(Please check out my video about this topic :))
Photosynthesis is important for all of us. It is the mechanism the plants utilize to convert light energy from a light source (like our sun) to chemical bond energy and fix the that enters the plant into organic compounds (glucose). This is what makes the plant alive, so that either humans can eat it and get the nutrients they need, or animals can eat the plant to obtain essential nutrients and later humans can eat the animal and get the nutrients from the animal. This is why photosynthesis is essential for life on Earth. But how do plants do it?
The process of photosynthesis takes place in the chloroplast, which is an organelle in the plant cell. Photosynthesis is a series of different reactions, which are subdivided into light dependent and light independent reactions. The chloroplast is enclosed by a double membrane, and it contains grana, which consist of layers of thylakoid membranes where the light dependent reactions occur, and stroma, where the light independent reactions occur. In order to convert this light energy into chemical bond energy that plants can use, we need some substances that can absorb this light energy first and foremost, and these substances are called pigments.
The chloroplast looks like this:
Pigments absorbing light energy:
Light energy is captured by the pigments in the plants. There are different kinds of pigments, all depending on what wavelenghts of visible light they absorb. In plants we have chlorophylls (absorb wavelengths of light in red, blue and violet range) and cartenoids (absorb wavelengths of light in blue, green and violet range).
There are two types of chlorophyll: chlorophyll a and b. Chlorophyll b and cartenoids are called antenna pigments because they absorb the light energy from the sunrays striking them and transfer photons of light to chlorophyll a, which is directly involved in the transfer of electrons which happens in light independent reactions. The picture below shows what wavelengths different pigments absorb:
Light dependent reactions: Light energy is directly used to make ATP and NADPH
The energy from the sun that is transferred to chlorophyll a by antenna pigments is used to excite electrons in chlorophyll a-molecules to make these electrons available to be caught by primary electron acceptor and then transported through the electron transport chain.The flow of electrons in the electron transport chain provides energy to reduce ADP and NADP+ to ATP and NADPH. Double bonds in chlorophyll a molecules are important because they are source of the excited electrons. The picture below shows the structure of chlorophyll a:
Light independent reactions, or the Calvin cycle: ATP and NADPH from light dependent reactions are used to fix carbon in carbondioxide to glucose.
This is a cycle where carbondioxide is fixed to form a 3-carbon sugar, phosphoglyceraldehyde (also called PGAL or G3P), after 3 runs of the cycle, so the cycle needs to run three times to produce one molecule of glucose. The Calvin cycle occurs only in light, even though it does not directly use light energy. Instead, it uses ATP and NADPH from the light reactions and oxidizes them back to ADP and NADP+.
Photosynthesis is important for all of us. It is the mechanism the plants utilize to convert light energy from a light source (like our sun) to chemical bond energy and fix the that enters the plant into organic compounds (glucose). This is what makes the plant alive, so that either humans can eat it and get the nutrients they need, or animals can eat the plant to obtain essential nutrients and later humans can eat the animal and get the nutrients from the animal. This is why photosynthesis is essential for life on Earth. But how do plants do it?
The process of photosynthesis takes place in the chloroplast, which is an organelle in the plant cell. Photosynthesis is a series of different reactions, which are subdivided into light dependent and light independent reactions. The chloroplast is enclosed by a double membrane, and it contains grana, which consist of layers of thylakoid membranes where the light dependent reactions occur, and stroma, where the light independent reactions occur. In order to convert this light energy into chemical bond energy that plants can use, we need some substances that can absorb this light energy first and foremost, and these substances are called pigments.
The chloroplast looks like this:
Pigments absorbing light energy:
Light energy is captured by the pigments in the plants. There are different kinds of pigments, all depending on what wavelenghts of visible light they absorb. In plants we have chlorophylls (absorb wavelengths of light in red, blue and violet range) and cartenoids (absorb wavelengths of light in blue, green and violet range).
There are two types of chlorophyll: chlorophyll a and b. Chlorophyll b and cartenoids are called antenna pigments because they absorb the light energy from the sunrays striking them and transfer photons of light to chlorophyll a, which is directly involved in the transfer of electrons which happens in light independent reactions. The picture below shows what wavelengths different pigments absorb:
Light dependent reactions: Light energy is directly used to make ATP and NADPH
The energy from the sun that is transferred to chlorophyll a by antenna pigments is used to excite electrons in chlorophyll a-molecules to make these electrons available to be caught by primary electron acceptor and then transported through the electron transport chain.The flow of electrons in the electron transport chain provides energy to reduce ADP and NADP+ to ATP and NADPH. Double bonds in chlorophyll a molecules are important because they are source of the excited electrons. The picture below shows the structure of chlorophyll a:
Light independent reactions, or the Calvin cycle: ATP and NADPH from light dependent reactions are used to fix carbon in carbondioxide to glucose.
This is a cycle where carbondioxide is fixed to form a 3-carbon sugar, phosphoglyceraldehyde (also called PGAL or G3P), after 3 runs of the cycle, so the cycle needs to run three times to produce one molecule of glucose. The Calvin cycle occurs only in light, even though it does not directly use light energy. Instead, it uses ATP and NADPH from the light reactions and oxidizes them back to ADP and NADP+.
No comments:
Post a Comment