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Photosynthesis

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Photosynthesis_Mr. Sapora

License: CC BY-NC 3.0

Ferns along the Tillamook spit gather sunlight from atop a standing dead tree (sang). [Figure1]

Every split second that sunlight hits a plant leaf photosynthesis is happening, turning physical energy (photons) into chemical energy (ATP and Glucose) that fuels the entire ecosystem. It could be said that this is one of the most important - if not the absolutely most important - biochemical reaction. It is happening every day all around you - the key to life as we know it - just take a look at the plants in Mr. Sapora's room and think to yourself, "this is the key to life".  Wow...totally...mind = blown.

License: CC BY-NC 3.0

Tiny saxifrage plants growing in the Alaskan arctic - harness what they can of the short amount of seasonal sunlight. [Figure2]

What can a tiny plant do that you can't do?

This tiny plant can use the energy of the sun to make its own food; we call these producers or autotrophs (self - feeding). You can't make food by just sitting in the sun, because you are a consumer or heterotroph (other - feeding) organism.  Plants, algae, and some bacteria have a special chemical pigment (chlorophyll) that allows them harness the energy of the sun and convert it into food.

License: CC BY-NC 3.0

Wavelengths of visible light absorbed by the chlorophyll molecule. [Figure3]

What is Photosynthesis?

Plants need food like the rest of us - they are alive after all, so they require chemical energy to live, grow, and reporoduce....a.k.a do all the things that living things do.  If a plant gets hungry, it cannot walk to Texaco and get a Hot Pocket though.  So, how does a plant get the food it needs to survive? Plants are producers , which means they are able to make, or produce, their own food. The food that producers make is the base of all the Earth's ecosystems - it is, once again, the key to life - a simple molecule that we call sugar, or glucose.  Yeah - know your C 6 H 12 O 6 folks.  How do they make this simple sugar molecule from sunlight?

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[Figure4]

 

Chloroplasts & 2 phases of Photosynthesis

Light-Dependent Reactions

Chloroplasts are the tiny organelles inside plant cells where photosynthesis takes place.  They have a lipid membrane and on the inside of that membrane is where the magic happens.  Light enters through the membrane and is absorbed by the pigment chlorophyll , which is contained in tiny disks called thylakoids .  These thylakoids act as a type of organic solar pannel, which gathers the sun's energy and then helps to convert it into chemical energy.   Water (H 2 O)  is also taken into the thylakoids, where the sun's energy is used to split the water molcule.  This creates a free hydrogen (H+) atom and energy used to to make ATP .  What is given off - oxygen (O 2 ) .  It is from the water molecule that we get the oxygen we breath.  This first phase of photosynthesis is what we call the Light-Dependent Reactions - because light energy is required for it to occur.  

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Light Dependent Reaction happening on the left side: sunlight and water are taken into the thylakoids and split - creating ATP, a free hydrogen, and giving off water as a waste product. Light Independent Reaction happening on the right (called the Calvin Cycle): carbon dioxide taken in and split using ATP, hydrogen atom added, thus creating glucose! #circleoflife [Figure5]

Light-Indendent Reactions

The next phase of photosynthesis does not require light energy (directly).  The ATP created in the first phase is used to split a carbon dioxide (CO 2 ) molecule, and the hydrogen atom (H+) is added in.  This second phase is called the Light-Independent Reactions , and it is what creates the glucose molecule (C 6 H 12 O 6 ) .

License: CC BY-NC 3.0

Plant cell (upper left) showing chloroplasts within. Diagram of a chloroplast (left), and actual electron microscope image of a real-deal chloroplast (right). Note the stacks of thylakoids. [Figure6]



Photosynthesis Equation

Photosynthesis is a process used by living organisms to make food (glucose).  The term photosynthesis literally means "light" (photo) "to make" (synthesis)...as in using light to make food.  It is also a chemical reaction.  On one side of the reaction you have the reactants (the things that react with each other): water and carbon dioxide.   Sunlight drives this chemical reaction through the machinery of the chloroplast (described above) and on the other side of the equation you have the products (the things produced by the chemical reaction): glucose and oxygen .

