IGCSE Biology Paper-4: Specimen Questions with Answers 143 - 144 of 279

Passage

The nervous system coordinates the responses of animals to changes in their environment.

Question 143 (1 of 5 Based on Passage)

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Shows the arrangement of the nervous system in a mammal.

Complete Fig. by writing the names of the missing parts of the mammalian nervous system in the boxes.

Nervous System

Explanation

Nervous System
Nervous System

Question 144 (2 of 5 Based on Passage)

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Short Answer▾

State the type of involuntary action shown by the flow chart.

Explanation

Simple Reflex

If we accidentally touch a hot pot on our stove while cooking, we would involuntarily (and nearly instantaneously) snatch our hand away from the pot. This response is called a ‘reflex action.’

Reflex Arc

  • Contact with the hot pot triggers the start of a series of events in the body to evoke a response. At the point of contact with the hot pot, skin receptors quickly send nerve impulses (electrical) to the spinal cord (central nervous system) via sensory neurons. In the spinal cord, the impulses are processed and a response is relayed back.
  • In the spinal cord, the interneurons (also known as relay neurons) make the connections between the sensory neurons (bringing the message from hand) and the correct motor neurons (taking the response back to the hand) . It would be not be useful if the response was sent to the wrong part of the body — in this case, a response sent to the leg wouldn՚t be too helpful as the stimulus is coming from the hand.
  • From the interneurons, the response is relayed to the motor neurons which project out of the spinal cord to stimulate your muscles (effector) to contract, causing you to snatch your hand away from the hot pot. This pathway taken by nerve impulses to elicit a response is known as a ‘reflex arc.’
  • This process happens so fast that the response occurs before the message reaches the brain. This results to a quicker time-to-response as the thinking process of the brain may be relatively time consuming.
Cell Body of Afferent Neuron

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