IB Biology HL C2.2 Neural signalling questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type
Multiple choiceWritten
Difficulty
EasyMediumHard

Question 1

Multiple choiceMedium1 mark

In a neuron, ATP availability is reduced while the membrane remains intact. Assume this affects sodium–potassium pumping only. After sufficient time, which paired change is most likely?

Show answer and explanation

Answer: C. ATP supplies energy for sodium–potassium pumping, which establishes and maintains ion concentration gradients. With less ATP, pump activity decreases; over time, the gradients weaken and the resting potential becomes less negative.

A: predicts weaker gradients but reverses their effect on the resting potential. B: assumes the pump becomes more active despite reduced ATP availability. D: treats the pump as dissipating, rather than establishing and maintaining, concentration gradients.

Remember: ATP-driven pumping maintains the ion gradients that support the resting potential.

Question 2

Paper 2Medium16 marks

A stimulus initiates an action potential at site A of an axon. Recording sites B and C are further along the same axon. The threshold potential is −55 mV.

Recording siteDistance from A / mmTime at which peak potential is reached after the stimulus / msPeak potential / mV
A01.0+30
B44.2+30
C87.4+30
(a)

State the threshold potential for an action potential in this axon.

[1]
(b)

Calculate the propagation speed of the action potential between B and C. Show your working and include a unit.

[3]
(c)

Describe how the time at which the peak potential is reached changes with distance from A. Use the data to support your answer.

[2]
(d)

Explain how local currents arising at A can bring the adjacent region of the axon to threshold and initiate an action potential there. Include the movement of sodium ions inside and outside the axon.

[5]
(e)

The experiment is repeated with the same stimulus, but with a reduced concentration of sodium ions outside the axon. An action potential is still initiated at A in the reduced-sodium condition. The maximum potential reached at B and whether an action potential is detected there are recorded.

ConditionMaximum potential at B / mVAction potential detected at B
Normal external sodium-ion concentration+30Yes
Reduced external sodium-ion concentration−58No

Using the data and the threshold potential, explain why reducing the external sodium-ion concentration affects propagation to B.

[5]

The best questions are still waiting

Unlock every question in this topic, then type, photograph or draw your answer and have it marked against the markscheme. Find out where you are dropping marks.

Unlock all questionsCompare Student and Student Plus