Lab 8 Photosynthesis A What is it 1 Photosynthesis is the conversion of light energy to chemical energy Photosynthesis light ENERGY SUGAR Cellular respiration SUGAR ENERGY ATP or other organic compounds 2 Photosynthesis is linked to cellular respiration a The compounds formed from photosynthesis may be broken down in cellular respiration to provide energy for the cell b But this isn t a circular process ATP from cellular respiration does not drive photosynthesis Photosynthesis energy from light CO2 H2O CH2O H2O O2 Cellular respiration C6H12O6 O2 CO2 H2O ATP B What organisms perform photosynthesis 1 The organisms with that specialized unique organelle the chloroplast Plants algae some protists some prokaryotes bacteria 2 The producers of the biosphere Organisms with chloroplasts are photoautotrophs 1 Autotrophs survive without eating other organisms They make their own organic molecules needed for their living from raw materials in their environment Photo because the source of energy to make their organic molecules is light C Chloroplasts in plants 1 Found mainly in the mesophyll cells of the plant tissue in the interior of the leaf typically 30 40 chloroplasts per cell 2 Chlorophyll the green pigment of plants is located inside the thylakoid membranes 3 Two cycled reactions occur in chloroplasts a Light reactions 1 Occurs in the thylakoid membranes 2 Light energy is converted into chemical energy ATP and NADPH b Dark reaction Calvin cycle 1 Occurs in the stroma 2 CO2 enters through the stomata 3 With the chemical energy from the light reactions CO2 is converted into a sugar a convertible form of chemical energy 2 D What is light 1 Electromagnetic energy that travels in waves the distance from the top of one wave to the next is the wavelength 2 Sunlight is composed of all the energy waves from radio waves to gamma rays 3 Our eyes are only capable of detecting a small portion of the electromagnetic spectrum a We call it visible light b Our eyes interpret the different wavelengths as different colors 680 nm Red Light 410 nm Note 1 nm 10 9 m 1 billionth of a meter Violet Light 4 White light is composed of all the visible colors of the spectrum mixed together 3 a With a prism we can separate the white light into its separate parts or colors b When our eyes perceive a color the object has actually absorbed all the colors except for the color being reflected back to our eyes c Chemicals that absorb certain portions of visible light and reflect the others are called pigments d Pigments that can collect and transfer electrons are called photosynthetic pigments E Chlorophyll is the green photosynthetic pigment within the thylakoids 1 It looks green because it is absorbing red and blue light and reflecting green 2 There are two chlorophyll pigments a and b a Chlorophyll a appears blue green because it absorbs violet and red b Chlorophyll b appears yellow green it absorbs blue and orange F Another class of pigments are called carotenoids 1 In living leaves carotenoids are found inside the chloroplasts where they function as accessory pigments to chlorophyll helping the plant harvest more light during photosynthesis 2 All of the different pigments can be in chloroplasts in varying amounts G We can measure the ability of a pigment to absorb certain wavelengths of light with a spectrophotometer 1 White light is separated into colors by a prism and selected colors or wavelengths of light are passed through the sample of pigment 2 The spectrophotometer indicates how much of that color was absorbed by the sample 4 3 The graph plotting pigment absorbance vs wavelength is called an absorption spectrum a Chlorophyll 1 Would absorb blue and red high absorbance values and these would show up as peaks on the graph 2 Green light would not be absorbed and would pass transmit through the sample low absorbance values b Carotenoids 1 Would absorb blues and blue greens peaks 2 Would transmit yellows and oranges low absorbance V I B G Y O R TODAY IN LAB WE WILL 1 separate plant pigments by paper chromatography a spinach extract will be placed onto chromatography paper b the paper will be stood upright into acetone petroleum ether c The pigments chlorophyll a and b carotene and xanthophyll should separate based on their solubility and may look like the following figure 5 2 Use a spectrophotometer to determine the light absorption characteristics of purified carotene and chlorophyll 3 Discuss what needs to be done for the photosynthesis assignment due next class 6