TranceAddictT7
Member
I was reading a thread on here about optimal CO2 levels when I decided it might be helpful to make a thread about photosynthesis, light reactions, Calvin cycle, and some specifics of plants for those that are interested. I'll try to make it as user friendly as possible.
Lets start off with the basic chemical equation for photosynthesis:
6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
(carbon (water) (light energy) (glucose) (oxygen) (water)
dioxide)
Photosynthesis is a crucial aspect in the lives of almost all organisms whether it be direct or indirect. Organisms acquire carbon skeletons and organic compounds used for energy in one of two ways: autotrophic nutrition or heterotrophic nutrition.
The former means to sustain oneself without eating things derived from other organisms. These kinds of organisms (like plants) produce their organic molecules from CO2 and other compounds from the environment. They are the main source of organic compounds for nonautotrophic organisms (like humans) and are therefore known as producers.
Almost all plants are autotrophs and more specifically, photoautotrophs because they use light energy to synthesize organic substances.
With me so far? Good. Now I mentioned light energy, lets see why this is important for plants.
All green parts of a plant, including stems, have chloroplasts, although the leaves harbor the greatest numbers. What are chloroplasts you ask? They are organelles that absorb sunlight and use it to drive the synthesis of organic compounds from CO2 and water. To understand how, we should understand them better.
There are close to half a million chloroplasts on a piece of leaf with a surface area of 1mm squared. They are found in the interior tissue of the leaf known as the mesophyll. A typical mesophyll cell has 30-40 chloroplasts. A chloroplast has an envelope of two membranes surrounding a fluid called the stroma. Within the stroma is a third membrane (thylakoid membrane) made up of tiny sacs called thylakoids. This is where chlorophyll, responsible for the green pigment on plants, can be found. Here is a picture to help with the anatomy:
Light energy is absorbed by chlorophyll that drives the synthesis of organic molecules in the chloroplast. Review the general equation of photosynthesis again. Glucose is not the direct product of photosynthesis, a 3-carbon sugar is, but for simplification we use glucose. Water is on both sides of the equation because while 12 molecules are used, 6 are produced again.
The net equation would become:
6 CO2 + 6 H2O → C6H12O6 + 6 O2
(it becomes clear that this is the reverse of cellular respiration, the reaction that humans use!)
It is important to note that while oxygen is produced, the O2 molecule given off by plants does not come from CO2, it comes from H20. This allows for the extraction of a positively charged hydrogen ion and its incorporation into a sugar molecule (note the chemical formula of glucose again and how many H's it has).
So what exactly happens in photosynthesis and why is water and carbon dioxide used?
Photosynthesis splits water and transfers electrons along with hydrogen ions from the water to carbon dioxide, reducing it to sugar. This is known as a redox reaction and more about them can be learned here: http://en.wikipedia.org/wiki/Redox .
Since the electrons transferred increase in potential energy as they move from water to sugar, the process requires energy, and is therefore known as an endergonic reaction. This energy, of course, comes from light!
Now that we covered the basics, photosynthesis is not actually a single process but two separate processes called the light reactions and the Calvin cycle. I will cover these processes in detail and they will help you understand the life of the plant in light and dark cycles. I will include pictures to help break down the cycles. Stay tuned for that. I will continue this thread as soon as I get a chance. Some of this might be repetitive to the people familiar with it but it never hurts to refresh your mind and to those that are learning I hope this helps you!
Lets start off with the basic chemical equation for photosynthesis:
6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
(carbon (water) (light energy) (glucose) (oxygen) (water)
dioxide)
Photosynthesis is a crucial aspect in the lives of almost all organisms whether it be direct or indirect. Organisms acquire carbon skeletons and organic compounds used for energy in one of two ways: autotrophic nutrition or heterotrophic nutrition.
The former means to sustain oneself without eating things derived from other organisms. These kinds of organisms (like plants) produce their organic molecules from CO2 and other compounds from the environment. They are the main source of organic compounds for nonautotrophic organisms (like humans) and are therefore known as producers.
Almost all plants are autotrophs and more specifically, photoautotrophs because they use light energy to synthesize organic substances.
With me so far? Good. Now I mentioned light energy, lets see why this is important for plants.
All green parts of a plant, including stems, have chloroplasts, although the leaves harbor the greatest numbers. What are chloroplasts you ask? They are organelles that absorb sunlight and use it to drive the synthesis of organic compounds from CO2 and water. To understand how, we should understand them better.
There are close to half a million chloroplasts on a piece of leaf with a surface area of 1mm squared. They are found in the interior tissue of the leaf known as the mesophyll. A typical mesophyll cell has 30-40 chloroplasts. A chloroplast has an envelope of two membranes surrounding a fluid called the stroma. Within the stroma is a third membrane (thylakoid membrane) made up of tiny sacs called thylakoids. This is where chlorophyll, responsible for the green pigment on plants, can be found. Here is a picture to help with the anatomy:
Light energy is absorbed by chlorophyll that drives the synthesis of organic molecules in the chloroplast. Review the general equation of photosynthesis again. Glucose is not the direct product of photosynthesis, a 3-carbon sugar is, but for simplification we use glucose. Water is on both sides of the equation because while 12 molecules are used, 6 are produced again.
The net equation would become:
6 CO2 + 6 H2O → C6H12O6 + 6 O2
(it becomes clear that this is the reverse of cellular respiration, the reaction that humans use!)
It is important to note that while oxygen is produced, the O2 molecule given off by plants does not come from CO2, it comes from H20. This allows for the extraction of a positively charged hydrogen ion and its incorporation into a sugar molecule (note the chemical formula of glucose again and how many H's it has).
So what exactly happens in photosynthesis and why is water and carbon dioxide used?
Photosynthesis splits water and transfers electrons along with hydrogen ions from the water to carbon dioxide, reducing it to sugar. This is known as a redox reaction and more about them can be learned here: http://en.wikipedia.org/wiki/Redox .
Since the electrons transferred increase in potential energy as they move from water to sugar, the process requires energy, and is therefore known as an endergonic reaction. This energy, of course, comes from light!
Now that we covered the basics, photosynthesis is not actually a single process but two separate processes called the light reactions and the Calvin cycle. I will cover these processes in detail and they will help you understand the life of the plant in light and dark cycles. I will include pictures to help break down the cycles. Stay tuned for that. I will continue this thread as soon as I get a chance. Some of this might be repetitive to the people familiar with it but it never hurts to refresh your mind and to those that are learning I hope this helps you!