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BIOL 1000 Lecture Notes - Lecture 2: Phototaxis, Ommatidium, Arthropod Eye

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limewasp808
20 Jan 2016
School
York University
Department
Biology
Course
BIOL 1000
Professor
Nicole Nivillac

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Document Summary

Light is captured by pigments, and the color that is expressed is the wavelength that was not absorbed. All pigments are related by conjugated systems. Conjugated systems have alternating bonds (double bond-single bond- Conjugated systems have delocalized electrons so that the photon can double bond) easily be captured. Light is a source of information in the way of photoreceptor which is a membrane protein with a non-proteins pigment bound to it (retinal) When light is absorbed by the pigment, it turns from a cis retinal to a. The change in retinal change causes the opsin to change in a process trans retinal called rhodopsin. Plants have eye spots that can sense light so that they can move toward it called phototaxis. Positive phototaxis is when an organism moves toward the light while negative phototaxis is when an organism moves away from the light. The eye is an organ that can sense light.

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Related Questions

The Eye Exam It was a sunny day in 2005, and time for Eric’s annual eye exam. Dr. Tim flipped through his charts. “You know, we really should measure your visual fields. It’s been at least ten years since you had that done!” “I hate them!” Eric grumbled. “I get disoriented and, anyhow, we already know I have a large blind spot.” He raised his hand, squinting through one eye. “Here. I can’t see my finger here.” “I know.” Dr. Tim was sympathetic. “But weren’t you just telling me you haven’t seen stars for a while? It’s important. You had that tumor on your pituitary gland. Your optic nerves cross in that area, right in front of the pituitary, so if anything is happening again we’d probably notice it first by changes in your eyesight. It really is important!” An hour later, Eric was seated in front of a large white screen, staring intently at a light in the middle. “Keep looking at that light, so your eyes don’t move. If you see another light anywhere else, push this button.” Eric began the test by focusing on the light he saw in the center. The machine then successively displayed points of light of varying intensity in different places around the entire visual field. When Eric saw the peripheral light, he pushed a button. He did his best to detect the flashes, but realized he was probably missing some. The machine mapped out where he could see and where he could not. Dr. Tim looked at the printout. His face grew serious. “Eric, we have a problem. You have limited peripheral vision, and it’s bad enough that I don’t think you should be driving! This looks to me like something called retinitis pigmentosa. We should refer you to a specialist.” He pulled out more papers. “Here, look at this. Here are your visual fields. The numbers show how well you can see in that area of your eye, and in the graph on the right the darker the box is the less you can see. Now here are a normal person’s visual fields. Do you see the difference?”

1. How do your eyes work? What is the difference between focal vision and peripheral vision?

2. What is the anatomy around the pituitary gland? Why are the optic nerves likely to be affected by pituitary tumors?

3. Eric has retinitis pigmentosa In this disease pigments lining your eye gradually break down, so you can’t sense the light that hits your eye. Why do you need the pigments in order to see the images and light?

Exercise #5: The Nervous system and Perception

Task #1: Color vision


Introduction

In the human retina, there are two kinds of light-sensitive cells: rods and cones. These cells are located on the outside of the retina, away from the vitreous humor and against the choroid layer, and are covered by a later of bipolar and ganglion cells as well as neurons. Light enters the posterior chamber through the lens and must pass through several cell layers before it is absorbed by the rods and cones.

Cones are involved in color vision at daylight intensities. Generator potentials in a cone excite one neuron, giving high-level resolution vision. Cones will not cause neural firing at low light intensities and are, therefore, nonfunctional at night.

Rods provoke black-and-white vision at low light intensities. A bipolar cell associates with several rods, so that generator potentials sum in their effect. This assures neuronal firing at low light intensities and provides a highly sensitive vision but with less resolution.

Receptor convergence. A ganglion cell, which receives input from a number of rods, spread out over the retina, cannot pinpoint the source of a light stimulus as well as a ganglion cell, which is stimulated by a single photoreceptor. In the case of a ganglion cell receiving the added input of several rods, light hitting any one of the rods can cause a neural spike in the ganglion cell, but the brain has no way to know which rod was excited. It is therefore harder to pinpoint the location of light stimuli on the retina when the stimulus is detected by rods (as compared to cones). The result is that our ability to see detail, or our resolving power, is considerably lower under dim light conditions than under bright light conditions.

