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Bioninja Ib Option Assignment

E.2.1  Outline the diversity of stimuli that can be detected by human sensory receptors

E.2.2  Label a diagram of the structure of the human eye

E.2.3  Annotate a diagram of the retina to show the cell types and the direction in which light moves

E.2.4  Compare rod and cone cells


  • Both types of cell are photoreceptors
  • Both types of cell are found in the retina


E.2.5  Explain the processing of visual stimuli, including edge enhancement and contralateral processing

Photoreceptors (rod and cone cells) in the retina convert light into nerve impulses

The impulses pass to bipolar cells, which relay the signal to the optic nerve (via ganglion cells)

Edge Enhancement

Signals from rods and cones follow both vertical and lateral pathways

Photoreceptors stimulate opposing bipolar cells but inhibit adjacent bipolar cells (lateral inhibition)

This makes light spots lighter and dark spots darker, with the contrast greatest at the edges (edge enhancement)

Hermann Grid Illusion

Contralateral Processing

Contralateral processing is when stimuli is processed on the opposite side of where it was detected

Information from the left half of the visual field is detected by the right half of the retina in both eyes and is processed by the right hemisphere

Information from the right half of the visual field is detected by the left half of the retina in both eyes and is processed by the left hemisphere

At the optic chiasma, information from both eyes may swap so that the left or right visual field is processed together

The optic nerves that swap sides are transmitting signals contralaterally, while the optic nerves that do not swap are transmitting signals ipsilaterally 

Impulses continue to the thalamus where the optical information is processed before an image forms in the visual cortex

E.2.6  Label a diagram of the ear

E.2.7  Explain how sound is perceived by the ear, including the roles of the eardrum, bones of the middle ear, oval and round windows, and the hair        .          cells of the cochlea

  • Sound travels as pressure waves in the air which push the membrane of the eardrum, causing it to vibrate
    • The degree of vibration will vary according to the frequency and amplitude of the sound waves
  • The ear drum pushes on the bones of the middle ear (the ossicles), which magnify the vibrations (~ 20 times)
    • The bones of the middle ear are known as the hammer (malleus), anvil (incus) and stirrup (stapes)
  • The ossicles push against the oval window, displacing fluid within the cochlea
  • Movement of the cochlear fluid affects the position of cilia on sensory hair cells
    • Cilia on hair cells vary in length and each resonates to a different frequency of sound
  • Activation of the hair cells generates nerve impulses which are transmitted via the auditory nerve to the brain 
  • The kinetic motion of the cochlear fluid is dissipated by the movement of the round window

Biology HL is a rigorous, two-year experimental science course for students who wish to understand the unity and diversity of living organisms on the molecular, cellular, organic, and ecological levels.  Laboratory investigations are an integral part of the course.  Throughout the course, students will design and carry out appropriate experiments and communicate the results to a wide audience.  At the end of year one, students complete an experimental science project with students in other experimental science courses.  The independent laboratory work produced by each students will be moderated by the International Baccalaureate Organization and will contribute to the student's overall IB score in Biology.  At the end of the two-year sequence, students will be prepared to take the IB Biology HL exam.

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