All Free Biology MCQs with Answers

2161. Maintenance of normal resting potential via movement of K+ inside the cell and na+ out is a/an ___________ process?

• A. Active
• B. Passive
• C. Diffusional
• D. None of these.

Explanation: The sodium-potassium pump uses ATP to move 3 Na+ out of the neuron and 2 K+ into it, both against their concentration gradients. Because energy is required for this movement, it is active transport. The likely alternative is passive or diffusional transport, which applies to ion movement through channels down a gradient, not to the pump.

2162. Type of neurons found exclusively in CNS are_____________?

• A. Sensory neurons
• B. Motor neurons
• C. Associative neurons
• D. None of these

Explanation: Associative neurons, also called interneurons, connect sensory and motor pathways within the central nervous system. They are found in the brain and spinal cord and generally do not extend into peripheral nerves. The likely alternative is motor neurons, but motor neurons carry commands from the CNS to effectors and can extend into the peripheral nervous system.

2163. Which of the following statement about neuron is incorrect___________________?

• A. They not only conduct impulses but also generate them
• B. They are not the only cellular component of nervous system
• C. They may show limited regenerative capabilities
• D. Like all the living cell, when they mature and divide to form similar cells

Explanation: Mature neurons are highly specialized and usually remain in the non-dividing G0 phase, although limited repair or regeneration can occur in some situations. They conduct impulses and glial cells provide additional cellular support in nervous tissue. The likely alternative is a, but neurons can generate action potentials as well as conduct them, whereas the claim that mature neurons divide to form similar cells is incorrect.

2164. Number of chromosomes in E.coli ?

• A. 1
• B. 2
• C. 4
• D. 6

Explanation: A typical E. coli cell has one main circular bacterial chromosome, although it may also carry smaller plasmids that are not counted as its main chromosome. Students may choose two because they confuse the chromosome with plasmids or with the duplicated state before cell division.

2165. Kingdom Fungi includes_______________?

• A. A cellular, eukaryotic organisms
• B. Non-chlorophylls, multicellular eukaiyotlc organisms
• C. Non-chlorophylls, multicellular,thailophytic organisms
• D. both B and C

Explanation: Fungi are non-chlorophyllous, multicellular, eukaryotic organisms and are traditionally described as thallophytic because their bodies are not differentiated into true roots, stems, and leaves. Therefore both statements B and C describe fungi, making option d appropriate. Students may choose option b because it is correct, but it is incomplete because it omits the thallophytic description.

2166. The respiratory surface of unicellular organisms is__________?

• A. Specific organ
• B. Cell membrane
• C. Cell wall
• D. Nuclear membrane

Explanation: A unicellular organism has no specialised respiratory organ, so gases diffuse directly across its cell membrane. Students may choose the cell wall because it is an outer covering, but the cell wall is not the selectively permeable surface through which respiratory exchange mainly occurs.

2167. Prokaryotes don't have:________?

• A. Cell membrane
• B. Nucleus
• C. Cytoplasm
• D. None of these

Explanation: Prokaryotes lack a membrane-bound, true nucleus; their DNA lies in a nucleoid region of the cytoplasm. Students may choose cytoplasm because prokaryotes are simpler cells, but they still possess cytoplasm and a cell membrane.

2168. Which is NOT an example of a microbial symbiosis?

• A. bacteria in the human colon
• B. tapeworm in the cow intestine
• C. bacteria passing through the placenta
• D. protozoans found within termites

Explanation: Bacteria in the colon and protozoans in termites can have mutually beneficial associations, while a tapeworm lives as a parasite in the cow intestine. Bacteria passing through the placenta describes transmission rather than a symbiotic association, so option c is the exception. Students may choose the tapeworm because it is harmful, overlooking that parasitism is also a type of symbiotic interaction.

2169. The terms procariotique and eucariotique were proposed by___________?

• A. Whittaker
• B. Chatton
• C. Haeckel
• D. Margulis and Schwartz

Explanation: Édouard Chatton introduced the terms prokaryote and eukaryote to distinguish cells without a membrane-bound nucleus from cells with one. Students may choose Whittaker because he proposed the five-kingdom classification, but he did not introduce these cellular terms.

2170. Gram +ve bacteria on treatment with crystal violet dye give _________colour?

• A. red
• B. green
• C. purple
• D. pink

Explanation: Gram-positive bacteria retain the crystal violet-iodine complex because their thick peptidoglycan wall is not decolorized by alcohol, so they appear purple. Gram-negative bacteria lose the crystal violet and later take the counterstain, so students may choose red or pink by mixing up the two Gram reactions.