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[Figure7]

The overall chemical equation for photosynthesis  can be summarized as:  in the presence of sunlight,   carbon dioxide + water → glucose + oxygen .

6CO 2  + 6H 2 O + Light Energy → C 6 H 12 O 6  + 6O 2


In Summary

Glucose is a sugar that acts as the "food" source for plants, and is also the food source for all of us consumers as well.  The oxygen formed during photosynthesis, which is necessary for animal life, is essentially a waste product of the photosynthesis process.  

Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose, in turn, is used for energy by the cells of almost all living things. Photosynthetic organisms such as plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants).

Actually, almost all organisms obtain their energy from photosynthetic organisms. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth. In eukaryotic organisms, photosynthesis occurs in chloroplasts . Only cells with chloroplastsplant cells and algal (protist) cells—can perform photosynthesis. Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms rely on other organisms to obtain their energy. These organisms are heterotrophs.

Photosynthesis Rap

Oxygen in the atmosphere

Plants are not in the photosynthesis business to make oxygen for us to breath.  If you remember from ecology, the atmosphere around 500 million years ago used to contain a lot more carbon dioxide than it does presently.  It was around this time that plants first started to spread across land and photosynthesis became widespread.  As a result, carbon dioxide from the atmosphere was taken-up into the tissues of plants as cellulose and oxygen was given off.  Over time, this slowly increased the amount of oxygen in the atmosphere to the current levels we have today.

Interactive Simulation

This interactive simulation of photosynthesis has animations along with text descriptions.

Open the resource in a new window.

http://www.classzone.com/books/ml_science_share/vis_sim/dltm05_pg39_photosyn/dltm05_pg39_photosyn.html

License: CC BY-NC 3.0


  [Figure8]

  Look at the amazing meat-eating plants pictured here! Called pitcher plants, they use their “pitchers” to capture and digest insects. But even these pitcher plants—like all other plants—make food by photosynthesis. They “eat” insects just to get extra nutrients.

Vocabulary

For a complete list of the vocabulary terms that you are required to know for Mr. Sapora's biology class - view the QUIZLET link here:  http://quizlet.com/_iqr9k

  • autotroph : Organism that produces complex organic compounds from simple inorganic molecules using a source of energy such as sunlight.
  • chloroplast : Organelle that carries out photosynthesis in plants.
  • glucose : Simple sugar with the chemical formula C 6 H 12 O 6 ; a product of photosynthesis.
  • heterotroph : Organism which obtains carbon from outside sources.
  • photosynthesis : Process by which specific organisms (including all plants) use the sun's energy to make their own food from carbon dioxide and water; process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy.
  • producer : Organism that produces food (glucose) for itself and other organisms.

Summary

  • All the energy used by living things on earth came from the process of photosynthesis.
  • During photosynthesis, carbon dioxide and water combine with solar energy to create glucose and oxygen.

Review

  1. Where does the energy for photosynthesis come from?
  2. Do all organisms which carry out photosynthesis have chloroplasts? Explain your answer as fully as you can.
  3. How is the process of photosynthesis central to sustaining life on Earth?
  4. What are the two products produced by photosynthesis?
  5. What two raw materials are needed by plants in order to perform photosynthesis?

Image Attributions

  1. [1]^ License: CC BY-NC 3.0
  2. [2]^ License: CC BY-NC 3.0
  3. [3]^ License: CC BY-NC 3.0
  4. [4]^ License: CC BY-NC 3.0
  5. [5]^ License: CC BY-NC 3.0
  6. [6]^ License: CC BY-NC 3.0
  7. [7]^ License: CC BY-NC 3.0
  8. [8]^ License: CC BY-NC 3.0

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