is a universal semi-fluid matrix found in both prokaryotic and eukaryotic cells, where cellular activities occur. This statement is correct. S5: Centrosomes are non-membrane bound organelles found in animal cells and are involved in cell division. The synthesis of lipids and steroidal hormones is primarily a function of the Smooth Endoplasmic Reticulum (SER). Thus, this statement is incorrect. Therefore, statements S1, S2, and S5 are not correct.
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