IB DP Biology- C2.2 Neural signaling- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Voltage-gated sodium (\(\text{Na}^+\)) channels open at the start of depolarization, allowing sodium ions to flow rapidly into the neuron.
This occurs between points \( 1 \) and \( 2 \) on the graph, where the membrane potential rises sharply from its resting potential of approximately \( -70~\text{mV} \) toward positive values, peaking around \( +40~\text{mV} \).
✅ Answer: (B) Between \( 1 \) and \( 2 \)
Question
The image shows a neuron.
What is the function of X?
A. Increases the speed of transmission along the axon
B. Increases the rate of exchange of sodium and potassium ions
C. Holds bundles of neurons together to form a nerve
D. Determines the direction of the action potential
Answer/Explanation
Answer: A. Increases the speed of transmission along the axon
Explanation:
The myelin sheath is a fatty layer around the axon that helps insulate the nerve fiber and speed up the transmission of electrical impulses by allowing them to “jump” between gaps (nodes of Ranvier) this is called saltatory conduction.
Let’s analyze the options:
A. Correct – Myelin increases the speed of signal transmission.
B. Incorrect – The ion exchange happens at the nodes, not due to myelin.
C. Incorrect – Myelin wraps individual axons, not bundles of neurons.
D. Incorrect – The axon hillock and other regions determine action potential direction, not myelin.