All Free Biology MCQs with Answers

2141. Which of the following is present inside the vertebral column______________?

• A. Brain
• B. Spinal cord
• C. Both of these
• D. none of these.

Explanation: The vertebral column encloses and protects the spinal cord, which is part of the central nervous system and carries impulses between the brain and the rest of the body. Students may choose both because the brain is also in a bony protective structure, but the brain lies inside the skull, not the vertebral column.

2142. Central nervous system of man consists of______________?

• A. Brain
• B. Spinal cord
• C. Both of these
• D. none of these

Explanation: The central nervous system consists of the brain and spinal cord, which together receive, process and coordinate nervous information. Students may choose the brain alone because it is the major control centre, but the spinal cord is also an essential component of the central nervous system.

2143. Which of the following ions are involved in the initiation of nerve impulse_______________?

• A. Na+
• B. K+
• C. Fe
• D. none of these

Explanation: Sodium ions initiate a nerve impulse when voltage-gated sodium channels open and Na+ enters the neuron, causing rapid depolarization of the membrane. Students may choose potassium because K+ is important in repolarization, but it does not initiate the action potential.

2144. Under resting membrane potentials:

• A. Outer surface of neuron is more positive
• B. Inner surface of neuron is more positive
• C. Both of these surfaces are equally positive
• D. none of these.

Explanation: During the resting state, the outside surface of the neuron is relatively positive and the inside is relatively negative because of ion distribution and selective membrane permeability. Students may choose option d because both surfaces contain positive and negative ions, but their electrical charges are not equal across the membrane.

2145. What is the function of synapse________________?

• A. To allow nerve impulse to move in backward direction
• B. To decrease the speed of nerve impulse
• C. To stop the nerve impulse
• D. To provide cytoplasmic connection between neurons.

Explanation: A synapse produces a small synaptic delay because neurotransmitter release and reception take time, so transmission across a synaptic pathway is slower. Option d is a common mistake because a synaptic cleft is a gap, not a direct cytoplasmic connection between neurons.

2146. Microscopic gaps between the neuron endings are called__________?

• A. Transmitters
• B. Synapses
• C. Pores
• D. Nodes

Explanation: The microscopic gap between the ending of one neuron and the next cell is called a synapse, more precisely the synaptic cleft. Students may choose a node, but nodes are gaps in the myelin sheath along an axon, not gaps between neuron endings.

2147. Which of the following cytoplasmic extensions carry the message toward the cell body___________?

• A. Dendrites
• B. Axon
• C. Both of these
• D. none of these

Explanation: Dendrites receive signals and carry them toward the cell body, whereas the axon usually carries impulses away from it. The likely mistake is choosing the axon because it is also a cytoplasmic extension, but its usual direction is away from the cell body.

2148. Which of the following neuron has a single long dendron?

• A. Sensory neuron
• B. Motor neuron
• C. Associative neuron
• D. none of these.

Explanation: A sensory neuron typically has one long dendron that carries impulses from a receptor toward the cell body, followed by a relatively short axon. Students may choose a motor neuron because it also has dendrites, but motor neurons usually have many short dendrites and one long axon.

2149. In which of the following neurons length of dendrite is greater than axon_______________?

• A. Sensory neuron
• B. Motor neuron
• C. Associative neuron
• D. none of these.

Explanation: In the school-level classification used here, a sensory neuron's dendron is longer than its axon because the receptor may be far from the cell body, while the axon carries the impulse onward to the CNS. The common error is choosing a motor neuron by assuming its longest process must be a dendrite, although its long process is usually the axon.

2150. Which of the following transmits nerve impulse from receptors to central nervous system?

• A. Sensory neuron
• B. Motor neuron
• C. Associative neuron
• D. none of these.

Explanation: Sensory neurons carry impulses from receptors toward the central nervous system, forming the afferent pathway. A motor neuron is the likely alternative for students who confuse direction, because it carries commands from the CNS to effectors.