In which order does light pass through the cells of the retina?

Light passes first through the ganglion cell layer, then the bipolar cell layer, before reaching the rods and cones at the back of the retina.

Which photoreceptor works best in dim light, and why?

Rod cells work best in dim light because their pigment is broken down by low light intensities and many rods feed into one bipolar cell, so their small responses add together.

How many types of cone cell are there in the human retina, and what distinguishes them?

There are three types of cone, each containing a form of iodopsin that absorbs most strongly in the red, green or blue part of the spectrum.

Explain how the three types of cone allow a full range of colours to be seen.

Each colour of light stimulates the three cone types to different degrees, and the brain interprets the ratio of the three sets of impulses as a particular colour.

OCR A-Level Biology B H422

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Monitoring Visual Function

The retina and its role as a transducer

3 things to know
Components 01, 02 and 03

Overview

Recall questions on the layers of the retina, rods in dim light and their poor acuity, the three types of cone and colour vision, bipolar and ganglion cells, the fovea and blind spot, the retina as a transducer, bleaching of rhodopsin and hyperpolarisation of rods, and dissecting an eye.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does the hyperpolarisation of a rod cell lead to impulses in the optic nerve?

Key term

Why does rod vision give no perception of colour?

Key term

Explain why rod vision has poor visual acuity.

Questions from this subtopic

Each one with the model answer underneath.

1
In which order does light pass through the cells of the retina?
Model answer
Light passes first through the ganglion cell layer, then the bipolar cell layer, before reaching the rods and cones at the back of the retina.
2
Which photoreceptor works best in dim light, and why?
Model answer
Rod cells work best in dim light because their pigment is broken down by low light intensities and many rods feed into one bipolar cell, so their small responses add together.
3
Why does rod vision give no perception of colour?
Model answer
All rods contain the same single pigment, so the brain receives no information about which wavelengths were absorbed.
4
Explain why rod vision has poor visual acuity.
Model answer
Many rods synapse with a single bipolar cell, so the brain cannot tell which of them was stimulated and two nearby points of light are seen as one.
5
How many types of cone cell are there in the human retina, and what distinguishes them?
Model answer
There are three types of cone, each containing a form of iodopsin that absorbs most strongly in the red, green or blue part of the spectrum.
6
Explain how the three types of cone allow a full range of colours to be seen.
Model answer
Each colour of light stimulates the three cone types to different degrees, and the brain interprets the ratio of the three sets of impulses as a particular colour.

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