Name ______Date ______Period _____ Score ______out of 25 Corrected by ______How does the Human Eye form an Image?
Look at all of the parts of the eye and find out what they do.
Directions: First, answer all the questions and then discuss them with a partner. Check your answers with the book, PowerPoint notes, or other resources. Points will be deducted for not writing neatly and legibly. If you make a mistake, erase it completely.
Parts of the eye In the diagram below, find the following parts and label them with the corresponding letter. a. Cornea d. Retina b. Iris e. Optic nerve c. Lens
The cornea Look at the shape of the cornea and location in relationship to other parts of the eye in the diagram above.
1. Where is the cornea located? ______
2. What shape is the cornea? ______3. Based on its location and shape, what do you think is the function of the cornea? ______4. What effect on light entering the eye does the cornea have? ______The iris The iris is the colored ring that surrounds the black spot on the eye, called the pupil. The iris can change its size, making the pupil larger or smaller. 5. Where is the iris located?
______6. What is the shape of the iris?
______7. Based on its location and shape what is the function of the iris? ______
8. What effect on light entering the eye does the iris have? ______9. Why do you think some animals (like cats) have differently shaped irises? ______
The lens You used lenses in a previous investigation that were shaped very much like the lens of the eye. There is one big difference: the lens in the eye can change its shape! 10. Think back to when you used the black and white lenses. Did they have the same focal length? ______11. What happens to the focal length of the eye’s lens when it changes its shape? ______Below are four diagrams showing light coming from the left and traveling to the right through the lens (see the arrows). Draw in how you think light would refract through these different shaped lenses. Remember to draw the focal point. (Refer to the PowerPoint Notes, textbook, & Rays Diagram Skill Sheet.)
12. 13. 14. 15.
16. Why does the lens of your eye need to change its shape? ______
17. How would the distance of the object being looked at affect the shape of the lens? ______
The retina All parts of the eye work together to control the amount of light entering the eye and focus an image on a small light sensitive area of specialized tissue at the back of the eye called the retina. The retina detects light and transmits the visual information to the optic nerve and onto the brain. Light sensitive cells in the eye are called photoreceptors.
Name ______Date ______Period _____
How does the Human Eye form an Image? Page 2 Photoreceptors: rod cells and cone cells There are two different kinds of photoreceptors in the retina, rod cells and cone cells. Rod cells are sensitive to the intensity of light. They see in black white and shades of grey. Rod cells are many times more sensitive to light than cone cells. Cone cells are sensitive to color. There are three kinds of cone cells. One kind responds most strongly to red light. A second kind responds most strongly to green light. The third kind responds most strongly to blue light. All the colors you can see are combinations of signals from all three kinds of cone cells. For example, yellow is seen when both the red and green cone cells send signals to the brain. Signals from all photoreceptors complete with light intensity and all detected colors are sent to the brain and assembled as the image we see as a mosaic of millions of tiny dots.
Putting it all together 18. Describe the process of how the eye allows an image to be seen. Use these terms in your explanation. Highlight or write each term in colored pencil. (2 points)
cornea retina cone cells iris photoreceptors optic nerve lens rod cells brain ______19. Describe the image seen by an animal that has very few or no cone cells. (2 points) ______
20. For what reason would an animal have excess rod cells? (2 points) ______
21. For what reason would an animal have excess cone cells? (2 points) ______