Final quiz

• The evolution of eyes, a fascinating aspect of biology, is a testament to the intricate and delicate balance of nature
• This intricate organ, which serves as the primary interface between individuals and their surroundings, has evolved over millions of years to allow organisms to interact with their environment more effectively
• The earliest organisms on Earth were simple, single-celled creatures that lacked specialized organs, including eyes
• They had photosensitive cells that could detect light and darkness, which was advantageous in an environment where sunlight was a vital resource
• It is from this primitive photosensitivity that the first eyes are believed to have evolved
• Evolution of eyes


  1. Random genetic mutations

  2. Development of more complex light-sensitive structures

  3. Emergence of true eyes in the Cambrian period

  4. Advent of the lens

  5. Evolution of color vision
• In the Cambrian period, approximately 540 million years ago, we see the first evidence of true eyes in the fossil record
• The trilobites, an extinct marine arthropod, were among the first creatures to possess compound eyes, composed of numerous individual visual units called ommatidia
• Each ommatidium was capable of sensing light and forming a pixel of the overall image, allowing the trilobite to see its surroundings in detail
• The lens allowed for the bending and focusing of light, leading to sharper, more detailed images
• Color vision enabled animals to perceive their environment in vibrant hues, conferring evolutionary advantages such as better food identification, predator avoidance, and mate selection
• Today evolutionary biologists are deciphering the origins of not just our own eyes but the dozens of different kinds of eyes that animals use
• Examples of eye adaptations

  • Fly eyes built out of columns
  • Scallops have a delicate chain of eyes peeking out from their shells
  • Flatworms have simple light sensitive spots
  • Octopuses and squids have camera eyes like humans, but with photoreceptors pointing out from the retina, towards the pupil
  • Nocturnal animals like cats have a reflective layer behind their retina called the tapetum lucidum, which improves their ability to see in low-light conditions
• It now turns out that all eyes, in all their wonderful variety, share an underlying unity in the genes used to build them
• By tracing the history of these shared genes, scientists are uncovering the steps by which complex eyes have evolved through a series of intermediate steps
• The evolution of eyes is a story of progressive adaptation and complexity
• These continual adaptations have equipped organisms with the ability to interact with their environment in increasingly sophisticated ways, enabling survival and prosperity in a diverse array of ecological niches
• As we continue to study eye evolution, we gain not only insights into our biological past but also potential directions for our evolutionary future
• Vision


  Occurs when light enters the eye through the pupil, and is refracted by the lens onto the retina, where it is transformed into electrical energy and sent to the brain
• Layers of the eyeball

  • Outer layer (cornea and sclera)
  • Middle layer (containing the iris and pupil)
  • Inner layer (retina)
• Chambers of fluid in the eyeball

  • Anterior chamber (between cornea and iris)
  • Posterior chamber (between iris and lens)
  • Vitreous chamber (between lens and retina)
• Aqueous humour


  Watery fluid that provides nourishment to the interior eye structures and helps to keep the eyeball inflated
• Vitreous humour


  Transparent gel-like fluid that fills the vitreous chamber and helps the eyes to stay inflated
• Components of the eye

  • Choroid
  • Ciliary body
  • Cone cells
  • Cornea
  • Conjunctiva
  • Crystalline lens
  • Fovea
  • Iris
  • Lens
  • Macula
  • Optic disc
  • Optic nerve
  • Pupil
  • Retina
  • Rod cells
  • Sclera
  • Tear layer
  • Vitreous body
  • Zonules
• Choroid


  The middle layer of the eye between the retina and the sclera, containing blood vessels that nourish the outer layers of the retina
• Ciliary body


  The part of the eye that connects the choroid to the iris, responsible for producing aqueous humour and containing muscles that allow the eye to focus
• Cone cells


  Light sensitive cells in the retina that function best in bright light and are essential for acute, color vision
• Cornea


  The transparent, circular part of the front of the eyeball that refracts light entering the eye onto the lens
• Conjunctiva


  The thin, moist membrane that covers the sclera and protects and lubricates the eyeball
• Crystalline lens


  The transparent structure inside the eye that focuses light rays onto the retina
• Fovea


  The small indentation at the centre of the macula with the greatest concentration of cone cells, where the most accurate visual information is registered
• Iris


  The colored, visible part of the eye in front of the lens that regulates the amount of light entering the eye through the pupil
• Lens


  The transparent structure that refracts incoming light and focuses it onto the retina
• Macula


  The yellow spot on the retina surrounding the fovea, responsible for detailed central vision
• Optic disc


  The visible portion of the optic nerve on the retina, where nerve fibers carrying visual information leave the eye
• Optic nerve


  Transfers visual information from the retina to the brain
• Pupil


  The circular opening in the centre of the iris that regulates the amount of light entering the eye
• Retina


  The light-sensitive layer lining the interior of the eye, containing rod and cone cells that convert light into electrical impulses sent to the brain
• Rod cells


  Light-sensitive cells in the retina necessary for vision in dim light
• Sclera


  The tough, white outer layer of the eye that provides protection and attachment points for the eye muscles