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Both humans and plants are able to respond to external stimuli - NSC Life Sciences - Question 4 - 2016 - Paper 1
Question 4
Both humans and plants are able to respond to external stimuli. Hearing occurs in humans followed by instant turning of the head to inspect the source of sound. Desc... show full transcript
Worked Solution & Example Answer:Both humans and plants are able to respond to external stimuli - NSC Life Sciences - Question 4 - 2016 - Paper 1
Step 1
Describe how this process occurs in humans
Answer
The hearing process in humans begins with sound waves being directed by the pinna into the auditory canal. These sound waves travel through the canal and strike the tympanic membrane, causing it to vibrate.
Once the tympanic membrane vibrates, these vibrations are transferred to the ossicles of the middle ear. Here, the footplate of the stapes (one of the ossicles) pushes against the oval window, creating pressure waves in the perilymph of the vestibular canal.
These pressure waves are then transferred to the endolymph of the cochlea canal, where they stimulate the hair cells in the organ of Corti. The hair cells convert this mechanical stimulus into an electrical impulse, which is then transmitted along the auditory nerve to the cerebrum of the brain, where the sound is interpreted.
Finally, the pressure waves pass into the tympanic canal, where they are absorbed by the round window.
Step 2
Turning of head to inspect the source of sound
Answer
The interpretation of sound leads to an investigative reaction in the brain. When sound is perceived, the cerebral cortex generates impulses that are sent to the neck muscles via the motor nerves. This results in an antagonistic action of the neck muscles, allowing the head to turn towards the direction of the sound source. Consequently, this movement enables the eyes to gather further information regarding the nature and source of the sound.
Step 3
Describe how plants respond to unilateral light stimulus
Answer
Plants respond to unilateral light stimulus through a phenomenon known as phototropism. The tip of the plant stem possesses the ability to detect light, and when exposed to it, the plant grows toward the light source.
This growth response is facilitated by the distribution of auxins, which are plant hormones produced at the growing tip. When light is received unevenly, auxins are distributed more on the shaded side of the stem.
As a result, the cells on that side elongate more than those on the side facing the light. This leads to bending of the stem toward the light, ensuring that the plant maximizes its light absorption for photosynthesis.