Photosynthesis (3rd Ed, 1981)

[Music] of all living things on this planet plants are the most prevalent of life forms through time-lapse photog graphy we see a plant's growth and development from a seed nothing has quite the same ability to colonize an area of land as plants dispersing themselves in many forms and sizes to cover the globe on land plants produce 150 billion tons of new living matter every year the most abundant life form on Earth but plants not only cover the land they pervade the Seas as well 50% of all plant life is found in the sea if green plants were to disappear Life as we know it on Earth would also disappear for all life is dependent on energy initially fixed by plants in a precise and regulated way plants can turn light water and a gas carbon dioxide into the energy and food for living matter energy that provides food for all living things this process of conversion is called photosynthesis we know that in the absence of light such as in this cave green plants cannot grow plants require the energy from sunlight to live only green plants are capable of fixing light energy of the sun into chemical energy the leaves of plants are actually well organized factories in which photosynthesis takes place explain simply leaves absorb the energy emitted by sunlight to power photochemical reactions carbon dioxide enters the leaf and is chemically combined with water arriving from the roots to produce carbohydrates the fuel necessary to all life oxygen a byproduct of photosynthesis is released from the leaf into the atmosphere this is a summary of what happens during photosynthesis but how does this all take place let us look even more closely at a leaf by peeling away a piece of its lower epidermis and examining it under a microscope the underside of a leaf is perforated with tiny holes called stata which are 1 1,000th of a millim wide carbon dioxide from the air diffuses into the stomata and oxygen diffuses out how do we know leaves produce oxygen oygen when oxygen is introduced into a solution of the Dy Indigo K the solution turns blue if a plant produces oxygen then it too will turn the solution blue after placing a plant into this solution we begin to see Thin Blue streams forming at the top of the leaves oxygen in the air turns the solution blue at the surface of the beaker this simple experiment proves that green Plants release oxygen through the leaves after an hour the plant nearly turns the entire solution Blue from its oxygen production green plants are responsible for replenishing the world's supply of oxygen that humans and all other animals need for survival however oxygen is only one product of photosynthesis carbohydrate is the other we can conduct a very simple experiment that enables us to observe the production of carbohydrates a leaf is removed from a plant that has been kept for some time in the dark the leaf is placed on a glass plate a photographic negative is then laid at top the leaf and sandwiched with another glass plate when a light is shined onto the leaf the difference in density in the negative will let varying amounts of light through to the leaf Surface after several hours of exposure the leaf is boiled in alcohol the alcohol removes the chlorophyll in the area where light was able to pass through a carbohydrate called starch is produced The Leaf is then stained with iodine the carbohydrates in the leaf will absorb the iodine and produce a positive image from the negative where light struck the leaf carbohydrate was produced leaving the positive image how are these carbohydrates made here we see Leaf cells under the microscope inside there is a constant stream of structures called chloroplasts chloroplasts do the work of photosynthesis they're green because they contain the light absorbing pigment called chlorophyll every color of visible light except green is absorbed the number of chloroplasts in photosynthetic cells varies a leaf cell may have 20 to 100 chloroplasts but a single- celled algae may have only one or two we can look even more closely at the chloroplast with the electron microscope the images this device produces are called electron micrographs here we see one of these pictures the inside of the chloroplast here magnified 40,000 times is shown to be made up of a series of membranes arranged in teers containing thousands of molecules of chlorophyll and other photosynthetic pigments the chloroplast is a remarkable Factory but how does it convert solar energy into cellular energy the actual process of photosynthesis was longlook upon as a mystery or Black Box what happens to light energy when it enters this box scientists have known for a long time that living cells cannot use light directly for fuel the chloroplast must somehow convert sunlight into chemical energy let us consider an example this light bulb cannot directly translate gasoline into light energy the gasoline is an energy-rich fuel however the bulb needs a different form of power we need a generator that can translate or change the chemical energy of the gasoline into electrical energy that the light bulb can use the photosynthetic engine in most plants is the chloroplast this is the green machine of the whole process chloroplasts convert solar energy into chemical energy this energy is carried in the chemical bonds of two substances one of which is at PP short for adenosine triphosphate in any living cell ATP is like money ATP can at any time be cashed in for energy therefore ATP is the energy currency of cells every living form of life on this Earth uses ATP when plants grow when fish swim when a human moves ATP is used up ATP is the universal energy carrying molecule of any living cell chloroplasts also convert sunlight into chemical energy storing that energy in another substance NAD pH short for nicotinamide adinin dicle atide phosphate when this substance picks up hydrogen and electrons from water it is reduced together ATP and reduced nadph provide the constant input of energy to fuel the production of carbohydrates in photosynthesis but scientists continued to break down the photosynthetic process into its component parts they found that the process includes two distinct groups of reactions one group is called light Reactions where chloroplasts convert sunlights into the chemical energy forms ATP and nadph the second group of reactions do not require light directly but use ATP and nadph to fuel the conversion of carbon dioxide into sugars these processes are called dark reactions the question was what happens in these dark reactions the classic research of Dr Melvin Kelvin of the University of California Berkeley helped to answer the question of how carbohydrates are made to find out how the cell can convert s carbon dioxide into carbohydrates Dr Kelvin stopped the photosynthetic process at different stages to find intermediate compounds in his original experiments Dr Kelvin used whole cells of the algae chlorella the researcher then took these cells and injected them into a culture medium in this setup the lights and carbon dioxide allowed to enter the culture are carefully controlled