Describe and explain how the typical mammalian eye provides a detailed colour image of close-up objects in high light intensities.

I would firstly begin with looking at the key words in the question such as "describe" and "explain": whilst trying to focus on those words during the entirety of the answer. This question is an essay style question and for optimum marks, students need to focus on both aspects of the question being asked. Firstly, we must look at how the mammalian eye provides a detailed colour image in general and then focus (in detail) what occurs to allow the image to be clear when the eye focuses on close-up objects in high light intensities. The mammalian eye is a very specialised organ within our bodies and it is made up of many parts. The cornea and the lens are structures which are both involved in the convergence of light. They combine light to allow it to focus on to the retina, providing a detailed close-up image. The lens itself is responsible for accommodation, the fine control of light rays, and consists of ciliary muscles and suspensory ligaments to help with this process. For close-up images to be seen clearly, the ciliary muscles contract within the lens, which reduces the tension in the suspensory ligaments allowing the lens to become thicker in shape. This creates greater refraction, allowing the close-up image to be seen clearly. Furthermore, in high light intensities, the iris (which controls the size of the pupil) changes shape to allow the right amount of light to focus for a clear image to be seen. The circular muscles contract whilst the radial muscles relax, reducing the diameter of the pupil. This reduces the volume of light that enters into the eye, protecting the eye from damage when it faces strong light intensities. The retina itself contains photosensitive cells which each comprise pigments that allow the eye to function in high light intensities. The cone cell, which specialises in maintaining high light intensities in a variety of different colours, individually synapses with bipolar neurones which gives greater visual acuity, allowing close-up images to be seen clearly. This allows greater resolution which is very important when focusing on images that are close-up. Finally, the presence of two eyes provides binocular Vision in itself which allows good depth perception.