Biology : Semester I

Section:

Section 2

Section Two:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 | Part 11 | Part 12 | Part 13 | Part 14 | Part 15 | Part 16 | Part 17 | Part 18 | Part 19

Biology: Photosynthesis and Cellular Respiration Photosynthesis: Food Production The presentation below will demonstrate many of the processes of photosynthesis. These processes are thoroughly explained throughout this unit, but you are encouraged to watch these demonstrations as often as needed and to take notes. Each button on the left will launch a new tutorial. Click here for a helpful list of terms used in this section and their definitions. Objectives After you have completed this section, you will be able to: Study the general equation for photosynthesis and indicate in which process each reactant is used and each product is produced. List the two major processes of photosynthesis and state what occurs in those sets of reactions. Distinguish between organisms known as autotrophs and those known as heterotrophs as pertains to their modes of nutrition. Describe the nature of light and how it is associated with the release of electrons from a photosystem. Describe how the pigments found on thylakoid membranes are organized into photosystems and how they relate to photon light energy. Describe the role that chlorophylls and the other pigments found in chloroplasts play to initiate the light dependent reactions. Describe the function of electron transport systems in the thylakoid membrane. Explain the role of the two energy-carrying molecules produced in the light dependent reactions (ATP and NADPH) and in the light-independent reactions. Describe the Calvin cycle in terms of its reactants and products. Study Guide Scientists often call Earth the water planet. Biologists, on the other hand consider the Earth a photosynthetic planet, as photosynthesis powers most of the life on Earth. Photosynthesis has effected the most dramatic changes in the chemistry of the oceans and atmosphere, changing the Earth from a reducing to an oxidizing planet by the production of oxygen several billion years ago.  That oxygen production continues today! Photosynthesis also limits the amount of carbon dioxide in the atmosphere. So, how does this important process impact you? Photosynthesis is the process by which plants, certain bacteria, and many protistans (diatoms, algae, and others) convert energy from sunlight to produce sugar, which cells then convert into ATP using the cellular respiration process. The conversion of unusable sunlight energy into usable chemical energy is associated with the actions of the green pigment chlorophyll. Most of the time, the photosynthetic process uses water and releases oxygen that we absolutely must have to stay alive. We can write the overall reaction of this process as: 6H2O + 6CO2 ----------> C6H12O6+ 6O2 Water + carbon dioxide ----------> sugar + oxygen Since most of us do not speak “chemicalese,” the above chemical equation translates to: six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen. The inputs and outputs of photosynthesis Usually, food production begins with green plants, nature's solar collectors. Plants use sunlight and simple environmental resources, such as carbon dioxide and water to produce sugar. This process is called photosynthesis. The Nature of Light We live in a world of color; red lights, green lights, color television sets, color computer monitors. When white light passes through a prism, the light is separated into different colors (or wavelengths): red, orange, yellow, green, blue, indigo, and violet. Light is a form of energy (stand outside on a hot, sunny day to test this idea sometime) and has some aspects that behave like a wave in water. Wavelength is the distance from peak to peak (or trough to trough). Energy is inversely proportional to the wavelength; in other words, longer wavelengths have less energy than do shorter ones. The order of colors in a spectrum, such as a rainbow or when light is passed through a prism, is determined by the wavelength of light. Visible light is one small part of the electromagnetic spectrum. The longer the wavelength of visible light, the more red is the color, and the lower the energy of the light. Likewise, the shorter wavelengths are towards the violet side of the spectrum, which also has a higher energy. Wavelengths longer than red are referred to as infrared, while those shorter than violet are ultraviolet. Think about sunscreen for a minute. Most sunscreens mention the  ultraviolet (or UV for short) protection, however fail to mention infrared protection (IR for short). Visible light is “sandwiched” between these two types of energy. Now go on to the next part.

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