Dark adaptation. If you go from a lighted area to a very dark room, you will not be able to see. After about ten minutes, however, you begin to be able to see again. This occurs because the rhodopsin pigment, which gets broken down when it absorbs light, is continually re-synthesized in the rods. When there is very little light, very little rhodopsin gets broken down and the amount of rhodopsin gradually builds up, making the rod much more sensitive to dim light.

When light strikes a receptor cell, it triggers a photo-chemical reaction that leads to neuronal firing. If a rod or cone receives high-intensity light, the visual pigments will be temporarily bleached and will not absorb any more light. Within a matter of a few seconds, enzyme systems in the cells will restore the visual pigment to its light-absorbing form. This can be easily demonstrated. If, after viewing a bright light, the eye is quickly shut or turned to a dark wall, the bright image will persist as a positive afterimage because the high generator potential causes the continued firing of neurons. If the eye is cast on a lighter background after a few seconds, a negative afterimage, or a dark image of the object will appear. This is because the still bleached cells are not receptive to the light coming from the light background.

According to the Young-Helmholtz theory of color vision, there are three types of cone cells, which respond respectively to red, green, and blue light.

All other colors are perceived as the brain interprets impulses coming from a mix of these receptors. If an object of one color is viewed for a long period of time at high light intensity, the cones for that color will become bleached. The afterimage of the object will be seen in the complementary color.

The Exercise 6 PowerPoint will demonstrate afterimages to you. Use the slide show option to project the square of red light on your entire screen in a dark room. After staring intensely at the square for 30 seconds or so, without shifting your gaze, click enter to change the slide to a soft white. Continue staring at the screen as the change is made. What do you see? What was the color of the afterimage?

Repeat this experiment using a blue square. Before doing the experiment, hypothesize what color the afterimage will be according to the Young-Helmholtz theory.

Hypothesis to be tested: (2 pts)

What did you see when the experiment was conducted? (2 pts)

Was you hypotheses accepted or rejected? (1 pt)

Explain the colors seen in these afterimages using the Young-Helmholtz theory. (5 pts)

Photosynthesis Lab Report

  1. Plant Structure and Function

  1. Through the process called __________ plants convert lightenergy into

__________ energy. Record your answerbelow.

  1. In which structure of the plant does photosynthesis occur?

  1. What is the difference between xylem and phloem?

  1. Based on lab, Exercise 1, what is the name and function of thestructure labeled with the letter “H”?

  1. Chloroplast
  1. Based on Lab, Exercise 2, draw and label each part of thechloroplast. Sign, date and prepare an image of your drawing andinclude it with this lab report.

  1. What part of the process of photosynthesis occurs in thethylakoid compartment?

  1. What is the name and function of the structure labeled with theletter “E” in Exercise 2?

  1. Photosynthetic Products

  1. What are the three products of photosynthesis?

  1. What happens to the glucose that is not metabolizedimmediately?

  1. In the test for starch, which tube demonstrated a positive testfor starch? How do you know?

  1. Based on Lab, Exercise 3 explain why part of the leaf was amberin color.

  1. Light Absorption
  1. What pigment is used by plants to absorb light?

  1. In the video demonstration in Exercise 4 what happens to thelight spectrum when a green filter is placed in front of the lightsource?

  1. In step 3 of Exercise 4, which color was not absorbed by thespinach pigments?

  1. Photosynthetic Pigments
  1. What process is used in Exercise 5 to separate the plantpigments?

  1. Look at the chromatogram results in Exercise 5. What color isreflected by chlorophyll a?
  1. Which pigment reflected an orange color?

VI. Effect of Light and Temperature onPhotosynthesis

  1. What was the conclusion of Blackman’s first experiment on theeffect of light on photosynthesis?
  1. In his second experiment, what effect did increasingtemperature have on the rate of photosynthesis?

  1. Record the data from Exercise 6 below.

Lamp Distance

Temperature

Ave Bubble/min

75 cm

50 cm

25 cm

  1. In the experiment in Exercise 6, what conclusion can be drawnabout the effect of light and temperature on rate ofphotosynthesis?

Summary Questions

  1. Why do heterotrophs depend on autotrophs?

  1. Name two reactants necessary for photosynthesis to occur.

  1. How would the process of photosynthesis be affected if a planthad no stomata?
  1. What tool is used to separate white light into differentwavelengths of color?

  1. Explain why we see the color green on the leaves ofplants.

  1. What color is absorbed the least by the petals on asunflower?

  1. Photosynthesis consists of two phases. Which phase would beleast affected by living in an area where there are shorter daysand long periods of darkness?

  1. How could air pollution affect food production and the priceyou pay for food at the supermarket?