Which of the following statements is correct regarding cell theory?
A. Only plant cells contain cell walls.
B. All cells have a nucleus.
C. All living organisms are composed of cells and products of cells.
D. Cells arise spontaneously.
Answer: Option C
Solution (By JKSSB Mock Tests)
Modern cell theory states that all living organisms are composed of cells and cell products, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells (Omnis cellula e cellula). Not all cells have a nucleus (e.g., prokaryotes, mature RBCs). Cell theory was formulated by Schleiden, Schwann, and Virchow. Spontaneous generation was disproved.
Explanation:
Double circulation (pulmonary and systemic) with a four-chambered heart keeps oxygenated and deoxygenated blood separate, increasing efficiency. R correctly explains A.
Explanation:
Penicillin, the first true antibiotic, was discovered by Alexander Fleming in 1928. He observed that a mold contaminating a Staphylococcus culture plate was inhibiting bacterial growth. The mold was identified as Penicillium notatum (now P. chrysogenum). Penicillin is extracted from this fungus and is effective against many Gram-positive bacteria.
Consider the following statements about the nervous system:
1. Motor neurons carry impulses from the CNS to effectors.
2. Sensory neurons carry impulses from receptors to the CNS.
3. Interneurons are found only in the peripheral nervous system.
Which of the above is/are correct?
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