the cultures are gently rocked back and forth in a temperature controlled water bath to ensure even exposure The Next Step involves the use of a radioactive tracer which is a radioactive isotope of carbon carbon 14 this carbon 14 is fed into the cells in the form of carbon dioxide and will trace the carbon compounds form during photosynthesis so they can be detected later after a specific interval some of the the cells in the culture are removed samples are released into test tubes containing alcohol the alcohol immediately stops photosynthesis in each sample taken thus each sample represents a further step in the chemistry of sugar or carbohydrate production during these reactions carbon and other chemicals are combined to form intermediary chemical compounds leading up to the formation of complex sugar the variety of carbon compounds formed during the various stages of photosynthesis can be separated the separation process used here is called two-dimensional paper chromatography the compounds containing the Tracer element carbon 14 produce a dark image on x-ray film the comparison of the negatives from each sample enable Dr Calvin to see the intermediate compounds which chloroplasts produced during the conversion of carbon dioxide into carbohy hydrates this discovery LED Dr celvin to create a model called the carbon cycle or the Calvin cycle in this cycle carbon dioxide enters the reaction and combines with a five carbon compound to form an unstable six carbon intermediate the intermediate breaks down into two molecules of a three carbon acid the three carbon acid is converted into either a simple sugar or a complex sugar such as glucose both end products of photosynthesis some of the simple sugar is used to regenerate the five carbon compound ensuring that the cycle will be perpetuated three molecules of ATP and two of nadph power the reactions which allow one molecule of carbon dioxide to move through the carbon cycle Dr Calvin's work helped to provide a clear picture of what happens in the dark phase of photosynthesis and won him a Nobel Prize but the remaining problem to be solved was how are ATP and nadph formed the work of Dr Daniel Arnon also at brookley has helped provide an answer to this question Dr Arnon first set out to prove that the entire photosynthetic process occurs in the chloroplast wh cells were not used in his experim instead Dr Arnon removed and isolated chloroplasts from the cell Dr Arnon introduced the use of spinach for experimentation the spinach is grown either naturally in sunlight or in controlled environments here the plants are grown in a chemical nutrient solution that enables Dr Arnon and his associates to utilize fresh leaves of spinach grown in the same way week after week year after year the leaves are ground in a sugar solution the mixture is then strained through cheesecloth to separate the stems veins and debris this filtered solution is poured into centrifuge flasks these flasks are spun at high speed in a centrifuge to further separate the chloroplasts from the broken fragments of cells after coming out of the centrifuge the chloroplasts appear as a dark green residue on the bottom of the flask in this way Dr Arnon isolated the photosynthetic machine from his research Dr Arnon found that not only could isolated chloroplasts carry out the whole photosynthetic process outside the cell but they could also form ATP and reduced nadp in light without carbon dioxide he called this new process photo phosphorilation when he turned the lights out and added carbon dioxide the stored up molecules of ATP and reduced NAD pH could complete the process converting carbon dioxide into sugar Dr aran's work has helped us to understand that in the light reactions of photosynthesis the absorption of Light by chlorophyll molecules leads to a series of electron transfer reactions that sets the oxygen of waterfree and produces ATP and nadph these high energy compounds are then used in the dark phase to operate the carbon cycle which converts carbon dioxide into sugars Dr arnan has continued his work and broken down the light phase of photosynthesis even even further here he exposes a thin tube of chloroplasts to Red Light the optimum light for photosynthetic reactions he freezes the chloroplasts in liquid nitrogen to a temperature ofus 300° C the sample is placed in a device that measures epr signals or electron paramagnetic resonance this enables him to trace the flow of electrons between compounds through this proc procedure Dr Arnon discovered another step in the light reactions of photosynthesis an iron-rich protein called ferrodoxin picks up the high energy electrons given off by chlorophyll when chlorophyll has been excited by light this reddish protein is seen here isolated from chlorophyll ferrodoxin is yet another link to our growing understanding of how photosynthesis takes place one product of photosynthesis is carbohydrate which form the basis of our food carbohydrates serve as major storage products for cellular energy and provide spare parts for the many needs of all living cells in order to maintain biological function we must eat these products or eat animals that have eaten these products the second product of photosynthesis is oxygen our supply of oxygen on this planet is continually renewed by photo synthetic activity of plant life we are beginning to recognize our responsibility to replenish plant life such as trees to protect our own well-being by preserving the natural ecological balance the fossil fuels we have been using over the past 100 years are all stored products of photosynthesis made by the sun's action on Ancient green plants recently we become alarmed by the fact that these fixed supplies are rapidly being depleted current energy forms such as coal and oil are products of ancient photosynthesis major energy forms on this planet have and continue to originate from the Sun an oil producing Euphoria plant is being used to produce liquid fuel it is nicknamed the Gopher plant because it can grow readily in the Arid desert its latex sap can be seen easily when a leaf is plucked Dr Melvin Kelvin is conducting the research in this area the latex in the plant is an Emulsion of 2/3 water and 1/3 oil which when separated yields an oil that can be processed in modern oil refineries the plant is dried ground then placed in a filter cylinder a distillation system will extract the oil from the pulp of the plant a solvent is boiled condensed bathing the plant material and removing the oil this is an example of how a large scale system can work these plants can fix light energy into chemical forms that can be stored for long periods possibly providing one of many necessary alternatives to supplement our energy resources when the solvent is boiled off a thick extract remains ready to be refined just like natural crude oil however unlike the oil we get from the ground this would be a renewable resource perhaps someday we will no longer have an energy shortage or a limited food supply as we learn new ways to utilize the intricate processes of photosynthesis [Music] [Applause] [Music]